Fitting a anti roll tank to a deep vee planing hull

Discussion in 'Stability' started by FishStretcher, Dec 28, 2013.

  1. BMcF
    Joined: Mar 2007
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    BMcF Senior Member

    True. The even trickier part in configuring any anti-roll tank system is the "tuning" of the fluid transfer dynamics so that the differential roll moment, opposing roll angular rate, is indeed reliably 180-degrees out of phase with the roll rate. With the short roll period that would be associated with such a small Deep-V vessel, I'm not sure it would even be possible to achieve the necessary fluid transfer rates.

    There is also the very real possibility that an anti-roll (or flume) stabilization tank setup on a small and relatively tender deep-V is going to make worse the already weak upright static stability. Put another way..if the vessel lists to on side (simple because of where passengers are standing) the fluid in the anti-roll tanks is going to end up biased toward the low side and aggravate that list.
     
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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    OK, we are talking about different things here. I was referring to a ballast tank situated low down toward the centre of the boat, intended purely to put the boat deeper in the water so it isn't so tender, not a device that transfers water from one side to the other, timed with the roll peroid. This is a relatively small vessel and I doubt the latter has any practical application on a planing boat like this one. But good luck to him if he can make it work ! I think that this boat lurching over when a couple of burly fishermen move to one side, is not going to be helped by ballast transference.
     
  3. TANSL
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    TANSL Senior Member

    Mr Efficiency, Gonzo and you certainly are talking about two totally different things but what FishStretcher was asking for is an "anti roll tank" which is what Gonzo is talking. Maybe FishStretcher has misspoken but in any case, the solution of a tank, whatever kind it is, does not seem useful in this type of boat.
     
  4. FishStretcher
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    FishStretcher Junior Member

    I believe we are talking about 10-15 gallons. Not 100.

    References I have found online, both theoretical and successfully implemented, though scarce, hover in the 1.5-3.0% of displacement range. This boat has a max displacement of about 3 short tons. Empty is about 2 short tons.

    It has been a long time since university- the last time I did these sorts of calculations, but it looks like 3" pipe is marginal for this sort of fluid transfer rate. 4" should be plenty, to the point that I add valving to tune the system. Assuming 15 degrees of roll.

    With the mass at waterline, the center of mass shouldn't be horribly affected, and the boat needs to have the LCG pushed forward a bit as it is. And if I botch it, I just fill them and have a nice freshwater washdown tank.

    I would rather not add an extended reverse chine for stability at rest, as design of such a thing is beyond me, and I suspect the great head sea performance for its size would suffer. Even though it has been done successfully. Look for the Kama II on YouTube for an example. But I am a backyard hack, not a boat builder. Fiberglass boxes that fit in the cockpit sole I can handle. But that's about it.
     

  5. gonzo
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    gonzo Senior Member

    I don't think that 85-130 lb of water will stabilize the boat. Even at fantastically fast transfer speeds, it will hardly counteract the forces when rolling. As for pitching, that would either involve two extra tanks aligned longitudinally, or four tanks connected diagonally with some very complicated control mechanism.
     
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