Self righting multihull?

Discussion in 'Multihulls' started by bjn, Feb 27, 2018.

  1. bjn
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    bjn Senior Member

    I found this video of a self-righting multihull, without a keel!
    (Looks like one hull has to have less buoyancy than the weight of the boat though, so probably needs lifting foils...)

    It's a scale model, but the concept seems to work!.
    See video from February 2018
    The “Bucket List” Prototype Building Blog – Harryproa http://harryproa.com/?p=424

    Video was posted today, so I'm kind of suspecting that he (Rob) made this model and posted the video as a response to this thread =)
    Thank you!
     
  2. CT249
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    CT249 Senior Member

    Michael Henderson had ballasted keels on "Misty Miller" and other catamarans in the 1960s. If I recall correctly, pics showed them self righting from about 80 degrees under sail, but the ballast made them very heavy. There's probably some info on the AYRS site archives, but when reading AYRS info from that era one must remember that they were (by their own admittance) so biased towards multis that they intentionally mislead people about them.

    As far as winching floating objects - how do you do that in conditions that are so bad that the boat capsized? At the very least one will normally have to wait until the weather improves, which brings problems of its own. I'm still not aware of any of the self righting systems that have really been proven to work after an accidental high-wind capsize.
     
  3. CT249
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    CT249 Senior Member

    May one ask if there's evidence that it self rights in heavy conditions?
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ------
    Sure, one may. Contact Quant Boats.

    PS- I'm not 100% sure the boat is described as "self-righting" but I think they say it is rightable by a single crew but Michi at Quant boats could give you the latest.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Here is a video of a model test of Rob Denney's Bucket List self-righting : Just noticed that "BJN" posted this above--sorry.

     
  6. Doug Lord
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    Doug Lord Flight Ready

    Self-Righting: For years there has been confusion about self-righting. The words originally meant that the boat would automatically right itself with no assist from the crew like almost all keelboats(and Robs Bucket List). Many people now seem to assume a boat is "self-righting" if they themselves can right it! Thats not self-righting....
     
  7. UpOnStands
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    UpOnStands Senior Member

    Re. Rob Denny's video. ummm Accommodation is in the main hull which must submerse by at least 2-3 meters for righting to occur?
     
  8. UpOnStands
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    UpOnStands Senior Member

    rough calculations for 40 foot cruising cat with 60 foot mast (off the water)
    assuming robust mast/rigging and positive floatation aid at masthead, boat inclination is 100 degrees. To reverse rotate the hull 15 degrees so that the center of gravity is now outboard of center of buoyancy the upper stay must be lengthened from 17.8 meters to 18.5 meters. Synthetic rigging?
    If boat is drifting hull first the wind is likely to catch the significant area of the boat and rotate it so the submerged stay does not need to be tightened.
    Mast base would have to be pinned but able to rotate.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    ===================
    You should probably check the web site-link in post 16 above.

    Bucket-List-Mk2-009-375x240.jpg
     
  10. UpOnStands
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    UpOnStands Senior Member

    The boat must pivot around the masthead float as demonstrated in the video and the description
    "The lee hull fills with water and is pushed under by the windward hull and beams. The buoyancy of the mast causes the windward hull and hence the centre of gravity to move away from the centre of buoyancy until it’s weight rights the boat"
     
  11. bjn
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    bjn Senior Member

    Accommodation and crew is in the WW hull.
     
  12. UpOnStands
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    UpOnStands Senior Member

    I see what your saying but the ama is traditionally much lighter, shorter, and smaller which makes the boat unstable when inverting.
    The model uses an ama much longer than the main hull to ensure stability.
    Not real sure how this would work.
     
  13. Dolfiman
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    Dolfiman Senior Member

    Here is a video showing "Golden Miller " at 80° :
     
  14. rob denney
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    rob denney Senior Member

    Based on numerous capsizes to 90 degrees on Elementarry, ELEMENTARRY – Harryproa http://harryproa.com/?p=1753I think the mast will act as a sea anchor and the boat will end up downwind. Not many cats (racing or cruising) will stay on their sides at 110 degrees for long before the float is destroyed or the rigging breaks. How do I know this?
    38 years ago, I capsized a racing cat in the Atlantic. It inverted quickly enough that I hardly slid down the shroud I was clutching. The boat then lay side on to typical Force 5-6 waves. Each time one went past, the boat would move sideways, the sails would fill and the boat would accelerate up to a knot or so. The motion (and the temperature) were bad enough that we got in the liferaft (cheap rental, which did not auto inflate, nor have a double floor) which we tied to the stern. There is a picture from the aircraft that found us (only just, the hired EPIRB was rubbish as well) with the liferaft streaming astern of the boat at 90 degrees to the breeze. The motion in the liferaft was worse than on the boat, but warmer. Each wave would cause it to jerk and spin so I had to hold onto the painter and play it to minimise the motion. Not all bad, it stopped me thinking about sailing at 1.5 knots to America, how I was going to pay back the loans and the scorn I would (rightfully) get for joining the stupid enough to capsize club.
    A cruiser would have needed more wind causing bigger waves to capsize, with bigger loads from the waves. The float or mast would not have had a chance.
    First, lets use sensible terms.
    The lee hull is the long one, (or 2 short ones arranged fore and aft in the picture above and the model, which is atypical of harryproas and makes no difference to the righting) which has the rig, rudders and false floor in it, but nothing else. It is always to leeward.
    The windward hull is the short one, closest to me in the video and has the crew, accommodation, and all the stuff usually on a boat. On a typical harry, it would be bigger than on the model.
    The lee hull supports about 40% of the total weight, the windward hull about 60%.
    The windward hull is shorter, has little effect on fore and aft stability when capsized as it is out of the water. The lee hull, when submerged has none either. Hence the need for a schooner rig.
    It is not a traditional set up and will not work for a proa that is. Nor will it work for a cat or tri, unless the crew weight is an appreciable part of the total. ie a beach cat.
    The model has a masthead float to compensate for the mast being set inboard. It does nothing after the lee hull starts to sink. It would not be required on other harryproas as the sealed, large diameter masts are in the lee hull so they don't capsize beyond 90 degrees.
    Hope this makes it clearer. If not, please say so.


    Agreed. As did Harvey, who owned Orion. It was only meant to work in flat water and daylight. As such it was a fun project, but pretty hopeless for real life so he removed the float.
    Derek Kelsall built a cat with a tricky arrangement of ballast tanks which could be flooded and drained so the boat would right stern over bow from inverted. There is a video somewhere of proving it on a lake. There is nothing obvious in the system, (the boat, rig and crew are a different story) that would stop it working in big seas. Walter Greene built a 50' cat with a sinker hull (no core) which in theory would flood and allow righting. Not sure if he ever used it in anger. Neither of these were self righting as both needed crew input. There is a proa with a small ballast keel being built in Italy. Should be self righting. In theory, it should not capsize in flat water.
     

  15. UpOnStands
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    UpOnStands Senior Member

    umm, how to ensure lee hull floods only in a capsize?
    How to ensure that the capsize remains "in plane" and doesn't fall off bow or stern?
    The mast lee stay seems to have a very acute angle.
    But you are right, if all goes well it is self-righting.
     
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