I know you already built one of these....will a skeg boat still be fast & efficient with the extra weight of the net winder in the cockpit?
The aluminum reel and net will weigh no more than 1,200 lbs total. And it's somewhat centrally located, atleast I try to mount it as far forward as is practical to help centralize the weight. The boat will weigh about what your basic lobster boat will weigh, then add in the 1,200 lbs of gear. So all things considered, it will be a pretty light boat for 38'. I'm looking for 24-25 knots wide open with a 18-19 knot cruise. I think those are realistic expectations for 500 hp in a basic 38' boat.
The 34' x 13' Calvin I built with a 500 hp Cummins did 33 mph with no reel or gear and light on fuel at sea trial, at about 96-97% engine load. We put approx. 7,000 lbs of water in the fish holds (to test how weight would effect it) and the boat still did 30 or 31 mph and was hitting 100% engine load, which told me with fishing gear and more fuel, I needed to take atleast 1" of pitch out of the wheel. I think the engine was hitting right at 2,600 rpms with the extra weight. I was impressed with the overall performance of the 34' Calvin Beal hull and the QSC Cummins. And these numbers are with 1.77 gear ratio and a 26" diameter prop. Gear it down to 2:1 with a 28" diameter prop, and the performace numbers may be a little better.
I'm thinking a 38' boat like the Wesmac or Flowers should do around 27-28 mph (about 24 knots) with the same engine.