Ballast on Self-Righting Trimarans

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

  1. John Perry
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    John Perry Senior Member

    Doug, I agree that the increase in take off speed attributable to the lead ballast is not huge, but obviously it will make some difference. From your figures the lead is 30% of total craft weight, so thats roughly 15% higher take off speed if foil sizes, angles of attack etc. are all the same, which they dont have to be of course. To achieve that extra speed for take off, again with same foils etc., you would need to overcome about 30% more drag. It may mean optimising your craft more for the take off speed range at the expense of top speed. One of the problems of designing sailing hydrofoils is that to get the thing to take off it helps to have big foils and big sails, but once you have managed to get foil borne you probably want to go very fast which requires tiny little foils and fairly small sails. Surface piercing hydrofoils help, but have their own problems of course. Once you are going fast on the foils, the lead ballast may not make a lot of odds, indeed it is conceivable that it might even increase your top speed by increasing the maximum available righting moment. Hydroptere takes on ballast for that reason, but I think they have their ballast more favourably located than you are proposing, at least from the speed point of view.

    I am not saying that your design is not going to work, I would never say that after the experiences I had with my own bifoilers back in the pre Moth foiling days. Whenever people who knew about sailing saw my boats I would get a pittying look and be told, purely in my own interests of course, that I needed to go away and rebuild the craft with three or four hydrofoils spread as widely apart as possible, in order not to be simply blown over sideways. I still have bits of the second prototype lying around and the irony is that if I now put it together and sailed it somewhere like Chichester harbour (which now has Moth bifoilers wizzing all over it) people would come up and advise me to stop messing about with a crude home made boat and just buy myself an off the peg Moth hydrofoil!

    Anyway, as I say, am not saying your boat wont work, just trying to get a better idea of what it is you are proposing. It sounds like it will be basically a bifoiler with a wand system like the Moth but you will add wide cross beams and small amas and there will also be a hydrofoil (fully immersed type?) under each ama. I also went for small amas for my second prototype, these were only for a bit of low speed stability and they did help. The moth sailors have now shown that amas are only for wimps! So, you will have a hydrofoil under each ama and since you say the cross beams have a large dihedral I assume that only the leeward one of these ama hydrofoils will be immersed. Does that mean that the craft will sail heeling to leeward? A nice thing about the bifoiler configuration is that heeling to windward rather than to leeward helps to balance the forces on the craft without the struts of the foils taking a huge amount of side load. This means the foils dont ventilate, the struts dont bend and the lift is mostly coming from well immersed surfaces. From the moment that I made a first hop off the surface I realised that heeling slightly to windward just feels right for this kind of craft. Perhaps if you incline the ama foils (i.e. give them lots of dihedral) you could again balance the craft with minimal hydrodynamic forces on the foil struts, maybe pivoting trailing struts. But then, what are your central foils doing - yes, I know, they are giving you pitch control. Hmm, I wonder, if you take off the main centre hull foil, could you get the pitch control from just the ama foils and a stern foil? If you used surface piercing ama foils that would give you the Hydroptere configuration - it does work, but perhaps you want to experiment with all fully immersed foils. So, fully immersed foils with wands on each ama plus a stern foil. Just thoughts, you can go round and round in circles with these ideas, sometime you probably want to stop and build something. I can see that other things being equal, your wide cross arms and ama hydrofoils will potentially give you several times as much righting moment as a bifoiler, so you have some potential there - a boat 'to be more accessible to people with physical infirmities' !! Good luck with it anyway.
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Srt/mpx

    Thanks for your comments John! Basically the SRT version of the system uses two foils on the main hull and one curved foil on each ama. The curved foil can also act as a surface piercing foil -and be 100% retractable. It could use a small planing ama + foil instead, though.
    The boat is designed to sail at an angle of heel(about 13 degrees) which creates a slight problem at main hull takeoff in that there will be a small component of lift directed to leeward-but that will be nullified by the ama foil. When the main foil is unloaded there is no more component of lift to leeward-in fact in gusts the main foil pulls down giving a slight component of lift to windward.
    Compared to other three-foil foilers this thing will have less drag when the main foil is unloaded(moderate to high speed). Compared to other trimarans under 20' this thing has more beam(22') but most importantly it has a system that allows it to fly the main hull in light air which no small tri I know of can do AND also be able to utilize the power to carry sail due to the wide beam as things pick up. Without the MPX foil system an oversquare small tri would be a bear to control.
    The numbers(if they are achieved) show that this boat has a better SA/ws ratio than a Moth, a better W/SA ratio and a better SA/D as well. Thats because of its awesome power to carry sail. And those numbers include ballast which is the point. I want to show that a trimaran(small one,at least) can be carefully designed to utilize fixed ballast and still have extremely high performance potential. This has very high performance potential but it could go even higher if you wanted to have the crew on trapezes and eliminate ballast and use a canting mast and, perhaps a canting main foil. My point is to produce a design that would allow a crew to sit comfortably on the side of a small cockpit or inside the cockpit(like a Rave or Hobie trifoiler) and have more speed potential than most any 18' trimaran and be a beachcat killer and self-righting to boot. I think it can be done.
    ---
    I agree about Veal Heel-it is a significant development in design and very little understood or appreciated by most people. It unloads the vertical strut, increases RM(for no increase in weight),allows the rig to lift vertically, lowers crew weight, improves upwind ability and more.
    I had the idea some time ago to do a high performance tri like the 18 except that it would be designed to utilize Veal Heal and in higher winds it would deploy small "power foils" that would pull down on the windward side. I can probably experiment with this on the model as well..
    --
    Again, thanks for your thoughtful comments ,John....

    Rough Sketch: half of a high dihedral trimaran using Veal Heal with small "power foils" deployed only over about 15knots boat speed.The "power foils" pull down using wand control and are retracted when not needed.
    click on image-
     

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  3. John Perry
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    John Perry Senior Member

    So who was it who first tried this Veal Heel ? !!

    Your proposed craft does sound promising and I can see that if you want to sit comfortably in the middle of the boat then a bifoiler is not really possible, you do need some lifting surface offset from the centreline. I note your emphasis on the 'awsome power to carry sail'. Fast sailing is ultimately all about minimising the water and air drag angles, at least that is one valid way to look at it. On this basis, the abilty to carry more sail is only useful in as much as it can reduce these drag angles. If more sail carying ability also means corresspondingly more drag, then the drag angles dont change and it just makes the boat harder to control, but I am sure you know that!
     
  4. Doug Lord
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    Doug Lord Flight Ready

    ==========
    Rohan Veal(I know, I know) sailed a Moth in numerous races early on proving how well it works. One of the spectacular things about it from a design standpoint is the increase in RM-up to around 30% with no additional weight- which can be used effectively on larger designs like the preliminary sketches below of a 30' self-righting keelboat foiler:
    http://www.boatdesign.net/forums/sailboats/foiling-keelboat-30-a-38395.html

    click on image-
     

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  5. cavalier mk2
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    cavalier mk2 Senior Member

    When this thread was launched I was thinking of a different kind of foiler- a narrow planing keel boat with low aspect foils to hold more upright at speed. This is what my trailer sailer needs. It would allow planing on a close reach and could recover from a mast in the water knock down. In an open 60 class you could eliminate lots of wide hull, ballast and crew- a smaller thin boat with long water line and narrower waterline beam for speed.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ============
    Interesting, but just out of curiosity why do "low aspect foils" spring to mind?
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    I was recalling the study published in Woodenboat years ago about adapting native working craft so they could safely carry more sail to avoid outboards. The idea is a wider stall angle with less to trip over, lower connective strains and no draft problems in shallow water. Those are more cruising and safe boating parameters- racers would probably want to go high aspect. The idea eliminates short buoyancy amas that get in the way of ballast recovery. If anything breaks on the foil end, the craft is still sailable under shortened sail-and self righting.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    ------------
    Sure would like to read that article-don't have the name or a link do you?
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    I'll look it up, I mentioned it once before...sorry for the time lag, this is boat building season. Low aspect foils can also be configured to be more forgiving of drift encounters......here it is- Woodenboat #92 "Sail and Hull Performance" by Colin Palmer.

    You'll have to search it out in their archives I don't have a convenient scanner.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Self-Righting Foiler

    For those that question the performance impact and/or the feasibility of a ballasted foiler rest easy-it's been done by Hugh Welbourn with the Quant 23 in June of 2015. The designers suggests it is self-righting and the builder suggests that the ballast makes it easy for a single person to right the boat. The first production boats are out and their performance is nothing short of outstanding:
    -- takeoff in around 5 kts of wind in flat water
    -- upwind foiling in 8kts with speed around 15 knots
    -- in 7-8 knots top speed close to 20 off the wind.
    -- 26+ knots top speed so far

    http://www.boatdesign.net/forums/sailboats/quant-23-foiler-scow-53468-8.html
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    Fun stuff, maybe we'll get big ones for the cup. The monohull guys would love it but it would probably take some hull flooding to right one. The SF Bay Pelicans have flotation along one side to roll them back up after a capsize and swamp.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Self-Righting Foiler Tri

    I missed my target weight on the model but if I built the boat from molds I could easily hit the target weight and, with ballast, she would definitely be self-righting. Next opportunity will be on a small fullsize version if I can pull it together. But I think the concept of a self-righting foiler tri has merit.
     
  13. cavalier mk2
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    cavalier mk2 Senior Member

    I think righting foilers can work but a scow is going to need more going on like flooding tanks in the big sizes or the ballast will have to be too big. 15 Cup sailors sitting on each others shoulders for a re-righting lever arm is asking a bit much. I like scows, I think they even have some Cup history in the 1800s. A wide boat could be set up with auto flood tanks on one side for true self righting though pumping out without power would take some work.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Scow

    Might be able to keep the weight down by using a canting keel. Just add Welbourn foils to this Tison design:

    [​IMG]

    [​IMG]

    Or this Reichel-Pugh idea:

    [​IMG]
     

  15. cavalier mk2
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    cavalier mk2 Senior Member

    I think everyone will expect cup boats to fly now. I liked the simplicity of the Quant 23 system. Having the sailors in constant chuff mode to power the hydraulics for that swing keel might keep them off the rail unless there are pump pedals out there.
     
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