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Prop Question

Discussion in 'Boats and Motors' started by Cat~n~Crappie, Jul 11, 2004.

  1. I am in the need of buying a new prop for my 30 HP Johnson. I have been searching Ebay for one and one of the variations I see in all the props is the "Pitch". So what affect does the pitch have on the prop? The ones I was looking at went from like a 9 up to a 15 pitch. I want whatever will make the motor run the best. The motor is on a 1990 16' Sea Nymph.

    Thanks for any help in advance.
    Cat~n~Crappie
     
  2. what kind of boat is it on?
    and if you know what pitch do you have now and what are your rpm's at wide open
     

  3. freyedknot

    freyedknot useless poster

    pitch 12 give 12inches of movement per one revolution of the prop..19 pitch gives 19 inches per revolution. carefull don't over rev you need a tach to find the best prop.
     
  4. "Pitch" is a theoretical number that says given no slipage that is the distance the prop moves forward through the water in one revolution. Basicly, the higher the pitch number the further it moves your boat forward with one revolution. However, you cannot go up in pitch without sacraficing RPMs on the motor. If your is like my 50HP Johnson, your WOT (wide open throttle) RPMS should be between 5000 and 5500. I currently run at about 5200 with my 16ft Deep V at WOT. Like BigJohn alluded to, I believe your pitch number will be different though depending on Motor HP, weight and hull type. Going up 1 "pitch" I believe has the effect of lowering your WOT RMPS by 500, but increacing your speed a bit. If your old prop has you within that 5000-5500 RPM range I would stick with that pitch otherwise you could maybe call your local Johnson dealer let him tell you what pitch they recommend for your motor/weight/hull. One other thing going to Stainless from Aluminum (and vice vera) will affect your RPMs too. I believe I read somewhere that the same pitch SS Prop will lower your WOT RPMs by 500 over the Aluminum prop due to less flex in the blades. You should be able to find the pitch stamped somewhere on your existing prop or take the model number off it and call the prop dealer you are looking at buying from and the should be able to x-reference it to one of their props.

    Barry