Capsizable Catamaran

Discussion in 'Boat Design' started by PlaningWheel, May 23, 2012.

  1. tspeer
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    tspeer Senior Member

    For a paraplegic sailor, a proa makes a lot of sense. They can sit with their weight to windward and not have to move for tacks. One of Rob Denny's Harryproas would be a good starting point. There are other threads on this site that have extensive discussions of proa designs for paraplegic sailors.
     
  2. quequen
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    quequen Senior Member

    That is, Colin, what my friend tells us all the time. In the mean time he run regatas on a 24' tied to an improvised, fixed, steel chair, and he defeat me all the "%&$*^ time!
    Water ballast could be a good option, perhaps some rotary veilers...

    Thanks Tom, I don't know much about proas, in fact I've never seen one in person, must do some research...
     
  3. PlaningWheel
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    PlaningWheel Junior Member

    Transferring a fixed amount of water ballast from hull to hull can be done quickly with compressed air.

    eg.

    At about 6 p.s.i. you can transfer about 1 cu.ft. of water / sec. through a 2" pipe.
    If you transfer 3 cu.ft. / tack and you had a scuba tank supply (72 cu.ft.) you might get 15-20 tacks before you ran out of air.
    Manually building up tank pressure between tacks is another possibility.

    I also like the idea of a proa but there are reasons why they are not very popular for everyday sailing.

    Colin
    http://www.ww.xbug.ca
     
  4. quequen
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    quequen Senior Member

    The scuba tank is a good idea, simple and fast, but actually I was thinking on some kind of rotational veiler having a simple gravitational valve, one at each hull, that fills a windward tank while drain the leeward one. They could be connected by a rope so the skipper will be able to rotate both at the same time.
    Rotating the veilers 180 deg on their vertical axis will make them act in the opposite way. A little bit of speed should be enought to make the system functional.
     
  5. PlaningWheel
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    PlaningWheel Junior Member

    Hi quequen

    What is a "veiler" is it a pump or a scoop?
    With simple gravity flow you only need one valve but your timing and your control of the valve during a tack would maybe need a bit of practice (but easy to learn).
    You would need a good wind. It wouldn't work in a light breeze.

    But if "veiler" is a pump you can always get things going again after a tack.
    When you have no wind, of course, it doesn't really matter because no ones going anywhere without an outboard.

    I prefer a fixed amount of treated water ballast over drawing and discharging water from outside (less maintenance, less resistance and no hull openings with devices that are hard to fabricate/maintain).

    I looked up 1 example of a hand operated bilge pump and they claimed 8 gpm?
    A 2 handed bilge pump would work better.

    If you want to raise 180 lb. 1 foot with 1/4 hp it would take less that 1.33 seconds (100% eff.) with losses say 10 seconds +/-.

    It would also be good if you could move yourself (on tracks?) from one side to the other perhaps just within the confines of the space between the hulls?
    But, of course, capsizing has to be a consideration.
    But is it a very big consideration given an unsinkable boat and the ability to use your arms?

    Yours,
    Colin
     
  6. quequen
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    quequen Senior Member

    Colin, here we call "veiler" a standard system to drain hulls at speed, very much like a spun acting by pressure difference. What I'm thinking on is just making the veiler rotative, having 3 positions at 0, 90, 180 deg. so it can fill, seal and also drain tanks. See attached file with my sketch.
    Tanks and veilers could be solved as an added, external device, making it easier to mantain and clean. I think that having 6 knots of speed this thing should overpass 8gpm easily. As you noted, it wil require some skill and you must to keep both hulls in water after a tack to fill the windward one.
    Hand pumps can also be a solution, a little tiring perhaps. Having some litium rechargeable bateries to operate an electric pump, or the compressed air tank, are good options.
    Moving the entire chair at one side before heeling sounds like a very good idea!, perhaps with a parallel system as the ones seen in architectural boards.
     

    Attached Files:

  7. PlaningWheel
    Joined: Nov 2010
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    PlaningWheel Junior Member

    Hi quequen,

    When I sailed a Hobie 16 we found that in high winds it was difficult to tack due to the high windage of the mast and the luffing sails. We would use the wave action to get about.
    If you add veilers it might be quite difficult to come about?
    In any case I mentioned scoops. I've sailed a few dighys where these small square scoops were in the bottom of the hull for drainage and sealed tight and flush with the bottom of the hull when closed. They should be available off the shelf?
    2 per hull.
    See attachment.

    Yours,
    Colin
     

    Attached Files:


  8. PlaningWheel
    Joined: Nov 2010
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    PlaningWheel Junior Member

    Hi quequen

    One more thought about sealed ballast tanks which ideally should be part of the structure adding no extra weight.
    In any case if you seal the tanks and air lines you could use a small electric tire pump (12 v) sealed in a box so that between tacks you could build up pressure in one tank while creating a vacuum in the other and then just open your water valve at the right moment.
    Or more simply apply a pressure or a vacuum to only one tank (with separate vent lines added to each tank) at double the positive or negative pressure.
    You could adjust your pressure requirements depending on how fast you want to tack given the conditions at the moment.
    It shouldn't require a very big battery.
    And I think adding small pressure gauges would look cool.

    And one more thought about the seat. If the seat rail(s) extended beyond the beam and the seat pivots (or maybe not) you might not need water ballast at all? Just a quick hand on the sheet(s) and tiller.
    The rail(s) should form a shallow arc from one side to the other (to keep the lee rail(s) out of the water).
    Small electric assist winch maybe? Your hands will be busy enough during a tack.

    Yours,
    Colin
     
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