I'm assuming you are posting
about a 35' Seahorse Coot, 28,000lb and 13' beam.
I put a John Deere 4045D into Boracay, a Roberts Offshore
44 that's about the same weight as the Coot.
With a (from memory) 22"x15" prop I got a maximum of 1700rpm and 8 knots with everything clean. From memory 1400rpm gave me 5-6 knots with everything clean.
I had the prop repitched and cut down to 20"x12.5" and I can now get 8 knots and 2500rpm with everything clean. However the engine does not sound happy.
At the moment I'm using 1700rpm to cruise
at 6 knots with good fuel consumption
. With the boat half dirty I now only get 2300rpm and 7 knots.
My prop man said that if I brought a new prop he'd go for less pitch
and slightly more diameter.
I'm thinking I'd like 10" pitch
, but this is less than most "tables" suggest.