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Prop Pitch

ocalaocala Senior MemberCandlerPosts: 244 Deckhand
Just did a repower on the boat. Went from a 89 Johnson 2 stroke 60HP to a 2010 Honda 50HP 4 stroke.
Its a bass boat. I was worried about the hole shot but with the new motor the boat jumps out of the water. 
Problem is I can't get to full throttle because it limits out at 6000 rpm's with a 13 pitch prop no matter how I try to trim it. . Being that the hole shot is so good could I jump to a 14 or 15 pitch and would that reduce the rpm's enough to get me at WOT without limiting out? Or does it work in the opposite direction. Do I need to go down in prop size.
Never had to worry about this stuff before so it's kind of new to me.

Replies

  • DeboDebo Junior Member Posts: 76 Deckhand
    Increasing pitch decreases rpms. A two inch pitch change equals roughly 300-400 rpms. I think you are  spot on with the prop you have currently. Good luck 
  • 4WARD4WARD Senior Member Cross Creek,FLPosts: 2,969 Captain
    Make sure you are testing it with a realistic average load in the boat.
     If you are reving out close to WOT by yourself then you are probably ok.
    You can have your prop repitched if you need to, cheaper than a new one.
    "I hate graveyards and old pawn shops
    For they always bring me tears
    I can't forgive the way they rob me
    Of my childhood souvenirs"... John Prine
  • Crkr23Crkr23 MelrosePosts: 725 Officer
    You might try raising the motor on the transom. If you can't get the rpm's higher with the trim, I suspect the motor maybe sitting a little low.
  • Crkr23Crkr23 MelrosePosts: 725 Officer
    Just looked back at your post, it looks like you're at the right rpm now. 
  • 4WARD4WARD Senior Member Cross Creek,FLPosts: 2,969 Captain
    Proper trimming should raise the rpm so that you can back off and maintain speed.
     If you are trimming to lower RPM, you are doing it wrong.
    "I hate graveyards and old pawn shops
    For they always bring me tears
    I can't forgive the way they rob me
    Of my childhood souvenirs"... John Prine
  • ocalaocala Senior Member CandlerPosts: 244 Deckhand
    4WARD said:
    Proper trimming should raise the rpm so that you can back off and maintain speed.
     If you are trimming to lower RPM, you are doing it wrong.
    That's how I do it. Back off on the throttle and trim it up to get more speed.  The issue is there is a lot of throttle left. Was thinking maybe a  14 might do it. 
    Also I didn't know a prop can be re-pitched. 

  • 4WARD4WARD Senior Member Cross Creek,FLPosts: 2,969 Captain
    How much throttle do you have left when it hits 6k? Are you at 3/4 or does it take a while to get there wide open?
    "I hate graveyards and old pawn shops
    For they always bring me tears
    I can't forgive the way they rob me
    Of my childhood souvenirs"... John Prine
  • ocalaocala Senior Member CandlerPosts: 244 Deckhand
    Crkr23 said:
    You might try raising the motor on the transom. If you can't get the rpm's higher with the trim, I suspect the motor maybe sitting a little low.
    Right now the anti-ventilation plate on the motor sits about 1 inch above the keel. Ideally having it even or a little below would help but the motor can't be lowered anymore. I suspect this may be part of the issue in that the prop is coming out of the water at higher speeds. 
    There was a dolphin on the motor when I bought it but I took it off. I don't think it would help in this situation as the boat handles fine and the hole shot is good.  
  • ocalaocala Senior Member CandlerPosts: 244 Deckhand
    4WARD said:
    Make sure you are testing it with a realistic average load in the boat.
     If you are reving out close to WOT by yourself then you are probably ok.
    You can have your prop repitched if you need to, cheaper than a new one.
    So far have tested it with me and a buddy our gear and a full livewell of ice.
    Trying to mimic normal conditions. 
    The boat is back heavy meaning the batteries and gas tank are in the back. The seats are in back along with a livwell in back that's filled with ice. Nothing in the front. 
    I suspect if it was just me by myself the issue would be more pronounced. 
  • capt louiecapt louie Moderator citrus countyPosts: 10,881 Moderator
    A little extra pitch won't hurt to try. I shoot for 5500 or a bit more WOT. Mainly for economy. Not worried about speed as long as hole shot good.
    "You'll get your weather"
  • ocalaocala Senior Member CandlerPosts: 244 Deckhand
    4WARD said:
    How much throttle do you have left when it hits 6k? Are you at 3/4 or does it take a while to get there wide open?
    Doesn't take a while at all. The boat jumps out of the water and I begin backing off because it gets there pretty quick. I'm guessing about 3/4 is right.  
  • 4WARD4WARD Senior Member Cross Creek,FLPosts: 2,969 Captain
    I’d try putting that dolfin back on. I’m guessing it’s cavatating and that may help hold more water down for it to eat.
    13 pitch is middle of the road for that motor, you shouldn’t have 1/4 throttle left. If it is spinning out, more pitch will probably make it worse.
    "I hate graveyards and old pawn shops
    For they always bring me tears
    I can't forgive the way they rob me
    Of my childhood souvenirs"... John Prine
  • Crkr23Crkr23 MelrosePosts: 725 Officer
    Call Ken @ Prop Gods, he's forgot more about props than most of us can hope to know.
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