Ballast on Self-Righting Trimarans

Discussion in 'Multihulls' started by Doug Lord, May 26, 2012.

  1. Doug Lord
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    Doug Lord Flight Ready

    I've done preliminary design work on an 18' tri designed to be 100 % self-righting( the real definition: the boat rights from a capsize or pitchpole w/o crew action other than slacking the sheets).
    The boat is, in essence, a two person highly powered 18' tri with one of the people(the weight of a person) in a bulb on the retractable daggerboard.
    The boat relies on rig integrity and a sealed mast. The idea is to allow high speed singlehanded sailing w/o fear of capsize or pitchpole particularly for disabled or physically restricted crew.
    ---
    In the old days it was always believed that a leadbelly could never plane with a ballast keel-now that is proved wrong every time an Open 60 or VOR 70 crosses an ocean(or a mono sportboat goes downwind). I wonder if a ballast keel/daggerboard designed for high speed could be viable on larger trimarans to facillitate self-righting in certain conditions?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Hydroptere

    Just a note for those that scoff at the very idea of ballast on trimarans: the Fastest Sailboat on the Planet uses ballast......
    It might have merit.
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    But ballast is such bad language to use around multihulls....you should have your mouth washed out with soap!
    What sort of proportions are you thinking of?
     
  4. John Perry
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    John Perry Senior Member

    Have also sketched that kind of arrangement, with or without lifting foil on the leeward float, I expect others have done so as well, but has anyone actually built one? Would you be thinking of using crew weight on the windward float, or trapezing off the windward float? One thing to watch out for is the hydrostatic pressure on the submerged float, not a major problem though.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    ================
    My idea for the 18 is below. Hydroptere does use water ballast in the windward ama but is in no way "self-righting". I believe a carefully designed high performance tri , like the 18 below would be, could use fixed lead ballast in combination with designed in features such as high ama dihedral,buoyant "curved pieces" that connect the ama to the cross arms etc.
    Check the numbers to see the potential....



    Picture: "curved piece" as used on a smaller(12' ) tri. All the "curved piece" is is a method to connect the amas to the crossarms(at high dihedral) by way of a very buoyant curved piece that raises the heeled CB of the AMA+ curved piece making capsize very difficult and allowing self-righting from past 90 degrees in conjunction with a ballast keel.
    click on image:
     

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  6. masalai
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    masalai masalai

    I am curious as to why so many threads seek this "self-righting" capability - DON'T TIP IT OVER IN THE FIRST PLACE. - - Such events are natures way of removing the stupid, - - and expansion of this "nanny state" point of view, successfully ensures that the stupid are not gleaned from breeding potential and breeding of more stupid people...

    Sailing has romance in survivability of severe challenges in long oceanic voyages... Usually seen as a mark of wisdom derived from experience of successful voyagers... Why make this credit available to incompetent fools?

    Recovering from the capsize of a relatively small "beach cat" in 'round the buoys' racing is all part of the fun and learning experience... How far will this idea extend ? (high performance motorbikes with "training wheels" as on 5yo or younger cycles?) Falling over is all part of a sensible learning experience (don't do that again because it hurt a lot)...
     
  7. fast company
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    fast company Junior Member

    They might have others along with them.
     
  8. masalai
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    masalai masalai

    Hi Fast,
    Would you go for a ride with someone who had training wheels on their High Performance HARLEY? - Then again it demonstrates the stupidity of the passenger...

    Most sailing schools go into detail on how to recover from a capsize and some even deliberately capsize to demonstrate what happens and how to recover... This explains why and what happens and should be part of training for all sailors finding their sealegs... Even on the finest of modern cruise liners they are supposed to have emergency drills and all commercial aircraft have the same sort of training...
     
  9. Doug Lord
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    Doug Lord Flight Ready

    Srt

    ===================
    My idea is particularly in reference to making sailing in small singlehanded high performance trimarans more accessible to people with physical infirmities. No high performance tri-self-righting or not- is suitable for "incompetent fools".
    Whether or not the idea has any further application in trimaran design is an open question.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Srt

    I think also that part of the design downside of high performance ,oversquare trimaran platforms( that would readily take out beach cats their same length) is the probability that such a boat, designed to be singlehanded and sailed by an ablebodied sailor would be extremely difficult to recover from a pitchpole or capsize without some design input into solving that problem. To ignore the speed potential of such a boat because of the poor or impossible recovery from capsize or pitchpole seems like a waste when innovative design could solve the problem both for ablebodied sailors and the physically infirm.
    Nothing to do with a nanny state, poor sailing,or incompetence: it has to do with the recognition of what is possible in a high speed singlehanded maximum performance trimaran and what is not.
     
  11. John Perry
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    John Perry Senior Member

    Hi Doug, I hadnt realised that you were talking about a 'flying' hydrofoil trimaran. However, I don't see why, in principle, such a craft could not be made self righting using lead ballast at the bottom of one of the main hull hydrofoils, provided of course that you are happy with the effect this would have on your take off speed. It does give you the option to make your hydrofoil from steel, possibly easier than the usual carbon fibre construction if you actually want it to be heavy! Take off speed would be most important in light winds when capsize tends to have less serious consequences, so perhaps leave the lead bulb ashore for light wind sailing.

    I am a bit surprised that you can have such a large reserve of righting moment with the mast tip floating, one ama just afloat (I assume) a relatively low ballast weight, and 15deg cross arm dihedral (btw, I am not sure how you would clearly define that angle). However, I assume you have done the sums. A large cross arm dihedral certainly helps, your bouyant 'curved pieces' will also help, I like that idea. Are you assuming a very light mast?. I found out when I built my bifoilers that it is not easy to make a lightweight mast that also has enough bouyancy high up to float near the surface and to prevent a 180 degree inversion.

    You give the bouyancy of the ama as 375lbs and the weight (of the whole craft I assume) as 400lbs, So when the craft is floating capsized, the ama will be almost submerged and will have little pitch stability. Since the ama is quite short, I think there is a good chance that the craft will then tilt so that the bow or stern are in the water, has your calculation of the reserve righting moment allowed for the craft being in that position?

    On the other hand perhaps I am misunderstanding you. Perhaps your 400lbs does not include the crew weight. In that case the total weight of the craft is 400+175lbs and even allowing for some of that weight being in the ama, the ama will then submerge when the craft is 90 degree capsized and the main hull will float lightly on the surface. That is what I was thinking when in my previous post I reminded you to watch out for hydrostatic pressure on the submerged ama, probably about 10 feet below the water surface for your dimensions. From the point of view of being self righting, that kind of balance between craft weight and ama bouyancy works well I think. It is actually how I designed my second prototype bifoiler. The idea was that with the craft on its side and the weight of the craft, including my weight, holding the main hull down to the surface, the dihedral of the ama cross arms and bouyancy of the ama would be enough to self right the craft. It almost worked, probably would have worked if I could make a mast as light as the ones on the latest moth hydrofoils!. At least, with the craft in this position I only had to lean slightly out from the main hull and it would right itself. The problem was that I would nearly always be hurled overboard when the craft capsized, and without my weight on board it would not submerge an ama. I would need to swim back to the craft, then pull down on the main hull to assist the empty weight of the craft to submerge an ama, then climb back on board. When I designed the craft I needed to make an estimate of how hard I could pull down to submerge an ama, allowing for me being no super fit athlete. Some kind of rope loop to get a foot into might have helped. That calculation determined the maximum bouyancy I could have in each ama and it was less than I would have liked for stability during low speed 'taxying' prior to take off.

    BTW, I am not sure this craft kind of craft is particularly well suited to wheel chair users, at least as a first prototype!
     
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  12. masalai
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    masalai masalai

    Ahhhh Thanks Doug,
    A wonderful objective... I have seem other clubs use something like minature "America's Cup" styling, even down to the winged keel, where the wheelchair sailors are lifted in and sit semi reclining... Looked fantastic and - - I was sort of jealous, and would have loved to have a go until I saw them race, as "they were highly competitive"

    To reduce the risk in pitch-polling I will agree, and more design work there would be useful. - - - I was in Perth (1975 to 1980?) when a severe front wrecked many "hire beach cats" in their usual lunchtime weekday peak just picking up boats and pitch-polling them along the Swan River, a bloody disaster....

    I would think in terms of more flair in the bows above normal waterline and jib shape to provide more lift at the bows as well as reshape the main to deliver less driving down force?

    I an no designer just throwing around ideas?.......
     
  13. Doug Lord
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    Doug Lord Flight Ready

    Srt/mpx

    =====
    Thanks, for your comments, John. This is right. Lots has to be tested with this concept and the (large) rc model is half complete. A full size version is too expensive for me, but hopefully if the whole thing works others may pick up on it-or just on the foil system.
    The foil system is critical to really tap into the potential of an oversquare trimaran platform. Without the bi-foiler configuration mainfoils the thing wouldn't fly the main hull until well over 15 knots windspeed ,which is unacceptable. The bi-foiler configuration allows the main hull to fly in 6-8knots of wind and a great by-product of the system is that at almost the very instant that the main hull takes off the main foils begin to unload and the ama foil begins to load up(or planing ama+foil) until at "X" speed the main foils are 100% unloaded except for what is required to control pitch. Using the main foils exclusively for pitch control allows the ride angle of the ama to always be right and appears to reduce drag significantly when compared to other three foil foilers I've looked at. Not only that, but since the main foils use a wand altitude control system, the sailing angle of heel of the whole boat is fairly well controlled as well as allowing for substantial gust response from the system when the wand calls for downforce from the main foil.
    As best I can tell one of the big drawbacks of small trimaran design has been the inability to use all the power a square or oversquare platform has because of the incredible RM of the boat which prevents main hull from flying
    early enough. This system fixes that.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    -----
    Hey, Mas-this type of boat is so powerful and fast that it is the perfect candidate for using foils to control pitch. The system I've come up with "turns over" more and more of the control power of the main foils to pitch control only the faster the thing goes. If I'm right, the thing will have extraordinary pitch control. I would think that in an ideal design using this system, you would want the forward sections of the main hull and ama to be designed to reduce drag cause by momentary wave impact so you would want them fairly "thin". The model I will test has a wider main hull than is ideal(theoretically) so we'll see how that goes.
    What I'm looking at is exploring ways that high powered ,oversquare small trimarans can be built lightly and relatively cost effectively to go hunt beach cats. The fact that in 2012 the trimaran platform in boats under 20' has the rep of being slow(compared to beach cats) is just simply a travesty, in my opinion.
    We'll see over time...
    Can the self-righting characteristic be beneficial in larger tris?
     

  15. Doug Lord
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    Doug Lord Flight Ready

    ===================
    John, I think the bulb, if it was integrated into the daggerboard/foil juncture similar to the Mirabaud "bulb"(below-or the Moth "bulbs" for that matter) would have a negligible effect on take off speed since the boat is so powered up and because the bulb can be designed to actually reduce drag. From a weight perspective, the boat is designed for the extra weight and has a W/SA number and SA/D number better than a Moth Foiler:
    W/SA(weight in pounds divided by SA in sq.ft.):
    1) SRT(with 175lb. crew)-2.71
    2) Moth( with 175lb crew)- 2.8
    (lower number is better)
    ---
    and-
    SA/D:
    1) SRT(with 175lb crew)-53.64
    2) Moth(with 175lb. crew)-35.51
    (higher number better)
     

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