142

NICEOLLS'S SEAMANSHIP  AND  NAUTICAL KNOWLEDGE

The number and spacing of intercostal longitudinal girders is deter-
mined by the breadth of the vessel. Two are shown at g and g, which
indicates that the breadth of this vessel must have been between 58 feet
and 70 feet, because one longitudinal only is necessary on each side
of the centre line when the breadth is less than 58 fpet. Note the
lightening holes cut in these longitudinals.
Solid floors, S, are usually spaced two or three frames apart with
open bracket floors, B and &, at the intermediate frames. Solid floors
are fitted at alternate frames when the frames are 33 inches apart,
and at every third frame when they are less than 33 inches apart
Exception to this rule applies, however, to the engine and boiler spaces
where heavy weights are concentrated and greater strength is required,
and to the region extending to one-fifth of the vessel's length abaft the
stem as this part is subjected to heavy pounding when labouring at sea.
F and R represent the frames and reversed frames of the open floors,
and B and b the plate bracket at their inner and outer ends. / and r
indicate the frames and reversed frames at the solid floors. N is the
middle line strake of inner bottom plating and letters n indicate other
eut and in strakes. M is the margin plate with a continuous fore
and aft angle on its lower edge and the short vertical angles at
frame space intervals apart already riveted in position, the lattei
being, of course, to receive the tank side brackets.

Fig. 23.—Cellular Double Bottom and Bilge Space.
In Figure 23 A is a centre girder. B a bracket. C a solid floor.
D, longitudinal intercostal girder. E, bracket. F, tank side bracket,
Gt frame. H, gusset angle. J, inner bottom plating. E, continuous
margin plate Bangle.
Web Frames.—A web frame is a specially deep transverse frame in
the form of a built girder. They are introduced wh«re decks have