eR _ DEC 22 1959 RESTRICTED g : 2 MANUAL ANSHI OF ICE SEAMANSHIP cee 1's nont * 8820 08 sol tase Pees Seeteee rN ce Pecos 6 cory ° toe OOO) oO ee esecces WARS esses ees oe . 4 Peeeees weanent,®,' 8000 00 00s, yO Corry 00 . : pod *.°,9,°,9 9 Bee ons te eeecece OOOO er ee feces ee teeeeee @eee- U. S. NAVY HYDROGRAPHIC OFFICE h opebeoo 1060 0 wwii ~RESTRICTED MANUAL OF ICE SEAMANSHIP H. 0. PUB. NO. 551 U.S. NAVY HYDROGRAPHIC OFFICE Washington, D.C. ------- 1950 -RESTRICTED FOREWORD The interest of the United States Navy in polar navigation dates back over a century, to the voyage of the United States Exploring Expedition under Lt. Charles Wilkes, in 1838-42, which made land- falls at several points along the Antarctic continent. In 1855 the U.S. S. Vineennes, Commander John Rodgers, explored and charted the Arctic Ocean beyond Bering Strait. Meanwhile, in 1850-51, the Advance and Resolute under Lt. E. J. de Haven, were engaged in a search for the missing British Arctic explorer, Sir John Franklin, and in 1853 the Advance was sent out again under Passed Asst. Surg. KE. K. Kane. In 1855 the Release and Arctic, commanded by Lt. H. J. Hartstene, went to the relief of Dr. Kane in the Arctic. Capt. C. F. Hall’s third voyage in search of Franklin was made under naval auspices in 1871 in the Polaris, and the Zigress and Juniata were fitted out with naval crews to go to his rescue in 1873. The increasing interest in the Arctic brought about by the Franklin relief expeditions led to the commissioning of the Jeannette as a naval vessel in 1879 to explore beyond Bering Strait under Lt. G. W. de Long. The revenue cutter Corwin cruised in search of the Jeannette in 1880, as did the U.S. S. Rodgers and U.S. 8S. Alliance in the two following years. In 1884 a naval expedition under Commander Winfield S. Schley, comprising the Thetis, Bear, and Alert, rescued the survivors of the Greely expedition in Greenland waters. Except to mention that the North Pole was attained by Commander Robert E. Peary of the Civi] Engineering Corps in 1909, and that the first man to fly over both Poles was Rear Adm. R. E. Byrd, USN (Ret.), later naval operations in Polar waters need not be touched on here. This publication has been prepared in an effort to make available the accumulated experience of past expeditions in a form convenient for use by present-day Polar expeditions, whether operating for military, commercial, or scientific purposes. It should be used in con- junction with the Sailing Directions for the appropriate coasts, of which the following have been issued by the Hydrographic Office : -RESTRICTED- lil RESTRICTED H. O. Pub. No.— Sailing Directions for— ae t (5. East Greenland and Iceland. 76. Baffin Bay and Davis Strait. ile Northern Canada. 136. Northwest and North Coasts of Norway. 138. Antarctica, H. O. Pub. No. 550, Ice Atlas of the Northern Hemisphere, should also be consulted for detailed information on monthly ice conditions in the Arctic. Most recent expeditions which have spent only late spring, summer, and early fall months in the polar regions have reported some surprise at the relatively mild temperatures encountered. Long summer day- light and the heat-buffering properties of sea water combine to pro- duce conditions far better than those experienced by the mariner oper- ating out of Boston, Mass., or Portland, Maine, in winter. A. Hosss, Captain, U.S. Navy, ( Ret.) Hydrographer. IV RESTRICTED RESTRICTED TABLE OF CONTENTS Chapter iL ORMATION AND GrowTH Or Sma: Icme- 22025050 22) sce SE AUISE ROL pEUEG C700 Pie se sc Mes Pe a Dey | AF ENE SraIe{e toy Spe Uy ag a a PPT EMG ONMMOMMSLOCESS Se, Mtoe sea an 0) ee UHC LO RNC O MOUs tao ae Aa wer eee Eka VG NS CE Comparison, of Arcticsand Antarctic Tee. _- 2. 42 See IRAE OCI Stl CellC ee setae hea Sd er, Aa et eee ee NR DMC RABSINICATION AND DESCRIPTION: OF Tom. 22-2002 2 ke COIL ee eee ans ee Seth, a ot oe Re ee BE SenmiGecsea se 1 Bea eee te Na ES ehe, ee ONL ee ae CoO lesb LT abl OMe oles atte ge Pn ree eet Se A PHYSICAL AND CHEMICAL PROPERTIES’ oF IcGE_»!_-22-22- 222252... Sineneuhuandelardness: 2. £200 kao be ee a ee siren algenoperties=a= = 5 6 oo yee ap See ee RSID CITT m Care stival Uy eevee a er ete enn ey ee Ep aN eee ee SPEAR NS 2 Os ce ee Tee a aR ee eo a PLOVER) AND. IRTET WOR TCH. 25) 22 seo ba oe Sa Factors Producing Translation and Differential Motion_________ ptm ck eee se tS Se Ee Bey Sie Edel ey ee eee te ne cine noms leer so, 5 ae eS ei hh a i be ee hase GoverninouD rite c2= 2 2 lus skola. et bes 6. VESSELS FOR OPERATING IN IcE______---__- Ss 5 2. eee eS CAT ORS NI sie See nese en Se yey ee eas oe eh ee SDM ain ese aeeeeeee ty Pia eee Lee eee te Oe (-sL REP ARING, Al VESSEL FOR: [cn OPERATIONS. =o. -==- = 22> 2-22 BEL ae con pon pe ee a ee ae ee TEYOPN Se yas ec gM ae elt on ap a a a a a Preparations En Route to Polar Regions_-________--_----------- San OPERATION SEONG OMAR ATHIRG =e mente ee ee ee ee SHEPOORGGeEReCHMIONS == he wom ee ee ee ee AN CHOLIN Deemer tee peaem ee eran ae orn t et! SS eS Micoring andy bialenain gers a fhe eat 8 se (8 Ae ea NA LCrA SES iki hee eenone ees Senne ered S27 = Bo eee oe Dantaperaiduepaits es = 202 ese Se ee es ese e RESTRICTED RESTRICTED Chapter 9. 10. ile 12. HANDIING AN UNESCORTED. VESSELOING ICES. 2 et eee hintry “nto le... 6 = hoses 2 Re 2 eee eee ‘Working Through*lee 2 a>. +2324 oe ee eee Speed of Advances 5-2 7s eee Hazardssin the lice. 2226 22 sent a ee eee Releasetofar Vesseliviee Sy eet: ee ee ee Precautions Against Being Beset:-- ._2__-__2_ <2. =). == ee Precautions: When; Beset--— 222 = eee Operating’ Boats and Séaplanes= 2-2. 2-2 ==. <2] se eee OPERATING AN ICHBREAKER. ._- $tiuo 22-5) tee Propellerss:* s+ 22 -=..22 2242 -.s e355 25. eee Perhorman Ce = 2 eee fe a= ee ee Se ee ee Operating-in Wee 225 ses = eo ce Se ee Anichorn pss ee. ae ee Oe as See A Bix plOSIVes 4228 98 Geil 22 Se ae ee es ee Bnemeering, Procedures. 220 S600 ofa te a CONVOYING IN lon = So eee ee Le eee iy pescOF Convoy 26 22-3 SS 2S a ee eee ‘Distance between Ships: 22 s2".20= 22 eee eee Coursesand Speed of Convoy=*- see Conducting, through) ces 3254.5 ee eee Ro winevingher= = - = > Lite. Se ate ee Re ee ee Breaking) Out Ships: . = = 2. 2 ee eee Convoy. Signals J == Diagram illustrating the conditions under which superior mirages may bestoumedsotinlace eslCe mMASSeSe= = sae oe ee ee The ice dock when completed. The ship rests on ice buttresses____- - After the ice has been removed from (A), a new layer of ice (B) forms below the ice layer, constituting the bottom of the future ice dock _- RESTRICTED Page 100 102 WAIL 123 124 Vil RESTRICTED BIBLIOGRAPHY MANUSCRIPTS AND REPORTS Betousoy, M. P., Tactical principles of navigation in ice, Pilot Chart of the South Atlantic Ocean, March—May, 1947. Brooks, C. E., Lieut. RCN, Arctic navigation, Ottawa, 1947 (RESTRICTED). GREAT BRITAIN, ADMIRALTy, Notes on convoying in ice, 1946. Notes on navigation in ice, Pilot Chart of the South Pacific Ocean, March— May, 1947. KRAvL, Orro RicHaArp, Navigating through ice, Intelligence Report, ONI, Serial 200-—C-49, 10 Sept. 1949 (CONFIDENTIAL). MerTcaLr, W. G., Operations in sea ice, Woods Hole, 1947. Unirep States Navy DEPARTMENT, Report on Operation NANOOK, 1946 (CON- FIDENTIAL). Report on U. S. S. Midway cold-weather cruise, 1946 (RESTRICTED). Report on Operation HIGHJUMP, 1947 (CONFIDENTIAL). Report of Task Force 68, 1947 (CONFIDENTIAL) Report of Task Force 39, 1948 (CONFIDENTIAL). Report of Arctic Summer Operation 1948, Task Force 80, U. S. Atlantic Fleet (RESTRICTED). Report of the 1948 Point Barrow Supply Expedition (BAREX~—48), ac- complished by Amphibious Force, Pacific Fleet, executed by Transport Divi- sion 11, September 15, 1948. Report of CTU 56.1.1, Bering Sea Winter Operations, January—February 1949, U. S. S. Burton Island (AG-88) (CONFIDENTIAL). Summary of Antarctic ice conditions, Hydrographic Office, Division of Oceanography, Study No. 85, 1946 (RESTRICTED ). U. S. S. Edisto winter arctic operation, January-March 1949 (CONFI- DENTIAL). U. S. S. Edisto report of resupply operation arctic weather stations Nanook II, July-September 1949 (CONFIDENTIAL). | BOOKS AND PERIODICALS AMERICAN BUREAU OF SHIPPING, Rules for building and classing steel vessels, New York, p. 91, 1946. Bartow, E. W., Deception of vision due to atmospheric conditions at sea, Marine Observer, v. 12, pp. 14-19, 1935. BrncHAM, E. W., Sledging and sledge dogs, Polar Record, vy. 3, pp. 867-385, 1941. GraHaAm, A. H., Radar aids detection of floating ice, Air-Sea Safety, pp. 12-15, December 1946—January 1947. GREAT BRITAIN, ADMIRALTY, White Sea Pilot, pp. 8-385, London, 1946. Hosss, W. H., The discovery of Wilkes Land, Antarctica, Proceedings American Philosophical Society, v. 82, pp. 561-582, 1940. RESTRICTED IX RESTRICTED JENSEN, CHRISTIAN, The polar ship Maud, Scientific Results Norwegian North Polar Expedition, v. 1, no. 2, Bergen, 1933. Jounson, H. F., Development of ice-breaking vessels for the U. S. Coast Guard, Marine Engineering, pp. 88-97, December 1946. Kocu, LAucE, Ice cap and sea ice in North Greenland, Geographical Review, v. 16, pp. 98-107, 1926. MALMGREN, Finn, On the properties of sea ice, Scientific Results Norwegian North Polar Expedition, v. 1, no. 5, Bergen, 1933. Maursrap, A., Atlas of sea ice, Oslo, 1933. PouLtrer, THOMAS C., Seismic measurements on the Ross Sea shelf ice, Transac- tions American Geophysical Union, v. 28, pp. 162-170, 367-384, 1947. Ryper, R. E. D., Note on a general-purpose boat for use in polar regions, Polar Record, v. 3, pp. 399-406, 1941. SHarp, R. P., Suitability of ice for aircraft landings, Transactions American Geophysical Union, vy. 28, pp. 111-119, 1947. SmirH, Epwarp H., Arctic ice, Scientific Results of the Marion Expedition to Davis Strait and Baffin Bay, Part 3, Washington, U. S. Coast Guard, 19381. Smiru, H. T., Abnormal refraction, and mirage at sea, Marine Observer, vy. 7, pp. 133-135, 1930. SmitH, W. E., The design of the Antarctic exploration vessel Discovery, Trans- actions of the Institution of Naval Architects, v. 47, pp. 1-42, 1905. Sverprup, H. U., Meteorology, Scientific Results of the Norwegian North Polar Expedition, v. 2, Bergen, 1933. TRANSEHE, N. A., The ice cover of the Arctic Sea, Problems of Polar Research, pp. 91-123, American Geographical Society, New York, 1928. UNITED STATES NAvy DEPARTMENT, Naval Arctic Operations Handbook, prepared by the Arctic and Cold Weather Coordinating Committee of the Office of the Chief of Naval Operations, 1949: Part I, General Information; Part II, Opera- tional Notes (RESTRICTED). Hydrographic Office, Sailing directions for Antarctica, H. O. No. 188, pp. 21-33, 1948. WILKINS, Husert, Under the North Pole (no place), 1931. X RESTRICTED RESTRICTED CHAPTER | FORMATION AND GROWTH OF SEA ICE An understanding of the formation, growth, and decay of sea ice is desirable for comprehension of many of the problems in ice seaman- ship. The climatic factors bearing on the formation of ice naturally vary from place to place and from season to season. However, a knowledge of the basic physics involved will be of great assistance to the mariner, enabling him to recognize certain salient features of ice and take advantage of its properties. CAUSE OF FREEZING In temperate and tropical latitudes, the ocean acts as a storehouse of radiant heat from the sun. The visible and infra-red wave lengths are largely absorbed in the surface layers, and the heat so stored is given off to the air at night and at other periods when the air is colder than the sea surface. In higher latitudes, however, as the nights begin to grow longer in the autumn, insufficient heat is stored in the short daylight period to compensate for the losses at night, and the temperature of the surface waters is therefore lowered. As the season progresses, the altitude of the sun becomes lower day by day; less radiation is received, and more is reflected from the sea surface owing to the low angle of incidence of the rays. Finally, the water reaches the freezing point and further loss of heat results in the formation of ice. Conditions then become even less favorable for the retention of radiant heat from the sun since, as will be discussed more fully in a later chapter, ice reflects much more of the visible radiation than does water. Cooling of the air in contact with the ice is accelerated, and as this cold air spreads, more ice is formed. INFLUENCE OF SALINITY Fresh water freezes at 32.0° F., but the salt present in sea water causes it to remain liquid until a lower temperature is reached. The greater the salinity, the lower the freezing point. Ordinary sea water, with a salinity of 35%, (35 parts per 1,000), does not begin to freeze until it has been cooled to 28.6° F. RESTRICTED 1 RESTRICTED Salinity may also affect the rate of freezing through its influence on the density of the water. Fresh water contracts on cooling and thus sinks below the surface until a temperature of 39.2° F. is reached. On further cooling it expands, so that its density decreases. If the cooling takes place at the surface with no other process of mixing at work, the coldest water stays there in a layer. It is then necessary for only this surface later to be cooled to the freezing point for ice to form. Water with a salinity of 5% ) has its greatest density at 37.2° F., so the entire body of water must be cooled to that tempera- ture before density currents cease. The temperature of maximum density decreases faster than the freezing point with increasing salin- ity, as shown in figure 1. The two temperatures coincide at a salinity of 24.7%, . This means that with a salinity of 24.7% ) or greater, density currents operate until the freezing point is reached, and the- oretically the entire body must be cooled to this temperature before ice can form on the surface. In nature, however, rapid cooling of still water often occurs under conditions where heat is removed from the surface layers faster than k--- j———-=-p--- ( ( ! | | { es | ' 1 ' ' ' | ' alte eari 4) q----4----4---- ---4----f fos anno aoe a ae me Ea TEMPERATURE ' 1 ' ' 4 1 1 ! i} ee | 4-4 -+---4---- Scns ee SALINITY PARTS PER THOUSAND Figure 1.—Relationship between freezing point and temperature of maximum density for water of varying salinity. 2 RESTRICTED RESTRICTED it can be supplied from the deeper layers through convection cur- rents, so that ice will form on the surface before the deeper layers have approached the freezing point. Salinity gradients in the sea may also diminish the thermal convection currents. If, because of discharge from rivers or melting of ice, the top layers have a lower salinity, the difference of density may be so great that the surface layer, although cooled to the freezing point, will be too light to sink below the warmer but more saline water underneath. A practical outcome of the foregoing is that if a body of water originally of uniform density is losing heat at the surface, ice will be formed most readily in fresh water, less readily in sea water of low salinity, and least readily in sea water of high salinity. The greater heat removal required to freeze sea water is due not only to its relatively low freezing point, but also to the increased tendency of the cooled surface water to sink as the temperature of maximum density decreases. THE GROWING PROCESS On account of its fairly high specific heat and low thermal con- ductivity, water loses heat slowly, so that the surface temperature of a large body of water will lag behind the rise and fall of the mean air temperature. In the Murmansk-White Sea area (lat. 65° to 70° N.), rivers usually freeze about 3 weeks after the mean air tempera- ture falls below 32° F. This phenomenon is probably representative of many similar regions. Ice forms first in shallow water, near the coast or over shoals and banks, particularly in bays, inlets, and straits in which there is no current, and in regions with reduced salinity, such as those near the mouths of rivers. It spreads from these areas as centers. Such ice, broken up and carried seaward by winds or currents, starts further ice formation in deeper water, where floating ice that has not melted during the previous season also acts in the same way. Wave action ordinarily hinders the formation of ice to some extent by mixing the waters of the upper layers. Old ice damps sea or swell and, at the same time, by cooling and freshening the water and providing nuclei of ice crystals, assists the beginning of the freezing process. Quickly recurring fresh winds with raised sea will hinder ice formation, breaking it up several times. The greater the depth, with water of salinity greater than 24.7%p , the later is the time of freezing. Asa matter of fact, complete freezing may never occur, as in the case of the central part of the White Sea; hence the necessity for following RESTRICTED 3 RESTRICTED the deep-water route in order to reach high latitudes during the season of ice formation. The first sign of freezing is an oily or opaque appearance of the water, due to the formation of needle-like spicules and thin plates of ice about one-third of an inch across, known as frazil crystals. These consist of fresh ice, free of salt, and increase in number until the sea is covered by slush of a thick, soupy consistency. Snow, falling into water, aids freezing by cooling and by providing nuclei for ice crystals. Except in sheltered waters, an even sheet of ice seldom forms immediately ; the slush, as it thickens, breaks up into separate masses and frequently into the characteristic pancake form, the rounded shape and raised rim of which is due to the fragments colliding with each other. The formation of slush damps down sea or swell, and if the low temperature continues, the pancakes adhere to each other, forming a continuous sheet. RATE OF GROWTH Sea ice may grow to a thickness of 3 to 4 inches in the first 24 hours, and from 2 to 3 more in the second 24 hours. Ice is a poor conductor of heat and the rate of its formation drops appreciably after the first 4 to 6 inches have formed; a snow cover, if present, still further reduces the conductivity, as shown in figure 2. Once a layer of ice is formed, snow falling on the surface retards growth TEMPERATURE — DEGREES FAHRENHEIT o° 15° 3OP O* 52 30° o° 152 30° | | | AIR | ! SNOW ! ICE ee WATER eee THIN ICE THICK ICE SNOW-COVERED ICE- Figure 2.—ldealized diagrams illustrating the distribution of temperature with air at O° F. and sea water at its freezing point of 30° F._ The rate at which heat is conducted through the ice from the water to the air (which, neglecting radiation, is proportional to the rate of freezing of the water or the rate at which the ice increases in thickness) is proportional to the slope of the thermal gradient in the ice away from the vertical. : RESTRICTED RESTRICTED by its insulating power. This is particularly true of loosely packed snow. A common assumption in the North is that heavy snow in the fall means a rapid break-up in the spring. With the subsequent de- creasing rate of growth, ice which has grown steadily throughout the winter is seldom more than 4 to 5 feet in thickness by the following summer. Perennial sea ice may grow in thickness during the summer by re- freezing of thaw water. Snow on the surface melts, and the water runs down through cracks and holes to form a layer of fresh water under the ice. Since the temperature of the underlying salt water is usually lower than the freezing point of fresh water, a layer of fresh water ice is formed on the bottom of the sea ice. In summer, there- fore, a floe melts away on top, but at the same time may be growing slowly on its undersurface. By this process, mud, stones, seaweed, or shells originally frozen to the under side of grounded floes may work right up to the surface. Diatoms frozen to the under side will similarly rise. An autumn period follows, with lower temperature but without ice formation, the supply of fresh water being no longer renewed and the sea temperature not being low enough for the freezing of salt water to begin again. In the second winter, growth continues by salt water freezing. If the ice is unbroken through the second winter, its thickness may reach 7 to 8 feet at the most. Ice in the Arctic polar basin is seldom less than 314 to £14 feet thick, and Nansen reports a maximum thickness of 13 feet 10 inches produced by about 4 years of normal growth. The action of blocks and floes being forced over each other or turned on end by some form of pressure is called rafting. Ice of much greater thickness than ordinary floes can be formed by rafting, tidal over- flow, or other types of flooding such as spray and splashing, but such areas will be of limited extent. The approximate thickness of ice may be predicted from figure 3 if the temperatures at a specified locality are known. Even if exact temperatures are not available, estimates can probably be made from a general knowledge of weather conditions in the region. The only complication in using this graph lies in calculating the “degree days of frost.” First it must be remembered that a temperature of 0° F., for example, is equal to 32° of frost. Secondly, the mean number of degrees of frost for each day, or group of days with the same mean degrees of frost, is to be used, not the mean degrees of frost for the entire period. Days on which the temperature was below freezing for only a part of the 24 hours can be ignored unless exceptionally RESTRICTED +) DEGREE - DAYS BELOW FREEZING POINT °F RESTRICTED aS 6 Seeto 20 40 60 ICE THICKNESS — INCHES Figure 3.—Graph for prediction of approximate thickness of ice. RESTRICTED 80 100 10000 RESTRICTED numerous. For example, assume a specified day had 8 hours below freezing, and the mean temperature for those 8 hours was 25° F. The degree-days of frost for that day are %4 x T=214. Suppose the next day had temperatures below freezing for the entire 24 hours, and the mean temperature was 20° F. The degree-days of frost for this day are 12. If the next 10 days had approximately the same mean tem- perature, say —20° F., and all hours were below freezing, the degree- days of frost for the 10 days are 520. The total degree-days of frost for the 12-day period described above would be 53414. A glance at figure 3 shows that the curve permits considerable approximation in calculating degree-days of frost without seriously affecting the final results. Obviously other factors such as wind, snow, and currents introduce complications difficult to evaluate and not allowed for in the graph. The lowermost end of the curve is none too reliable be- cause freezing weather may exist for a number of days before ice starts to form. In addition, the number of variable factors affecting cooling, mentioned heretofore, is difficult to evaluate. Once a layer of ice has begun to form, the curve is much more reliable. The annual history of ice in far northern harbors is shown in figure 4. The size of such curves will differ from place to place, but their shape will undoubtedly be similar. The important things to note are the steady increase in thickness for two-thirds to three-fourths of the total period, the brief flattening off, and finally the sudden drop at the end. COMPARISON OF ARCTIC AND ANTARCTIC ICE Differences in underlying factors specific to the region develop cor- responding differences in the features of the ice. An example of one of these agencies is the low mean annual temperature of the Antarctic. The warmth of the Arctic summer has no parallel in the far South and, mainly because of this thermal difference, the ice sheets of the northern polar regions are unlike those of the southern. The margin of the Antarctic cap, overflowing its land support, is free to spread over the sea until fracture detaches huge strips, sometimes including 10 to 20 miles of its front. In Greenland, by contrast, the edge of the inland ice ends on land, and icebergs irregular in shape are formed. The tabular or box-shaped berg is, therefore, in general, characteristic of the Antarctic while the pinnacled, picturesque berg is typical of the North. The Antarctic sea ice surrounds the continent, while the Arctic sea ice is a central mass surrounded by land. The ice moves around and 963067°—51 RESTRICTED 7 2 RESTRICTED outward from Antarctica and gathers in a belt formed by the meeting of southeasterly and northwesterly winds in the vicinity of the 60th parallel. There is a close correspondence in the formation of this belt of ice with that formed in the Arctic which follows down Davis Strait and eastward off Greenland. In the Antarctic it is unusual for sea ice to be more than 1 or 2 years old. The drift in both the Weddell and Ross Seas carries the pack out into the open oceans in a little over a year. In the Arctic, on the other hand, floes of great age are frequent. Ice formed off the Siberian coast takes from 3 to 5 years to drift across the polar basin and down the eastern coast of Greenland. Ice of this age, therefore, becomes pressed and hummocked to a degree unknown in ice formed in lower latitudes. The warmth of the Arctic summers also has its effect and the result is worn-down, more or less even, floes of great thickness known as “polar cap ice.” During the summer, melt- ing on the surface is considerable, as a rule about 2 feet, and pools of HES seer aaa P| |) a cra cA eas HAA 71 ||.) | | aa Sept June July THICKNESS OF ICE — INCHES Figure 4.—Course of thickness of ice formed in two typical sheltered harbors in the Northern Hemisphere at the latitudes indicated. 8 RESTRICTED RESTRICTED fresh water are formed on the floes. This is not a very marked feature off the east coast of Greenland, north of latitude 72° N., but in Baffin Bay the floes become covered with a maze of deep pools. In the Ant- arctic, surface pools on floes in the pack are almost unknown. The outstanding difference between Arctic and Antarctic ice, which is ap- parent to the navigator, is the softer texture of the latter. PALEOCRYSTIC ICE The extreme development of sea ice is found in the channel between Grant Land and the northwest coast of Greenland. Here the early explorers encountered ice masses so thick and irregular that they were assumed to be closely packed bergs of glacial origin. Later observa- tions, however, indicate that this paleocrystic ice consists of remnants of Arctic pack that is blocked by the tip of Peary Land from drifting down the east coast of Greenland and instead is trapped along the north coast of Greenland and Grant Land. Intensive hummocking of this pack over a period of years produces tremendous floebergs. RESTRICTED 9 RESTRICTED CHAPTER II CLASSIFICATION AND DESCRIPTION OF ICE Ice met at sea consists for the most part either of icebergs originat- ing from glacier and continental ice sheets, or of sea ice formed by the freezing of the top layers of the sea itself. Sea ice proper accounts for probably 95 percent of the area of ice encountered at sea, but bergs are important because of the manner in which they drift far from their place of origin, constituting grave menaces to navigation. A certain amount of ice may also originate in rivers or estuaries as fresh- water ice, but it is already in a state of decay by the time it reaches the open sea and its importance is no more than local. With some risk of over-simplification, figure 5 outlines the re- lationships between the chief categories of ice, and gives an indication of the cycles of formation and disintegration. Land Ice Sea Ice WATER VAPOR SEA WATER c ° = SNOW SLUSH > é ee | Ps NEVE PANCAKES ° | | : E nn 7 CAP Ae IC ‘GLACIERS SHELF ICE FAST ICE—>PACK ICE—»ARCTIC PACK (Arctic only) PALEOCRYSTIC ICE (Antarctic only) PROOGGy 10 5 ie) ioe] ie] D Q n ' ‘ ' ‘ = a = z e) 7 ce) A | ie} 7) > a ° ° |] < Ae CE BERG ys essen 82) 4° KAUINNVIOC RS @e— UGS he ae ; | | | : BERGY BITS FLOEBERGS FLOES = | gs s STORIS B GROWLERS “> GLACONS 3 °° BRASH $ y = SEA WATER “ WATER VAPOR Figure 5.—Synoptic diagram showing the general relationships between the various kinds of ice occurring in the sea. 10 RESTRICTED RESTRICTED ICEBERGS Icebergs are large masses of floating (or stranded) ice derived from the fronts of glaciers, from glacier ice tongues, or from the shelf ice of the Antarctic. They are products of the land, and not of the sea. Their structure, and to some extent their appearance, depend upon the source from which they are derived. Arctic bergs originate mainly in the glaciers of Greenland, which has 90 percent of the land ice of the north polar region. Svalbard, Novaya Zemlya, and Ellesmere Land also produce a few bergs. Arctic bergs are irregular in form and take many varied shapes. Most com- mon are the irregular dome-shaped bergs, produced by glaciers that have plowed across the uneven foreland on their way to tidewater which differ entirely from the flat-topped, straight-sided bergs orig- inating where the ice sheet itself is thrust directly out into the sea. In color, bergs are an opaque flat white, with soft iridescent hues of blue or green. Many show veins of soil or rock debris; others may have yellowish or brownish stains, probably due to diatom films. Un- der certain conditions of illumination, an iceberg will appear dark in contrast with the sky or with other bergs in the direct sunlight, and this phenomenon has often led mariners to report islands where none exist. The higest berg yet measured in the Arctic stood 447 feet out of water; 230 feet is a common height for a large berg. These figures refer to bergs soon after calving; the highest so far observed to the southward of Newfoundland was 262 feet. The longest iceberg meas- ured in those waters was 1,696 feet long, although one several miles long was reported in 1928. The ratio of the mass of the submerged portion of a berg to its total mass 1s equal to the ratio of the specific gravity of the berg to that of the water in which it is floating. On account of the origin of glacial ice In compacted snow, berg ice contains up to perhaps 10 percent of trapped air and is therefore somewhat less dense than ordinary ice. Measurements of the specific gravity of ice in Greenland bergs have given values close to 0.90, while the cold sea water in which they float has a specific gravity of about 1.027, so that about seven-eighths of the mass is submerged. It is often erroneously assumed that a berg with one-eighth above water and seven-eighths submerged should be float- ing with a draft seven times its height above water; but these ratios hold good only for mass, and not for linear dimensions. Actual measurements on Arctic bergs show that the draft is seldom more than RESTRICTED 11 Figure 6.—Tabular iceberg off Scott Island. five times the exposed height for the blockiest bergs, and may be as low as one or two times the height for the pinnacled and irregular types. Tabular bergs, the most common type in Antarctic waters, are de- rived by breaking off floating portions of the continental ice sheet. Bergs of great size, much larger than any found in the North, may be produced in this way. In January 1927 the whale-catcher Odd J sighted one off Clarence Island which was about 100 miles in length and width and floated about 130 feet out of water. There are nu- merous reports from the Antarctic of bergs 1,000 feet out of water and even higher, but these observations were made from sailing ships and have never been confirmed by a trained scientific observer. Poul- ter measured the average thickness of the floating ice barrier in the Bay of Whales as 760 feet with 94 feet out of water, or a draft of seven times the height. He determined that this ice was formed from com- pacted snow and frost, without glacier material from the highlands. Elsewhere in the Antarctic, névé bergs are encountered with a draft only about twice the height. These are formed at localities like Rob- ertson Bay, where precipitation is at a rate greatly in excess of abla- tion. Where glaciers in the Antarctic lead across a sloping foreland to the sea, irregular bergs like those of the Arctic are produced. On a clear day an iceberg can be seen at a great distance, owing to its brilliant luster; during foggy weather it may not be perceptible 12 RESTRICTED RESTRICTED until dangerously close aboard. When the fog is dense but the sun is shining the first appearance of a berg is in the form of a luminous white object ; while if the sun is not shining it is a dark, somber mass with a narrow streak of black at the water line. Diffusion of light in the fog will produce a blink around the berg that augments the appar- ent size of the ice mass. Relieving stresses set up by temperature changes, and responding to vibrations from sound or wave action, bergs may at anytime calve off large sections of ice, which after falling into the water may bob up to the surface again with great force, often at a considerable distance away. Bergs are often so balanced that this calving, or merely melt- ing of the under surface, will cause a shift in the center of gravity with consequent capsizing and readjustment of the mass to a new state of equilibrium. Vessels and boats should therefore keep well clear of bergs that give evidence of disintegrating or overturning. Bergs may also possess underwater spurs and ledges at a considerable distance from the visible portions, and should be given a wide berth at all times. In fair weather, icebergs can be of great assistance to navigation in floating ice. They may mark shoals, break up consolidated pack, and afford reference points to assist in conning through ice. Having a relatively small “sail area” in proportion to their bulk, bergs are not affected by wind to the same extent as pack ice, and with a wind blow- ing the pack past a berg, the optical illusion may arise that the berg is being carried to windward, cutting a channel. Illusion or not, such a lee may be a desirable place for a vessel to le to avoid heavy ice; there are cases on record of vessels laying out an ice anchor to a berg under such circumstances. ge epee ee ge OES Oe =k. Ob! Sonal —=.190 +. 25 ALE AE RS it Sos pare Ren Denese Eta, tes SH Ge —= 98-2) |— LOSS ee eos —0. 35 26 RESTRICTED RESTRICTED A negative value in the above table means that the volume increases with decreasing temperature. The expansion of pure water on form- ing ice at 32° F. is equivalent to a coefficient of expansion of —900 in the units of the table. The annual course of temperature in the pack ice of the East Sibe- rian Sea, from measurements made in the /aud from 1922 to 1924, is given in the following table: TEMPERATURE IN THE SEA ICH, °F. i low = 3 eee. = Oe racis January ee March April May June Ost 2 eee —18.4 | —23.6 | —20. 4 —6. 9 18. 7 29. 3 Qk 3 —11.4] —16.4]| —14.8 —4,2 16. 5 26. 6 SQ) tS Se eee —2.0 —6.3 —5. 8 .9 LSB" 24. 6 0) =< Sa eae eee 6. 8 2.7¢ 2.3 6. 1 15. 4 23. 9 SO Meena ee esas 20. 3 16. 7 14. 7 iL, a eS, 7 252 Distance below surface Septem- Novem- | Decem- of ice, inches July August ber October ber ber Qas24* 2 ee eee 32. 0 32. 0 23. 5 9. 9 —9, 4 —21.8 Gee ere ee 31.8 32. 0 29. 7 18.3 0 —11.9 3023 533 ee 29.7 30. 6 30. 4 26. 1 10. 6 5 5). e 28. 9 30. 0 30. 0 29. 1 19. 2 10. i 0). 2 oa ee 28. 8 29. 8 29. 7 29. 5 Pails, WB), 7 SPECIFIC GRAVITY As indicated in discussing the thermal expansion of ice, the specific gravity of pure ice is about nine-tenths that of water at the freezing point. The exact value for water is 0.9921 at 32° F., and for pure ice 0.9168. Sea ice will contain a proportion both of salt or brine, which will increase the specific gravity, and of air, which will reduce the specific gravity. Malmgren found extreme values of 0.924 for newly formed ice, and 0.857 for the top of summered ice, in which the brine cells were replaced with air bubbles. He found that in general sea ice less than one year old had a specific gravity greater than 0.90, but that it fell below 0.90 after the ice had weathered a summer. Glacier ice, such as makes up icebergs, has a fairly high apparent air content; but it is likely that the air is under considerable pressure RESTRICTED 2] RESTRICTED and therefore does not lower the specific gravity as much as would be expected, since most determinations of the specific gravity of berg ice give values not far from 0.90. SALINITY When sea water freezes, the first ice crystals that form are practi- cally salt-free, but they are surrounded by a brine that is saltier than the unmodified sea water and tends to sink below the surface. When the crystals cement together, some of this brine is entrapped among them, so that, on the average, a piece of newly formed ice will have an appreciable salt content. A microscopic examination of a section of such ice would show areas of nearly pure frozen water alternating with zones of brine. As the temperature decreases, the freezing point of the brine is reached, more water solidifies, and the remaining brine becomes more coneentrated. This process may con- tinue until the brine cells are so concentrated that they become sat- urated with respect to salt. At very low temperatures, crystals of salt will also be found interspersed in the mass of sea ice. The faster the ice forms, the greater the salt content, since more of the brine will be trapped in the ice structure without a chance to sink. This fact is illustrated in the following table, from observations by Malmgren: SALINITY OF SEA ICE AS A FUNCTION OF TEMPERATURE Memperature of formation, bens se ae 3 1s —22 —40 Salinity, parts per thousand (%%p)------------ 5. 64 8. 01 8. 77 10. 16 The saltiest piece of ice encountered by Malmgren had a salinity of 14.59%,. The salinity of the sea water in which it was formed was around 30% ,. Since the rate of freezing determines the salinity of sea ice, and the thicker the ice the lower the rate, the salinity of newly formed ice will decrease from the surface downward. The following table, again from Malmgren, illustrates this: SALINITY OF NEW SHA ICE AS A FUNCTION OF DEPTH Distance from surface, inches. 0 2.4 5.2 18 32 37 Saline (noice 2 cee 4 6.74 6.28 6.31 4.37 3.460 eaein A snow covering over the floe will result in the formation of ice of lower salinity, since the rate of freezing, as illustrated in figure 2, is lowered. Once formed, however, ice tends to freshen. It is well known that the freezing point of ice decreases as pressure increases; this is illus- 28 RESTRICTED RESTRICTED trated in figure 10, and is the phenomenon that makes ice skating possible. Since the brine cells in the ice have a greater specific grav- ity than the ice crystals, the ice in contact with the bottom of each brine cell is under a slightly greater pressure than the rest of the block, and the ice directly above each cell is under a slightly lower pressure. Each cell therefore is slowly melting the ice directly under it, while the ice is resolidifying over it. The brine therefore slowly travels downward under the influence of gravity, leaving the lighter ice behind. This process is greatly accelerated the following sum- mer, when the temperature may not be low enough to refreeze the melting above the brine cells. The result is that air holes remain in the ice where the brine cells have been, and ice with a specific gravity under 0.90 forms. RESTRICTED 29 RESTRICTED CHAPTER V MOVEMENT AND DRIFT OF ICE FACTORS PRODUCING TRANSLATION AND DIFFERENTIAL MOTION Sea ice, other than fast ice in sheltered bays or along the coast, is continually in motion as a result of the effects of wind, tide, and cur- rent. Although this motion may be the same for a time over a con- siderable area, there is a number of factors tending to produce differential motion of adjacent masses. Cakes, for example, vary in area and thickness, so that effect of wind and current differs on differ- ent masses of ice. Wind and current are also subject to continual local variations, wind from the usual meteorological causes and cur- rent from tidal effects. The swinging or turning of floes is due to the tendency of each cake to trim itself to the wind when the pack is sufficiently open to permit this freedom of movement. In close pack this tendency may. be pro- duced by pressure from another floe; but since floes continually hinder each other, and the wind may not be constant in direction, even greater forces result. Thus wind produces rotation as well as translation. This screwing or shearing effect results in excessive pressure at the jutting corners of floes, and forms a hummock of loose ice blocks. Ice undergoing such movement is called screwing pack, and is extremely dangerous to vessels. In its motion the ice opens and shuts like an accordion; there is always a certain number of lanes present, otherwise the ice could not move. In summer these lanes remain open, except in very high lati- tudes, but in winter they are soon frozen over with young ice. Swell also tends to break up the ice, as well as the vertical movement of the tide in narrow or shallow waters. As a result of all these agencies, the ice is alternately being broken up, even throughout the winter, and subjected to pressure. The onset of pressure or release of pressure may happen at any time of year, even during the lowest mid-winter temperatures. HUMMOCKING As moving floes are driven together or pressed against fast ice, bending, tenting, or rafting occurs, according to the degree of pressure and the composition of the ice. Definite ridges may thus be formed, 30 RESTRICTED RESTRICTED the lines of which are at right angles to the direction of impact; or confused pressure areas of hummocky ice may be formed. The longer the pressure lasts, the greater the chaos produced. Pressure ridges may be as high as 50 feet where grounded against a coast, but in deep water away from land the greatest height is from 20 to 30 feet, al- though it is more usual to find ridges of 10 to 15 feet. A ridge is at its highest when first formed. A certain amount of settlement soon iakes place, owing to the sinking down of the whole mass under the weight of the hummocks until hydrostatic equilibrium is reached. The weight of a ridge is ultimately supported by a downward exten- sion of ice under water, which may be as much as 4 to 5 times the height of the ridge above. During summer, the pressure ridges change in outline and the sharper features soften to the form of rolling hil- locks. Snowdrifts form against the ridges, the balance of the weight alters, cracks form due to differential loading, and the opening and closing process goes on. The release of pressure gives rise to lines of weakness in ice fields in the form of cracks or lanes. These are often parallel to pressure Figure 11.—Hummocky ice floes in Eureka Sound. RESTRICTED RESTRICTED ridges, but owing to internal stresses an ice field does not necessarily crack in its thinnest part. Thus, cracks are frequently found passing through ridges and hummocks of considerable height. Thin half- melted ice may be left holding, but this is in many cases destroyed if the wind changes. REGROUPING OF ICE Any wind will tend to regroup ice that is more or less scattered over «a considerable area. As the wind rises, the separate floes form lines in a direction at right angles to the wind direction. These chains break up when the wind changes, and after a time realign themselves at right angles to the new wind direction. When the wind blows from the shore, a channel of open water usually forms between the coast and the ice or increases in width if already existing. On the other hand, a wind blowing on to a coast or on to fast ice tends to reduce the Figure 12.—Airplane photo of huge iceberg showing direction and effect of deep-water currents. Although the berg stands about 280 feet above water, it extends more than 1,000 feet below surface and is affected by currents which run too deep to move neighboring ice. RESTRICTED width of the channel previously existing. If the wind is strong enough, hummocks will be produced along a line approximately perpendicular to the wind direction. The air temperature as influenced by the wind also has an effect on the grouping of ice. If the wind which has regrouped ice is a cold one, the lowered temperature may cause further freezing, so that the masses may become joined by new formation. In this case the ice would not be so readily broken up and regrouped by a change of wind. On the other hand, if the weather is mild, cakes brought together by a change of wind will not join together. The rate at which the different floes travel is not so much dependent upon the size and depth of the floe as upon the nature of its surface. Since the pack is made up of a conglomeration of young ice, old floes which have been subjected to pressure, and icebergs, it varies radically in resistance to wind and current. Surface irregularities, such as hum- mocks and pressure ridges, act as sail areas, and the rate of movement of a floe depends to a certain extent on the amount of hummocking in proportion to the area and weight of the floe. Asa result of previous pressure, hummocked floes in turn become the cause of still further pressure. When two floes are moving at different rates, either the dis- tance between them is increased and a lane produced, or the distance between them is decreased and the floes brought into physical contact. In gaining momentum, larger floes will accelerate more slowly, but once underway, they will carry their way long after smaller floes have stopped moving. In the early stages, therefore, the large heavy floe will be charged by smaller floes overtaking it; in the later stages, it will itself be the attacker of smaller floes in its path. Because of their size and weight, the smaller floes will be disrupted and the floe surface materially modified, thereby creating new possibilities of further dif- ferences in speed. LAWS GOVERNING DRIFT While the general direction of the drift of icebergs over a long pe- riod of time is known, it may not be possible to predict the drift of an individual berg at a given place and time, for bergs lying close to- gether have been observed to move in opposite directions. They move under the influence of the prevailing current at the depth to which they are submerged, which may often be in opposition to the existing wind and sea or surface drift. The International Ice Patrol has had considerable success in predicting the drift of bergs off Newfoundland by determining the surface current patterns through the methods of physical oceanography. RESTRICTED 33 RESTRICTED Pack ice drifts with the wind and tide, usually to the left of the true wind in the Southern Hemisphere, and to the right in the Northern Hemisphere. The speed of drift may not depend entirely upon the strength of the wind, since it is influenced greatly by the presence or absence of open water in the direction of the drift, even though the open water is somewhat distant. Neglecting the resistance of the ice, Ekman’s theory of wind drift calls for the ice to drift 45° from the wind direction. Observations show that the actual drift is about 30° from the wind direction on the average, or very nearly parallel to the isobars on a weather map. In winter, when the ice is more closely packed and offers more resistance, its drift deviates less from the wind direction than in summer, and tidal influences become more important. The speed of drift of pack ice can be fairly closely determined from the wind speed. Observed average speeds of drift of ice in the Northern Hemisphere range from 1.4 percent of the wind speed in April to 2.4 percent of the wind speed in September. There is a northward tendency in the drift of Antarctic ice, on which the left-hand component due to the earth’s rotation is superimposed. The pack therefore travels westward and northwestward around the continent, and into and around the Weddell Sea in a clockwise direction. The general circulation of the ice of the Arctic Ocean is determined by the direction of the ocean currents, which are the result of two chief factors: the circulation of the atmosphere above the polar basin and the surrounding adjacent seas, and the influx into the polar basin of water of oceanic and river origin, with a compensatory outflow of the water from the polar basin. Above the central part of the polar basin, the cap of cold air has an anticyclonic (clockwise) movement which causes a movement of the polar cap ice in the same direction. Because of the deflecting influ- ences of the earth’s rotation, all movements in the Northern Hemis- phere tend to incline to the right. The ice moves slowly under the action of wind and current toward the opening between Norway and Greenland. The speed of the cur- rent increases as it approaches the opening, particularly its western mouth between Svalbard and Greenland, and great masses of ice (the storis) are carried swiftly southward along the east coast of Greenland. The ice that floats southward, east of Svalbard, soon melts in the warm waters derived from the Gulf Stream. 34 RESTRICTED RESTRICTED CHAPTER VI VESSELS FOR OPERATING IN ICE WOODEN SHIPS The earliest vessels to be navigated in the ice of polar regions were the ordinary wooden sailing ships of the day. A strengthened ver- sion of this type of construction, with the addition of auxiliary steam engines and a feathering or hoisting screw, was favored until recent years by whalers and sealers, in whose experienced hands it proved highly successful. Compared with contemporary sailing vessels of ordinary type, they had heavier bow framing, usually with sheathing of ironbark or greenheart along the waterline to withstand the scor- ing action of ice, and with iron plating at the stem; but otherwise they were little modified in design or construction from the general ship- building practice of the period. A notable example of this type was the auxiliary barkentine Bear, a vessel of 728 gross tons measuring 190.4 x 29.9 x 18.8 feet, built at Dundee, Scotland, in 1874 as a whaler and sealer. She was acquired by the United States Navy in 1884 to relieve the Greely Expedition at Cape Sabine, then was transferred to the Revenue Cutter Service (later the Coast Guard) and was operated in Alaskan waters until 1926. In 1933 she was acquired for the second Byrd Antarctic Expe- dition; next she served with the U. S. Antarctic Service Expedition in 1939-41; and finally she returned to Greenland waters for patrol duty in the early part of World War II. The exploration vessel Discovery, built in 1901, which has also served in both the Arctic and Antarctic, represents perhaps the ulti- mate development of this type of craft. Her plans and description can be found in the article by W. E. Smith. A similar but smaller type of auxiliary wooden vessel has been evolved for the requirements of the Norwegian seal fishery, and these have also been used as expe- dition ships. The Quest of Shackleton’s 1921-22 expedition, a vessel of 240 gross tons, 110 x 24.9 x 11.8 feet, is a typical example. Such sealers were employed in Greenland waters by the German Navy in 1940-41. More recently, a number of wooden auxiliary sailing vessels have been built as reparations in Finland for service in the Soviet Arctic. RESTRICTED 39 RESTRICTED The major drawback of vessels of this design in ice is their inability to withstand lateral ice pressure if they happen to become beset or are deliberately frozen in. Although the whalers successfully wintered in the Arctic by allowing their ships to freeze in at a location well sheltered from the open sea, a long list of ships lost through ice pres- sure when frozen in or “nipped” could be compiled. DeLongs’ Jean- nette and Stefansson’s Harluk in the Arctic and Shackleton’s Endurance in the Antarctic would be included. As a means of circumventing this disastrous possibility, a few ships were designed with flaring sides and easy bilges so that there would be no vertical surface for ice to bear against. The horizontal pressure of the ice would thus have a lifting rather than a crushing effect. Nansen’s Fram, built according to these principles, proved successful. The design was further perfected by Christian Jensen in 1917 in Amundsen’s Maud, which spent several winters frozen in Arctic pack and successfully negotiated the Northeast Passage. The J/aud was a wooden vessel of 392 gross tons, measuring 107.1 x 41 x 15.9 feet. She was built with double layers of planking and diagonal bracing in the hold, and had a 240-horsepower oil engine in addition to three-masted schooner rig. ICEBREAKERS With the development of powered vessels came the possibility of designing a vessel to cut or break through ice. Specially strength- ened tugs or ferries were being used for this kind of work in harbors, both in the United States and abroad, shortly after the steamboat was introduced. In 1899 there appeared the first seagoing icebreaker, the #rmack, built in England for the Russian Government. Built of steel, with 114 inch plating along the waterline, this vessel displaced 10,000 tons and had engines of over 10,000 horsepower with three screws aft and one forward. Although without precedent, her design proved successful for her intended employment, and she may be re- garded as the prototype of all later seagoing icebreakers. The Wind class icebreakers of the United States Navy and Coast Guard, described in the paper by Rear Adm. H. F. Johnson, represent the latest development in United States seagoing icebreaker design. With over-all dimensions of 269-foot length and 63-foot beam, they displace 5,040 tons on 25 feet 9 inch draft. As originally designed they were powered with six 2,000-horsepower Diesel generator sets con- nected to motors on the shafts. The electrical arrangements permitted production of 5,000 horsepower on each of the two after shafts, or 3,300 horsepower each on all three. The bow propeller has been found 36 RESTRICTED . RESTRICTED to assist in penetrating ice when the tips of the blades are below the under surface of the ice, both by inducing turbulence to break up the ice and by washing it back out of the way after it is broken. The double bottom of these vessels is carried up above the load water- line, the two skins being 15 inches apart. The outer plating is 154 inch high-tensile steel at the waterline, tapering to 1% inches on the bottom. The pronounced flare to the underwater sections, resembling that of the Maud, is matched by considerable tumblehome in the top- sides, for the purpose of reducing the fouling of top hamper when working around heavy ice or other vessels. The bow of the Wind class has the characteristic sloping forefoot of icebreakers, which acts to slide the bow of the ship up onto ice too heavy to break by the forward motion of the ship alone. The weight of the ship thus exerts a bending action on the ice, which is much weaker in tension than in compression and therefore breaks. Since icebreakers must at times back into ice, the shape of the forebody is reproduced in the afterbody. In the Wind class there is a notch in the stern for towing. This is heavily padded to receive the stem of any vessel that has to be towed into ice, thereby eliminating the possibility of the tow running down the icebreaker should it be suddenly stopped by striking an unusually heavy piece of ice. The extra power from the vessel close-coupled astern can also be of assistance in breaking ice. The vessels can be assisted in their attack on the ice by reducing stick- ing from static friction through the use of wing tanks and heeling pumps, which transfer 220 tons of water from one side to the other and produce a 10° rollin 144 minutes. Ballast can also be shifted between fore and after peak tanks to change trim, to assist in backing off ice, or to present the most advantageous angle of attack under different loading conditions. Vessels of this class can successfully maintain a speed of 4.8 knots in 5-foot thick ice, using the bow propeller, although there is some ques- tion as to value of such a propeller in heavy pack in the open sea. Without the bow propeller, they can open channels in 10-foot broken polar ice at a speed of advance of 1 knot, by backing and ramming. CARGO SHIPS Modern steel merchant vessels are not suited for unassisted naviga- tion in any but the most open kinds of floating ice. The chief source of weakness is the bow plating, but other structural deficiencies can be gathered from the following extract from the rules of the American Bureau of Shipping: RESTRICTED 37 RESTRICTED (1) General—vVessels constructed with special strengthening which is at least as effective as that described in this section will be distin- guished in the record by the words “Ice Strengthening.” (2) Special strengthening for navigation amongst ice should cover an area which extends from the stem to the midship three-fifths length (i. e., one-fifth of the length from the stem) between lines which are respectively at least three feet above the load line, and three feet below the light load line. (3) Intermediate frames having a strength of at least 75 percent of the strength of the fore peak frames should be fitted over this area; the intermediate frames should extend from the deck next above the strengthened area to a lower level than the top of the frame brackets or floor plate. (4) Side plating should be of midship thickness. forward to the strengthened area; the thickness of the shell plating over the strength- ened area should not be less than 0.6 inch in vessels under 250 feet in length, and need not be more than 1 inch in vessels over 500 feet in length; the thickness for intermediate lengths may be obtained by interpolation. (5) Rudder scantlings, rudder stock, steering gear chains, etc., should all be at least 10 percent above the ordinary requirements of the rules. (6) Zailshafts i single screw vessels should have a diameter at least 5 percent and those in twin screw vessels at least 10 percent greater than required by the rules. (7) Propeller blades made of cast iron should not be used. (8) Sea connections should be so arranged as to minimize the risk that attends their attachment to plating which is subject to ice damage. Main injections should be provided with steam connections for clear- ing the strainers. Arctic-constructed vessels with icebreaker assistance could penetrate any part of the Bering Sea, according to the experience of the Burton Tsland in January-February 1949. A 3:1 ratio of these vessels to icebreakers could be maintained, as compared with a 1:1 ratio necessary with unstrengthened ships. A few cargo vessels, built with an ice-breaking bow, form a class intermediate between the sea-going icebreakers and the strengthened cargo vessels. One of these was the Vascopie, which was operated in northern Canadian waters by the Hudson’s Bay Company from 1912 until her loss in 1946. 38 RESTRICTED RESTRICTED SUBMARINES In 1931, Sir Hubert Wilkins published a book advocating the use of submarines in ice exploration, advancing the argument that a sub- marine could dive under ice that was impenetrable by the strongest icebreaker, and that even the densest Arctic pack contained leads in which a submarine could safely surface. He obtained an obsolete United States submarine, the Vautilus, in which he navigated to the edge of the pack near Svalbard in September 1931. At this point it was discovered that the diving rudders of the Nautilus had been lost, so that it was impossible to continue under the ice and test the prac- ticability of the submarine for ice navigation. The experiment with the Vautilus has not been repeated by a civilian explorer. In 1944 a German submarine navigated under the Northeast Green- land Pack, surfaced inside, and fired two torpedoes at the U. S.C. G. C. Northwind. The submarine escaped by submerging and running beneath the pack. LST’s LST’s may be used for transporting and unloading cargo in the polar regions with the assistance of LVT’s carried along. To strengthen LST’s in order to improve their serviceability in ice, Douglas fir wood sheathing 55g inches thick should be installed from the turn of the bow forward and covered with 14-inch steel plate. Sheathing abaft the turn of the bow may be omitted. The bow doors should have 14-inch steel plate quilted over the wood sheathing men- tioned above. Bracing timbers should be fitted between the bow doors and hull adjacent to bottom of ramp. The flaps on the bow doors should be welded shut and otherwise made an integral part of the door. The bottom plating in the way of the bow voids should be strengthened to prevent possible rupture from below. The hull forward of the propeller guards should also be strengthened to prevent puncture when the stern swings into ice. In an experiment with two LST’s on an expedition to Barter Island, a steel propeller was fitted to one shaft of each and the usual bronze propeller left on the other shaft for comparative purposes. It was found after the voyage that, except for minor pitting, the steel pro- pellers were in almost new condition whereas the bronze propellers on both ships were bent. An LST, even though specially strengthened, is not a suitable vessel to absorb the punishment entailed in following an icebreaker through the heavy, close pack of the type encountered between Point Barrow 963067°-—51—4 RESTRICTED 39 RESTRICTED and Barter Island. The type of ice floes in this area requires it to make continuous approaches at steerage way. Moreover, icebreakers, because of their peculiar hull form, create a strong stern suction that swirls ice in behind them. Because of the running start required by the icebreaker in breaking heavy ice and the nonhomogeneity of the pack, it is impossible for an LST to follow closely enough behind the icebreaker to take advantage of the lane she makes. As it is necessary to make contact with the ice at bare steerage way in order to minimize damage to the LST, an average speed of only 1 to 2 knots can be maintained in heavy, close pack. Damage to LST’s may be sustained by swinging into one piece of ice while trying to avoid another. It was found that the LST immediately behind the ice- breaker is subject to more punishment than the last one in a column. From this fact, it may be concluded that a reasonable number of LST’s could follow single file behind an icebreaker in the type of ice encountered in this area. However, when the icebreaker cannot maintain a straight course, the consequent twisting and turning of the LST’s make their conning exceedingly difficult. It is believed that convoying cargo ships through ice of the Alaskan coast presents certain features which may not hold in other Arctic areas and which are assuredly different from the task in Antarctic areas. VESSELS FOR ALASKAN AND CANADIAN WATERS The vessels used at present for navigation in the waters east of Point Barrow have evolved from many years of accumulated expe- rience in that region, which began with the whalers in the 1850's. They commonly winter in the area. The desirable characteristics of such vessels are listed by a veteran navigator as follows: 1. Strength—sStrength of construction is of vital importance for obvious reasons. A wooden vessel should be sheathed for 4 to 6 feet abaft the fore edge of the stem with either plates or strakes of 14-inch steel, flush-fastened. Strakes are preferable to plates on account of the ease of renewing them if damaged. The hawsepipes should be constructed so as to allow the bower anchors to stow flush with the ship’s side; otherwise, the projecting flukes will act as an obstruction in ice. Where this cannot be accomplished, anchors should be catted prior to entering the ice. 2. Power—Diesel power is preferred because fewer engine per- sonnel and no boiler feed water are required. Fuel supplies are readily available at Norman Wells, Fort Smith, and other points in the region. 40 RESTRICTED RESTRICTED 3. Speed.—The short navigable season of the Western Arctic makes speed a necessity, in order to take full opportunity of every patch of open water. 4. Endurance-—Endurance is another quality of prime importance, in view of the large distances that often must be traversed through ice in making good a course between two ports. 5. Maneuverability.—A relatively short, beamy vessel is considered easiest to handle in ice. The trim of the vessel must also be carefully adjusted. 6. Shallow draft—The necessity of taking shelter in the shallow bays and inlets, and the desirability of being able to work between grounded ice floes and the shore, imposes a maximum limit of 12-foot draft for vessels in this area. Even the M/aud which, after weather- ing several years of navigation north of Siberia, was then bought by the Hudson’s Bay Co., proved unsuitable for work in Northern Canada because she drew more than this. The motorship Port Ross of the Hudson’s Bay Co. is a good example of this class of vessel. Built of wood in Nova Scotia in 1938, she measures 128.4 x 24.4 x 12.7 feet, registers 272 tons gross, and draws 11 feet 8 inches fully loaded. She has a single monel screw, driven by a 240-horsepower Fairbanks-Morse Diesel. RESTRICTED 41 RESTRICTED CHAPTER VII PREPARING A VESSEL FOR ICE OPERATIONS In the preceding chapter the design features which render a vessel suitable for operating independently in ice were discussed. The lim- ited number of such vessels in existence generally makes it necessary to conduct operations in ice using vessels of ordinary type convoyed by icebreakers. Although in such cases it is impossible to make the structural modifications just described, proper care in preparing a vessel for work in ice will add greatly to the safety of the operation and the comfort and efficiency of the personnel. When navigating in ice a vessel runs the risk of being damaged in various ways, so that both prevention and remedy depend largely on the extent to which she has been prepared for the voyage. The pri- mary phase of preparation consists of the measures taken while in port and en route to the area of operations, since both facilities and time are limited in the frozen areas. The second phase comprises the pre- cautions taken while in the operating area. Needless damage, delay, and work can be eliminated by a taut ship with an alert and energetic crew. However, regardless of all preventive measures taken, damage to the vessel is not always avoidable, so that the third phase of main- tenance, that of making repairs to the vessel after it has been dam- aged, may be and usually is necessary. Remedial measures, anticipated or improvised, skillfully made, will in many cases be the salvation of the ship. FITTING-OUT SHIP The following check-off list of items to be attended to before leaving the home port for polar waters has been compiled from the combined experience of naval combatant. types, naval auxiliaries, and merchant ships. Not every item, therefore, will be found applicable in indi- vidual cases, but careful consideration should be given to all. 1. Screws.—Equip the ship with steel propellers. Provide a spare propeller for each shaft. If propellers have removable blades, see that all blades are interchangeable. Test the spare bosses in drydock to see that they fit the shaft. Provide wrenches for boss and propeller nuts. Since the propellers are especially vulnerable when operating through ice, consideration should be given to fitting the ship with some 42 RESTRICTED ee RESTRICTED type of propeller guard. In small] vessels provide suitable tackle to change propellers at sea; in larger ships see that docking plans are available. 2. Rudder.—Provide spare rudder assembly or temporary rudder and rudder stock. Fit steel-wire pendants from each quarter to after part of rudder blade; these will permit steering if the steering gear is damaged, and prevent losing the rudder if unshipped. 3. Watertight integrity—Test all bulkheads, peaks, and tanks by hydrostatic pressure. 4. Pumps and piping.—Test all sounding pipes and bilge and tank pumping pipes for leaks and fractures. Check the operating condi- tion of main drainage pumps, electric submersible pumps, and aux- iliaries such as handy billies and P-500 pumps. Provide full allowance of spare parts. Renew any hose not in good condition. Clean all holds, scuppers, bilges, and rose boxes. After cleaning, take suction in each bilge well for an over-all operating test. In loading cargo, see that no sand, sawdust, or coal dust is introduced into the holds. 5. Fire lines.—Test all water-releasing equipment such as mains and cocks and renew any defective ones. 6. Cargo stowage.—¥or free passage of water to bilges and easy access to side plating in case of damage, stow cargo well away from the sides and tom in position. Load the ship so that she will be 3 or 4 feet down by the stern when in the ice. If in ballast, consideration should be given to the desirability of flooding the after hold most of the depth of the shaft tunnel in order to immerse the rudder and screws and minimize damage to them by ice. 7. Underwater openings and projections.—Inspect all inlet and out- let fittings in drydock. Remove all projections, such as scupper guards and ringbolts, on the ship’s sides above and below the water- line; these catch ice and slow down progress. 8. Wooden planking.—If a wooden vessel is exposed to conditions where water freezes around her, the ice will adhere to the calking in the seams and pull it out, causing bad leaks. The preventive is to apply a second layer of uncalked wooden sheathing, breaking joints with the main bottom planking, with fastenings that penetrate only part way through the latter. This sheathing will also protect the bottom against the scoring action of ice along the water line. Fresh water ice, such as is found in river mouths, is harder than sea ice and is particularly severe in scoring action. Wooden vessels that operate in such waters are frequently sheathed with sheet steel along the water line, well nailed both through the middle of the sheets and RESTRICTED 43 RESTRICTED along the edges. Copper sheathing would similarly be used on a copper-fastened hull. NavShips 250-336 gives the following particulars concerning wooden sheathing : Wood sheathing, in order to give adequate protection to the hull against ice and marine organism attack, should begin at a point above the load water line when the vessel is at her deepest draft and com- pletely enclose the hull, including the keel and all deadwood, the sternpost, the wood skeg, if any, and all other exposed parts of wood. The thickness of this sheathing varies from approximately one-half inch to 2 inches, according to the size of the vessel. The keel shoe should be sufficiently wider than the keel to cover the bottom edges of the sheathing fastened to the keel. If it is not, the shoe itself should also be protected by sheathing. When sheathing is used for protection against ice alone, it should extend high enough up the sides of the hull to form a belt of suffi- cient width to afford adequate protection against floating ice at any draft. This may require spiling of the sheathing strakes. Sheathing for this purpose is secured to the shell of the vessel generally by means of screws, the heads being slightly below the surface of the sheathing. A metal cutwater should either be placed over the stem iron or butted and welded to the aft face of the stem iron. This cut- water should extend vertically across the width of the sheathing belt and sufficiently far aft to provide the proper cutting action when ice fields are entered, thereby protecting the forward edges of the wood sheathing. The portion of wood sheathing that is placed under this metal cutwater should be tapered. Ice sheathing requires wood capable of resisting severe abrasive action and which can hold fastenings well. The species preferred for this purpose is Australian ironwood. White oak has given satis- factory service. Other species having the properties that indicate they could be used satisfactorily are red oak, hickory, pecan, and rock elm. Black locust and live oak also have the required properties but are not readily available. The properties of the foregoing woods responsible for their selection are high toughness and hardness. White oak is used almost exclusively for keel shoes for the same reason that it is used for protection against ice. 9. Bracing in bow.—If feasible, install timber bracing in the fore- peak, using horizontal “ice beams” extending from side to side at the load water line and bearing on fore and aft planks placed between the frames. Additional support to the fore peak bulkhead on the 44 RESTRICTED RESTRICTED side toward No. 1 hold is also desirable. In small vessels, considera- tion should be given to reinforcing the stem with concrete. 10. Repair materials—Provide a supply of timbers, shores, quick- setting cement, sand, hull plates, angle irons, clamps, wedges, jacks, canvas, collision mats, etc., for the temporary repair of holes and leaks. Stow these near vital places most likely to be damaged. As outboard repairs below the water line may become necessary, con- sideration should be given to carrying diving equipment with neces- sary accessories. 11. Lookout stations —Build a shelter in the eyes of the ship for forecastle ice lookouts. Rig a crow’s nest as high as possible on the mast and winterize with radiant heater and antiglare windows. Pro- vide a protected conning station above the pilot house. Winterize the pilot house. 12. De-icing gear.—Provide a number of hardwood or nylon-faced mallets at least 6 inches in diameter for removing ice. Scrapers can also be used, but they are more likely to remove paint, with subsequent rusting. 13. Sounding boat.—Install a portable echo sounder in a small boat for use in leading the ship into uncharted coastal waters. 14. Carrying animals—If dogs are to be carried, consult the paper by Surgeon-Commander Bingham on the care of dogs at sea. If wild animals or birds are to be brought back from the polar regions provide suitable cages, or the materials for making them, and obtain an ample supply of food. In installing the cages, consider whether warm weather will be encountered before returning to the home port and allow for the necessity of keeping the animals cool, of providing a place to thaw out frozen fish or seal meat, and of abating the sanitary problem involved. 15. Mooring gear—Provide the following: (a) “Dead men” made up of wooden planks (oak) of approximate dimension 3 x 10 inches x 6 feet. “Dead men” are expended each time the ship is unmoored. It takes at least four at each mooring, and the ship may have to be shifted as often as once a day while unloading operations are being conducted. (6) Straps made up of 6- or 8-inch manila or %-inch wire approxi- mately 6 feet long with a large eye splice in each end. Straps are expendable with the “dead men” and an equal number should be provided. (c) Toggles of hard wood similar to a 4-inch mallet head with trailing lines. Each mooring line is secured to a manila strap with RESTRICTED 45 RESTRICTED a toggle. Normally the toggle will be recovered, but a good surplus should be on hand in order to provide for losses when freezing makes it necessary to cut lines on unmooring. (zd) Mooring lines of size normally used. There should be no losses, but one has occasionally to cut off the eye if a toggle is frozen and cannot be withdrawn. (e) Picks, shovels, and buckets with lanyards attached to be used by line handling party in burying “dead men”. (7) A number of long wooden spars or telegraph poles for use as fenders and for construction of heavy temporary brows while along- side the ice. The above gear is used for mooring to shelf ice or to bay ice in Antarctic operations, as well as for general Arctic service. Also pro- vide ice anchors, which are stockless single-fluked hooks, and ice axes, which have longer handles than ordinary axes. In Operation HIGH- JUMP to the Antarctic, the Vorthwind found ice anchors to be much more expeditious and efficient as holding gear than “dead men”. She used 200-pound single-fluke anchors. On the other hand, Task Force 80 found that “dead men” have greater holding power than ice anchors in the Arctic. 16. Main injections.—Install steam lines on intakes to prevent clog- ging with brash ice. 17. Electrical equipment—Add at least 25 percent to the allowance of 1.835 specific gravity storage battery acid normally carried. Ther- mally insulate below-water engine-room bulkheads behind and above the main switchboards to eliminate condensation with subsequent water dripping on exposed elements of the board. 18. Gas bottles —Provide inside stowage for acetylene, oxygen, and other gas bottles in “stand-by,” since if used directly from outside stowage in cold weather, up to 75 cubic feet volume is lost. 19. Small stores, ship’s store, or slop chest.—Provide ample supplies of warm clothing, footgear, smoked glasses, face lotion, and antichap lipsticks. Allow 25 to 50 percent increase over normal consumption of cigarettes and candy. If tropics are to be crossed, arrange cool storage for candy bars. 20. Recreational facilities —Provide an adequate ship’s library, sup- ples of comic books, recent motion pictures, beer, and hobby-shop equipment. 21. Personnel.—Thoroughly screen men before sailing and eliminate psychiatric misfits. Give the rest complete medical and dental check- 46 RESTRICTED RESTRICTED ups. Carry a medical officer and dental officer if feasible. Require men using spectacles to equip themselves with a spare pair before sailing. 22. Miscellaneous supplies —Provide poles and extra boat hooks for fending blocks of ice away from the ship’s side and the screws in particular. Provide crowbars, which should be short, four-sided, and wooden-handled. Provide demolition charges, detonators, and fuzes or cable and blasting machine. Allow for the possibility of being forced to winter in the ice by loading provisions for all hands for 15 months, or providing sporting rifles, shot guns, ammunition, fishing gear, and vitamin supplies. Provide ice saws for cutting docks in ice floes, or freeing the ship if frozen in. BOATS Any ship operating in polar waters should carry boat capacity for 150 percent of personnel aboard, since life jackets, floater nets, and small rafts are worthless if men are not rescued within a few minutes. Unless this requirement is met, operation plans should be formulated so that two or more ships are always in company. The Navy standard 40- or 50-foot motor launches are considered tc be practical lifeboats for such regions, if they are provided with sail and with a canvas weather-cloth covering in the wa:st. Both the 40-foot motor launch and the Coast Guard 26-foot self- bailing surf boat have been operated satisfactorily under adverse con- ditions. The former has penetrated deep into pack ice with little difficulty. Motor whaleboats and LCVP’s are also considered desir- able for operations in which landings are to be made in ice. Not only may the boats be damaged by contact with ice, but they may also be cut off from the ship by drifting floes brought in by a wind shift or tide, or by poor visibility. Therefore, all boats should contain emergency rations and survival kits including sleeping bags, firearms, a Very pistol, and medical supplies. In addition, all boats should be radio-equipped. Boat crews should have their full outfits of cold weather clothing with them at all times while in the boats. Hoisting slings on all boats should be reinforced for handling in rough weather. Wooden motor boats to be used in ice, particularly young ice, should be copper-sheathed forward along the waterline, as otherwise they may receive serious damage from ice cutting into the stem. Since this protection adds greatly to weight, it has been recommended that RESTRICTED 4] RESTRICTED a new boat be operated in ice for a few hours, and then be sheathed only on the portions that exhibit signs of wear. Boat engines should be cooled by fresh-water circulating systems or by air. A salt-water cooling system is likely to become clogged from slush drawn into the injection line, resulting in overheating the engine. Use a series-parallel circuit with four batteries instead of the usual two for starting boats. If temperatures below 20° F. are expected to be encountered, engine heaters should be provided for all boats to eliminate starting failures. A water breaker filled to 75 percent capacity will not crack when frozen solid. The paper by Commander Ryder cited in the bibliography describes a light boat specially built for use in polar regions. This paper should be consulted if it is planned to use small boats extensively around a base camp. PREPARATIONS EN ROUTE TO POLAR REGIONS The following check-off list covers items of maintenance and prep- aration that should be carried out before entering the ice zones. 1. Painting and lubrication.—Paint topsides and decks; regrease the rigging with a light coating; put winter grade lubricants in all the deck machinery. 2. Antifreeze —Put ethylene glycol or alcohol in the cooling systems of motor boats and any other exposed internal-combustion engines. 3. Batteries —Fill all storage batteries in boats with 1.280 specific gravity electrolyte. Keep batteries as near full charge as is possible at all times. 4. Water tanks.—See that no water tanks are over 90 percent full. Owing to the risk of contamination with sea water from leaks caused by contact with ice, use the potable water (if any) in the fore peak tank first. All water tanks adjacent to the outer skin of the ship should be equipped with heating coils. 5. Towing gear—Rig towing bridle forward for immediate use in the event of necessity of being towed by the icebreaker. Break out towing gear and keep it available on the fantail for possible use in towing another ship. 6. Mooring lines —Manila has a tendency to freeze or dry-rot in the center if exposed to cold for long periods. A line permitted to drag through snow and water becomes ice-coated immediately and is hard to handle, slipping in gloved hands and on winch drums and capstans. 48 | RESTRICTED RESTRICTED Therefore, keep mooring lines dry by stowing below decks or under canvas covers. 7. Instruction.—Familiarize personnel with the operation of the main drainage system. Hold regular instruction periods on safety precautions in handling cargo, life and personal hygiene in frigid climates, survival, ete. If in the Arctic, indoctrinate personnel with regard to contacts with natives and compliance with game laws. RESTRICTED 49 RESTRICTED CHAPTER VIII OPERATIONS IN POLAR WATERS SHIPBOARD PRECAUTIONS If the ship has been fitted out according to the procedure outlined in the previous chapter, the chief dangers to be met are those resulting from low air-temperatures and from water freezing on the topsides, either through sleeting and snowing or from taking aboard spray or green water in cold weather. Sweep decks clear of snow before it has an opportunity to form a crust or become trampled and hardened. ‘This is particularly essential on the bridge and on the gangways. Extreme care should be exercised when using scrapers to remove ice close to electric cables and equipment because of the possibility of breaking them loose from switch boxes and other connections. Salt water hosing is a rapid means of melting snow and clearing decks but should be used only in nonfreezing weather after making sure that overboard deck drains are not frozen. It is not advisable to use mixed steam and water for ship de-icing since the ship will run out of steam too rapidly. A better method is to use the condenser feed as a source of warm water and by a heat exchanger raise the temperature to about 150° F. The water may then be used to cut into ice masses, making use of the weight of the ice to break them away. The worst ship icing conditions are said to be found in the Newfoundland-Belle Isle area when the water tempera- ture is 30° F., the air temperature 20° F., and the wind force 4. All running rigging that can reasonably be covered should be pro- vided with canvas covers as previously recommended for mooring lines. Lowering a whale-boat with ice on the falls and cleats is a very dangerous operation. Canvas covers are considered a necessity for all deck winches and appliances. They are also essential for open boats if the bilges are to be kept dry. Cover the deck space or hatch used for helicopter operations with a tarpaulin so that the snow can be removed in a minimum of time. Secure firemain cut-out valves on firemain risers to weather decks and drain plugs at lowest point between riser and plug. Drain fire hose on weather deck and dry in heated compartment before restowing in racks. Keep proportioners in heated compartments adjacent to a hatch or door where access to weather decks will permit rapid connec- 90 RESTRICTED RESTRICTED tion to be made with fire plugs. Drain them after use, and dismantle, dry, oil, and reassemble the chamber change-over valves. In using fire hoses at freezing temperatures, satisfactory results can be obtained if good pressure is maintained ; however, when the pressure is reduced or the hose is secured, the nozzle and plug become frozen, and the nozzle must be replaced. Steam deck machinery should be carefully looked after to prevent clogging with ice. In extremely cold weather it should be operated daily, and condensed water drained out after use. If circumstances require that steam capstans and winches be ready for instant action in freezing weather, warm them up and leave them turning over at slow speed, taking care that they are not permitted to stop. When operating in pack ice, keep the ship’s main engines manned and ready for immediate use at all times. In steam vessels, take pre- cautions to insure that no water of condensation remains in the main steam pipes or engine cylinders. Ice anchors should be stowed under shelter to prevent icing-up. ANCHORING It may be advantageous to lie at anchor when in brash, but as little of the cable as possible should be paid out. The capstan should be kept ready for weighing in case of the approach of large masses of pack ice. When anchoring in rotten ice in shoal water, get into the ice as far as possible to avoid the swell; but if the water is deep and ice is present, anchoring should be avoided. It may be preferable to lie to and keep power available to move the ship as necessitated by the shifting floes. It is not recommended to anchor to the bottom while in pack ice, as in most cases it is useless and will probably result in the loss of the anchor and cable. Having decided to ride to an ice anchor, choose a strong floe which can shelter the vessel from the surrounding ice. To insure as nearly as possible obtaining the shelter of a natural dock, it would be well in making fast to a floe to take a position where a bight is formed by two strong projections. Such places may often be found. They offer at least moderate security in the event of other ice setting toward the ship, the projecting angles of the floes receiving the first shock. If the ice is not too thick, a dock can be sawed out. With two or more ships in company, time is saved by employing all hands to cut one dock large enough to take in all the ships. However, the degree of safety will then be lessened, for the larger the dock the less likely it is to have strength to resist pressure without eventually breaking. RESTRICTED 91 Figure 13.—Showing the effect of the propellers in keeping the stern of the icebreaker clear of ice while hove to. Lay the anchor from the side of the floe where a patch of open water is formed, or where the surrounding ice is least packed. When riding to an anchor the movement of the ice must be continually observed. If there is a risk of the ice surrounding the ship, weigh anchor and move into a more open region off another floe. Therefore keep the engines ready for immediate action. If a small berg or larger bit drifts down on the ship, it can frequently be avoided and permitted to drift clear by judicious use of the engines while at anchor. In selecting an anchorage in a bay or harbor which is open to drift- ing ice, the shallowest depths should be chosen, provided other condi- tions are suitable. A vessel should not select an anchorage too close to a glacier cliff since calving of the barrier may endanger the vessel or set up a heavy swell making the position uncomfortable. In bays or fiords where fast ice exists, the tidal currents may cause this ice to drift in and out of the harbor, rendering the anchorage un- safe. Fast ice ina harbor usually moves along a tidal crack and, under the force of onshore winds, may acquire violent motion. Vessels should quit moorings at the edge of fast ice whenever onshore winds blow. 52 RESTRICTED RESTRICTED Vessels taking winter quarters in a harbor should select a site where protection from ice is afforded to seaward by islands, islets, rocks, or shoals. Moor in shallow water, allowing for the height of seas and tidal range which may be experienced in the harbor. Run out steel wires and anchor cables to shore moorings. Stretch and anchor cable across the seaward side of the anchorage to impede ice drifting down upon the ship. Unship rudder and propeller, if possible. Drain boilers and secure all sea connections at the hull. MOORING AND UNLOADING The following procedure for mooring alongside either bay ice or shelf ice not too high above the ship’s deck is based on the experience of the U.S. S. Bear while serving with the United States Antarctic Service Expedition in 1939-41. Although ice conditions in the Antarctic are seldom the same from one year to the next, it has been found that the general condition of the fast ice in the Ross Sea changes very little, particularly in regard to offering a clear “dock space” for mooring alongside. The thickness of the fast ice in the Bay of Whales during the months of January and February was found to be approximately 12 to 15 feet, with an above-water height of 3 to 4 feet and with sufficient strength to hold the weight of the equipment unloaded. Break-ups occur without warning, and ships moored to the ice edge must be prepared to get under way on short notice. Sometimes cracks will develop between the ship and the barrier, but the ice may not break up for several days. Prevailing winds and currents coming from under the barrier tend to cause the broken pack ice to drift to the westward. With this condition a starboard-side-to mooring has been found to be the most desirable. Prior to arrival alongside the ice, all gear should be put on deck in order and line handlers instructed as to how and where to bury “dead men” and how to secure mooring lines. Secure manila strap and/or wire strap to each “dead man,” depending on the use of hawsers and cables. Obviously if a “dead man” has both a manila strap and a wire strap, either wire or manila lines can be secured to it. At least four mooring lines should be ready to run with a toggle attached to the eye of each line. The Bear made it a normal practice to place her bow head-on against the ice and to hold this position by steaming ahead slowly. Line- handling parties were disembarked onto the ice via Jacob’s ladders. After passing over and securing the bow line and bow breast, the ship was warped around until she lay alongside the ice, and the stern lines RESTRICTED 93 RESTRICTED were then put over and secured. This procedure of placing the bow against the ice may not be considered advisable for large vessels. If the commanding officer prefers, the line-handling party may be sent to the ice by boat and the ship held off until the “dead men” are planted and all preparations made to receive the mooring lines. Then the ship can be brought alongside in the normal manner of tying up to a pier. ; Plant “dead men” well in on the ice shelf so that an almost hori- zontal pull will be made on the mooring lines when hauling the ship alongside. A trench for a “dead man” should be dug about 4 to 6 feet deep with sides at a slight angle as shown in figure 14 in order to give better holding power and to avoid the tendency to pull the “dead man” out before it is well frozen into place. The “dead man” with the manila strap attached is buried in the hole and covered over with ice. A few buckets of water thrown on top of the fill will help freeze it in place in a few minutes. The mooring line is passed EYE IN MOORING LINE WITH TOGGLE ATTACHED FIRST POSITION \ OF SHIP i Figure 14.—Mooring ship to the Antarctic ice shelf. 94 RESTRICTED Figure 15.—Unloading cargo from U. S. S. Yancey (U. S. S. Merrick in background). Lengths of telegraph poles hung vertically over side of ship are used as fenders. 963067 °—51——_5 RESTRICTED 90 RESTRICTED through the eye of the strap that protrudes up through the ice from the “dead man,” and is secured with the toggle passed through its own part for quick release. Check toggles frequently to see that they are free for easy slipping. If wet snow or sleet falls, they may become frozen in place. Four mooring lines distributed as shown in the sketch are recom- mended. The number should be kept to a minimum to keep the ship safely secured but also to facilitate a hurried unmooring to clear the area during a break-up. The Bear found that many break-ups oc- curred at night when there was a limited number of men up and avail- able to slip the lines. Lengths of telegraph poles 12 to 16 feet long, hung vertically over the side of the ship, make the best fenders. There is usually some ground swell in the Bay of Whales which will cause a vessel to work up and down. Cane fenders have a tendency to ice up and may catch on the edges of the shelf ice because of its height above water. The use of ice anchors in mooring alongside the Antarctic shelf is generally not recommended. The surface of the ice is too soft to provide adequate holding power. Mooring to a timber with strap and toggle requires less manpower, makes weighing much easier and quicker, and eliminates the possibility of losing an expensive metal anchor. PRECAUTIONS (a) To facilitate unloading, moor ship as close to the ice as possible. (6) In unloading heavy equipment, land it as far inboard on the ice as booms and cranes will permit so as to avoid having heavy weights on the edge of the ice near the ship. (c) Skidding of heavy weights from the ship to the ice is not rec- ommended unless shelf ice conditions appear to be exceptionally good and no crevasses are observed between the ship and the barrier. When skidding is necessary, heavy cribbing made up of long telegraph poles should be used in order to distribute the weight as far inboard on the ice as possible. (d) The ship must be kept constantly ready for unmooring and getting under way. A quick break-up may call for that action. If more than one ship is tied up in the same vicinity, the situation may be more complicated, and no time should be wasted in getting clear. (e) Unless coming alongside to moor, a vessel should not steam too close to the barrier. Bergs frequently calve without warning. (7) Men should not be permitted to wander over the ice away from the ship until a careful check has been made for crevasses. 36 RESTRICTED Figure 16.—Ships moored to ice showing tracks left in the ice from unloading operations. Camp HIGHJUMP in the background. (g) Material should be unloaded only as fast as it can be moved inland. Every effort must be made to reload material onto the ship if a break-up occurs. In the Arctic, unloading cargo over the ice is considered practical over land-fast or land-locked ice, but not over ice in open areas. Fast, smooth ice would present no difficulties for trucks or tractors provided it was thick enough to support the weight. Rough, hummocky ice would be more difficult but could probably be traversed by careful se- lection of route and use of a small bulldozer. In the event the ice is covered with soft snow and there are large amounts of cargo to be RESTRICTED 97 RESTRICTED landed, a metal landing strip mat would serve very well to make a smooth roadway to the beach. In land-locked areas during the winter months, natural slips for unloading can easily be cut out by an ice- breaker thus entirely eliminating the problem of mooring lines or “dead men.” It is recommended that land-locked areas be selected and checked by aerial scout before planning large scale over-ice movements. : Tracked vehicles can carry cargo over most shore-fast ice shelves and onto the frozen ice or snow-covered beach with no prior road construction. Weasel (M29C) cargo carriers were found satisfactory over solid pack and were used extensively in tows with one or two 1-ton sleds. Cargo and passenger off-loading was conducted at King Island, Nome, and St. Lawrence Island onto shore-fast ice shelf with ease. Summer open water conditions at these ports, however, are hazardous and difficult, unloading being often delayed by high seas. WATER SUPPLIES It is important to a ship’s economy to be familiar with various sources of water supply in polar regions. Clean snow, of course, is a source of pure fresh water; but if a large quantity is to be thawed, it will be more economical of fuel to use ice, on account of the poor heat-conducting properties of snow. Choose the clearest, most brittle ice, such as is to be found in hummocks and pressure ridges. This will be the oldest ice and most nearly free of salt. Sea ice more than 2 years old is generally salt-free enough for drinking purposes. The pools that form on the surface in summer contain water suitable for cooking purposes, which can be pumped aboard with handy-billy pumps at a distance of 30 or 40 feet from the edge of a floe to avoid the admixture of salt spray. Fresh-water streams can frequently be found on land in the sum- mer. They generally occur in association with glaciers and are caused by thawing of the ice in contact with bare rock masses. There is generally an alluvial deposit at the mouth of glacial streams with steep shelving offshore. Such streams should be approached with caution. It is advantageous for vessels to carry 1,000 feet of fire hose with suction attachment and two portable pumps for use in shipping water. The procedure is to anchor a suitable distance off the mouth of the creek, plant an anchor on shore, warp stern in, and run the fire hose buoyed, if necessary, with damage-control tim- bers. A pump should be placed at the suction and another on deck. 98 RESTRICTED RESTRICTED In this manner, much time may be saved in taking on water, which is usually done at about 4,000 gallons an hour. Although individuals vary regarding a taste for salt, water with a salt. content of 1 or 2%, will often be chosen in preference to distilled water.