Page 151 - statbility for masters and mates

Trim 139
the position of the centre of ¯otation which is l metres from aft. The ship's length is L metres and a weight `w' is on deck forward.
Let this weight now be shifted aft a distance of `d' metres. The ship will trim about F1 and change the trim `t' cms by the stern as shown in Figure 15.4(b).
W1C is a line drawn parallel to the keel.
Fig. 15.4(b)
`A' represents the new draft aft and `F' the new draft forward. The trim is therefore equal to A F and, since the original trim was zero, this must also be equal to the change of trim.
Let `x' represent the change of draft aft due to the change of trim and let `y' represent the change forward.
In the triangles WW1F1 and W1L1C, using the property of similar
triangles:
or
xcm tcm lm Lm
x cm l m t cm Lm
; Change of draft aft in cm Ll Change of trim in cm where
l the distance of centre of flotation from aft in metres, and L the ship's length in metres
It will also be noticed that x y t
; Change of draft F in cm Change of trim Change of draft A:
The effect of shifting weights already on board
Example 1
A ship 126m long is ¯oating at drafts of 5.5m F and 6.5m A. The centre of ¯otation is 3 m aft of amidships. MCT 1 cm 240 tonnes m. Displacement
e