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  1. #1

    1999 Yamaha GP1200 porpoising mods to help

    1999 Yamaha GP1200 porpoising mods to help anyone know the best way to help reduce porpoising it would be greatly appreciated any advise the machine is stock now any other mods also thanks I am looking a Solas impellers but not sure what to do first

  2. #2
    first off there are plenty of threads already in greenhulk about fixing the porpoising problem... not to be a dick but please use the search function.

    are you using the machine in big water or smooth water. example, big water = lake erie or bigger, smooth water = small inland lakes and the such.

    I have found that many of the fixes for smooth inland water is vastly different when you run in the big water vs the smooth. a simple rideplate and intake grate will fix you for the smooth stuff, even a factory long plate from ebay, aka 97/98 gp1200 rideplate.

    Drop your sponsons all the way down if you still have the factory sponsons.... you will lose a bit o speed but reduce the porpoising.

    rough water requires a different approach.

    the 99 ski has the 5 degree nozzle and the short ride plate, both are going to make porpoising worse, especially when the watergoes from mild chop to 3-5 foot spaced 1.5 to 2 foot waves (non breaking).

    I had a R&D rideplate and I have the R&D intake grate... while both helped to reduce the porpoising my 99 gp1200 made, it slowed me down, especially after i shimmed the plate down some.

    I recently got a shredmaster plate, It rides very differently but it helped with the propoising alot, and I gained speed over the shimmed down R&D plate.

    I have no radargun or gps numbers to confirm, however I do use the onboard speedometer. While the onboard speedometer will be incorrect for the speed you acheive, it should atleast be repeatable. I find my gauge to be VERY repeatable, and so it is usable to verify speed losses or gains through modifications aslong as you dont change the way the speedometer sensor gets its waterflow.

    back to the ski.
    I have custom made trim tabs on it, that i am actually thinking about removing. They did help reduce the porpoise more when I had the R&D plate on there, but I would like to see what happens with my shredmaster on there alone.

    Having seen a few different designs for intake grates I want to get my hands on the riva grate... looks to have a deeper wing on it to pull the boat more, probably lose more top speed but increase the hookup.

    What have i learned?

    The smooth water approach works well, you want a longer plate but angled to keep the bow up. keep the 5 degree nozzle and throw a set of trim tabs on there if you havent... i beleive protec is the only source for the 99 trim tabs now. a intake grate will help aswell but lower your speed 1mph or more.

    Rough water approach. you want the longest plate you can get on that beastie, with minimal nose lift. an intake grate is a must must must, i cant recommend a brand yet because I have only tried one, and honestly im experimenting with making my own.

    A zero degree nozzle will help keep the nose planted when your slamming through the waves. but the 5 degree can be kept if your willing to play with your trim and drop your speeds for more comfort.

    honestly I've tried 2 different impellers... the solas X0 and the solas concord... i have a concord in my blaster and the grip is amazing for acceleration..... but for some reason on the gp1200 it seems to make a very minimal impact. With the X0 i get higher speeds and very similar acceleration. go with the X0 if your hell bent on changing the impeller.

    I have some pump modifications coming soon too, but I'm not on here alot.... not that i like to keep things to myself, i just find it a chore every once in a while..

    please find my post on the sparkplugs, try them and you will thank me.

  3. #3
    the_natrix thanks for your info, you know your stuff, I am new to this gig. I play in Michigan mostly StClair I call saint sludge Burt Lake Otsego one day Oahu !!! my daughter left right after my dad passed away last October so I will go with the anger also with tequilla !!! depression hurts too much !

    I will also try to find your spark plug article but if you could get me a link that would help

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