Ship Operations - Intact Stability

The MEPC approved new MARPOL Regulation I/25A which requires oil tankers for which a building contract is in place after 1 February 1999 to meet:

1. an initial GMo >0.15m, during loading and unloading; and

2. under all conditions at sea, a minimum righting arm curve having adequate magnitude, area and range in addition to item (1), above, with the ship loaded in “the worst possible condition of cargo and ballast loading, consistent with good operational practice”.

MEPC also approved a Unified Interpretation to Regulation I/25A relative to the above condition. The Interpretation clarifies that the vessel should achieve compliance with all cargo tanks filled to a level corresponding to the maximum combined vertical moment of the cargo plus the free surface inertia moment at 0o heel for each cargo tank. The maximum free surface moment for all ballast tanks is also to be assumed.

Cargo density should be based on a cargo deadweight (with full departure consumable and 1% total ballast water) determined at a displacement corresponding to the minimum transverse metacentre (KMT). In calculating the initial transverse metacentric height (GMo), the maximum free surface at 0o heel for each ballast tank may be used.