Page 165 - statbility for masters and mates

Change of trim Change of draft aft due trim
Change of draft aft due trim
Change of draft forward due trim
Change of draft forward due trim Original drafts
200
37:35 cm by the head
Bodily sinkage 8:3 cm Changeoftrim w d
Ll Change of trim 73:5 37:35
Trim 153
MCT 1cm 124:5 60
150
18:3 cm
Change of trim Change of draft aft
37:35 18:3cm 19:05cm; or
76:5 37:35 19:05 cm 150
6:300 m A 0:080 m
6:380 m 0:180 m
6:200 m A
Ans. Load 124.5 tonnes in forepeak tank. Final draft forward is 5.770 metres.
Using change of trim to ®nd the longitudinal metacentric height (GML)
Earlier it was shown in this chapter that, when a weight is shifted longitudinally within a ship, it will cause a change of trim. It will now be shown how this effect may be used to determine the longitudinal metacentric height.
Consider Figure 15.13(a) which represents a ship of length `L' at the waterline, ¯oating upright on an even keel with a weight on deck forward. The centre of gravity is at G, the centre of buoyancy at B, and the longitudinal metacentre at ML. The longitudinal metacentric height is therefore GML.
Now let the weight be shifted aft horizontally as shown in Figure 15.13(b). The ship's centre of gravity will also shift horizontally, from G to G1, producing a trimming moment of W GG1 by the stern.
The ship will now trim to bring G1 under ML as shown in Figure 15.13(c).
In Figure 15.13(c) W1L1 represents the new waterline, F the new draft forward, and A the new draft aft. It was shown in Figure 15.4(b) and by the
Bodily sinkage
5:500 m F 0:080 m 5:580 m 0:190 m
Change due trim New drafts
5:770 m F