In article ,
Gould 0738 wrote:
:I'm not trying to be sarcastic here or question your knowledge, but
:this seems to contradict your comment about a decrease in speed.
:Comments? I'm just trying to understand.
:
:Thanks,
:Bob
:
:
:Bob:
:
:Assumptions include:
:
:1. You are not retuning your engine for the high altitude operation, and will
:be running a mixture somewhat lean on oxygen.

That is correct.

:2. That you have two different size props for a valid reason, i.e. your boat
:needs the decreased resistance of the smaller diameter prop to achieve proper
:RPM at the higher elevation.

Actually, the smaller diameter prop is the one I use at low elevation.

I inherited the boat from my Dad and he always switched between the two
props, so I can only assume he did that for valid reasons. I
personally have not done any testing to verify that though, which is why I
posted the question.

:If your boat runs the same at the higher elevation with the larger prop, why
:the H would you bother to screw around changing it?

See above. I've always run with the larger diameter (15), but smaller
pitch (15) prop at high elevation and the smaller diameter (14.25) but
higher pitch (17) prop at low elevations, and performance has always
been fine...WOT right where it should be, no cavitation, etc.

One thing just occurred to me. is the first number of the prop spec
the diameter or the pitch? On the low elevation prop, it is stamped
14 1/4 17 which I assumed was diameter and pitch, respectively.