I've followed all of the threads about prop size for this model as I have a 32-3 with the same engine/trans as described above, and a fixed 2-blade 15x11 Martec prop, and it only make 5 knots at 2500rpm. From what others with the same boat/engine/prop said l should be making around 6 knots at that rpm.
At full throttle the engine turns at 3800rpm and the boat makes just over 7 knots. I beleive that the tach is inaccurate because the boat speed is right where it should be for full throttle, but the rpm isn't. From what I understand the engine should limit itself to 3000rpm (max rpm per the manual) even if it is under-propped just by virtue of how a diesel operates. (...?) The alternator could have been upgraded at some point in time without the tach getting re-calibrated, a likely cause for what I think I am experiencing.
I'm tempted to just drive the boat at 3000rpm, which makes 6knots and coincidentally (?) is 80% of full throttle rpm....
Any experienced people's advice about this?
BTW, all of the speeds were measured with gps with no wind or noticeable current. and the boat has new bottom paint -nice and clean...
Thanks,
Jeff
1986 32-3