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Old 04-26-2012, 01:45 PM
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EJ OJPROP EJ OJPROP is offline
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Join Date: Mar 2005
Location: East Tennessee
Posts: 553
Tim - I see the last 200 - 300 RPM not gain much MPH with any prop regardless of who built it. The blade shapes are much different. The other is a more tradtional work boat type shape while ours is not that style. There are may other differences as well, rake and pitch distribution to name two.

Blade thickness is a major factor in top end. A thinner cross section IS faster. I used to thin my tunnel boat props to the point of breaking, in fact they would break and not last very long at all but I could thin a few more MPH put of it. When one of those props breaks you can end up upside down under water. Thin to win we used to say. Last I looked these boats were nowhere near 100 MPH nor do they have numbers on the side. As I said we prefer to build a good all around propeller that will last.

The RPM we see on the ski boats should not cause deflection at all. We still run our "old style" 3-blades on flatbottom v-drives with overdrive transmissions, prop turning faster than engine RPM, turning 5500 to 6500 RPM with no flex issues. You will see more load and pressure on blades with the wakeboats loaded to the gills than you do with a 1:1 turning 5000 wide open

Our current XMP 3-blades do have a different shape, even from our 4-blades. I built the prop pictured, 13 X 13 RC, in 1990 specifically for the CC boat. The blade shape I used was from a wooden pattern originally designed by my great grandfather Oscar in the late 1940's for racing applications.
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Eric Johnson
Johnson Propeller Co., Inc
OJ PROPS 800-359-9730

Last edited by EJ OJPROP; 04-26-2012 at 01:55 PM.
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