Basic Principles
Enclosed watertight spaces (spaces below freeboard deck or within enclosed superstructures or deckhouses) are to be provided with means of draining. This may be achieved by connection to the bilge system or by gravity drain. In general, a gravity drain is permitted wherever the position of the space allows liquid to be discharged by gravity through an appropriate opening in the boundary of the space. Unless specifically stated (see 4-6-4/3.5.2 or the following paragraph), the discharge can be directed overboard or inboard. Where directed overboard, means are to be provided to prevent entry of sea water through the opening in accordance with 4-6-4/3.3. Where directed inboard, suitable arrangements are to be provided to collect and dispose of the drainage.
Non-watertight spaces (open superstructures or deckhouses) and open decks, where liquid can accumulate, are also to be provided with means of draining. In general, a gravity drain is permitted for all non-watertight spaces. All such drains are to be directed overboard.
Gravity drains are to be capable of draining the space when the vessel is on even keel and either upright or listed 5 degrees on either side.
In addition to the requirements identified below, for specialized offshore support vessel types, see Part 5.