There's a lot of hurdles to overcome with an outboard transmission: Weight, size, reliability in a harsh environment - to name a few. I would think an automatic, variable pitch prop, would be the way to go but - how. Centrifical clutch that would engauge at "x" rpm and increase the pitch might work but how would you reduce the pitch? Servo motor capable of increasing/decreasing pitch under load? Whole lotta hurdles fer sure.
