[alberg30] Prop size and tip clearance.

[Bob Lincoln]

From: "Bob Lincoln" <lincoln at cc.UManitoba.CA>

On checking my prop there is less than 1/4 inch tip
clearance at top, and about 1/2 at bottom of aperture.  The
prop is stamped 13 x 11.  According to Skene and Nicholson,
the best fit is an 11 inch prop which gives proper clearance
at top and a bit more than recommended at bottom.  The 13
inch is quite oversize and probably cavitates, giving me
2500 max rpm versus design 3000.  The shaft is not centered
in the 14" vertical space, something like 1/4" off.  Without
raising the question of diesel vs. gas, or shaft
revolutions, have people found any success with an 11 inch
diameter prop rather than a 12 or 13?  I have received
conflicting advice--e.g. "get the largest you can fit in the
aperture" versus Skene (Elements of Yacht Design) and
Nicholson (Boat Data Book).  Any comments?
Bob Lincoln
#590

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