74 tournament skier wood rot

Discussion in 'Restoration Projects & Questions' started by dyne74, Jul 23, 2008.

  1. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,321
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    dyne74,

    The 18 I/O has a little hook molded into the bottom right at the transom. If someone sanded the bottom flat at the transom it could cause your bounce, or your bottom could have rocker in it.

    When I had my I/O rebuilt, they did sand the hook out, but I converted it to an outboard, so it did not matter.

    The hook was small. At the transom it was only about 1/8 deep and the length was about 1/4 as I recall. It went all the way across the bottom. You could make it as large as necessary to stop the bounce. I would use white MarineTex. The Allison bass boats have a larger hook at the transom to help with bounce. It used to be a common practice for stern heavy boats.

    The advantage is that it is not noticeable. Trim tabs are ugly, and I hate to add weight to a boat or airplane.

    A prop with no cup and minimum rake will help also. A doel fin or similar part will help too, but it will put rollers in your wake. I suspect that trim tabs will tend to put rollers in your wake too, although I have never tried them.

    jim
     
  2. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,321
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    I just reviewed your pictures. If you would use an aft facing bench observer seat placed well forward it would move your cg considerably forward with passengers. I know that this would create an issue with carpet, but it would help significantly. Aft cg is a problem with the I/O. There is a picture of the original set up in this thread.

    jim
     
  3. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,321
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    I looked at the pictures again. Your boat sits lower in the water in the stern than mine did with the I/O. The trailer axle is also further back than mine was. I suspect the 3/4 plywood is the culprit.

    If there is a trim limit pin in the drive, I would remove it and see if it will trim in further. I think you can cure the porpoise with a hook at the rear of the bottom if you make it big enough. The faster you go, the more effective the hook will be. The teams don't use this technique because they are primarily concerned with pitch up off the dock. The hook would not help there.

    Sorry for the multiple posts.

    jim
     
  4. markbano

    markbano Hydrodyne 18 Specialist

    Joined:
    Nov 4, 2005
    Messages:
    854
    Boat Model and Year:
    1973 Hydrodyne Tournament Skiier
    I don't disagree with anything Jim or Greg is saying, but will add my experience. I have an outboard, albeit with a heavy (512 lbs) 3 litre V6 outboard. I also have a wedge to help trim the boat more nose down. That helped, but did not completely solve my problem of some minor porpoising as I burned off fuel in the bow-mounted fuel tank. I could always get rid of the porpoising by trimming full down but that would result in vibration in the boat and felt awkward.

    I did, finally, put a 60lb bag of concrete mix up front in the very bow. It is in a heavy protective bag and is snugged into the bow cavity forward of the fuel tank where it can't move. I agree that blocks would not be a good idea. It made a big difference for the better. I know adding weight is not ideal and other things should be tried first. However, if you end up with no other solution, this works. As Greg points out, the ski teams use forward balast as a necessity on multi-rigged boats to even out the weight. If you are too stern heavy, then balast up front may be your only solution.

    What seems strange to me is why the boat would be so stern heavy. However, if you have added weight in back, you may need to add some up front. Also check your prop selection. Jim can help you more with that.

    Hope this helps.

    Markbano
     
  5. dyne74

    dyne74 Hydrodyner

    Joined:
    Feb 21, 2008
    Messages:
    30
    Boat Model and Year:
    74 Hydrodyne I/O
    Trim tabs, instantly better!! Planes out perfactly, I had to rebuild the motor though, but she goes like stink now! I have a problem, I'm looking for a fuel pump rebuild kit, There is nothing wrong with my pump now, but I would like to have a spare kit in case it fails. It's an AC mechanical fuel pump, the new Sierra number is 18-7267 or Carter M73039. I know I can buy the whole pump, but I only want a rebuild kit. I don't know if anyone has done a rebuild on one and knows the part number. 35 years old, I don't trust it and I don't really want to spend $150 on something I may need. Any help would be great.
     

Share This Page