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  1. #1
    bowsniper's Avatar
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    GAS weight and top speed

    Have any of you ever actually logged the difference in mph with a full,half and almost empty tank on high speed runs?

    How many rpms or speed have you gained. Or lost?


  2. #2
    LaveyT's Avatar
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    I have thought about what you are asking but it seems like the differences are small on my ski's. The speed is slightly lower (sorry no figures) but it doesnt seem to me the RPm Changes much at all. I think the slippage just goes up.
    Plug your numbers in here, Im guessing the slippage is god awfull compared to a prop driven boat. I suppose you use the average pitch of the impeller.
    http://www.rbbi.com/folders/prop/propcalc.htm

  3. #3

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    On my Pro 785 , I run only 5 gallons of fuel , I did notice , better handling ,( more response form the steering ) especially when on a smooth lake . Also installed foam into the stock tank , i get about 30 to 40 minutes run time . with The foam inside the tank , seems to run better too .

  4. #4
    bowsniper's Avatar
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    Hmm, better steering and handling..... i can see that bappening. Intersting point. I would think on a pro785 ,a full tank would help keep the nose down a lil better and keep bouncing to a minimum.

    I'm going to watch the top speed at full, half and when the fuel light is blinking and see if the speed changes on the top end this weekend and note the handling differences in turning.

    More weight creates more momentum in 1 direction.makes it harder to overcome while attempting to turn.

    Ill get back to ya with some numbers.if there is any!
    Thanks for the inputs.

  5. #5
    bowsniper's Avatar
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    I wonder if in bouy course racing if the skis are full of gas. If not, in a hard turn low on gas it could suck air and loose power for a second or go lean and smoke a piston.
    Any racers out there to enlighten us? Skigolfnut are u around?

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Only GPS numbers are useful for this sort of thing. As the bow rises the MFD display accuracy changes, so higher MFD displayed numbers mean nothing if the hull attitude has changed.

    And the MFD speedometer is not super accurate to begin with. Generally speaking as soon as you mount a GPS on your watercraft your actual measured speed decreases by several mph, or more

    And GPS speed is not measured by setting the 'max speed memory mode' and letting it do the work. GPS can have momentary accuracy errors too. Your maximum sustained speed with you watching the GPS display for a consistent reading over multiple seconds is the real speed.

  7. #7
    RLACEMAN's Avatar
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    I have tried this on all my skis. Generally you will get 1 less mph with a full tank, compared to a 1/3 tank or less sometimes 1 1/2 on lower powered skis, RPMs don't seem to be affected. On my 15f the difference is less than 1mph. Acceleration is affected a little more by the weight difference.

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