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  1. #1

    What makes the Seadoo "lean" into turns?

    Hey guys, I'm mechanically inclined (I'm actually a mechanic, lol, stupid I know...) but I'm a real Seadoo newbie who's trying to learn fast. This site is sure helping!

    Something I've never understood is this: What feature of the Seadoo is it that makes it lean into turns? I sure love the handling of the new Seadoos. It's like a sport bike (something I'm a little more familiar with) on water! I ask partly out of curiosity, and partly because I'm thinking of removing the OPAS, but don't want to if this is what makes the Seadoo turn so nicely.


  2. #2
    Never Time To Ride antoniodef's Avatar
    Join Date
    Nov 2006
    Waterford, Michigan
    Kinda off topic, but how do you like the rive grate? Any increase/decrease in speed? Better hook-up? Thinking of getting one for my g/f ski. I sold my ski Getting a new one for me this summer hopefully, but wanted to ride the SHO and X first. In the mean time I tweak on hers.

  3. #3
    My new toys at work bruinsrme's Avatar
    Join Date
    Jul 2007
    Worcester MA
    Riding in a straight line the pump output pushes the ski forward. Just like a car when the gas it floored the ass end sinks and the front end goes up.

    Now when the energy of the pump output it drawn off of the center of the keel (drawn onto its roll axis) the back end of the ski pushes in that in the opposite direction in which the water is being pushed. With forward momentum and the force of the pump over a period of time (milliseconds) of course depending on the speed of the craft and angle or the pump output will determine much the ski will roll to compensate for the change in the direction of the pump output energy.

    In short the direction of the pump output forces the backend of the ski to roll, that roll is tranfered to the length of the hull. Once the the direction of the pump output is return to nuetral the ski will try to right itself to once again return to nuetral buoyancy.

    The pump output is our rudder.

    the attached pict is the Stennis doing a snap roll at high speed.
    When a trident sub is at max speed and puts the rudder at full the sub will roll about 8 to 12 degrees .
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #4
    Oh, very good explanation! Thanks! That's cool to know. So removing OPAS wouldn't effect this "rolling" at all. Is turning impaired at all when OPAS is removed?

    Antoniodef, I sadly can't comment on the Riva grate yet. It took so long to get here that I ended up installing it when winterizing the ski. Next year I should have some impressions.

  5. #5
    My new toys at work bruinsrme's Avatar
    Join Date
    Jul 2007
    Worcester MA
    on trident subs and on the NAS and seawolf subs they have vertical stablizers to limit the amount of roll is incurred during the turn.

    With OPAS, I the corresponding fin is drawn AWAY the hull, meaning in a right turn the right fin is PUSHED AWAY from the hull.
    With that said at slower speeds the advance and transfer may be more than at higher speeds.
    Advance - how far the vessel continues on the original heading
    Transfer - the point at which the vessel starts to turn.
    On larger vessels this is critical. On PWCs less, but advance would be the feeling that the ski isn't responding to the steering change and then the transfer would be when the ski starts turning the sensation that the rider wants to continue on the previous course while the ski is going elsewhere.

    Now OPAS is a beast in itself because of the up/down left/right motion which is dependent of speed and pump loading as well as steering.

    As you enter a turn you slow down and if you drop in speed the OPAS may drop changing the waterflow (dynamics) across the hull. If the control surface size is increased (which occurs when the fin drops) it should "dig in" and cause the hull to roll into the turn there by decreasing the amount of hull in the water and causing the boat to turn quicker.

    Is turning impaired with the OPAS removed.
    I will be better to answer that in a couple of weeks. My experience with OPAS is that once the transfer starts and the OPAS fin appears to dig in the turn feels too sharp which may result in over steering. Then I find myself turing the handlebars to compensate for the affect.
    I imagine without OPAS the advance and transfer may increase slightly but carve better/smoother but carry spped better through the turn due to less drag. With the OPAS removal it seems you would be able to powerslide the ass end of the ski a little easier due to the lessened resistance of the hull.

    The handling will surely be different with or without OPAS.
    Last edited by bruinsrme; 10-09-2007 at 12:10 PM.

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