Equivalent size in a four blade?

ls1geezer

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May 15, 2011
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I have a 1990 Wellcraft Eclipse 186 with an Alpha One 4.3L 175hp sterndrive. I just managed to damage my prop so it?s time for a new one. I have no problem with performance, as this is my first boat so I really have no reference. The damaged prop is a 14 X 21? three blade. I have been told that a four blade is smoother and better balanced. What would be the equivalent four blade to my present three blade?
 

craze1cars

Lieutenant Commander
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Dec 26, 2004
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1,822
Re: Equivalent size in a four blade?

Probably a 19 pitch. Normally need to drop an inch or two when adding a blade to maintain your rpms. But that's a guess based on limited data provided so far.

It would be better if we knew your current prop's top speed, and what RPMS the engine is turning at that top speed. It also depends on whether you current prop is stainless or aluminum, and whether the 4 blade you are considering is stainless or aluminum. If you change materials, it can really have an impact on rpm and performance, even in the same pitch.
 

ls1geezer

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May 15, 2011
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6
Re: Equivalent size in a four blade?

Thank you for your prompt reply. The present prop is aluminum and for cost I would like to stay with that.As for the other data I only had the boat out three times so did not pay too much attention. And with a damaged prop I can't go out and get any accurate numbers. For what it's worth I do believe the present prop is the factory original
 

craze1cars

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Dec 26, 2004
Messages
1,822
Re: Equivalent size in a four blade?

If you're starting with aluminum, and buying another aluminum, and only adding a blade....

I'd guestimate to drop 1" of pitch to maintain your current RPM. Pretty sure Solas Amita 4 blade is available in a 20 pitch, and would probably be a good choice to be comparable to what you had for reasonable cost.
 
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