New forecastle, fixed ballast and a failing GM on a 4,850 DWT coaster
A 3,250 GT, 4,850 DWT general cargo ship of 92.4 m LOA has a summer freeboard assigned under the 1966 Load Line Convention as amended (Type B, 2,080 mm), a summer draft of 6.05 m, and an approved stability booklet that requires a minimum GM of 0.35 m in all conditions. During a docking the owner raises the forecastle by 1.1 m, fits a new enclosed deckhouse aft of the bridge, and adds 60 t of fixed ballast in the forepeak to correct trim. The loading computer is not re-approved. On the next voyage the chief officer reports departure KG 6.62 m (read from the old booklet), KM 6.85 m, a free surface correction equivalent to 0.11 m of GM, and a mean draft of 6.00 m. The owner then asks whether he can take 120 t of steel coils on the hatch covers at an estimated VCG of 9.0 m to fill a late booking.
1. Assess the departure stability condition and state what the master should do.
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Do not sail. Corrected GM = KM minus KG minus free surface correction = 6.85 - 6.62 - 0.11 = 0.12 m. The approved booklet requires 0.35 m, and the general intact stability criterion (IS Code 2008, part A, 2.2) requires at least 0.15 m. The ship fails both, and the margin is not marginal. There is a second, more fundamental defect: the 60 t of forepeak ballast and the new structure changed the lightship, so a KG taken from the old booklet does not describe this ship at all. The flag or recognised organisation will require an inclining test or lightweight survey (SOLAS II-1/5-1), a re-approved stability booklet and a re-approved loading instrument before she trades on that booklet. Until then the departure condition cannot be verified. The correct immediate action is to redistribute or add ballast low down and re-check against a corrected booklet; 0.12 m is a no-sail figure, not a figure to be trimmed to.
2. Can the owner keep the existing load line marks and certificate?
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No. The raised forecastle and the new deckhouse change the superstructure length. Under ILLC 1966/88 regulation 37 the tabular freeboard may be corrected for superstructure efficiency, and the conditions of assignment (openings, air pipes, guard rails, freeing ports) and the visibility requirement in regulation 22 must all be re-checked against the modified ship. That means the assigning authority, flag or recognised organisation, must re-verify the freeboard and the position of the marks; the existing certificate and marks cannot simply be carried forward. Note the direction of the incentive: a longer efficient superstructure can justify a smaller tabular freeboard, which would permit a deeper draft, but only if the assignee grants it and the stability at that deeper draft is proven. The owner's assumption that a bigger forecastle automatically makes the ship safer at the same marks is not a load line argument.
3. What would the 120 t of hatch-cover cargo do to the GM, and can it be carried?
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It makes the stability worse. With the coils at a VCG of about 9.0 m and a displacement of 4,850 + 120 = 4,970 t, the new KG is (4,850 x 6.62 + 120 x 9.0) / 4,970 = (32,107 + 1,080) / 4,970 = 6.68 m. GM = 6.85 - 6.68 - 0.11 = 0.06 m, less than half the 0.15 m regulatory minimum and far below the 0.35 m in the booklet. Deck cargo also needs hatch covers rated for the stack load, securing to the CSS Code, and load line and visibility checks against the new freeboard deck. So the coils cannot be carried in this condition. They could only be considered after the inclining test, a re-approved booklet and loading instrument, and a stowage plan showing the GM and the GZ area criteria satisfied at the departure draft.