Sailing Dinghy Design

Discussion in 'Sailboats' started by Tim B, Mar 12, 2003.

  1. Doug Lord

    Doug Lord Guest

    Retractable Foils

    astevo-it seems to me that a well thought out retractable main foil that blended in with the bottom shape when retracted could be the answer to an allround foiler: good in lite air thru heavy air. The concept could be applied to a hull like a 14 even easier.
    The design challenge is to be able to retract the foil simply (a daggerboard within a daggerboard; the outside board supporting the foil that fits flush with the hull bottom when retracted;the "inside" board used in non foiling conditions.) ; with a lot of work I'm certain it could be done. There would be no multiple configurations just a transition from displacement(?) sailing to foiling by lowering the foil. Simple and possible.
    The hull width on a Moth presents a problem with some retractable ideas whereas the 14 lends itself perfectly to a main foil that disappears when you don't need it.
    I don't think multiple configurations are needed or desirable: just one simple easy to use disappearing mainfoil would make a true all round foiler...
  2. Guest

    Guest Guest

    foiling facts

    Sure there is no reason why the International Moth class could not ban anything as it has done before. I think the reason so much time has now passed without a big uproar is that maybe there is some good in the foilers.

    I do not believe that the foilers have affected class numbers at all! it just a convenient thing for some to say. The class like many classes has problems keeping thier numbers up.

    Moths are not too difficult to sail, it just that you have to learn to sail them, it's a skill like you would learn to windsurf or ride a bike. Most of the fleet are very good at it and sail around easily, sure there is a capsize here and there but they only take 30 seconds to right and sail on. Most of the time they are sailing them as any class would. Watching for other boats, wind shifts etc. For some reason most sailors are not too keen to learn new tricks. Unfortunately the current moth designs have led them to the narrow boats they are which I feel may be the real reason for numbers dropping.

    Foiler development is still in it's very beginnings and if they can do what they are doing now (like winning a worlds heat by 5 minutes) then imagine how things will be 5 -10 years.
    Their current foiling wind range is approx 12-20 knots (8-9 knots wind on reaches) , so to foil in winds down to 7 knots and improve handling in strong winds is very achievable. What classes don't start to have handling problems in winds over 20 knots?
    Rohan had only used his foils two or three times before the worlds and prior to travelling there he did not think he would even use them for lack of practice. I think third was very good considering the learning curve during the regatta and a DSQ too.

    If foilers take the next step then you do not need these narrow hulls anymore, would'nt that make them easier to sail? Faster and easier, would it really be a disaster. The current boats would not be obseleted as they can foil too, nor have they been devalued.

    The A class scenario, it was Brett Burvill sailing past one on a reach with the wing mounted design moth foiler. Sure an A class is probably faster overall, for now! Remember as the wind and waves pick up so does the wave drag on water born boats, but a foiler does not see the waves, it just goes faster. Rohan has a GPS on his boat and in 15 knots of wind reaching he is consistently sailing at 18-20 knots boatspeed.
  3. John ilett
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    John ilett Senior Member

    Last message posted by John Ilett.
  4. astevo
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    astevo Junior Member

    i wasnt at the worlds so i dont about any attempts to ban foils outright, my previous poats was related to the ideas of having multiple foils for different wind strength. i much prefer your system which self regulates height/lift.
    Have you given any thought to the retractable ideas? The only problem i have with the foils in the current set up is the fact that they seem to suffer greatly in the light airs. I know many have problems with foilers in general (i dont) its just im not sure about what happens in the marginal conditions. If they were more compeditive in light air they would surley be accepted by most (at least i hope so).

    cleary there is the possibitlity of furthre development and i would hate to see the situation where foils are banned. What i do hope to see is that the foils must stay on for a reagtta. In the last agm there was an ideaof a one equipment rule. im not sure whether the intention of this was to ban foils or to limit a problem of multiple rigs which at the time did not exist. i voted against this as did the majority, so it didnt get up. i do however feel that the foils should be used in all winds. this would foster development at a greater rate simply by creating a focus on low speed marginal foiling conditions. once the foils can be used in all strength their popularity might be extended.

    im dont think it is the foiler discussion that has reduced numbers. In fact id say there are more people with moths now than for a while recently. the excellent production boats from John and Mark thorpe have brought stability to the class and as a result the fleets growing in many states due to people wiling to spend up on a new boat without the fear of it being obsolete the next year.
  5. Ian Ward
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    Ian Ward Junior Member

    I am really glad that you have recovered the discussion to a reasonable footing. I think it has gone off track recently.

    While this is my first contribution to this forum, I have been following its path for some time. My qualification to comment is as a life long Moth enthusiast, designer and builder, International Moth class world president for 10 years, 2nd in the Moth worlds twice in Scows, survivor of the Moth Scow -> Skiff transition and was the first to introduce both wing mounted foils on Moths in 1997 (Trifoiler style) and Centreboard/Rudder foils in 1998 (first ever Bifoiler). Am still developing foilers and have just succeeded in sailing the first ever "Unifoiler" Moth last weekend.... yes, that's right, only one foil in the water!.

    I find this to be a really good design discussion forum site but this particular discussion has run out of steam a little, diverging to some crazy, ill informed statements. The main reason seems to be that it is just that, a discussion, rather than a place where new ideas are shared. In fact I really wonder if there are many new ideas out there at all? Most contributions seem to be simply confirming what is already known. This is of course important, because there is a lot of misinformation about what really matters in design.

    Discussion about Moth rules and popularity etc should be handled on the Moth website and is the concern of the Moth class. In the interim,
    I think Moths are the ideal test forum for foilers as they are a state-of-the-art class already. If you can't beat a current Moth in all conditions in a regatta, then it is not a real improvement! This is a far healthier scenario than for most other class developments where a manufacturer generally comes up with a slight bigger version of an existing class and makes it one design. Of course it is a little faster ...sometimes...., but there is no competitive yardstick. Many of these developments are actually backwards steps, but there is no valid comparison available.

    I would like to propose we begin a completely new thread, to encourage a collaborative group to actually design a new boat (a bit like Linux) where we split the contributions into Hull, Rig, Foils, class rules etc and discuss each separately but in detail and with a common aim in mind. Perhaps it could be a big Moth singlehander or an open two man 14. Do you think this could work?. We would then hopefully move from conjecture and existing class prejudices to real design contributions and perhaps encourage people to build, test for themselves and contribute the results.

    To get things going I would like to share some thoughts, new ideas and experience....
    I have recently modified an old non-winged scow Moth hull, placed a single foil on the centreboard and a retractable surface running foil at the bow. No rudder T foil at all. Total cost of materials to make the foils is about $200, even less if you simply modify your existing centreboard!.
    I took it out last Sunday and got it up and going in about 10-12 kts of wind. There are many things to improve yet, but in principle it all works fine, no capsizes and some good bursts of speed on reaches!. It is really amazing to realize it is possible to sail with only ONE foil in the water!.
    The principle is not new, Rich Miller has a sailboard already doing 35 kts with a similar arrangement. This is just the first application to dinghies. There is a long way to go yet, but 35kt Moth is a real possibility...that should really set the A class discussion to rest!

    This means it is possible to use existing, old boats and adapt them to foils. I see no need for a new range of specialist hulls just for foiling. In fact some of the older and more stable hulls may perform even better as they are still good in light winds. It is also relatively cheap to make the necessary modifications. The boat is launched in the same way as a normal dinghy. In conclusion, it is indeed possible to have a low cost, high speed, easy to handle foiler suitable for begginers and speed demons alike, which should put to bed all the conjecture that has been rasied about foilers to date.

    In my opinon, most of the fears about foiling come from not being able to imagine what is possible, not actually having a go and even worse, doing nothing to actively develop a solution! Some of those who looked at the original Brett Burville foiler Moth contraption were horrified at its ungainly, impractical but fast foils and immediately wanted to ban these from the Moth class. It is only with imagination and some real drive from the Isletts etc that we have made real progress, and I am sure there is a lot more to come in terms of simplification, speed, handling and low cost! There is only one way to find out, I encourage all of you to give it a go and develop your own solutions!

    I believe the International Moth class should be proud to be the only class prepared to allow foil development.
    Without such an open forum, Moths would have remained Scows and foiler development would have ceased at Trifoilers.
    In the long run I am sure Moths and all future classes will benefit. You can't sit around on a displacement hull forever and still say you have the fastset singlehander! The alternative is that foiler development will continue, bypass Moths as sailboards have done and a new, much faster foiler class will emerge, perhaps even surpassing the Moth in numbers. Who would want a difficult to sail, short, slow narrow skiff .......would then be the argument!!

    I agree completely with the contributions of John Islett, Doug Lord and Andrew Stevenson.

    Looking forward to some new contributions, fresh ideas and building activity!
  6. Doug Lord

    Doug Lord Guest

    Foiling Dinghies/ retractable foils

    Ian and John or anybody else that might know: are there any older, wider Moth designs that are competitive with the skinny Moth in light air up to say 8-10 knots of wind?
    Sounds to me like Ians idea-- especially with at least a retractable bow surface foil-- and maybe retractable daggerboard foil could be just the solution.
    Whether on Moths,14's, a new boat or a canting keel foiler the solution seems to be to make the foils disappear in light air.
    With that solution- which looks awfully close to me- then the boat goes from a basically external system added on to a fully integrated 100% all round sailboat that just happens to be extraordinarily fast! How can anyone resist such an exciting prospect for Moth's, 14's or "other"??
    I mean if you sail or want to sail current semi glued to the surface"high performance" dinghies you obviously love speed under sail-why sail a double trap 14 with an asy spin otherwise? Or an A- cat ? Or a 49er etc.
    Since speed under sail is what really excites everybody that races a sailing dinghy whether they admit it or not shouldn't the design of a new, modern high performance dinghy focus on the practical adaptation of foils to the boat in a way that allows a smooth, easy , simple transition in modes from light air to foiling? Whether it is LEGAL now or not in the I14 class the work done here with contributions from everybody MIGHT just push the design envelope far enough to prompt a serious examination of the results by all high performance development classes. I think that would be a hell of a great contribution to sailing dinghy design as well as to sailing technology in genaral:instead of an incremental jump in performance we could ,perhaps, contribute to a huge leap in the technology of sailing fast....
  7. astevo
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    astevo Junior Member

    good to hear from you.
    just quickly a few questions
    - do you still use the y foil that miller uses?
    - also in the miller article he talks about having to unroll the foil from tack to tack. Is this necessary in the scow where the righting moment is larger and you dont have to worry about the ankle stresses that occur on boards?

    in all this are we looking to design new boats to new rules? or is the objective to create a really fast boat within existing rules. Untill recently the discussion was based around designing the ultimate moth or I14 and for my part this is what i am concerned with.
    essentially if you have a mono foiler the existing problems with the moths being too short are negated , the feeler has to be within a few metres of the lift anyway, sure a new class could have some more sail but ideally we are talking about developments with yardsticks as you said. if you change too many variables you can never be sure what makes the boat go fast. clearly the moth is an ideal test bed

    ive said it before but im still concerned about foiler performance in underpowered conditions. Most of us know that Wardy was foiler champ back in the day, so im interested to hear what the performance was like when the boat wasnt foiling.
    i made some drawings of a similar concept about a year ago but i never got into the details of making it workable and so, like many things it never got built.

    how about bringing it down to balmoral so we can all have a look?
  8. Ian Ward
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    Ian Ward Junior Member

    G'day Stevo,
    I used a Tee foil because thats what I had available at the time. Am right now building an inverted Y as it gives lots of advantages, all outlined by Miller in his article at

    I tilt the foil and keep the sensor horizontal.
    This means that I do not need to retract the foil as it has about the same area as a normal scow centreboard and provides all of the necessary lateral resistance in light winds. No extra drag as it is raked neutral with no lift in the light.

    Actually, when going upwind in light winds it feels really good, even compared to a normal scow. Can't tell if its faster, but it is certainly not slower. Much depends on the angle of attack setting. This is no different situation to the extra drag of a Tee foil rudder on a skiff Moth.

    When foiling it is canted to leeward, give extra righting moment and the lift gets me foilborne.

    No need to discuss rules etc really. This is a non-winged scow with an odd shaped centreboard. Complies entirely with existing Moth rules. Even pre-wings rules. It is not intended to be a new class and could be used on 14's if they were interested.

    I will now set up the inverted Y foil before racing. As you may guess, there are many small things that need to be tested and adjusted to get everything working smoothly and under control in all winds...a long way to go yet!
  9. tspeer
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    tspeer Senior Member

    As you wish - see "Foiler Design"
  10. astevo
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    astevo Junior Member

    assuming that you are steering with the canard foil, how big a fin have you put on the bottom of the canard?
    im assuming that you steer the canard as it would be easier to do, and also it allows for the boat to pivot on the rear foil which can actually provide some side loads.
    you said that the foils stay down at all times, im wondering what the drag of the pointy canard is like when fully submerged.
    especially if it is supported by a blunt strut
  11. Ian Ward
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    Ian Ward Junior Member

    Hi Stevo!
    It is always dangerous to assume.. :)

    Steering is with a normal rudder, the boat came with one and it is really easy to use.
    A stern rudder tracks and is balanced, a canard is inherently unstable and would require positive steering at all times. A canard would however be more efficient in terms of surface area, especially with a 30 degree forward raked stock, so that it is used only for lift when steering is not required and provides progressively more steering moment when turned.

    Yes, the foils stay down but I do not use a pointy canard, it is an eliptical standard foil section pivoted with a string adjustment of th eangle of attack. With no tension, the canard runs neutral with almost minimal drag. I have a supercavitating canard, but it has high drag in light winds and is only suitable for consistently strong breezes.

    The canard strut is an aluminium foil section, with relatively low drag (470 spreader), far from a blunt strut!
  12. Andy P
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    Andy P Junior Member

    I’ve just discovered this forum ( linked from the AUS moth site).

    I'm Andy Paterson, designer and bulder and sailor of Int Moths and Uk Cherubs.... and the first foiling moth in 1994
    Bringing the topic back to dinghy design ( my foiler postings later on the foiler

    attached lines for Paterson 7 UK Cherub... current and 3 of 4 recent UK
    Notable for slab sides and flat floor with low chines to the bow.
    This gives fine entry, all the way to top of the stem
    The boat is early planing, and very fast in light winds and downwind in all
    conditions vs other cherubs.
    The upwind performance in a blow has not been so good, which I think is due
    to our crew weight of ~ 20 stone vs the faster boats with 26 stone.
    But on a series average, it is faster.

    I find that nosediving is a concern but not a problem. The fine bow has low
    drag in a dive, so the boat doesn’t slow too much, the apparent wind stays
    back, and recovery is likely as long as the crew stays back.

    The disadvantage of the shape is that it needs to be sailed very flat or
    preferably heeled to windward if conditions allow.

    The lines are a completely different to the 12 footer lines earlier in the thread.
    The Cherub is relatively low power, so the flat hull shape works well.

    Andy P

    Attached Files:

  13. Phil S
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    Phil S Junior Member

    UK Cherub

    Do the UK Cherub rules require the solid flares? They seem to be cumbersome to build compared to moth wings. They also appear very low and subject to wave impact.

    There was at least one NZ 12 built like this last year. I beleive it was only just off the pace.

    The standrad Woof type 12ft skiff hull is unusual compared to every other class. I am not sure even the 12 people really know why they developed that way. My interpretation goes a bit like this. The kite on the big bow pole means heaps of lee helm. The most comfortable way to balance the helm is to heal the boat over. Most other hulls would then go like a dog. But the deep flared 12 hull changes from a narrow canoe to a flat planing shape as they are healed so they can still go fast. At the same time the wide planing shape provides a more stable platform as well as moving the supporting volume further to leward, increasing righting power.

    They do not always sail healed over but when needed to get up to a mark or headland it seems to work very well.

    It is amazing what a good designers can achieve when they are not hobbled by silly rules.
  14. ggggGuest

    ggggGuest Guest

    Cherub Rules

    No, the Flares aren't a rule requirement, boats have been built with frame type wings and with concave flared topsides. The flares are probably lower aerodynamic drag though, and don't really seem to hit the water. Constructionally its a straightforward way to achieve a large chine angle to the topsides and get the beam, without the business of attaching tubes or whatever. Andy's boats don't have any side decks, the helm just sits on the inside of the flare, hence the shallow angle.

    A Woof type, given a vestigial chine could be made to measure as a UK Cherub, they're not poles apart, but conventional wisdom is that the more vertical topsides are superior on a (relatively) small rigged single string boat where you're more often hunting for power and its easier to keep the boat flatter.

  15. astevo
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    astevo Junior Member

    12 design

    Jim walsh had a bit to say about the 12's previously, but for what its worth here is my two cents.
    i think tht the 12 have evolved away from a flat bottomed boat because of safety. with out the chine they have less tendency to carve and launch you off as you lean over. also by having the narrow and heavily flared stern sections it allows for control downwind.
    when you watch a 12 downwind they have a visibly weird motion as they launch themselves clear of the water then land on the back of the next wave. essentially because of the flare you can sink the bottom as you land rather than skipping and triping over the wide flat area in the back of similar skiffs. this theory was passed on to me by a James Moore, who had sailed aus cherubs then won a championship in the 12's.
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