Sea chest maintenance

A sea chest is a rectangular or cylindrical recess in the hull below the waterline from which seawater cooling and service pumps draw water. It is covered by a removable grating and often fitted with baffle plates to smooth flow at speed or in a seaway. Sea valves and strainers sit between the chest and the pumps.

In dry dock the gratings are removed and the sea chest is cleaned of barnacles, silt and marine growth, inspected for corrosion and cracks, and recoated. Grating fastenings, gaskets and bolts are checked for watertight integrity, anodes inside the chest are renewed, and the connected sea valves are overhauled and pressure-tested.

International biofouling guidance identifies niche areas such as sea chests, bow thrusters and hull appendages as locations where the number, location and design of the recess increase biofouling risk compared with open hull plating. Lower water flow inside the chest lets fouling establish even where the main hull coating is still effective.

A sea chest typically has baffle plates to smooth incoming flow, sacrificial anodes for corrosion protection, and sea valves and strainers where it connects to the pumps it feeds. All of these are inspected and, where needed, renewed or overhauled during a dry docking.

Anodes inside the sea chest are inspected at every docking and renewed when they are substantially consumed, the same practice applied to hull anodes generally. Unusually fast wastage inside a sea chest is worth investigating in the same way as on the open hull.

Sea chest cleaning, inspection, anode renewal and sea valve overhaul are normally carried out together in dry dock, when the grating can be removed and the recess fully accessed. The chest sits below the waterline, so this work is scheduled around the same docking as the ship's other underwater checks rather than done separately while afloat.