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Thread: Trim tabs

  1. #1
    davesgpr's Avatar
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    Trim tabs

    What gains are seen by filling in the pockets on the stock trim tabs? Is there any sanding done on the side that meets the hull to match up with the rideplate in the back? Is this dangerous????


  2. #2
    African-American
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    Yeah was wondering the same, maybe make them nice and smooth ?
    how about if they were lowered at the back or the front was raised ?
    and do i really need them ?

  3. #3
    davesgpr's Avatar
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    I want to raise them .170 in the front, but not much room in the back. The only thing I can do is sand the back down some.

  4. #4
    philip_gpr's Avatar
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    "how about if they were lowered at the back or the front was raised?"

    waste of time trying that, ride is terrible

  5. #5
    2000 GPRXP 4tec shooter98xpl's Avatar
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    every ski is different, just cause something didn't work on someones ski does not mean it won't work on yours. If you think there maybe a gain, simple way to do it, try it out. Thats part of what these guys on here call "testing".
    I learned from my seadoo days not to listen to most things said on the boards, sometimes doing the opposite is better. I was told I couldn't run a lightened flywheel and lightened pto on a big bore rec 951 ski. I rode, raced and had a blast with this setup. You just have to try things out and see what comes of it.
    SHOOTER

  6. #6
    philip_gpr's Avatar
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    ... well some things are just not worth testing yet again

  7. #7
    Has anyone tried machining (not shimming) the tabs to perfectly match the angle of the rideplate?
    If you had a 5 degree plate, 5 degree tabs, and 5 degree nozzle, it seems like it would make everything work together under the ski. Instead of draging the rear of the tabs through the water. Dont forget the different angle of attack at high speeds.

    That logic might not hold water, but I would be curious to see if anyone has tried it with exacting measurements?

  8. #8

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    Quote Originally Posted by porksword View Post
    Has anyone tried machining (not shimming) the tabs to perfectly match the angle of the rideplate?
    If you had a 5 degree plate, 5 degree tabs, and 5 degree nozzle, it seems like it would make everything work together under the ski....

    That logic might not hold water, but I would be curious to see if anyone has tried it with exacting measurements?

    It does make sense. Keep in mind though that water behaves "harder" the faster you go. Because of this, you need less and less surface area to help generate "lift" If everything were set at 5 degrees, it would be great up to the point where lifting the boat out of the water and balanceing the boat on top of the water become equal. When you have to much lift, things begin to change. One of the results of to much lift at high speeds is porpoising. The boat literally lifts itself out of the water.

    It is a balanceing act finding just the right amount of lift to keep the minimum amount of hull (surface area) out of the water to get your best speeds. That is why so many people say that it is different for every given boat.... to many variables.

    You may find that as you go faster, you may have to change your angles (decrease them).

    For instance, if your boat had been set up and ran perfectly at 72, then added a different pump or increased horsepower to get up to 75, you may find that while getting there you have to decrease your ride plate or trim tab angles to reduce your porpoising and settle out the boat. This is just a scenario. For others making speed mods the changes may occur at 68 to 71 or 76 to 79 etc. etc.

    I agree with Phillip in this case because in the past people, (myself included) have found that with that much lift (all 5 degree set up) the GPR has serious issues staying in the water in anything less than glass. The porpoising starts at about 64-68mph, depending on rider weight, sponsons, sponson angle, body position, etc.

  9. #9
    philip_gpr's Avatar
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    "Has anyone tried machining (not shimming) the tabs to perfectly match the angle of the rideplate?"

    Here are some comments on testing I have done.

    First off everyone would probably agree the more you shim the tabs down the more stable the ride becomes.

    Likewise if you remove the tabs the ride gets very loose.

    I have tried all sorts of different angles (using shims).

    The angle of the trim tabs has a huge effect on ride quaility. Much more than the rideplate.

    With the stock tabs flat seems to be the best position.

    The Riva and R&D tabs come with a slight angle on them. But they are also thicker. (Remember - the more you shim the tabs down the more stable the ride becomes.) They will work fine if you keep the slight angle. They also work fine if you shim them to remove the angle.

  10. #10
    philip_gpr's Avatar
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    "For instance, if your boat had been set up and ran perfectly at 72, then added a different pump or increased horsepower to get up to 75, you may find that while getting there you have to decrease your ride plate or trim tab angles to reduce your porpoising and settle out the boat. This is just a scenario. For others making speed mods the changes may occur at 68 to 71 or 76 to 79 etc. etc. "

    yes yes yes

    Most of us simply use the rideplate angle to dial in the ski.

    I strongly believe that when a ski does not have the expected top speed that in most cases the ridplate is not in the ideal position.

    1) Either the front of the rideplate is too low in the water

    2) or the reverse and it is recessed too much up into the hull.

    3) or the angle is wrong (usually not enough)

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