The big power guzzlers on the plane are holding the boat up on the plane (esp. with a Deep V) & dragging the gearbox / leg through the water!
Couple of thoughts:
- the actual trim ram is an easy one - a lot of outboards already have them fitted, so all you would need is an automatic method of firing the up / down realys instead of the usual two switches.
- without repeating all of the above, but because of all those variables you would probably need as part of your control circuit:
a water speed sensor
a fore / aft clinometer
a throttle position sensor
trim sensor (for feedback)
You would then need to do a fair few test runs to gather data on boat angle & speed at various trim, throttle, speed & load (i.e weight i nthe bow or stern) settings.
Then you can buy a £5 PLC and a couple of op amps from Maplin, and having worked out the optimal trim angle for various throttle / speed settings program in a curve (with feedback loop form the trim sender) and then overlay a boat angle modifier (to, for example handle the moment when you have 4 pie loving mates sat at the back and the settings you spent weeks optimising go out the window).
Probably also worth having an "E-stop" button in case it gets confused or the trim angle sensor packs in (which appears to be quite a common failure) & tries to motor the engine clean out the water or plant your nose into thre back of a wave at 30 knots.....
So yes, it's feasible on paper, but probably easier just pressing the switches on your throttle lever!