I know someone considering the purchase of a 21' Parker center console,
the model with the 21-degree transom deadrise. The boat itself weighs
2750 pounds. Great open fishing boat.

Parker recommends three Yamaha engines in its four stroke line: 150 hp,
200 hp and 225 hp.

For a boat with the same hull but with a pilothouse cabin that brings
the hull weight to 3250 pounds, the Yamaha performance page indicates a
top speed of 39.3 mph with the 150 hp engine running 5600 rpm and
burning 17.5 gph. At a cruise speed of 25.6 mph at 4000 rpm, the rig
burns 7.8 gph.

I'm recommending the 150 hp engine for the 21-foot center console. I'm
guessing a top end of 42-43 mph with a fuel burn of 15-16 gph, and a
4000 rpm cruise of of 27-28 mph, burning 6.5 to 7 gph.

I don't see any need to step up to a 200 hp V6 on this boat. The days
you can comfortably run more than 25 mph in a 21' boat are rare on
Chesapeake Bay. The 150 is about $4000 less than the 200.

Any comment on the extrapolations?