Glossary Term
Sea Chest
A sea chest is a recessed intake space built into the hull below the waterline that collects seawater before it is led into onboard systems. On yachts and superyachts, sea chests feed services such as engine cooling, generator cooling, air-conditioning seawater circuits, fire main suction, and other seawater-dependent equipment. The arrangement usually includes shell openings, gratings, internal piping connections, isolation valves, and sometimes marine growth prevention equipment.
The term also carries a maintenance meaning because sea chests are classic trouble spots for fouling, blockage, corrosion, and coating breakdown. IMO biofouling guidance identifies sea chests as niche areas that are especially susceptible to biofouling, recommends that they be targeted during inspections, and notes that their design should allow inspection, cleaning, anti-fouling treatment, and, where fitted, growth-prevention measures. The same guidance recommends taking the opportunity during routine propeller polishing to assess sea chests for macrofouling.
Class survey language treats the sea chest as part of the hull inlet and valve system rather than a hidden void that can be ignored. ClassNK’s survey rules call for the main parts of valves and cocks on shell plating, sea chests, and related inlet arrangements to be opened up and examined, together with their fastening to the hull.
When a sea chest is in poor condition, the yacht may first show symptoms elsewhere: high seawater temperatures, reduced cooling performance, pump cavitation, unstable HVAC service, or repeated debris alarms. Access, coatings, grating design, blanking arrangements, and associated pipework and seawater service lines all influence how manageable the system will be over time.