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  1. #1
    mrbtd's Avatar
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    Why did washers on the trim tabs work ???????

    This is making me crazy. First 2 times out on my 01 gpr with the basic mods and Jims Plate I had a horrbile bouncing problem. After the 1st time I stepped the sponsons and it got better but was still bad. After the 2nd time I added 1 washer under each trim tab bolt and it was GONE... Completely GONE.

    Why did it get so much better ? Is it that the water hits the tabs at a bad angle ?


  2. #2
    My son (mohawk man) jeffsntx's Avatar
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    The tabs put a bigger "footprint" on the water when they are shimmed down.

  3. #3
    r33pwrd's Avatar
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    Another question on them.... If you do not have a "bouncing problem" is there a benifit to shimming the tabs? I see a lot of people doing it but not a lot of reasons why? I remember someone saying they can give you lift.... If this is true can you gain speed from shimming them?

  4. #4
    Moderator RX951's Avatar
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    Here is some good information of the [Basic] operation of what is taking palce when you added the washers in the trim tabs. These links below relate more to mechanical trim tabs on larger baots, but the philosophy is the same in realationo to what is taking place when you made the adjustment you did on your GPR.

    http://lencomarine.com/howtrimtabswork.html
    http://www.boatus.com/boattech/trimtabs.htm
    http://www.boatsafe.com/nauticalknowhow/captpat1.htm
    http://www.diynetwork.com/diy/bo_enhancements/article/0,2021,DIY_13717_2278824,00.html

    Trim tabs are small surfaces connected to the trailing edge of a larger control surface on a boat or aircraft. The angle of the tab relative to the larger surface can be adjusted to null out hydro- or aero-dynamic forces and stabilize the boat or aircraft in a particular desired attitude without the need for constant control inputs.
    References:
    Wikipedia®

    Trim tabs work by adjusting (usually electric/hydraulically/manually at the touch of a switch) the tab up away from contact with the passing water; or down (sometimes also referred to as trimming in, or digging the tabs in) further into the water. Adjust the tabs down, into harder contact with the water if you like, and the aft end lifts and the bows lower. Adjust them up, easing contact with the water, and the transom squats lower and the bows rise.
    Trim tabs are fitted to all kinds of PWC, Powerboats, inboard shaftdrive, inboard sterndrive, and outboards.
    Both Fixed Tabs and Power Trim ‘n’ Tilt are different basic types of Trim Adjusting devices.

    I hope this helps for new an current members reading this !

  5. #5
    mrbtd's Avatar
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    Thanks a ton....Note from above -

    "Adjust them up, easing contact with the water, and the transom squats lower and the bows rise"

    My bow was to high - transom to low.

  6. #6
    Happily Self-Employed WFO's Avatar
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    There is a balancing act going on under your boat. The trick is to keep enough boat in the water (front of the boat) to keep the grate in the water. If too much boat is out of the water (nose too high), the grate comes unhooked, causing the bouncing or porposing. The trim tabs push the nose down. So does running less angle on the rear of the ride plate. The fun part (for me anyways) is finding the correct spot where the sponsons, ride plate, and trim tabs work together to yield the best speed and best handling in any water conditions.

    Oh and it's really hard to adjust your handling (plate and tabs) with a full tank of gas. That weight is on the front of the boat (duh) and keeps the nose down.

  7. #7
    Moderator RX951's Avatar
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    As WFO said also.
    Also note that as you begin to do testing on getting your handling fine tuned, you will find that It will/can vary at higher speeds. If you are doing high speed runs on low fuel, take note also that the handling and attitude on a boat on a full tank is different than a boat with only 3 gallons.
    When lift is mentioned and you try to obtain lift in order to gain more speed, speed will increase due to less wetted surface under the boat. Now, also keep in mind that you want enough lift to not casue the intake gullet to become unhokked from the water. There is such a fine line there and many many factors play into it. My GPR's handling is may not be applicable to somebody elses as there are so may factors that can come into play. One can give a starting point, but there is a lot of tuning and testing in order to dial the boat in to your liking.
    Rider's attitude sitting on the boat plays as well. Sitting planted on the ski is different than the superman position vs the stretched back position.
    Here is a helpful hint that a Key forum member told me 2-3 years ago: Every .010 in adjustment can account for roughly 1 mph in speed once you begin to find that sweet spot your boat likes. You may have to overshoot your target in order to find that spot, but you will find it. Once you do, you'll see how much faster the boat will go and still retain stability.
    Just keep in mind that you need to keep the contants/variables the same every time; riding style, water condition, fuel level, RPM, ect…
    There are many fast boats on this forum and I'll bet ya that every single one of them have different measurements in how their ski is setup, as well as riders weight, pump shoe, prop pitch, rideplate angle…..it can go on and on and on…

    Keep asking questions members !! This is what the forum is about !

  8. #8
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    You are absolutely correct Rich, And the fun part is when you set up a ski a certain way and it handles awesome. And then you do the same thing to another ski and the ski does not like it at all, But that is what's fun about this sport.

  9. #9
    r33pwrd's Avatar
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    Ok so reading everyone of those links you posted as well as evryones feedback... im still a little confused... The links make it sound like tabs are for "correcting problem" (I dont have any bouncing at all) Also always confused because some run NO tabs others run Shimmed tabs??? I realize there is more than one way to skin a cat.... So will I assume that the ones running NO tabs are running less ride plate angle? The ones with shimmed tabs are more angle on the plate (wouldnt these fight eachother?) Not questioning anyones setup just trying to learn... I have spent a good amount of money on my ski but the one thing I have always been confused about is the tabs........

  10. #10
    Hydrotherapy's Avatar
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    glad this thread came up as i am also left scratching my head....

    so the fastest set up should be no tabs,but as my riding is at sea i have gone from cut riva tabs back to stock with no washers,
    can i be faster if i made some home made tabs which are thinner than stock or does any less than stock not work due to the recess in the hull they sit in......

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