self righting boats

Discussion in 'Boat Design' started by rick gray, Nov 9, 2014.

  1. rick gray
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    rick gray Junior Member

    I hope to get info on self righting design principles. on a hull that is based on older SEA SKIFF style hull> Thanks Rick
     
  2. Tad
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    Tad Boat Designer

    Why?

    Any boat that floats is self-righting, the questionable part is, at what loading or heel angle will it stop being self-righting?

    What do you mean by "self-righting"?
     
  3. gonzo
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    gonzo Senior Member

    The ideal design is stable when upside up, and very unstable when upside down. If you are referring to the open cockpit powerboats, they will swamp before reaching the instability point. I wouldn't consider them self righting. You could design a boat with a similar hull, but a self drain cockpit, wider side decks and an enclosed waterproof house.
     
  4. rick gray
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    rick gray Junior Member

    have you seen US. small rescue boats? if rolls upside down they will continue to upright every time!! it has a tunnel /venturey tank up above centre of gravity? sloshes water to one side or other on rotation.like photos or plans.
     
  5. TANSL
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    TANSL Senior Member

    The equilibrium of a ship is completely precarious. A small perturbation is enough for the ship to leave its equilibrium position. What to measure is the ability of the ship to regain his starting position or also the work to be done to heel the ship a certain angle.
    This is how the stability of a ship is measured.
    All this has nothing to do with the possibility that the boat is self righting (if self righting understand as the ability to recover the right position, helpless, after the ship has rotated 180 degrees).
    Tad's question is very relevant.
     
  6. rick gray
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    rick gray Junior Member

    self righting

    Hello:There was a show on TV that followed the small(30 ft+)rescue vessels on colombia river at sea, the boat could roll upside down and with the momentum the water ballast would shift(baffled) and cause the boat to right itself in direction of roll>
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's not practical to make a sea skiff type hull form self righting, except at very low angle of heel.

    The rescue boats you point to, are very specialized and present several severe compromises, in order to get it's self righting ability. If you're willing to accept the convoluted set of discontinuous concession and compromise necessary for this particular design attribute, then yes, you can butcher a sea skiff into a self righting design, regardless of heel angles.

    What pray tell, are the reasons behind trying to do this to, this grossly ill equipped (for this role) hull type? Will the service envelop require this duty? If so, why are you starting will the wrong set of shapes (sea skiff), to accomplish it?
     
  8. Alik
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    Alik Senior Member

    We published a paper on self-rigthting boats design, exactly about physical principles. Here: Nazarov A., Suebyiw P., Leeprasert A., Piamalung A., Surasorn M. Small Patrol Boats: Design for Self-Righting// International Journal of Small Craft Technology, RINA, 2013.
     
  9. rick gray
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    rick gray Junior Member

    Just dreaming !! will do reality check!!
     
  10. ThomD
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    ThomD Senior Member

    The big thing to consider, after you have guranteed the boat will not sink, and will return to an upright position, is the health of the people just made the rotational trip, or for that mater the health of the boat. You can have people with broken limbs; sailboats, demasted. With power boats you would have to have a motor system, that was able to survive the rotation, and without loosing a beat keep running, or spilling all it's fuel over the now traumatized occupants, or at least their boat. I don't know much about motors, but I do know that small aircraft run into all sorts of novel motor issues with the gyrations they go through, even in conservative flight.
     
  11. rick gray
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    rick gray Junior Member

    Of course you are correct< i would expect the engine to stall and gas drain from carb . no seat belts ,OH WELL? with design matt it has become possible for some
     
  12. TANSL
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    TANSL Senior Member

    Existing self-righting lifeboats, do have seatbelts for passage. And, of course, drip trays and everything needed for the engine, despite giving the boat a full turn, can continue to operate.
     
  13. YD Marine
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    YD Marine Junior Member

    You need to have a buoyancy tank on the roll bar which will supply moment to correct the heel of the boat.
    Also have enough buoyancy volumes filled with pvc material or strongly blinded as much as possible in the useless spaces.
    Fast rescue boats are useful samples for your boat.
    Not lifeboats or rescue boats but fast rescue boats.
     
  14. rick gray
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    rick gray Junior Member

    yes i remember tank in roll bar to cause rollback.
     

  15. PAR
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    PAR Yacht Designer/Builder

    You can have all the foam filled roll bars you like, but a typical sea skiff hull will have down flooded enough, before that bar comes to play, that the Jolly Green Giant himself, with the world's largest pancake flipper wouldn't be much help.

    Is there a specific boat you had in mind to try this on? Other then dreaming, is there a logical reason and rational for this approach to a sea skiff? Boats that self right are highly decked over, typically with quite heavy structures, to tolerate this nautical indignity. This wouldn't be typical of a sea skiff.
     
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