[Fr. Frank]

I have a 20' Seafari cuddy cabin with a 90hp Mercury Optimax. I cruise at 24 mph, and WOT is about 33-34 mph. I get just a hair over 5 mpg at cruise. My 90 Optimax actually produces 105-110 hp at the propeller.

If you're running a 90* degree CrossFlow OMC outboard, you should cruise at about 23-24 mph at about 3 1/2 mpg, and I would guess a top speed of 28-30 with the right propeller. These motors actually produced about 85-90 hp at the prop.

If you're running a later Loop Induction ("Looper") with the VRO system working, I think you should see a slightly better top speed of 30-32, and 3.5 to 4 mpg at cruise, again, with the right prop. The Looper 90 actually produced about 95 hp at the prop. If the VRO system is disabled, your performance will be comparable to the CrossFlow system.

As a Marina manager in the early 80's, I rigged many new 20' SeaCrafts with a single 85 hp V4 Evinrude outboard or single 90 hp Mercury 6 cyl. They performed quite well with that power. By far the most common OE power was a 115 hp motor.