Re: 35 hp. OMC Mars motor
MARS...the Military Amphibious Reconnaissance System
The military wanted an outboard that could withstand being under 400' of salt water for 7 days, be pulled to the surface and fired! This is done by tilting it upwards to drain water from the intake and exhaust manifolds, then purge the cylinders by pullling the manual start a few times.
They are actually very similar to the typical 2 stroke 35hp OMC motor. They dont have any special valves or anything to keep water out, just indentations in the side of the pistons to purge water from the cylinders. The powerhead also is shrouded in a sound deadening jacket to shroud engine noise, keeping it stealthy. THey also talked about the ignition system being potted in plastic to keep out moisture, but so are the standard OMC motors, so not sure what they meant about that one.
Sorry that is all I know from a Popular Science article I have.
Would be interested in dunking one 400' in salt water for a week and pulling her up to see if she fires?!?