1974 Evinrude 50 prop change

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mobilehomer

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Aug 21, 2011
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Thanks in advance, I have a 1974 14' Tri hull with a 1974 Evi 50, original prop (13.75 X 15). Broke the prop this week. I am happy with speed and plane. If I change to a 4 blade, what dia and pitch to keep same performance? 5500 rpm, 27 mph by gps. I would like the advantages of a 4 blade. but is it worth it?
 
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steelespike

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Apr 26, 2002
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Re: 1974 Evinrude 50 prop change

I don't think a 4 blade is in your future but we may be able to improve your speed.
Answer these question for us.
1. Was your old prop a little tired perhaps even original to the motor?
2. Is the anti vent plate(just above the prop) about even with the bottom or slightly above?
3.Is the bottom clean and smooth.
 
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mobilehomer

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Aug 21, 2011
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Re: 1974 Evinrude 50 prop change

The answer to all three is yes. After reading som posts I was thinking that a 4 blade might help on bottom end. But, as I have no experience with props, if you feel that the original size and pitch would be best, sounds good to me. Thanks, Ken
 
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steelespike

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Re: 1974 Evinrude 50 prop change

You said you were happy with speed and plane and the prop was tired so a new prop should give you a little boost.
True a 4 blade has good low to midrange performance but you likely would lose a little top end.
If you were to go to a 4 blade you would drop 1" in pitch to maintain rpm. Diameter just follows the design.
 
jimmbo

jimmbo

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May 24, 2004
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12,961
Re: 1974 Evinrude 50 prop change

Your old original prop did not have any cupping in the blades, a new 15in prop with cupping might end up overloading your engine. Adding the cupping is like adding an extra couple of inches pitch.
 
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