Catamaran Hull Damage Repair: What We Found Under a Bad Fix
When we bought Paikea there was a small repair above the rudders that didn’t sit right. The previous owner had a story about it — a cable, he said. We were fairly sure he was telling porky pies.
Grinding it back confirmed it. The rudder had been driven up into the hull with enough force to punch a hole through the inner skin nearly as big as Shayne’s fist. Both sides. They’d hit something hard at speed — a grounding most likely — and rather than fix it properly they’d packed the void with polyurethane foam, the non-structural kind, and glassed over it. The foam had been sitting against the inner skin for years trapping bilge water. The core behind it was shattered.
The good news, if there is good news in that situation, is that this is a catamaran. The hole flooded one aft compartment. The boat stayed afloat. A monohull in the same situation is a different conversation.
Shayne ground back all the old work to sound laminate, wide tapered edges so the new glass has a proper bonding area, and repaired it properly. The fairing mix went on wet-on-wet straight after laminating — no waiting for a secondary bond, better adhesion, one less step. Peel ply over the top so the surface is ready to sand without the filler clogging the paper.
The laminate schedule is worth understanding. The inner layers are stitched double bias — fibres at +45 and -45, straight and continuous, which makes them stronger in tension and compression than woven cloth for the same weight. The outer layer is woven. The reason is tearing resistance. With stitched fabric the fibres are only held together by resin, so if something catches the surface it can pick up a thread and pull it out. You can see exactly this on the old hull — carbon uni just tearing away where something has scratched it. Woven cloth is mechanically interlocked, the threads go over and under each other, and you physically cannot pull a toe out the same way. Slightly weaker in pure structural terms, significantly better at handling the kind of abuse a hull sees in the real world.
One section got finished in carbon because Shayne ran out of fibreglass. Mixing carbon and glass in a structural laminate isn’t ideal — carbon is considerably stiffer so you end up with a hard patch that loads differently to the surrounding material. In a heavily loaded area that matters. In a lightly loaded section of hull above the rudder it’s acceptable, and it’ll be well and truly encapsulated in epoxy so moisture isn’t a concern.
The repair also informed the new rudder design. The lesson from this grounding is that when a rudder hits something hard enough, the shaft doesn’t break — it transfers the load straight up into the hull. The new rudders will have sacrificial tips: softer foam, one layer of glass, designed to break away cleanly in an impact before that load goes anywhere near the boat. You keep sailing, you fix the tip later.
The transom modification visible at the end of the video is a separate story — Shayne had to get inside the hull to do the repair, cut the transom out to do it, and decided while he was in there not to put the original back.