C L DUBEY – EXERCISE – 08 (DRY DOCKING)

Fluid GM = 1.047m
New GM = (1.047 – 0.382)m
                 = 0.665m

5. A vessel of length 140m, displacement 5210t, KG 5.8m, KM 6.1m, MCTC 130tm, TPC 14t, CF 2m abaft midlength is afloat in a drydock at a draft of forward 3.9m and Aft 5.2m. the water level in the dock is 6m above the top of the blocks. Calculate the virtual GM and drafts F & A, when the water level is lowered by 1.5m.

Solution –

Draft Fwd = 3.9 m,
Draft aft = 5.2m
Corn to aft draft = 0.631m
Hydrostatic draft = 4.568m
Now, Water  level = 4.5m.

Since water level is almost same to hydrostatic draft we will consider that ship has taken block aft but not overall.

Reduction in aft draft = 70cm
Or, 70 = P/14 + P ⨯ 68/130 ⨯ 68/140

Or, P = 215.06 tonnes
GG₁ = P ⨯ KM/W
= 215.06 ⨯6.1/5210
= 0.252m

GM = (0.3 – 0.252)m
       = 0.048m

Now Trim caused = 215.06 ⨯ 68/130 ⨯ 100
= 1.125m,
Ta = 1.125 ⨯ 68/140
= 0.546m, T_f = 0.578m