Why intact buoyancy matters at command level
A vessel's reserve buoyancy — the watertight volume above the waterline — is the margin between a stable, floating vessel and one that is endangered. Partial loss of intact buoyancy means water has entered a compartment that should be watertight. The Master's task is to arrest progressive flooding, stabilise the vessel, and make a command decision: fight the flooding and remain at sea, or abandon.
The situation is time-critical. Floodwater rises fastest at first, when the head differential between sea level and compartment sole is greatest. Delay in identifying the source and isolating it compounds the problem geometrically.
Initial assessment — what the Master must establish immediately
- Which compartment(s) are flooding and through what source (collision damage, grounding, a failed skin fitting, stern gland failure, open sea cock)
- Rate of ingress: is it controllable with the vessel's own pumping capacity?
- Effect on stability: list, trim, reduction in freeboard — any of these changes the vessel's ability to resist further flooding
- Whether the flooding is communicating to adjacent compartments (progressive flooding)
On a small yacht, the Master should physically go below rather than rely solely on reports. Direct observation is irreplaceable at this stage.
Control actions
Close all watertight doors and hatches to limit progressive flooding. Isolate the sea cock or skin fitting if it is the source. Deploy portable pumps, activate bilge pumps, and organise bucket bailing if necessary — all simultaneously, not sequentially. Use collision matting, softwood wedges, or proprietary damage control plugs to stem ingress at the breach. If a skin fitting has failed and cannot be isolated, plug the through-hull from inside.
Heel the vessel to raise the damaged area above the waterline if flooding is in a low-freeboard section and stability permits this action safely.
The command decision
The Master must continuously compare rate of ingress against pumping capacity. If the pumps are winning, the vessel remains viable. If not, the Master must act before the vessel loses the reserve buoyancy needed to conduct a controlled abandonment. A vessel with severely reduced freeboard or increasing list is already compromised; waiting for further deterioration removes the option to abandon safely.
Mayday must be transmitted as soon as the Master judges the vessel is in distress or likely to be — not after all other options are exhausted. Search and rescue assets need time to reach the vessel. Under SOLAS V/33 the Master has a duty to ensure the safety of those on board; that duty begins at the assessment stage, not at the point of capsizing.
Logging and accountability
Record all actions, times, and decisions in the deck log. If the vessel is subsequently surveyed, this record establishes what was done and when.