There is a discussion going on in another online forum I read about multihull capsizes. I thought I would just take a moment, and explain how most capsizes happen.
This is a discussion that really is only relevant to racing boats, pushed to the max. This stuff isn’t going to happen to your cruising cat. Orma 60 trimarans are the boat that comes to mind first, as well as the widely documented crash and burn of the AC 45 earlier this summer in San Francisco.
Most crashes happen when the boat gets going really fast, off the wind in following seas. In those conditions, great acceleration is experienced as the boat comes down the front of a wave. At the same time, because the boat speed is so great, the apparent wind goes way forward, and the boat is all trimmed up as if sailing upwind. As the boat reaches the bottom of the trough of the wave, the leeward hull or ama is put under tremendous downward pressure into the water. If its’ buoyancy fails, and the hull submerges, the speed of the boat is slammed to a halt, and naturally, the windward aft quarter of the boat lifts. At the same time, the apparent wind now shifts back to true, which is from behind, and it helps topple the boat into a classic pitchpole. A few years back, during a Route de Rhum race from Spain to the Caribbean, something like 15 boats did this trick!