C L DUBEY – EXERCISE – 08 (DRY DOCKING)

Therefore , Draft F & A = 6.380m

9. A vessel of displacement 4740t, mean draft 4.22m, length 120m, KM 6.0m, KG 5.5m, CF amidships, TPC 10t, MCTC 79tm, is to be dry docked. If the GM on taking the blocks F & A is to be not less than 0.3m, what is the maximum permissible trim by the stern? At what drafts F and A would she become unstable?

Solution –

GM should be 0.3m, then GG₁ = 0.20m
We know that –
0.20m = P ⨯ 6.0/4740
P = 158 tonnes
We have P ⨯ d = (trim ⨯ MCTC)
= 158 ⨯ 60/79

Trim = 120cm
= 1.2m
Therefore, maximum permissible trim = 1.2m by stern

For unstable GG₁ = 0.50m,
P = 305 tonnes
Trim = 3.00m
Ta + T_f = 1.5

Rise = P/ TPC ⨯ 100
= 305/1000
= 0.305m

Draft should be fwd = (4.22 – 1.5)m
= (2.72 – 0.305)m
= 2.415m

Aft = (4.22 + 1.5)m
= (5.72 – 0.305)m