How can I temporarily patch a hole in my boat's hull in an emergency?
I have a 9-metre GRP cruiser and carry wooden bungs, rubber sheet and basic tools. If we hit something and hole the hull below the waterline, what should I do first, and how can I hold a temporary patch in place?
Answer
Slow the flooding with a tapered bung for a small round hole, a firmly braced rubber-backed panel for an irregular opening, or an external collision mat for larger damage. Start pumping and call for help immediately if the water coming in threatens the boat; a temporary patch buys time but does not restore hull strength.
Find and control the leak
Put everyone in lifejackets, establish your position and give people separate jobs: finding the leak, pumping and communicating. Send a DSC distress alert and a voice Mayday on VHF Channel 16 if flooding creates grave and imminent danger. Do not wait until the batteries or radio are submerged.
Check seacocks, hoses, transducer housings and the stern gland first. These can cause serious flooding without hull damage. Close the relevant seacock if a hose or fitting downstream has failed. An intact transducer housing may accept its dedicated blanking plug, usually a safer and more effective option than an improvised patch.
- Run the electric bilge pumps and put someone on the manual pump. Keep strainers clear of debris.
- Lift sole boards carefully and trace the water to its source. It may travel between compartments before reaching the bilge.
- Reduce speed or stop if movement increases flooding. Keep people clear of loose machinery and shifting floorboards.
- If practical, shift movable weight to lift the damaged area towards the waterline without compromising stability.
Keep clear of live electrical equipment in floodwater. Never send anyone overboard beside a moving boat or a running propeller.
Plug small holes and through-hulls
A tapered softwood bung is the quickest answer to a roughly circular opening. Choose one whose taper spans the hole diameter, insert the narrow end and seat it with controlled taps. Do not drive it hard enough to split a damaged fitting or enlarge fractured laminate.
If a through-hull has broken away, plug the opening through the hull itself. If the fitting remains secure and only its hose has failed, close the valve first. A purpose-made compressible foam plug can suit an uneven opening, provided it is secured against displacement.
Cloth wrapped around a bung can help it seal against an irregular edge. For a narrow split, press folded cloth or rubber into the opening and hold it with a backing pad. Keep hands clear of sharp laminate. Avoid forcing wedges into cracks, as they can spread the damage.