motor mount height on '67 bowrider

[doughert0]

Bushwacker recently responded (5-2-09)to a thread in the classic seacraft forum in which I asked if a 90HP motor would be OK for my 19-8 Seacraft Bowrider. I presently run a 115. He mentioned that the cav plate should be 1" to 1.5" above the bottom of the transom Vee. I finally measured mine, and it is less than 1/2".

Many years ago, not realizing that the transom was set up for a single engine 25" shaft, I bought a new engine with a 20" shaft and cut the transom. (When I bought the boat, it had twin 60's.) I had no guidance at the time, so the cut
was designed to make the cav plate come out about even with the bottom of the Vee.

I can increase the height of the cav plate to 1-1/4" by raising the motor one notch. As Bushwacker pointed out, my performance seems to be very poor - could this be
because the motor is 3/4" too low? Also, at WOT, the top of the prop is out of the water. So I always thought it might be too high!

The consensus answer to my question was that a properly set up 90 should give me at least as good performance as I am presently getting with the 115.

Any comments or suggestions?.

[Bushwacker]

I originally mounted my 115 with cav plate flush with bottom because 34 years ago I didn't know any better! When I switched from an aluminum to a stainless 13.75 x 15" pitch OMC SST prop, I raised motor 1 hole and picked up about 3 mph in top speed, which is what they claimed/recommended for that prop. It had a fairly heavy trailing edge cup which allowed it to still get a good bite on the water at the higher position. It would ventilate in rough seas so I'd have to trim it down then, but that's to be expected with a raised motor. It proved to be a good change.