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Old 18-05-2014, 10:18   #1
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prop for 32' irwin classic

What deterimines prop size for a 32' Irwin? Is it engine or displacement? PO changed out the atomic four for a 3 cyl universal. Has a 14' 3 blade, but not sure of pitch. Looks to be to big for boat. Thanks
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Old 18-05-2014, 13:21   #2
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Location: Oro Bay Puget Sound
Boat: Irwin sloop
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Re: prop for 32' irwin classic

The equation includes power, shaft rpm, and displacement. My Irwin 32 has a Perkins 4108 with a 1.51 reduction and a 12x12 three blade prop. That gives a 1 7/8" clearance between blade tip and hull and although there is room for a larger diameter prop I've been warned against reducing the prop/hull clearance and risking paint and gelcoat erosion. This combination works well for my situation and our local prop shop did the required calculations. Check the hull clearance, and then the rpm at full throttle when underway. If both are acceptable you're fine although I agree that is a big prop to be dragging while under sail. If the clearance or RPM are insufficient a reduction in diameter or possibly a two blade prop might be worthy of consideration.
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