Originally Posted by Guy
How could it be the correct pitch if it's turning to many rpm?
It's not turning too many rpm, I
am actively revving it up to say 2800. I can't get over 3200 in gear
though. I understand that a bigger prop or a different pitch would not allow the engine
to rev up more while delivering more thrust in lower rpm scales.
I am just wondering why I seem to have to rev up (way) higher than a year or two ago to reach the same speeds with the same prop. As said, I got 5-6 knots with 2000 rpm, now I need 2500 - 2800 to get up this same speed. On 3100 rpm, I can get to 7.5 - 8 kts. This just doesn't seem right.
Some 108 engines need to turn up so they can reach 50 HP. A 36hp rated Perkins makes full power at a much lower rpm.
I wouldn't even assume my boat would "need" the full 50 hp to get to speed X. It's a 37 foot modified fin keel
boat after all. Jeez, I got her to 4.5 knots easy with a dinghy
tug tied alongside, with a 15 hp outboard