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Q3 (10 Marks) International Conventions
SSEP • Written Exam

Explain the following with respect to MARPOL Annex-I

(a) Pump room bottom protection. (6)

(b) Intact stability of oil tankers. (7)

(c) Subdivision and damage stability of oil tanker. (7)

Appeared In: Nov 2023

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Explain the following with respect to MARPOL Annex I:

Part (a)

Pump room bottom protection.

Part (b)

Intact stability of oil tankers.

Part (c)

Subdivision and damage stability of oil tankers.

Part (a)

Pump room bottom protection (Regulation 12A of MARPOL Annex I): The pump room of an oil tanker (the space containing the cargo pumps) is required to have a double bottom (a protective double bottom) beneath it, so that in the event of grounding the cargo/pump room is protected and oil is not released. Regulation 12A requires that the pump room bottom be protected by a double bottom of a specified height (the double bottom height is to be not less than the value required by the damage stability/Regulation 19, typically about 2 m or the value from the formula), and that the pump room be located so that the cargo tanks are not directly above the sea. The double bottom provides a void/ballast space between the pump room and the sea, reducing the risk of oil release on grounding and providing access for inspection. (The pump room bottom protection is part of the general requirement that the cargo tank length be protected by a double hull/double bottom.)

Part (b)

Intact stability of oil tankers (Regulation 27 of MARPOL Annex I): Oil tankers must have adequate intact stability. Regulation 27 requires that the ship's intact stability be such that, in the intact condition, the ship meets the criteria (e.g. the metacentric height GM, the righting lever curve, the area under the curve, the angle of vanishing stability) so that the ship is stable in all loading conditions (departure, arrival, ballast, partial load). The intact stability criteria (from the IMO Intact Stability Code and Regulation 27) include: the initial metacentric height GM0 not less than a minimum (e.g. 0.15 m for tankers? - the value is set by the code), the righting lever GZ at 30 degrees not less than 0.2 m, the maximum GZ at an angle not less than 25 degrees, the area under the GZ curve, and the angle of heel not exceeding limits. The ship must carry a stability booklet and the loading conditions must be checked to ensure the intact stability is maintained.

Part (c)

Subdivision and damage stability of oil tankers (Regulation 28/19 of MARPOL Annex I): Oil tankers must be subdivided and have sufficient damage stability so that, in the event of collision or stranding (a defined damage - the "damage extent" of a side or bottom breach), the ship remains afloat and stable with the required residual stability. Regulation 28 (and the related Regulation 19 for the double hull) requires that the ship, when damaged (with the specified side damage length, penetration and vertical extent, or bottom damage), must have a residual stability such that the ship does not capsize and the margin line is not submerged, with the required metacentric height and righting lever. The subdivision (transverse and longitudinal bulkheads) limits the flooding to a compartment, and the damage stability ensures the ship survives the flooding with the required freeboard and stability. The ship must be able to survive the damage with the cargo tanks intact (the double hull protects them) and the residual stability criteria (e.g. the final waterline, the angle of heel, the GM) are verified by the stability booklet and the damage stability calculations.

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