Originally Posted by prairie tuber
I think you are looking for a solution to a problem that does not exist.
Prairie, I completely agree. Tape up the air intake and run the engine. The air held in the engine cover will keep the engine going for quite a while.
After several years of operating in surf, I havn't had an engine fail yet due to water ingress through the air intake and then into the carb. Even with the boat flooded to the top of the sponsons, and the air intake being occasionally submerged by passing waves, no water was drawn into the carb. Have a look at the zapcat website and see some outboard engines being pushed to the limit in big surf.
Engine failures I have experienced in surf have been due to;
1. fuel starvation (air vent on fuel tank shut to prevent water entering tank) - hence why flexible non vented tanks are good.
2. Fuel starvation (fuel line severed due to kit not being secured well enough)
3. Engine stalling at low revs when re-entering water off the back of a wave (back pressure on the exhaust?) This may also explain an outboard engine cutting out if being overtaken by small surf at slow speed(?)
Kelson, In your original post you anticipated that the air intake would cause problems if overrun by a wave. In my (repeated and painful) experience, being overrun by a sizable wave often leads to far worse problems- damage to boat and crew caused by being pitchpoled and then dumped on by a couple of tons of surf! SIBs don't surf very well.
My suggestion is that you do everything possible to ensure that you can outrun the waves or take them on the bow! Consider geting a sea anchor (I now use a 6ft military drouge parachute bought from a surplus store in california) and use it if the engine does fail.
Have fun in the surf!