Did some testing of the trim tabs on Wednesday. I found there to be *some* improvement. The boat's highest speed had been achieved running an 18" cupped SS prop with the jack plate way high, trim maxed out, allowing considerable 'slip' of the prop. The highest speed was 42GPS. That setup performed less than ideally at other speeds, though and the holeshot was loud, dramatic and lousy.
With the 17" cupped SS prop and the jackplate lowered fully, the holeshot is much improved, cruising at 25mph is very nice and the top speed dropped a bit to 38.5gps. Trimming is limited to maybe a quarter of the trim range (limited by porpoising).
Adding the trim tabs helped damp the porpoising a bit which allowed the application of more trim angle (about half).
With the tabs lowered a 1/2" the result is that I can use some trim and with the 17" prop, achieve a solid 40gps.
Now I have a very rounded set up, great out of the hole, terrific controllable, comfortable, sustainable on-plane cruise (25gps) and a respectable top speed of 40gps with great manners, sharp turns, no slide-out, no wallowing, very predictable handling. I am VERY pleased.
Although I'm still considering upgrading the powerhead, the bare truth is that it does not NEED it.
Now, all that is left is to install the new fancy carpets on the lids!