I've been reading some of the prop-related discussions with interest but can't get my head around one thing.
My engine, according to the manual, should be set up to have a WOT range of between 4500-5500rpm, which seems quite a wide range.
With the current prop (which is I don't know what, but I guess it is stamped on it somewhere) it maxes at exactly 5500rpm which suggests that the choice is spot on for maximum speed. But, I am not going to be using over 5000rpm much as the engine sounds harsh and thrashy over that and the fuel consumption is epic.
So my question is, if I changed the prop to bring the WOT revs down to say 4800, should I expect a big drop in the top speed (currently 35.5-36kt @ 5500rpm) or would it be about the same within a couple of knots? I guess it depends on what the power curve of the engine is (Johnson 115 2str) i.e. how many hp you get at 4800 against how many at 5500?
I am doing this mainly to get (I hope) a better cruising speed at lower revs, so say 3000rpm which gives me about 18 knots now might give me 20-22 knots with a prop change, but I am wondering whether it will knock a lot off at the top end. I don't go at full speed that often but it is still nice to be able to burn people off occasionally if you know what I mean
Would it achieve what I want or doesn't it work like this?