TENDING SHIP AT ANCHOR 311
Anchor buoys, although very useful for marking the position of
anchors, have fallen into disuse. This may be owing to the fact tnat
vessels do not as a rule stay long at single anchor; also, there is the
possibility in steamers of getting it foul of the propeller.
Effect of Long and Short Scopes of Cable.—The holding power of
an anchor varies with the amount of cable out. The shorter the scope
the more upwards is the pull of the ship on the anchor, and consequently
the less hold it will have. Vice tersa, the longer the scope the more
horizontal is the pull, and the better the anchor will hold, the best
position being attained when enough cable is out to ensure the pull
being quite horizontal with some of the cable along the bottom. One
anchor with a sufficient scope for this purpose will hold better than two
anchors with an insufficient scope
A vessel anchored in deep water, with a proportionately long scope
of cable out, will ride easier in a sea, than when in shallow water under
the same circumstances, owing to the catenary* of the cable giving more
elasticity.
Veering Cable.—When it becomes necessary to veer cable in order
to gr?e more scope, precautions should be taken for veering it slowly
and gradually. To veer away until slack, and then hold on, allowing
the vessel to tighten it suddenly, would be very likely to break tbf*
anchor adrift. With respect to dragging, the saying "prevention
is better than cure" applies with special force. An extra length or
two of cable, given in time, may ensure the anchor holding, whereas,
if not given and the anchor starts, it may be impossible to get it to hold
again.
A ship at anchor will be influenced by one or both of two forces, i.e.
the tide acting on the immersed part of the hull, and the wind pressure
on the exposed parts of the hull, and on the spars, rigging, etc. In a
tideway the principal factor in the management of a vessel is the helm.
A "weather tide" is a tide setting to windward.
A "lee tide" is a tide setting to leeward.
Usually the effect of the tide on a vessel at anchor is greater than
that of the wind, though in strong winds, or weak tides, the reverse may
be the case, especially with vessels light or in ballast.
A vessel at anchor riding to the tide is moving through the water.
If riding to a 3 or 4-knot tide the vessel has the same relative
* A catenary is the curve which a chain or rope assumes when suspended
"Between two points. The curve of a tow-rope when a ship is towed, also,
when a ship is at anchor, the curve of the cable between the hawseprpe and
-fee point where it rests on the bottom are examples of catenaries.