This is a reply to Bruce Goldman:
How weird; we run generally at 1600rpm, and that gives us 7 knots in still (-ish) water, and 9 knots with a following tide.
2500rpm seems excessively high ..and must generate a lot of noise, I’d have thought (and use a lot of fuel). Perhaps you have a non-standard prop (..or a damaged prop?..) which needs higher revs to push the boat along ..could that be it? Or for some reason you have a different gearbox or reduction drive?
The fastest I’ve driven ours is about 2100rpm to push forward in a head-on sea, but that almost doubles our hourly fuel consumption!
2500rpm seems – I have to say it again – incredibly high ..as if for a different engine entirely.