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  1. #1
    NIXON'S BACK!! cincygpr's Avatar
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    College Kid Build Thread

    I decided to create my own build thread, even though BoostCrzy and I seem to be doing the same things to our skis!

    A bit of history first...

    Bought the ski (2002 GP1200R) at the end of the season in 2006 from an Army soldier who had previously been stationed in Hawaii and was being transferred to Germany, so he didn't have much use for the ski anymore and needed the money more. Drove about two hours to meet him, and the ski was even better looking than he had originally described it to be. Upper hull was in good shape, it started right up, felt good going for a ride in the Ohio river. Lower hull was a bit rough from him beaching it, but I decided I could fairly easily patch that up.

    The ski had 40 hours on it at the time, and he was asking $4000 for the whole setup; a trailer, the ski, and quite a few extras. I had recently sold my 1997 Sea Doo XP for about 1200 dollars more than I had paid for it, so I had very little invested total in the GPR. Paid cash on the spot, and up home I went with my new prize.

    The ski sat for the 06-07 winter, and taken out for a summer of good riding in 2007. During one ride, however, the 'engine overtemp' light began buzzing, so I knew the cat had to be replaced. After a half hour of nursing the ski back to the docks (about 3 miles), I got it back to the garage and pulled the pipe (after letting it cool off!!). Turns out the cat-con material separated from the housing completely and lodged itself downstream into the pipe. Got a homemade D-plate cut on a waterjet at my then current worksite, welded it in, and it worked like a charm. Stepped the sponsons while I was at it, and took it out a few more times.

    Ran a top speed of 64.1MPH one way before the ski had a feeling like someone slammed on the brakes. After a few attempts to start, it finally fired, but wouldn't go any more than 3000RPMS. My immediate thought was a powervalve fell into a cylinder. After a few months of not really working on it, I took it to Keith's Leisuretime Motorsports (GREAT shop if you're in the Dale Hollow Lake Tennessee area) and Keith there got me all fixed up with new R&D billet valves, but the real problem was the carbs were all gunked up from the previous owner.

    Ran a best of 63MPH this summer so far, with a few tenths still on the table if the skiiers weren't out. Tore it apart this past weekend to prep the beginning of the modding bug for me!

    This year, I plan on installing:

    Speedfreeks cut Nu-jet 6.5 impeller, pitched to 12/18 and set back
    Kerry package 1300R Riva plate
    1200R intake grate
    Pump plug kit

    I'm studying Aerospace Engineering at the University of Cincinnati in Cincinnati, OH, and currently co-opping at the GM North America Corporate Wind Tunnel in Warren, Michigan. So i'm pretty involved with the study of fluid flow over various streamlined and bluff bodies, and through lots of researching and reading, i'm still looking for answers as to WHY certain hull and ride surface mods work.

    So, hopefully in this thread, I will be able to look into the reason why stepped sponsons reduce porpoising, why Leo's mod works, why the GPR hull is designed how it is, and i've got a few ideas of my own that the Fountain guys may be proud of as well as document my own build.

    But first, the required thank you to all the guys on this board! This site is an absolute WEALTH of knowledge for anyone wanting to mod a ski... I searched for about six months before I actually got an account on here.

    Enjoy!
    Last edited by cincygpr; 06-17-2008 at 08:28 PM.


  2. #2
    BoostCrzy's Avatar
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    Definately going to be a great comparison between the different parts we have....ill be checkin in for updates!

    -Jack

  3. #3
    Hydrotoys's Avatar
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    Good luck. We're here to help.

    Buy a good camera. Keep us foto-junkies fed!

  4. #4

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    I am doing a similiar build. Just wondering on why you picked the Kerry package 1300R Riva plate? Thanks

  5. #5
    NIXON'S BACK!! cincygpr's Avatar
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    It happened to be the most convenient one for sale, to be honest, not much more of a reason!

    I have read that it offers good performance on lake water conditions, so i'm going to give it a try for awhile.

    I also haven't read about much testing performed on it, so I may try to snag a Jim's plate from someone for comparison.

  6. #6
    BoostCrzy's Avatar
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    Do you have any pics of the plate bottom, Cincy?...just for comparison?...is it skegged?...have you measured the angle?....i have my FF plate from Jim setup with just under 1 inch (.990) at center tail....and around .020 on the sides against the shoe....this was my sweet spot during testing....(lake - 1 foot chop) ....

  7. #7
    BoostCrzy's Avatar
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    Quote Originally Posted by cincygpr View Post
    i'm still looking for answers as to WHY certain hull and ride surface mods work.

    So, hopefully in this thread, I will be able to look into the reason why stepped sponsons reduce porpoising, why Leo's mod works,

    Leo's mod basically creates a larger surface area for the boats stern to ride on as it gets on plane...reducing the amount of rotation required to get up....this makes for a speedy transistion during acceleration....

    ....as for stepped sponsons.....my theory is: ..the steeper angle also contributes to rotational transition and gets the boat settled into higher speeds...and if the bow begins to raise too high they will contact the water surface and correct for it....
    Last edited by BoostCrzy; 06-18-2008 at 08:21 AM.

  8. #8
    NIXON'S BACK!! cincygpr's Avatar
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    Quote Originally Posted by BoostCrzy View Post
    Do you have any pics of the plate bottom, Cincy?...just for comparison?...is it skegged?...have you measured the angle?....i have my FF plate from Jim setup with just under 1 inch (.990) at center tail....and around .020 on the sides against the shoe....this was my sweet spot during testing....(lake - 1 foot chop) ....

    It's a 1300R Riva (new-style) plate with the mounting surfaces machined for more angle... apparently it's a Kerry package plate, and apparently once modified, it will yield better numbers than a simliarly modified R&D plate (but not necessarily a Jim's FF Plate!!). When comparing it to a stock rideplate, it has:

    -- Similar skeg features on the side riding surfaces
    -- About 2" greater length on the trailing edge of the middle riding surface (to clear the 1300R extended pump)
    -- The center riding surface is at a greater angle than the stock plate, resulting in small skegs

    My expectation is superior rough water handling as the stock plate when shimmed level with the shoe, and greater speed and handling in smooth water when the angle is increased.

    I haven't mounted it up yet; gotta get home this weekend and the following weekend to swap the impeller and plug the pump shoe. I have a week off of work during the 4th of July week, so that'll be a huge test-n'-tune time for me to dial everything in.

    And regarding the sponsons:

    Your theory is what I was thinking; porpoising is a sinusoidal vertical displacement of the nose... the pump 'pushes' the ski about its width-wise axis resulting in a lifting of the nose when the intake is stuffed sufficiently, but when the nose pitches up, the pump unloads slightly, resulting in slightly less thrust, resulting in the nose falling, where it repeats the process indefinately unless something damps this motion, which is where the stepped sponsons come into play. They act like the damper in a car's suspension, allowing the sine wave motion of the ski to settle by providing a negative moment counteracting the positive moment of the pump thrust.

    And you are right about Leo's mod too!! It also eliminates the 'hook' action on the water that the rub rails provide. So, it not only increases the surface area, providing greater lift (but increasing the surface drag on the hull), it decreases the pressure drag caused by the rub rails essentially dragging water along until they lift above the water. The reduction in pressure drag offsets the small gain in surface drag.

    More later!!!
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  9. #9
    BoostCrzy's Avatar
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    .....cake i tell ya!

  10. #10
    NIXON'S BACK!! cincygpr's Avatar
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    I'll update with pics a little later... got the pump shoe filled...

    And used Bondo... for 7 bucks total! Didn't have enough time to swap the impeller though...

    I'm curious to see what the back to back differences are between a polished rideplate and a sanded rideplate; there's a lot of back-and-forth discussion about polished resulting in less drag, or sanded resulting in less drag (due to disturbing the water tension)...

    Anyone have a stock rideplate they're willing to let go for free/cheap for the sakes of a bit of testing?

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