[Public-list] Props for diesels

[Michael]

>I also have a prop question; my A30 has a Yanmar >3GM30 with 2:61 gear; I
was
>told that a 12x10R 3 blade was appropriate

That's a really large engine with a bunch of reduction, too.
I have a 2 QM 15 swinging a 13X12 2 blade. Full ahead, it'll push the boat 7
1/2 knots under ideal conditions. I don't have a tach, but like to keep the
boat speed at 5 1/4 knots (keeps me honest as far as putting the sails up to
you know... SAIL .

Anyway, it's the diameter of the prop. that'll give you the 'punch' you are
looking for. Because the aperture of the Alberg limits us to about 13" wheel
diameter, I really doubt you will be able to efficiently use all the power
you have available. I have been told props are at max. theoretical
efficiency when their numbers are 'square', i.e. 12X12. 13X13, etc. The tug
I have been on until recently  has wheels 78X64 and it outperforms most
everything in it's HP. range, so I'm inclined to think there is as much art
as science in wheel selection.

Michael Grosh
#220 Checkmate
Tug Endeavor



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