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  1. #1

    Default Problem with cavitation on small 14ft boat

    I have a 14ft aluminum boat with a Tohatsu 3.5 hp short shaft. When I run it wide open, I get some cavitation. Transom on boat is 17 inches. Any suggestions on how to fix this problem?

  2. #2
    Lieutenant Boss Hawg's Avatar
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    Default Re: Problem with cavitation on small 14ft boat

    I just discussed the same problem a freind is having with about the same boat today- We discovered he was'nt triming his motor down enough -
    Don't know if thats your solution to your problem

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  3. #3

    Default Re: Problem with cavitation on small 14ft boat

    Tried that.....thought maybe I should have a long shaft on it, but everything I have read said a short shaft was the right length. Even thought of cutting down the transom, but wasnt sure about doing that?

  4. #4
    Moderator QC's Avatar
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    Default Re: Problem with cavitation on small 14ft boat

    Where is the anti-ventilation plate compared to the bottom of your boat? BTW, this probably ventilation not cavitation. Commonly referred to incorrectly and that's why the thingee that's supposed to help prevent it is an anti-ventilation plate . . .

  5. #5

    Default Re: Problem with cavitation on small 14ft boat

    Quote Originally Posted by QC View Post
    Where is the anti-ventilation plate compared to the bottom of your boat? BTW, this probably ventilation not cavitation. Commonly referred to incorrectly and that's why the thingee that's supposed to help prevent it is an anti-ventilation plate . . .
    Where can I get an anti-ventilation plate??

  6. #6
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    Default Re: Problem with cavitation on small 14ft boat

    Your motor already has an anti-ventilation plate...all outboards do. It's just that folks incorrectly call ventilation cavitation...and call the anti-ventilation plate the anti-cavitation plate. It should be even with the bottom of the keel at the stern/transom, plus or minus an inch.

  7. #7

    Default Re: Problem with cavitation on small 14ft boat

    It appears that it is even with the keel....it just seems like the prop should be alittle more into the water....it only occurs when i'm running it wide open....which I tend to do since it is a small engine

  8. #8

    Default Re: Problem with cavitation on small 14ft boat

    3.5 hp on a 14 footer is probably way under-powered. I just went from a 9.9 to a 20 on my 14 foot tinny.

    If the shaft length is correct, then motor tilt/trim is the next issue. My guess would be that you have it tilted to far up.

    Another possible culprit could be damage to the prop - nicks and gouges causing turbulent flow over the blades.

    And maybe just being that underpowered? I don't know... Does your 14 actually plane with a 3.5?

    -dm

  9. #9
    Chief Petty Officer
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    Default Re: Problem with cavitation on small 14ft boat

    No more motor than he has, he is probably just "boiling water" causing the prop to "bite air". If I were using a small motor like that on a much larger boat, I'd be inclined to run it at a slower rpm to avoid his phenomenon. Speeding it up or running it faster is not gaining any appreciable speed. Of course, it's doubtful the motor turns up fast enough to experience cavitation which could show some evidence of literally burning the back side of the prop.

  10. #10
    Moderator QC's Avatar
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    Default Re: Problem with cavitation on small 14ft boat

    Yeah, I was gonna mention speed too. For reference I have a 14 ft. Sea Nymph tinny that planes with two people and a 5 horse and runs 12 MPH. There are heavier tinnies, but not a lot of lighter ones. I guess the point being that a 3.5 may be stuck trying to get over it's own bow wave and causing the venting, but a 9.9 would make my boat fly . . .

  11. #11

    Default Re: Problem with cavitation on small 14ft boat

    Quote Originally Posted by QC View Post
    Yeah, I was gonna mention speed too. For reference I have a 14 ft. Sea Nymph tinny that planes with two people and a 5 horse and runs 12 MPH. There are heavier tinnies, but not a lot of lighter ones. I guess the point being that a 3.5 may be stuck trying to get over it's own bow wave and causing the venting, but a 9.9 would make my boat fly . . .
    The boat is a 1978 Laudau, very well made and it does have some weight. And perhaps you are right, it may be under powered and that running it wide open wont get me any faster that running it 3/4 way open. And no, it does not go fast enough to plane. So maybe that is the problem, too much weight and not enough motor....I have a 10ft plastic Pelican bass boat that I use the 3.5 on and I didnt want to have to get another motor, so I thought I could use the 3.5 on both....but maybe not.......Thanks....guys

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