FOILER 1 Grand Prix

Discussion in 'Sailboats' started by Doug Lord, Feb 22, 2006.

  1. gggGuest
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    gggGuest ...

    Dear oh dear guys, a lot of determined opinions here with insufficient experience to back 'em up. I've sailed on the same track as some of the top foil Moth guys and a former helm of mine is one of them. 500m plus staying on foils without crashing is not an isue for them. Doesn't make for very interesting video though.

    These boats are way way more impressive than you think when you seem them stacked up alongside you, video doesn't give you the half of it. As for "nobody cares about absolute boatspeed or whether a foiler can bet a A". Nonsense: everyone cares, that's the big thing everyone talks about. I don't think absolute speed or even increased speed is a way to increase sales figures, but its guaranteed to have a huge impact on the incidence in bar room conversation.

    I really don't see an alternative to learning in low riders first. When wing tip floats hit the water you get a massive off centre drag hit. On a foiler I'm quite sure that's going to stuff you in the water. Floats might make a low rider more accessible to the beginner, but they have major downsides - they cause the boat to invert immediately on capsize and be much more difficult to recover from a capsize.
  2. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

  3. CT 249
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    CT 249 Senior Member

    Thanks John.

    I'm not quite sure that world-wide, you will get 7-25 knots 95% of the time, though. But yes, these are VERY successful racing designs.
  4. Doug Lord

    Doug Lord Guest

    Buoyancy pods / Rave / Rave-added info

    Jim, I have to disagree with you on buoyancy pods -you should read the stuff on the UK site about them. I sailed a 14 footer that I built years ago with pods and a main hull beam to length higher than a Moth and they really help. If the pod buoyancy is below the all up weight of the boat the pods will sink just like the wing would normally and if the beam with the pods is wide enough a capsize is unlikely in the first place. I never had a pod cause any form of directional instability in well over 100 hours of sailing my experimental boat.When you sail with pods you don't sail with them in the water-and keeping them out is how you learn.And you do learn because you don't capsize. The penalty for incidental contact is not a capsize,pitchpole or spinout -just a slight slowing. The Moth guys on the UK site all thought it would help(if I remember correctly). The pods don't have to extend down like hulls-they're there to prevent rollovers BEFORE you get on foils. After foiling they would have little or no affect on the boat.Foiling stability
    is greater than seahugging stability and most of these guys want a Moth to foil not to invest 2-3 seasons to master a seahugger. Using pods will help you to master a seahugger while preventing most capsizes and allowing the begining Moth sailor to foil much sooner. In addition to that the characteristics of handling the boat with foils but not flying would be learned by starting out with foils. And as John said they don't have to foil just because the foils are there but when they are comfortable and using guidance from people like John they can then foil when they are ready and in suitable conditions. I believe pods would make a huge difference in the USA where they would help to maintain the excitement level by providing a much, much quicker transition to foiling.
    The fact that they are illegal for class racing is a moot point in the USA since all this is just starting-beginners could be allowed a waiver or something like it for a given period of time. That time frame would be much less than making that beginner roll over every two minutes for a year or so. Again, the pods HELP to learn the characteristics of sailing a very narrow boat-they don't insulate the sailor from those characteristics.
    Raggi, the Rave is a neat boat to sail and capable of real high speeds. Unfortunately, it is also out of production. The Rave foiling system uses the foils to develop righting moment so the crew can just sit in the center of the boat. Quite a cool ride!
    edit: Raggi- it occurred to me today that thats really not the whole story on the Rave compared to a monofoiler. The boat was heavy and would not foil well in light air especially upwind. From a technical perspective the monofoiler has an advantage due to a technique developed by Rohan Veal: heeling the boat to weather. This allows the vertical fin to be unloaded reducing the chance of ventillation and allows part/most of the lateral resistance to be generated along with lift by the hydrofoil. According to the guys that have sailed the Moth this in turn allows the boat to point at least a well as any other monohull upwind while still foiling.Upwind foiling in a Moth is it's best point of sail from a course perspective as best as I can tell, and certaily in comparison to a multifoiler that can't use it's foils in the same way. From my experience sailing a Rave and talking to Moth sailors I'd bet a Moth would take the Rave thruout the 8-15knot range and maybe even at somewhat higher windspeed. Another technical point is the difference in rigs: the Rave rig is, in essence, a low cost modification of a cat type rig whereas the Moth uses a rig that has been proven superior for high speed sailing and is another key to the Moths incredible foiling performance-especially upwind. Hope that gives you a more well rounded perspective on the two types of foiling.
    Last edited by a moderator: Mar 3, 2006
  5. Eric Sponberg
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    Eric Sponberg Senior Member

    The People's Foiler Drawings

    This seems a perfect time to post some drawings. I have worked with Doug Lord on developing the People's Foiler concept, to get the basic parameters of the boat down on paper so that we can study it further and begin a more detailed design when the opportunity comes.

    I am not a foiler sailor, I am a naval architect. I have never sailed a Moth or a foiler-equipped boat. My business is designing boats to meet client's needs, and to advise on how they can and should be built. It did not take a long time of study of the videos available on Moth foilers to understand how they perform. I listened to Doug explain his ideas for foiler design, his background in model foilers, hydrofoil control, and I probed him with questions on design, construction, and performance to better understand how this boat could be built.

    I came away thinking that there were some pretty innovative ideas there that would be worth pursuing. Certainly, everything about the boat is buildable, there are no new gadgets that have to be invented, really, just current technology that needs to be put together in the right combination to make this boat perform as intended. At this early stage, I don't know all the answers. Will the boat sail as we hope--easy to launch off the beach; able to foil in low wind speeds; able to accommodate up to two people of varying weights; able to go totally airborne and re-enter the water without crashing; able to flip upright easily in the event of a crash???? These are all questions that will require at least one prototype, and preferably two prototypes, to be built and tested. Neither Doug nor I have the funding personally that it would take to put these prototypes together, but somebody out there might, and if they have an interest in this project, we would like to talk to them further. We have put cost numbers together in a design, build, and test program that we think is realistic.

    I do know this much--I think this boat will work--that is, it is possible to build, it will sail, and the ideas incorporated into the design are worthy of development and hold a lot of promise. Properly funded, built and tested, I think this boat holds a lot of potential create a whole new realm of sailing.


    Attached Files:

  6. carlos reynoso
    Joined: Mar 2006
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    carlos reynoso New Member

    Boat Comparisons

    Just curious, Doug and Eric, but have either of you guys had a discussion about the commercial viability of foilers with Greg Ketterman at Hobie? Greg's a good guy, an engineer and supremely qualified to offer an important opinion on the matter.

    When it comes to putting techno-creative ideas on the water and getting people to actually buy them rather than argue, Greg has mountains of experience in the area. If this were my boat project, Greg's the first guy I would call for background on the matter. Next, I'd call Andy Zimmerman, the former CEO of Confluence Watersports, the makers of the Windrider Rave. Andy was instrumental in the concept, design and marketing of the Rave and now has his own product development business in North Carolina.

    Both of these guys would be terrific sources of info on what works and what doesn't in the selling of a foil-borne boating product in the US market. If you only consider the process from the very tiny, racing oriented foilers from other parts of the world, you have completely ignored the realities of the market here in the US and you do so at your own peril.

    Nothing of these two individuals have ever been mentioned in any of Doug's postings. Instead, we've been routinely exposed to reports about foilers in England and Australia with nary a whisper as to how they've already performed in the US marketplace. If you like, you can try to purposely define the AeroSkiff as a monofoiler which would suggest that you find none of the Rave/Trifoiler lessons appropriate. I would suggest that the general boat buying public doesn't view it that way until they are already very well educated as to what is and what isn't a mono or multi foiler. To them, if it has foils, it's a foiler. If you want to create a differentiation in that perception, then you'll have to spend the money to do it.

    You can read about the Trifoiler in Greg's own words here:

    Here's Hobie's, still maintained, web page on the Trifoiler:

    Also, just curious about this aspect; has a foiling Moth ever paired-up with a Hobie Trifoiler in conditions that would suit both boats to see which boat can go the fastest? The Trifoler was timed at the 1999 Weymouth Speed Week at 31.6 kts. and un-officially clocked at 38 kts. in winds gusting to 30. Is there a Moth, anywhere, capable of that type of top-end speed? And yes, both boats can be sailed solo.

    I've sailed both the Rave and the Trifoiler at Hurricane Gulch in San Pedro, California and "in the right conditions" both of these boats ARE capable of very quick speeds coupled with neck-snapping acceleration and G-forces when turning. Commercial pricing for both of these boats was entirely within the proposed guesstimates of the AeroSkiff and yet.... why are they not still being sold by the manufacturers if they were such wonderful boats in the mind of Joe Public?

    Mind you, the Trifoiler and Rave were designed by two very smart guys in the boat business in Ketterman and Bradfield and you'd have to be thinking that you have something better to say about the genre than did they. The designs were coupled with very well supported marketing campaigns by crews of guys hauling foiling boats all over the country to bang the drum of high speed sailing. Many, many thousands of dollars were spent on the effort and it went, essentially, nowhere with the Average Joe, sailing public.

    I'm not saying that each of you guys, Doug and Eric, aren't smart dudes. I recognize that both of you have a lot on the ball. I am saying that the Average Joe, boat buying public is going to have to make a quantum leap in acceptance of technology, pricing and usefulness in order to get their collective heads wrapped around the idea of a boat of this type. That process is going to cost many, many tens of thousands of dollars before you sell enough boats to come close to recouping the necessary investment for tooling, R&D, marketing and just plain old seat time answering tedious questions on the Internet.

    I'm negative because the day Doug started posting about this issue, the assumption was present, that once he tossed his idea in front of folks on the Forum, that he was ready to hear the good, the bad and the ugly about his concept. Apparently he is not ready in that regard.

    It's my opinion that the concept, in it's present state, is principally on the ugly side of the argument. It's too fiddly, too expensive and too esoteric for the so-called marketing scheme of it being a "People's Foiler" that would be snapped-up by the buying public. Get the prices and ambitions down into the realm of $8,000 (retail) for a finished boat with VERY simple, set-it and forget-it controls and you're entering the realm of a doable concept.

    Right now, this boat is a serviceable concept for a very small niche market of enthusiasts. If you can build it in vacu-thermoformed skins, injected foam, sandwich interiors, very simple, inexpensive rig and hardware, etc., it may just be possible to bring it down to a manageble, conceptual number for an average guy who might be interested. As it stands, it's going to be properly categorized as a novel technical product and it will likely suffer the same fate as the Rave and Trifoiler.

    You don't have to like me for my opinions and you can call me negative if you want. I happen to call it pragmatic from a business perspective. Then again, you may have way more money for these types of exercises than do I, so you don't have to analyze things in the same fashion.

    We'd all like to see your success, but this Forum is not the crucible of proof. It's out there...

    Chris Ostlind

    Attached Files:

  7. Doug Lord

    Doug Lord Guest


    Carlos, (I guess: who exactly wrote the last post? seems to be from Carlos yet is apparently signed by Chris Ostlund?): I've talked to Greg Ketterman several times but not about the details of this foiler; in addition I spent many hours listening/talking with Dr. Sam Bradfield who inspired me to build the F3 RC foiler which you can check out on along with a tribute there to Dr.Sam.
    I've explained numerous times and in different threads about why I believe the monofoiler will succeed where the multifoiler hasn't. Basically, it comes down to speed-not top end speed but the ability to take off in light wind as demonstrated with the Moth. And the fact that the monofoiler doesn't use the foils to develop RM... And does use the foils to help with lateral resistance.... And only has one wand/ altitude control system..And is more than likely faster than either the Hobie Trifoiler or Rave in winds of 8-15. And the fact that the Rave and Trifoiler require too much assembly time as compared to a proposed monofoiler-ready to fly in less than a quarter of the time based on actual comparisons between a Rave and my 16' monofoiler. And that the multifoilers were too heavy...
    As to top end speed the multifoilers have the edge but suffer from the additional weight required to make them strong enough to take the sailing loads imposed by the foils-loads that are not experienced on the Moth or other bi-foil monofoiler.The Moth is now close to 24 kts. and Rohan Veal thinks the top end speed can go much higher. I do too....
    But from a marketing standpoint the ability to take off early-- in light air-- is the most important consideration for any Peoples Foiler, in my opinion.
    The International Foiler Moth says it all for now in terms of performance, light weight, and even ease of homebuilding- nothing under 20' touches it for "bang for the buck" and it is available NOW!. The new foilers have a golden opportunity-it's an exciting time.

    Note to whomever: I love discussing foiler issues with reasonable people-Dr. Bradfield, Eric and I and others can go on for hours, but there are posts in this thread that approach the subject as a Daddy would his unruly teenage son with lots of attitude and comments to me and others like : "stop before you hurt someone","it's ridiculous" or words to that effect and many more such comments. Posts in which uninformed comments such as either the Moth or my boat being "fiddly" ,uninformed comments about pitchpole combined with the aforementioned ugly, aggressive attitude.
    Those kinds of comments will go nowhere wth me but I'll try to answer most comments and
    questions as best I can.
  8. Chris Ostlind

    Chris Ostlind Previous Member

    " Those kinds of comments will go nowhere with me but I'll try to answer most comments and questions as best I can."

    And therein lies the disclaimer that gives pause to an investor in your scheme. The use of the word "most" is more than telling, Doug. When you get around to the full disclosure mode, you let us all know, will you?

    Yes, I posted as Carlos. Why not?... you post as Lorsail. Others post without using their real names. Get over it. When you answer all the questions that have been posed, I'll stop using fake names to get you to answer those that are posed, but never answered.

    Number One question on the hit parade that has never been answered....

    Why don't you use your own money to build the tools and fab the series of production prototypes to prove you have the goods and not just fluff? It's only too convenient that the hype has exceeded your grasp. Where's the money, Doug? As they say in the film business... ideas are cheap.

    That's a suitable question for someone to ask who may be interested in funding your enterpise and you've always dodged the issue. If you can;t fess-up here, when can you get clean?

    If you can hype it, you should be able to be very open about it. Otherwise, you're always going to be generating the feeling among the Forum readers that you only believe in the product to the point that someone else will pay for the enterprise. I have a childhood friend like that. He'll hang around the gang of guys as long as we're buying.

    Now that's sincerity and commitment at its finest.

    This whole thing could have been a fun discussion if you'd been willing to accept constructive criticism. Instead, you try to dodge the issues with regularity because there is a huge hole in your hype and when someone drives through that hole, you ignore the reality in order to continue to blow hype. Dude, that's not effective salesmanship in front of an educated group of listeners. Actually, it's more like the behavior of a politician than a sincere enthusiast with an interesting idea.

    I think your skin is too thin to be an effective marketer of a new product. If this style of questioning bothers you, I can't wait to see what you do when you actually get a boat in front of the buying public.

    Chris (aka Carlos and whomever)
  9. Doug Lord

    Doug Lord Guest

  10. RHough
    Joined: Nov 2005
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    RHough Retro Dude

    Please explain how the Tri-Foiler and Rave use the foils to create RM and the Moth does not. I don't understand.
  11. Doug Lord

    Doug Lord Guest

    Wands / feelers

    Gladly. The Rave uses two mainfoils forward and one aft on the rudder; the two mainfoils are symetric but are set at a +2.5° angle of incidence relative to the flight waterline(which is nominaly parallel to the static waterline).Each main foil is equipped with a wand for altitude control and because they are independent of each other they also develop righting moment. In fact, the Rave has a maximum speed because if the speed is exceeded the forward cross can break. In other discussions Tom Speer quotes one of the guru's behind Spitfire(40' surface piercing foiler,ballasted) that the reason he didn't use the foils to generate RM like the Rave, Skat, Eifo, Volantis and the Hobie Trifoiler is because "you only have to lift (ballast) once" whereas with a foil based RM system the faster you(the faster the wind blows) go the more RM must be generated by the foil system.
    The foil loading at takeoff on the Rave is greater than that of a Moth and, just guestimating, is about 50% greater or more in a 15k wind. The Trifoiler uses the same idea, different system: the foils are all moving foils(the Rave foils are retractable but locked in position for foiling and they use flaps to change lift) and are attached to long feelers sticking out in front of the boat. The RM is generated effectively in both boats by the sensors' reaction to the boat heeling. On the Rave the wand tension can be varied to increase the downforce on the windward foil and or upforce on the leeward foil.
    The Moth on the other hand develops RM by the use of crew weight and crew technique: the boat is heeled to weather and that gets the whole CG further to windward than if the boat were sailed flat like many dinghies(the Moth hydrofoil, when heeled, also contributes to the lateral resistance) . That combination and low foil loading( around170lb.'s per sq.ft.)allows light air takeoffs and excelent performance upwind.As I said earlier the Moth would probably take the Rave and Trifoiler in 8-15knots of wind -at least on a course -due to the superior pointing of the Moth.
  12. RHough
    Joined: Nov 2005
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    RHough Retro Dude

    Thank you Doug.

    It seems the reason that negative lift is needed is to remove the requirement to shift ballast.

    For a three point foiler to work, the rudder/rear foil must be kept in the water, so shifting ballast to remove the drag caused by the weather foil lift would be a solution.

    The Moth numbers look like this:

    Crew CG about 4' off centre (Beam limit is 2.25M and no trap or sliding seat)
    Mr. Cheeseburger here weighs 200# :mad:
    The Boat weighs 70#
    total weight of boat + crew = 270#

    RM = 4' x 200# = 800 lb/ft

    If it takes a 30% SCP to weight ratio to foil that give a SCP requirement of 81lbs

    81lbs and 800 lb/ft of RM gives a sail arm of 9.9ft

    The sail arm gets longer as the boat foils higher and SCP is reduced. The boat should be fastest at the lowest possible foiling height. Just enough to keep the displacement hull out of the waves.

    If the design is scaled to 16 ft. we get:
    Crew Arm 6'
    Boat 150-200 lbs
    Total 350/400 lbs
    RM 1200lbs
    SCP required 120 @ 400 lbs total
    sail arm = 10 ft
    SCP @ 350 lbs = 105 lbs
    sail arm = 11.4 ft

    We have a boat 16ft LOA with a 10ft beam. Look what happens when we free ourselves of the mono-hull rut:

    Crew arm 11'
    Boat 200 lbs
    RM 2200 lb/ft
    we use the rig off the 16' mono for a sail arm of 11.4 ft
    that gives a SCP of 193 lbs or over 48% of total weight.

    The boat would have a Catamaran configuration with Moth type foils in each hull. The rudder foil would be midships and very little (if any) down force would be needed from the weather foil (it has a 10ft arm to work with).

    The boat would be inherently stable, would be able to foil at any speed a Moth can and would have a higher top speed. Basic flying height trim to adjust for wave height would be part of the foil control system.

    If Hobie can build a bullet-proof 16 at 320lbs, a 200 lb foiling cat could be built using the techniques that yield 70lb Moths. No amount of sliding seat and or trapeze is going to give the narrow minded 16ft mono the advantage, since the same things would be even more effective on the FoilCat(tm) :D
  13. Doug Lord

    Doug Lord Guest

    Foil Cat™ whuped around a course by Moth/16' monofoiler in 8-15 !

    Ah, but you forget:
    1) surface penetrations are a good indicator of drag on a foiler and you have 33% more drag(WRONG: 50% MORE DRAG!) than a two foil monofoiler-or thereabouts.
    2) To use your 11' arm with the windward foil not doing any work(essentially in neutral) the lee foil would have to lift the weight of 80% of the whole boat. That would mean each foil would have to be around 1.79 sq. ft. or 3.58 sq. feet all up over 1.9 sq. ft more than a 16' monofoiler.Or you would have to accept higher foil loading than a Moth(with the crew at max extension-11')
    3) A major, major advantage of a monofoiler is it's ability to heal the boat to weather a technique that allows it to point incredibly well upwind especially when compared to multifoilers.
    The Moth: 11', 1.04sq.ft. foil area, 169lb.s per sq.ft. foil loading at 80% on main foil, hull 60 lb.s, upper end of ideal crew weight for upwind foiling: 160 lb.s, 81 sq. ft. SA per sq. ft of foil area - mainfoil only.
    16' monofoiler. 1.6 sq.ft. main foil at 169lb.sq.ft. foil loading @ 80%, 180lb. hull, 160 lb crew, 145 sq. ft. SA, 90 sq. ft. SA per sq. ft. foil area-mainfoil only.(not a scaled up Moth)
    Foil Cat™ --Lets start like this: almost realistic possible all up sailing weight 220 pounds, crew weight 160lb.'s (to keep them all the same). 380 all up. Mainfoil area 3.58 sq.ft.(2 @ 1.79) assuming 11' arm and weather foil unloaded. Lee foil would then be required to lift 80% of the 380lb boat weight
    which is 304lb.'s. Foil loading just counting the lee foil would be the same as a Moth and foil loading below the max crew extension would be less than a Moth(but see below: SA per sq.ft. of foil area is much less than Moth or 16' monofoiler-higher drag). This, in essence is a light weight carbon Rave without beam of a Rave. It would probably be faster as a tri rather than having two 16' hulls and more beam would unload the foils better at higher speeds. SA per sq.ft of foil area=51 sq. ft.(mainfoil only). Likely as a tri to be very fast in higher wind ranges while not being able to take Moth around a course in 8-15 due to poor pointing characteristics.This boat can't be heeled to weather like a Moth and that is probably the single greatest advantage of the Moth type.
    Hope this helps and hope I got the figures right-I'm tired-so long....
    3/13/06 Rave- 12' foil cl to foil cl, each foil 1.7 sq.ft., SA 195 sq.ft., SA/sq.ft. of foil area-mainfoil(s) only:57.35-this is important: compare with the amount of SA per sq. ft.of foil area for both monofoilers.Foil loading 368+160=528 or nominally 264lb.'s per foil-just to hold her up. However, since the Rave develops RM using the foils and the heeling moment loads the foils the additional loading at take off will be: approx .7lb per sq.ft. pressure at, lets say, 11' up so that HM=136.5 X 11=1501ft. lb.'s. Now, it's convenient to divide the HM by 2 so that it is applied equally to both per side,divided by the distance from the CL to the foil CL gives the load applied to each foil=750.75divided by 5.5=136.5lb.'s. So leeward foil= 264+ 136.5=400.5lbs divided by 1.7=235lb.'s per sq.ft.Windward foil=264lb.'s MINUS 136.5=127.5lbs for a foil loading of 75lb.'s per sq.ft . The low foil loading of the windward foil helps explain why it works so well at developing RM even though it is set at a 2.5° positive angle of incidence relative to the flight waterline. Actually this fixed angle of incidence is reduced a very small amount by the shroud loading.(the tube twists slightly).
    On the Foil Cat™ the crew at maximum extension is NOT a limit on RM because ,assuming the boat has independent wands the thing will do the same thing the Rave does: develop virtually unlimited RM necessitating either a max wind speed limit, boat speed limit or both in combination with reefing. And , because of this the structure will have to be much stronger than a normal cat which probably means that the weight quoted above may be somewhat unrealistic.
    Last edited by a moderator: Mar 13, 2006
  14. RHough
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    RHough Retro Dude

    Not even close to 50% more drag. The foils produce drag two ways, Profile drag and induced drag. The Lifting area of the foil(s) would be the same for any given weight, no matter if it was 1, 2 or 3 foils. Thus the induced drag would be the same. The vertical strut or foil that connects the lifting foil(s) to the hull has only profile drag. For the same total lifting area the strut(s) would have the same area and the profile drag would be the same. There might be a small increase in drag when comparing 3 vertical struts to 2 or comparing 2 struts to 1, but nothing on the order of 50%, since profile drag is a small percentage of the total (profile + induced).

    Nope, for a given total weight the foils have to produce lift=weight. If a mono-hulled foiler with in-line foils had an 11' crew arm, no extra lift is required of the foil, since lift=weight. It is the same physics as a planing skiff, the hull of a skiff is not thrust down when the crew is on the wings.

    I'm not sure how any extra force to resist leeway is created by heeling the boat to weather. The force that prevents leeway comes from the vertical foil, not the horizontal foil. Heeling to weather vectors a tiny bit of the lift to weather, but would also vector some of the side force of the vertical foil downward. The combination of reduced horizontal area and downward thrust from the heeled vertical fin would require higher lift from the horizontal foil and thus increased induced drag from the lifting foil. I don't see a net gain from tilting the whole thing into the wind.

    Just as a mono-track foiler is limited by crew induced RM, a FoilCat(tm) could be limited by crew induced RM. The foils could be limited to zero lift or a very small amount. The weather hull/foil could fly before the rig was overstressed. The top of the mast could be tuned so that it would de-power as the design limit was reached to help control the boat. Therefore the rig could be built only as heavy as a mono with the same RM. The neat thing about the FoilCat(tm) or "EffCee" as they would be nicknamed (Frigging Cool) :) is that you could haul your playmate around in style, she wouldn't be huddled in terror under the boom ... :D

    My point is, that foiler Moths have evolved as they have because they are not allowed to have a multi-hull configuration. The Hobie Tri-Foiler and the Windrider Rave evolved from a requirement to not move the crew and a desire for high speed.

    If the paper is clean, and there are no rules other than sail power. It has not been proved that a single track foiler is the optimum solution for a foiling craft.

  15. Doug Lord

    Doug Lord Guest

    wrong sums it up

    1) Three foil fuly submerged multifoiler systems DO NOT lift the same weight as an equivalent sized monofoiler.To go from a two-foil monofoiler to a three foil multifoiler, with wand atitude control(or feeler altitude control), drag will increase at least 50% because the multifoiler will have(NEED) more foil area to function properly even with a crew because ,among other reasons, the RM produced by the crew will be less than 1/3 that produced by the altitude controlled foil system automatically in max conditions. You could experiment with a multifoiler that had a single wand controlling both mainfoils but the thing would probably be unsailable because as the crew moves to weather the lee foil would not be able to develop the extra lift required and the lee side would sink.It's the same exact princible demonstrated on any cat that fly's a hull: the displacement on the lee hull approximately doubles when the boat flys the windward hull.There is no 11' arm unless there is buoyancy or dynamic lift on the lee hull; the dynamic lift on the LEE hull MUST increase as the heeling moment increases.
    A multifoiler, with fully submerged foils, MUST use a dual altitude control system or be flown manually.
    2) The 'heeling to weather technique" has been PROVEN in actual conditions on the Moths-it is not theory but fact.
    3) You said: " The foils could be limited to zero lift.." Huh? Hard for a boat to fly with zero lift! The fact is that you need an altitude control system: wands, feelers or manually controlled joystick- all of which have worked; without one of these a fully submerged foiler will not fly.
    4) the multifoilers evolved with the crew in the center because of a desire to keep weight low and a realization that on a boat with two independent fully submerged foils the RM generated by the foils would be far greater than that generated by a crew considering the extra weight of a place for the crew to sit and for the dual side to side control systems required.In fact the thing that allows the high top speed on the Rave and Trifoiler is the virtually unlimited RM developed by the foils.
    5) A three foil surface penetrating foiler could be sailed just using ballast because the foils adjust automatically for the load at any given speed . It would also be able to be built very lighty compared to the fully submerged altitude controlled foiler.And it would always sail at minimum wetted surface(for a three foil system).
    But it has a -perhaps- fatal flaw: ease of ventillation caused by the proximity of the high lift area of the foil to the surface. In the Moth class this "multifoiler" configuration was tried
    and did not perform -upwind or downwind -as well as a two foil monofoiler.
    Your Foil Cat™ -assuming you realize it needs independent altitude control systems and you realize the foils most certainly must lift- would be a fun little boat -and with any luck maybe a little faster top end than the Rave with earlier take off. But a monofoiler would take it around a course in 8-15 more than likely...
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