Trimaran From a Tornado Cat

Discussion in 'Multihulls' started by upchurchmr, Oct 31, 2011.

  1. upchurchmr
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    upchurchmr Senior Member

    Idka,

    First - I have a cat and I want a tri.
    Second - in light wind you can balance a tri so that only the Vaka is in the water. Given that I can already fly the Tornado on one hull I should have enough bouyancy to be efficient (surface area).
    Third - the try will have the beam to provide power when the Vaka is flying (similar to a cat with wings). Note that the Vaka will fly a little earlier if I have less than the original Tornado beam of 10' - that assumes the beam is somewhat less than 20'. 16 to 18 was what I was thinking.

    What are you trying to say about the Weta? It looks like a good boat, but why do I see so many ads saying " only sailed a few times"? The articles I have seen say the designer wanted a dingy which had amas which could be balanced out of the water at a medium wind speed, then enhancing the stability with less than full bouyancy amas. So he designed the boat with sail area and height which would not overpower the amas at high wind speed. In the middle range and high range of wind speed the Vaka is probably planning. Looks like a real interesting combination of choices that probably makes an enjoyable boat.

    Fourth - I want a 20' boat.
    Fifth - I want to fly the Vaka. (Talk to Doug if you misunderstand that)

    Note that better seating for average wind can be had with a tri if the Akas are above the Vaka deck line (I made a mistake above - I meant to compare to Chris Whites Discovery 20). Thats nice if I choose that. Trapeze will not be necessary if I limit my self to the Tornado rig, but I can still use them for more sail area or in higher winds. So I don't have to limit myself.

    Sixth - I want a tri.

    Thanks for your opinion, did that answer your questions?
    Comments are still welcome, but I was looking for boats or suggestions on how to do what I want.

    Marc
     
  2. Doug Lord
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    Doug Lord Flight Ready

  3. idkfa
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    idkfa Senior Member

    upchurchmr sorry but "Why a tri?" and please don't say "I want one," again.

    How is it better than a cat? The top french designers have answered this... It would be nice if the beach multi family caught-up.

    SerjKu has, btw nice tri.
     
  4. idkfa
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    idkfa Senior Member

    There used to be open-water cats, not any more.

    Where are beach tris, we have a few, none successful yet, but we have few new very high performance cats like AC45, VX40, etc, successful. And AC has gone cat even after BMW-Oracle was a tri.

    It is more than just flying the vaka, there is nothing wrong with doing that, it is good to do, at times. I'm not at all suggesting one goes the Farrier way.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    idkfa, from your T20 thread:

    =============

    I said it there and I'll say it again: I think to fully utilize the advantages of a tri the boat must be designed to fly the main hull-and do it early. Tris that are ultra light and not designed to fly the main hull can be very fast-like Randy Smyth's Scissors or the Gougeons "Victor T" but I'm convinced that a properly designed "max Tri" would beat either of those boats and all beach cats.
    ---
    Marc, you say you want to fly the main hull but you don't want to use foils-I presume that means not using "foil assist" in the ama-right?(like the big tris)
    If that is true you have a bit of a problem because you'll have a boat supported by a Tornado hull static but then when you fly the main hull what supports the boat then? A smaller hull(shorter waterline) would be slow, another Tornado hull as the ama would be too heavy. You could go Randy Smyth's direction and use relatively small sail area, an ultra light platform with very small amas-and it would be fast.
    You could use a smaller ama combined with "foil assist" and still fly the main hull. The problem with that is(and its true of almost every small tri) when you fly the main hull. If you design the boat to be narrow so that the main hull flys earlier you're take off angle of heel will be high(closer to capsize). "Foil assist" in the ama would pretty much eliminate pitchpole IF the boat was wide enough. A narrow boat takes away one of the big potential advantages of a tri-power to carry sail in strong wind.
    I live in Florida and most of the time we have 8-10 knots of wind. If you had a tri that only flies the main hull in 15 knots or more you're just flat out of luck. That is the number one reason my 18 footer is designed to fly the main hull in 5-7knots of wind-not necessarily to go faster- but to have the "flying" experience most of the time I go sailing. My tri is designed to take off early and also to be very wide to use the inherent design advantages of a tri to the max.
    Take the time-like you're doing- to think thru the options very carefully and best of luck.
    =====================
    Thought I'd check out a 20' tri, 300lb all up weight(probably would be more), 17' beam(you said 16-18'), 236sq.ft. sail on a 29' mast(Tornado rig) and 320lb crew. CE-CLR @ 14' . This is to get some idea of when such a boat would fly the main hull:

    (RM with main hull just flying)

    1)RM boat= 8X 300= 2400ft.lb.
    2) RM crew=
    --a. center+2'= 320 X 10'= 3200 ft.lb.
    --b. max w/o trapeze= 320 X 16.5= 5280 ft.lb.
    3) Total RM(crew+boat)=
    --a. crew +2' center= 5600ft.lb.
    --b max w/o trapeze=7680 ft.lb.
    4) By taking total RM and dividing it by the CE-CLR distance and then by total sail area you get the pounds per sq.ft. pressure for that condition:
    --a. crew +2' center: 5600/14= 400; 400/236= 1.69lb.per sq.ft. pressure
    -
    --max w/o trap: 7680/14=548; 548/236= 2.32 lb/sq.ft.
    ===========
    So, as a frame of reference, an F18 cat reaches its maximum RM in 1.8lb.per sq.ft. pressure(before depowering) and a Tornado in 1.7lb.sq.ft. pressure(before depowering) and that means that this particular tri would not fly the main hull untill a bit over 15 knots of wind with the crew sitting near center, and way, way over 15 knots of wind with the crew sitting on the weather rail.
    This is meant to help you to be able to think out what you want technically so you can get an idea of where you stand. Hope it helps.
    =============
     
  6. idkfa
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    idkfa Senior Member

    The Weta is less than 100%,
    Farrier about 150%,
    Flying vakas takes 250+%,

    So why not three tornado hulls? The volume is about right, unless you go the foil way -a bit less...

    Not really suggesting you do, but ask the question.
     
  7. Corley
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    Corley epoxy coated

    I like the idea of building a few hull shoes in strip plank with a developed ply topside that way you get efficient semicircular hull shapes without having to spend ages making the shape in a small simple boat like what your proposing with a high fineness ratio developing the topside shape in ply wont be difficult.

    Seems a bit of an overkill to use a tornado hull for floats I'd tend towards a wavepiercing design. I've been looking at doing some hulls for the T20 suggestion but I've come into my busy time of year at work and am spending any spare time on my Kraken 25 and Formula 40 projects.

    I like the floats Tim Clissold has drawn for timberwolf in NZ they are augmented with foils but it doesnt mean yours have to be.
     

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  8. upchurchmr
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    upchurchmr Senior Member

    Doug,

    Thanks for the number, I have seen them (did them myself). That looks just about what I was thinking about.
    Flying early is one way to go, I expect to aim for something a little earlier than a Tornado, but not really early. Texas typically has light winds except mid spring and mid fall, with a few high wind days (you can count on having quick buildups to strong winds, you just can't count on when).
    I am thinking about 150% displacement in the amas, so they will be smaller overall than the Tornado main hull. Sounds pretty middle of the road, doesn't it. Of course, anything over 100% will allow me to fly, contrary to Idkfa's comment about 250%. Foil stabalized will allow me to go lower in displacement on the Ama, if I wanted to . Given that we have the occasional terrifying burst of wind (the only real reason to go sailing in my opinion) I will probably stick with over 100%. A simple strip planked hull would be relatively easy to build a new smaller one, and I can look into Corleys method for reduced build time.
    Every one seems to forget that the big yellow sail in the pictures above would be a reasonable addition for light weather, so I could fly earlier if I choose.

    I don't expect this to be the new beach tri standard, so this boat would not have to justify itself to others like Idkfa.

    Corley I will have to look at Timberwolf, I haven't yet accepted wavepiercing - a little slow I admit.

    Ikdfa - Please justify your cat idea. So far all I hear is some unsupported statements. Perhaps you could whip up some data like Doug?

    Marc
     
  9. aussiebushman
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    aussiebushman Innovator

    Idkfa has asked the critical question.

    Why not either build a small cuddy over the tramp and leave it as a cat OR add a simple vaka with the tornado hulls as amas? If you want a tri, then the Tornado hulls will make reasonable amas, but I can't see the point of using one as a vaka. You might find an existing dinghy or even canoe that would do the job but it would also be very simple to build the simplest stitch and glue job in 6 mm ply and some light glass cloth.

    The beams could be a simple telescopic arrangement with the original cat beams sliding inside new centre sections (bits of old masts) with locking bolts.

    Your real problem is that you will get apparently conflicting advice from all of us. However, please consider that many of us have been down similar thinking paths and have discarded many concepts in favour of better ones.

    Regards

    Alan
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Marc, if you use a Tornado as the main hull and the finished tri weighs about 300 and the crew about 320 the Tornado hull will float almost as immersed as it is when flying a hull on the cat(1" less approx.). That will mean that the transom/bottom intersection will be below water at static, right?
    So you have the displacement of the boat at 620 plus, you have a Tornado main hull with a 20/1 L/B ratio*.
    In trimaran design, getting the ama to have a high L/B ratio is critical on a tri designed to fly the main hull especially if it will support the entire weight of boat and crew by buoyancy alone because at the speeds of the boat, when the mainhull flys, the wavemaking resistance will be very high.
    My point-and question-is how do you get an ama to support this weight and be shorter than a Tornado hull without:
    a. decreasing the L/B ratio( instead of 20/1 like the main hull-wider like maybe 14/1) ?,
    b. increasing the immersed section of the ama in such a way that wetted surface increases tremendously as the main hull flys?
    ----
    A good check would be to compare the immersed wetted surface of the ama design you choose(when flying the main hull) to the static wetted surface of the Tornado main hull while it supports the full weight of your boat. If the ama you choose has more wetted surface than this you're barking up the wrong tree, in my opinion. The ideal would be to have a 20/1 or so L/B(like the Tornado hull) with wetted surface no greater than the Tornado hull used as the main hull on your boat.
    You can see that if the wetted surface increases and/or the L/B ratio decreases as the ama takes the load you are increasing drag. That is the crux of the design problem when designing a tri to fly the main hull, in my opinion.

    Just trying to help you think it out-which you appear to be doing pretty well.
    =========
    * See ahead for post 49 . The L/B ratio of a Tornado flying a hull is in the vicinity of 16/1 instead of 20/1. It is approximately 20/1 with the boat sitting level. The heeled waterline beam is what should be used when considering an ama that matches or exceeds this value. Detailed design work is always necessary and it is important to doublecheck stuff like this IF you're doing a design based on this hull.
     
    Last edited: Nov 15, 2011
  11. Doug Lord
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    Doug Lord Flight Ready

    =======================
    Alan, I can't see a single reason why a Tornado hull couldn't be a main hull on a suitably designed tri-except keeping the all up weight low enough.
    Other than that why do you think the Tornado hull wouldn't work or is bad in this application?
     
  12. upchurchmr
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    upchurchmr Senior Member

    Aussiebushman,

    I can't see where Idkfa has asked any question worth answering.
    I don't want a 23-25' boat, is that allright? If not why don't I just go buy a Tremolino I saw advertised?
    I don't want a cuddy - what ever gave you that opinion?
    You obviously have never see the Tornado beams, they are not going to fit any mast section I have ever seen as a sliding joint. If they did I would need two boats just to start.
    Lets note that if I did want a longer boat and used the Tornado hulls as amas, Russel Brown noted that they did not work very well on his Trinado and he quickly changed therm for more purpose designed ones.
    The tornado hull has a significant transom (for a narrow boat). Using it as a ama or Vaka would require movement of the human ballast to get the most performance - not burrying the transom -just as is done on the Tornado typically.
    Alan I expect conflicting advise, I invited it to start with. The best thing I hoped for was advice with some backup information. Please note Dougs input.

    Doug - the transom immersion will be as you state, except everyone should realise that the Tornado can be sailed carelessly and drive the transom underwater just by not moving the people (with every wind speed change, actually). This boat will be no different, it is intended as a day sailor where the sailor(s) need to pay attention and react.
    Why do you assume a shorter ama than the main hull? BMW Oracle certainly did not take that approach (not really comparing myself to that design team). I have assumed fairly long, approaching 20', an overall oval shape (approximately semicircular bottom), boyancy shifting forward as the ama is immersed deeper, with a small transom. The idea of a wave piercing upper deck or at least the Nacra style rounded deck to help with pitchpoling when flying seems desirable (remember ~150% bouyancy). Tornado hulls still have significant freeboard when flying if we are still making a comparison. I would prefer not to have a tall ama, rather something closer to a circular bottom and hull with ~6 inches of a flat side. That should put the 100% waterline at the top of the flat. One of these days I'll see if that actually works physically.

    I think you are right about the static bouyancy check, but if I hit the same surface area while flying I still will be going faster due to more power applied. You might notice that the Tornado hull when flying has large flat surface areas forward, the transom may be slightly immersed (for best speed). I think that a reasonable ama shape would always have less surface area, depending on the overal height.

    Actually I think the major question for a cat or tri is the question of tripping or pitchpoling. When comparing the Tornado to other contemporaries in the 60's you can notice the mast farther aft. This helps with retaining more resistance to tripping since the CG of the boat and ballast (crew) can be shifted farther aft than a boat with the mast at 40% of the length.

    You are very cleverly working me around to the justification for lifting foils to reduce the ama wetted surface and wave making. I do understand the utility. Remember the ability to put foils on after the initial launch.

    Did you ever see the AYRS publication showing a Phoenix (18') cat with a T-foil for anti pitchpole? Fairly clever, if you think a small foil, used at only high speed is a reasonable approach.

    Marc
     
  13. Corley
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    Corley epoxy coated

    I understand what your trying to achieve and I think its a good aim. I also am in favour of boats without any concessions to comfort when racing. A low freeboard dead simple off the beach tri with purpose built floats would be a great performer. It should be relatively faster in light and heavy conditions than an equivalent catamaran and probably nearly hold its own in medium conditions particularly with the more efficient headsails you can set in the fore triangle.

    I'd not use tornado beams either but a purpose made foam sandwich or light plywood style beam with a downwards curved outer end where it meets the float to minimise wave drag with an insertion style fitting for the float to spread the forces out, you could make the beams cantilever or fit water stays to go for a minimum weight compression strut beam arrangement. At 16/18' BOA with a carefully designed beam the weight penalty for cantilever will not be severe and keeps messy stays out of the equation. I'd also have a semicircular traveller arrangement to give good mainsail adjustment and allow for some fore and aft bracing for the beams.

    After looking at a variety of off the beach catamaran hulls for a tri conversion I came to the same conclusion that beach cat hulls would make better vakas than amas if you want performance.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    ---------------------------
    I didn't assume a smaller ama-you said as much here:

    ================

    Who me ??

    --------------------------------
    I think in this design you have to pay very close attention to wetted surface, but even more importantly to the L/B ratio of the ama because of its higher speed. I don't know how much you've read about the Moth class and hull design before they started flying but there are some good lessons for multihulls in that development. When I first saw a skinny Moth(10/1 L/B) I wondered why they went for that box section instead of a low wetted surface semi circular section. The answer was that thru developmental testing it was found that a high L/B was much more important from low speed to high speed than was wetted surface. On the Moth they had to choose because they could not get a semicircular ,low wetted surface hull skinny enough. The longer the hull, the less to choose from but something to remember.
    -----
    BMW Oracle-USA-17--Marc, the approach taken by USA 17 was taken as a direct result of the fact that the ama used lifting foils.
    While I don't know the design lift for that boat I do for the old ORMA 60's and the new MOD 70: the ama foil on these boats lifts 70% of the total weight!
    That changes how you design the ama: take a look at the ama of a Mod 70 compared to the main hull-both theoretically support the same weight -the ama when flying the main hull- but look at the shape difference:it's because the buoyant part of the ama supports far less weight than the main hull does static since the foil supports up to 70% of the total weight!
    -
    An aside:I know I seem to bring up foils a lot-almost as much as Gary does(!) but its only because too many people seem not to realize how critical the judicious use of "foil assist" is to modern high performance trimaran design. If you consider a foil lifting 70% of the boats weight then you are talking about an ama(in boats 20' and under,at least) that can be dramatically smaller than it would otherwise have to be. That saves time and money(and weight) which could be used to buy the foils-or you could talk to Gary Baigent about how he built his foils- or me about how I built my curved foils for the model and the final boat in a year or so. You could even check with Phil of Phils foils to see if he has any stock curved foils and trunks yet. A number of the A Class cat guys have modified their boats for curved foils-some themselves and some thru a guy on the gulf coast(nearer you than me) whose name you could get from Bob Hodges. There are ways to accomplish this without getting too far into unknown territory and there are bunches of people that could help. The design of your whole boat could be drastically improved..... Thats it-no more from me on foils in this thread unless I answer a question-its your decision.
    -
    Take a look at this picture and compare the rocker of the main hull to the rocker of the ama-and remember the ama supports 70% less weight with buoyancy than does the main hull but supports the SAME weight in total when the main hull is flying since the foil is carrying 70% of the all-up weight-
    click on image(please):
     

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  15. Doug Lord
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    Doug Lord Flight Ready

    ============
    Great comments, as usual, Corley. This is sure where the technical aspects of high performance trimaran design come in:
    Type A--- the ultra light approach: like Randy Smyth who beat the Tornado in the Everglades challenge with his exceptional tri, or the Gougeon Brothers that with "Victor T" beat all the current C Class catamarans in 1969 with their tri.
    Neither of these tri's fly the main hull.
    --
    Type B--- The Max Tri approach: where the design seeks to use the utmost in technology to take advantage of the design opportunities inherent in a trimaran configuration. These boats must be designed to fly the main hull.
    It is my opinion that boats using this approach will not only be faster than beach cats but faster then "A" above.... There is a downside to this approach
    when comparing it to Max out cats the same length( no foils on either) : If the cat is designed to fly the windward hull in 8 knots of wind but the tri can't fly the main hull until its blowing 15 there is a problem, a very serious problem for the tri.
    -----
    Lots of opportunities and pitfalls in high performance small trimaran design....


    Pictures: Top 3 Scissors/Sew Sew(Randy Smyth), Last: Victor T. Funny(not really) I can't find a single picture of a high performance Type "B" trimaran design 20' or under, so USA 17 will do:
     

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