High performance small tri project

Discussion in 'Multihulls' started by frosh, May 13, 2007.

  1. frosh
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    frosh Senior Member

    I would like to now transfer the sub-thread that has developed for some time into this new thread which is inspired by Frank Bethwaite's HSP that commenced in the 1960's and continued for 20 years with him building and testing 19 different human powered versions. We now continue his contribution with my own tri project, which although more of a a true tri than those of FB, which were more accurately monohulls with side bouyancy pods, is truly in the same spirit as his HSP work.
    I am going to try and transfer the postings that relate to this topic specifically, to this new thread, if I can work out how to do it.

    This is a huge coincidence to talk about two types of optimum hull shapes when I am about 90% complete in my experimental tri project.
    The Vaka is as long and narrow and light as I could make it given that the main constraint was for a 2 person high perfomance off the beach style craft, that was light enough for 2 average sized adults to be able to pick up the fully rigged tri and carry it a short distance without too much effort.
    Vaka is 5.6m x 0.4m with a semi planing/planing bottom shape. The transom is half the width of max. beam and a fairly flat arc section compared to the rest which is an arc section of steadily decreasing radius as one moves closer to the bow.
    Amas are fully planing designs based on on the US lake scows shapes but built to optimum strength to weight ratios.
    The tri is designed to be balanced by crew weight rather than ama bouyancy, and will incorporate a trapeze for the crew.
    In lighter winds almost no water contact is expected for the leeward ama.
    In stronger winds, which is the common situation in the Perth WA summer season, the total displacement will be shared between the vaka and leeward ama which I expect will be planing in such a fashion that ama immersion will be very slight. In addition I have already tested the vaka in a proa configuration and it goes from displacement to planing mode with no noticable hump at the transition. I will be testing the completed tri around August this year. I will post more later with some pics.
  2. Chris Ostlind

    Chris Ostlind Previous Member

    Well, the coincidence continues, Frosh, as I was just cycling through the list of interesting projects with which I was trying to maintain some measure of connection. Then, you posted the update on your project boat.

    I really like the whole range of potential multihulls in the off-the-beach envelope of possible craft. I'm especially drawn to those trimarans that require considerable crew activity to maintain their footing. Getting the amas down in size a bit and reducing the overall weight of the boat is a big help in almost all areas.

    I'm really looking forward to seeing your pictures and hearing of your trials.

    I can't remember which rig configuration you are planning on running. Can you give me a refresh on that part of the design? And how about the choice of boards (rudder and keelform)?

  3. frosh
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    frosh Senior Member

    Update on experimental small tri

    Hi all, this is mainly in response to Chris' last posting. I weighed my 7'6" by 1'11" amas at 22 lb. each complete. I normally work in metric but I can think in the Imperial scale also. Vaka around 90lb. Carbon crossbeams maybe 12lb. for the whole set. Overall beam 10ft. Skinny 21 and a half ft. carbon mast with adjustable tension triple diamonds stays. Carbon boom, soft mainsail 110 sq. ft. ala James Wharram Tiki wingsail (with luff sleeve, and fairly high aspect), with small carbon gaff. Jib about 50 sq. ft. Should weigh in all up around half of an F18 catamaran, I hope. F18 is 385lb.
    2 assy kites, tiny one about 85 sq ft. for Perth (20 -25 knot Fremantle Doctor) For the "medical" definition see:
    Also a 190 sq ft assy kite if we find we want push the limits a bit.
    You asked about under water foils. Carefully selected timber hand foiled WRC, with 2 layers of epoxy glass, around the size of that on a 29er. Very light, and daggerboard close to a NACA 0010 and rudder blade close to a NACA 0012, and quite high aspect. Only fitted to vaka; no foils on amas. I expect to keep the daggerboard fully down all the time.
    I will get myself into gear in a few days and get the digital camera out and start posting photos of the various bits, as everything is separate at the moment.
    Really happy to hear of your continuing interest.
    Other interesting development is that Rob Denney who lives a couple of miles from me spoke with me on the weekend and he has agreed to crew with me when he is available. His feedback and suggestions will surely be very valuable, in the ongoing evolution of this project. I expect the tri to go extremely quickly on some points of sail, but have no clue how fast it might be expected to get around a triangular course. I can't wait to find out though! :?: :) :)
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  4. Phil Stevo
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    Phil Stevo Junior Member

    I have never seen an Itzacat. Must have been a WA boat.

    The first Kitty was built as a NZ Q class 12 and won the second Interdominion 12ft championship in Aukland. The Q class and Aust 12 assoc replied by banning cats. It was certainly faster in 1958, but the skiffs are much different now. It would be very interesting to see a 21st century 12ft cat against the 12s.

    In the 60s and 70s I went to a lot of cat regattas, The planing XY and other similar hulls could not match the narrower quickcats etc. Similarly at 20ft the Attunga was no match for the austral and later the tornados. Narrower always semed better. Maybe todays build weights will change things, good luck. (My first own design and build was a 12ft cat with narrow hullls which normally beat the Kittys)

    Maybe I got lucky last year with the development canoe, but it is not out on a limb in design, just a development in known directions, known to work well on other classes: Basically straight, narrow and light seem to be universal tickets to success.

    Anyway you are having a go, so no critism. Try not to make it too complicated, make it easy to test, not too many inovations or you will never know which ones are working and which are not. Do not go the path of Doug L and create something so out of left field that it has just lead to ridicule. Maybe a more standard rig initially will be a better test of your platform.

    You need everything else proven to be right before the wing mast. I have one down on my ultimite list of Moth develpments, but no point if everything else is not perfect. There is lots of design info published by Steve Clark's Cogito team to start with but building it strong and light is the real challenge.
  5. Doug Lord

    Doug Lord Guest

    Of ********* and men.......

    Nobody should be afraid of ridicule and let that stop them from trying any experiment or experiments. For the most part ridicule emanates from those who don't understand what you are trying to achieve or the degree to which somethng that appears not to have worked did work. There is an element of criticism that is well founded ,well reasoned and very constructive; there is another element of criticism-ridicule- that emanates from uninformed small minded people whose opinion is not worth the cyber space it
    uses. No one should be afraid of a cyber MOB and hold back on ideas they think are worthwhile-that goes for discussing them and doing them and showing others what you've done. One bit of constructive criticism is worth a hundred
    bits of trash from useless jackases.
    I made many mistakes on my first full size foiler design/construction but I also did a lot right including the weight, learning about manual foil altitude control systems, a square topped jib, the Swift solo(Bram Daly)sheeting system and many other things. I'm glad I did it and a damn proud I had the guts to try. The next one will be much,much better.
  6. frosh
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    frosh Senior Member

    Good responses from both Stevo and Doug. And that is really saying something, as I am normally the person most guilty of saying that Doug has a one track mind and is usually coming up with ideas out of fairyland. Doug, from what you said in the last posting, I have to be man enough to take back some of my past criticisms of you.
    Phil, I am very familiar with the Quickcat having been a member at Elwood Sailing club in the 60's where Quickcats were probably the biggest racing class. BTW I raced a Sailfish at Elwood in those days, my second ever boat. The Sailfish had a lot in common with the Aussie Moth apart from the fact that it had a beam of only 3 ft. I had a huge amount of fun with it. The Quickcat was certainly extremely fast for it's era.
    As far as making it simple goes.-- I already have the mainsail, jib and two assy kites that were custom made by a professional sailmaking firm to my overall specifications. I have never used either kite as yet and they are brand new, sitting in their sail bags. The main and jib have been used about 5 times when the boat was in a "tacking proa configuration" It went better downwind than upwind but we were on a big learning curve, very similar to you when you sailed your DC the first few times. Furthermore my crew was my son who although being a very accomplished windsurfer, knows almost zip about regular yachts, so I had to try and teach him the basics, like sheeting a jib correctly, how to perform a tack etc. This was very difficult for me because I was sailing a lightweight powered up boat that was quite radical anyway. The biggest problem was that on one tack it was a "Pacific proa" and on the other tack it became an "Atlantic proa". This just became too much to cope with and although it showed promising bursts of speed, with the vaka clearly planing, there is no way we could have sailed it around a triangular course without a lot of swimming.
    Therefore the decision was made to give back the ama which I had borrowed from my 23ft. home designed and built OC2, and start with new amas. Origiinally the amas were going to be close copies of a Hungry Tiger Moth, but stretched out to 12ft. and with a broader transom.
    I had a mistake happen while vacuum molding the first hull in my female mold that I built with great effort. There were large areas where the outer skin of 200 gsm woven carbon which was nicely in place in the mold did not fully join up with the 5mm klegecell foam core. Unfortunately I did not know this yet and spent a lot more money and time bonding a second layer of carbon onto the inner surface of the foam. Finally after removing the hull from the mold I discovered the weakness. After a lot of soul searching and anguish, I decided to put the carbon foam hull and female mold out for the next rubbish collection, as I couldn't stand looking at them anymore.
    I then went off at a tangent and decided to build 2 amas without a full mold, only a bottom surface mold, in a shape close to that of an American Inland lake scow. Anway it is almost finished and I will post some photos on this site very soon.
    Bye for now, and regards.
  7. Paul Scott
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    Paul Scott Senior Member

    frosh, glad you are messing about with a gaff rig. A few years back, while in the design stage of my 40' uldb cruising sled, which was 30' at that stage (I know, I know...), I was talking to Paul Bieker about a gaff rig, which I didn't wind up doing ($$$$$), and I wound up going with Bob Perry, but it looks like the idea reappeared a year or so ago at the Wooden Boat Institute at Port Townsend, Washington State, USA, on a 15' footer that Bieker designed for them. I'm sorry, I've lost the web site for it (arrghghghgh), but I think the article was in Woodenboat. You might find it interesting, esp. how they are using the gaff/mast for twist control.

    Doug, keep on it. You're having what I call Intense Fun. Like we all are. That's ok in my book.

  8. Doug Lord

    Doug Lord Guest

    wing tip rig

    Thanks Frosh and Paul. You guys may find this interesting. It is a blurb I wrote about my "wing tip rig" about 10 years ago. Probably the most significant( if anything is) thing is the upper outhaul. Don't have very much info from full size testing since its only been used on one 16 footer; the results in model testing are encouraging though:

    The Wing Tip Rig represents a powerful planform for a sail that unlike most modern fully roached or square top rigs does not require full battens (which don't work too well on models).** Further it features a drag dissipating tip design and an upper outhaul resulting in a capacity to shape the sail better than any existing sail. The essence of the Wing Tip Rig™ is better sail shape, drag reduction, and light weight (compared to fully roached sails).
    Wing Tip Rig background
    The first Wing Tip Rig was used on a on a 16 footer I designed in 1975.
    The top of the sail has a short adjustable gaff. It is a modern version of the gaff rig. Using vang tension allows very precise control of sail twist-it adjusts the range of gust response.
    The newest version of Wing Tip Rig(F³-see below) has been refined to provide performance closer to a solid wing than any existing soft sail planform.
    The Wing Tip Rig in its primary embodiment on the Spinnaker 50, F3 and America One mains(and on the aeroSKIFF jib) does a number of things:
    It provides an aerodynamically superior planform without requiring full battens.
    The tip shape reduces induced drag for more power upwind.
    The outboard top corner (peak in gaff terms) is adjustable using an upper outhaul which works to control the camber at the top of the sail.This works wth the mormal outhaul on the foot to give unparalled sail shape control.
    The lack of full battens allows superior performance in lite air as compared to fully battened sails-particularly in models.
    Twist, over the whole sail planform, is easier to induce and to remove than in virtually any other sail type allowing perfect matching of the sail to prevailing conditions.
    Depowering is easy and is automatic, when the rig is set up properly, providing excellent gust response.
    The benefits of the Wing Tip Rig™ are less drag, more power and more effective depowering.
    There is a measurable difference in model performance with the Wing Tip Rig™ when compared to an identical model without it!
    The only time it was used on a full sized boat the upper outhaul had a spring that pulled the "peak" forward and a line that ran down the mast to pull the peak aft. It was a bit of a problem to hoist. On models no such problem but then again it can only be adjusted on shore unless rigged to a servo.The model version and maybe a future full size version uses a "gaff"(extruded carbon on models) that fits into a bushing in the top of the mast and is free to rotate completely independently. Might still have some potential....
    Back to the topic a bit:
    I think the greatest drag reduction on sailboats
    (seahugger or foiler) will come from rig improvement.
  9. Paul Scott
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    Paul Scott Senior Member

    frosh, I think the LARGE windsurfer-ish hulled Bootiful (the smaller one) might prove your point. Hope it isn't moldering in a field somewhere.

  10. gggGuest
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    gggGuest ...

    I'm pretty sure it is, it having failed to achieve anything of worth...
  11. Paul Scott
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    Paul Scott Senior Member

    ggg- I know this is off topic, but judging from the press on it, the smaller one was ok (was it around 30'??), and it was the 60' that was the problem. ??

  12. gggGuest
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    gggGuest ...

    I don't know enough to really comment. But I wonder why a 60ft version would be expected to be much faster than a thirty foot one?
  13. CT 249
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    CT 249 Senior Member

    Frosh, thanks to you and Phil for hte FW info, but you brought up some bad memories with the ItzaCat.

    I'm fairly sure it was one of those I was asked to test many years ago for the Design Council of Australia. In anything but the moderately breezy reach in flat water in the vid, it was a wet, slow, evil-handling nose-diving wave-smacking helm-tugging platform-flexing sail-distorting heap.

    It still got the design award, despite the fact that the only person who sailed it (me) said it had distinct problems and that the planing cat idea was around long before Noah. As one of the guys from the award panel said to me, the idea was pretty much to find reasons to bestow the award, not to withhold it.

    Isn't there a basic physical problem? Cats have thin hulls. Thin hulls mean that the stagnation point is very small in area, so the boat will not develop much dynamic lift and won't plane well most of the time.
  14. frosh
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    frosh Senior Member

    Lots of interesting stuff here!

    Sorry, but I would have liked to respond earlier, but have been flat out at work.
    Anyway CT, Doug, and Stevo and any other interested parties, here goes.
    Starting with the Itza Cat. I would say it is a crude design, probably would go well on certain points of sail in moderate to stronger winds, in fairly smooth water only. I don't really know. My only info is from studying the video, and there is a much longer one out there on the net, than the short video in my earlier link. As far as racing it around a triangular course it would be awful IMHO.
    It was put up be me solely to illustrate that a multihull is not forced necessarily to always have every hull as a narrow displacement style.
    I am hoping that my tri will have the best of both worlds, (and not the worst of all worlds). Most of the displacement will be borne on the vaka which IMO is about as good as you can get to a small boat hull that has high performance capability, as either a displacement hull, or a planing hull. In stronger winds, my expectation is that more weight will transfer to the leeward ama which should strongly resist immersion by producing lots of hydrodynamic lift at speed. The Vaka has certainly not shown a perceptible transition hump when moving say though the 10 knot barrier while accelerating, in their previous trials. The planing amas are rather small, something along the scale shown in Hydroptere, but without the lifting foils. I have posted Freeship pictures of both the main hull and amas before. Here is another image of the whole thing assembled. Remember that the vaka is 40cm in beam with an arced bottom. The amas are 59 cm in beam at max point. and mostly flat bottomed, except for a slight V in the tail area. Chines are a little radiused over the entire length. The Vaka has very sharp chines in the rear half.
    Now a bit about the gaff rigged mainsail. Aspect ratio is roughly similar to an International Moth, but with only four short leach battens, a luff pocket sleeve, and sail area of 10 sq. m. The gaff is very interesting and I have manufactured two very different ones. One is a simple carbon tube which fits inside a pocket sleeve at the head of the sail. It has an adustable outhaul, but no control lines leading down to the deck. It has a spectra line leading from the mid point of the gaff to the very top of the mast, and this line can be adjusted for tension. It's tension setting makes a huge difference to the fullness and general shape of the upper half of the mainsail.
    The second gaff is more exciting IMO but not yet tried. It it like a short fully carbon sail batten with a lot of width for its short length. It is carefullly varied in thickness so that when under compression takes up a true aerofoil shape, just like a properly manufactured full length sail batten. The gaff batten slides inside the pocket sleeve also, as did the tube version. (not at the same time of course), it is one or the other. The adjustment lines fitted at strategic points, and when tensioned can create a fairly low cambered mainsail shape at the very head of the sail, or a more deep shape. Either way there should be some auto gust response as the adustment lines would not restrict the aft end of the aerofoil batten from falling away slightly under high wind pressure.
    I will be testing both gaff versions in a few months time.

    Attached Files:

  15. tspeer
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    tspeer Senior Member

    Here are some papers that describe different design philosophies for determining the shape of trimaran hulls. Note that design of the topsides can be almost as important to performance as design of the underwater shape. Antrim selected wide, elliptical sections for the aft end of his ama, not so much for planing, but for reducing windage of the windward hull. Both Shuttleworth and Antrim cover the change in total wetted area with righting moment for trimarans compared to catamarans.

    Shuttleworth and Antrim both talk about the fore-aft shift in buoyancy as the righting moment changes. Shuttleworth's stability indices can be converted to a footprint plot that shows the importance of providing reserve buoyancy forward in the ama to prevent diagonal capsize/pitchpole. From the looks of the drawing above, I'd say the amas are way too far back - their center of buoyancy needs to be ahead of the center of gravity by an amount that depends on the L/D of the rig.

    Shuttleworth, John, "Reflections on the Design of Brittany Ferries GB", Jan. 1982.

    Shuttleworth, John, "Multihull Design For Heavy Weather", Heavy Weather Sailing 4th Edition, International Marine, Camden, Maine, 1992.

    Shuttleworth, John, "Beyond the Tektron 50 - the design of the new Dogstar 50", Mar. 2002.

    Antrim, James K., "Design of a 40 ft Multihull for Offshore Racing," Marine Technology, Vol 27, No. 5, Sept. 1990, pp 285-299. (Available on SNAME Small Craft CD)
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