Page 159 - statbility for masters and mates

Original drafts Bodily rise
Change due trim Ans: New drafts
8:000 m A 0:900 m
7:100 m 0:180 m
6:920 m A
7:000 m F 0:900 m 6:100 m 0:180 m
6:280 m F
17:75 cm say 0.18 m
Trim 147
Example 5
A ship arrives in port trimmed 25 cm by the stern. The centre of ¯otation is amidships. MCT 1 cm 100 tonnes m. A total of 3800 tonnes of cargo is to be discharged from 4 holds, and 360 tonnes of bunkers loaded in No. 4 double bottom tank. 1200 tonnes of the cargo is to be discharged from No. 2 hold and 600 tonnes from No. 3 hold. Find the amount to be discharged from Nos. 1 and 4 holds if the ship is to complete on an even keel.
Centre of gravity of No. 1 hold is 50 m forward of the centre of flotation Centre of gravity of No. 2 hold is 30 m forward of the centre of flotation Centre of gravity of No. 3 hold is 20 m abaft of the centre of flotation Centre of gravity of No. 4 hold is 45 m abaft of the centre of flotation Centre of gravity of No. 4 DB tank is 5 m abaft of the centre of flotation
Total cargo to be discharged from 4 holds Total cargo to be discharged from Nos. 2 and 3 Total cargo to be discharged from Nos. 1 and 4
3800 tonnes 1800 tonnes 2000 tonnes
Let `x' tonnes of cargo be discharged from No. 1 hold
Let (2000 x) tonnes of cargo be discharged from No. 4 hold
Take moments about the centre of ¯otation, or as shown in Figure 15.10.
Original trim 25 cm by the stern, i.e. 25 cm Required trim 0
Change of trim required 25 cm by the head, i.e. 25 cm
e
Fig. 15.10