Cavitation plate & keel

Discussion in 'Bubba's Outboards' started by SS minner, Sep 12, 2009.

  1. SS minner

    SS minner New Member

    Messages:
    39
    State:
    California, Missouri
    I have a 1967 Merc 110 9.8 h.p. motor I've been running for the past two years. I,m trying to get as much top end speed as possible. When mounted on the boat the Cavitation plate is 2 inches under the bottom of the boat. Do any of you think it would help the performance to raise it even with the keel?
     
  2. countryboy79

    countryboy79 New Member

    Messages:
    358
    State:
    nc
    I'am not sure about that but I'll tell you what i done. I got a 60 hp on a 16 foot jon boat. I run in a lot of shallow water so i raised the motor up to the last hole in the mont. Its about 4 inches higher than what its post to be. Doing that made my boat have more top end speed. Maybe that will help you.
     

  3. oh no

    oh no New Member

    Messages:
    11,108
    State:
    Indiana
    On racing boats,,, the center line of the prop is just under the water,,,,lol,,, that's why they have such a big rooster tail.

    That is a little impractical,,, but that is the way they run,,,lol,

    I don't think 2" below is too far down. You probably need more HP or a different prop or a whale tail.
     
    Last edited: Sep 13, 2009
  4. oh no

    oh no New Member

    Messages:
    11,108
    State:
    Indiana
    Hey check behind your carbs,,, sometimes small motors have restrictor plates that only allow so much air in,,,like NASCAR,,,, the racers I know get them out of the way,,,,Gain some HP.

    The little hydro planes use adustable expansion chambers,,,, that slide in and out like a trombone,,,,lol,,them little buggers will do 60 mph with old 10 hp Mercs....
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    If your anticavation plate is 2 inches below the keel then its setting in turblent water when trying to push your boat. You need the center of the prop shaft even with the keel. I would never go more then and inch below the keel on any motor. It causes drag and slippage. Build you a small jack plate say about six inch set back and it will allow you to pull that motor up in cleaner water to get a better bite.
     
  6. nevets91

    nevets91 New Member

    Messages:
    604
    State:
    rock hill south carolina
    i always try to get the cavitaion plate even with the bottom of the boat my self. i have been running my 30 horse about 3/4 inch below and thinking or raising it also
     
  7. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    I noticed the same thing with a 9.8 merc I had. I raised it up to where it belonged, and posted a pic of it, shooting a rooster tail and doing near 21 mph.

    It was on a 14' jon-boat
     
  8. SS minner

    SS minner New Member

    Messages:
    39
    State:
    California, Missouri
    Where could I see the picture?
     
  9. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    It may still be in the library where his jack plat building directions are. Bob paul and I know what to look for in raising one but you guys experminting be sure to watch and not get it out of the water to far so it won't intake water.
     
  10. Iowa_Josh

    Iowa_Josh New Member

    Messages:
    1,463
    State:
    Central Iowa
    Yes, running it too low will slow you down. Higher is faster until you cavitate.
     
  11. SS minner

    SS minner New Member

    Messages:
    39
    State:
    California, Missouri
    I raised the motor today and took it to a small lake to try it out. I can,t really tell if it helped or not. I raised it to where the cavitation plate is even with the keel. I may try to raise it more and see how it works. I have no way of gauging MPH, so maybe I should invest in a sonar? Thanks for all the help!
     
  12. etexun

    etexun New Member

    Messages:
    375
    State:
    Texas (Nea
    Do you are a buddy have one of those little hand held GPS units? I have one that will tell you speed. I have used it on my old boat before I bought a sonar that had speed on it.
     
  13. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    That pic has long been lost. It was on a jon-boat, that was only rated for a 6 hp engine. Very light weight and narrow boat.

    If you've got it raised up and even with the bottom, leave it alone for the health of the engine.
     
  14. Whistler

    Whistler Well-Known Member

    Messages:
    3,084
    State:
    TN
    Bobpaul, is this it?

     
    Last edited: Sep 14, 2009
  15. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    Yup. That's one crazy SOB in that boat.

    If he had any sense, he wouldn't have put a 9.8 hp engine on a boat only rated for a 6 hp, but it was fun:smile2:
     
  16. THE PAN MAN

    THE PAN MAN New Member

    Messages:
    1,213
    State:
    hartsburg mo.
    sometimes a fella has to push it a little. makes life worth livin:big_smile:
     
  17. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Whom ever said you had any sense Bobpaul:smile2:
     
  18. Todd Strong

    Todd Strong Active Member

    Messages:
    1,023
    State:
    Cambridge, Ne
    A small rooster tail from mine, I need to invest in a jack plate.
     

    Attached Files: