I have reason to believe I'm significantly over-propped, which I can fix at haulout easily enough, but I would like to get my
pitch numbers right. With a low-hours Beta 60 and a clean, if heavy-displacement,
steel full keeler, I hit cruiser too low (1800 RPM) and can't get above 2,050
RPM in relatively flat seas when I hit
hull speed under
motor. I do not have evidence of overheat or overpressure, however, which is good.
I've input my numbers into this worthy app (
Vicprop - Prop calculator for Displacement and semi-displacement hulls), but the fact is, I have a 19 inch four-blade feathering prop (a Variprop D-107) on a
steel full keeler and that isn't going to change. What can change is the
pitch in forward (overpitched in reverse means I can stop and back down "with authority" and I don't care if I'm lugging for 30 seconds). But I do care I can't get the
engine revving at
hull speed a full 600
RPM short of its rated max, meaning unneeded strain and poorer
fuel economy at
cruise speeds (75-80% WOT).
Any thoughts on how to calculate proper pitch for a given prop width are welcome. It's probably a drop from the present 15 to 11 or 12, but I'd rather do the math before I tinker with the stops in the hub. As a side note, everyone unhappy with their
fuel burn or their RPM should understand this topic as it really makes a large difference in terms of efficiency and wear. Here's the prop. The original was an 18 x 13 three-blade fixed prop; this is a 19 x 15 (can be changed) four-blade feathering. It works a charm in every other respect.