Sailboard rig

Discussion in 'Sailboats' started by AleX`G, Aug 10, 2006.

  1. AleX`G
    Joined: Jun 2006
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    AleX`G Junior Member

    What are the benefits of the sailboard rig.
    I heard that the shape is very good. I like the wishbone boom idea but how do they actually work.
    Is the boom pivoted on the mast in the vertical direction?
    Then a rope is used to pull down the boom at the back to tension the sail.
    Does the sail actually produce more lift or does it just have a more favourable L/D ratio.

    In other words is it better than a jib and mainsail?
     
  2. frosh
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    frosh Senior Member

    Hi Alex, (you again), First of all sailboard rigs work best on sailboards, and have been tried on conventional sailboats with very limited success.
    To answer your specific questions first.
    The boom clamps around the mast on modern rigs and has little ability to swivel around this connection, although it "gives" a bit.
    There is no line from the rear of the boom tensioning the boom downwards.
    It has better L/D ratio than almost all other rigs except possibly a very sophisticated wing sail found on a C class catamaran.
    It would definitely be more efficient than a main and jib.

    The sailboard sail is controlled by the arms and body of the sailor which is more precise and quicker adjusting than a mainsheet system.
    The rig is often canted with the head of the sail well to windward. This means that the resultant lift vector is forward and upward, which unweights to an extent the entire sailboard. This has the effect of reducing the all up displacement of sailboard and sailor while sailing quickly.
    The mast produces almost no turbulence onto the luff of the sail on high quality rigs due to the pocket luff design.
    The twisting off of the upper 40% or so of the sail works almost perfectly and automatically to wind pressure reducing induced drag forces significantly. :)
     
  3. Doug Lord

    Doug Lord Guest

    Sailboard rigs/derivations

    Alex, sailboard rigs have certainly led the way in performance and especially high speed sailing . Barry Spanier designed the rigs on Russell Long's sailing hydrofoil "Longshot" based on his extensive sailboard sail design experience.(He has also agreed to consult on the aeroSKIFF 14 rig, see below) The square top main was seen first or close to first on sailboard rigs. But the most significant advances in sailboard rig design started out with "RAF"(Rotating Asmymetric Foil) design that addressed the serious problems of mast disturbance on the lee side of a sail. Later, "camber inducers" were used that allowed the sock luff to be designed so that the windward and leeward sides of the sail were smooth. The camber inducers started out as little plastic and cloth devices and have progressed to molded plastic units into which a full length batten fits. Camber inducers help to lock in the draft in a sailboard sail. Sailboard sails are also designed for a very narrow range of wind speeds and for different types of sailing such as course racing, wave sailing ,speed sailing etc. These different types of sail mainly vary the aspect ratio.
    In the last few years the Moth class has used camber induced sails similar to the windsurfer sail but w/o the wishbone. Moth Foilers are arguably the fastest or close to the fastest sailboats under 20' beating much larger cats,skiffs etc. At Moth speeds- like at sailboard speeds- the camber induced sail has tremendous advantages over a "normal" rig.
    On almost every sailboard rig I've seen the wishbone is tied to the clew of the sail with an adjustable outhaul like any other sail; the lines are run up each side of the wishbone to allow some adjustment while sailing. Because of the rig design and placement of the wishbone sailboard rigs do not require boom vangs with the out haul doing some double duty.
    Here is a bit on the Wylicat( Jim Wylie) design that uses what is called a "choker" on the wishbone to vary camber in the sail instead of
    an outhaul:
    Wyliecat Performance Yachts: Rig FAQ
    Address:http://www.wyliecat.com/info/wishbone_rig.html Changed:6:46 AM on Sunday, August 3, 2003
    -----------------
    I'm using a variation of a wishbone /sailboard
    rig on a new model(F100), on the aeroSKIFF 14 and on my new personal boat. The idea is that the wishbone is parallel to the deck like a normal boom but allows the sail to come all the way down to the deck like it does on sailboard with the rig raked aft. But on my version the mast doesn't rake very much(compared to a sailboard rig) so I wanted some way to get at least the forward third of the sail down as close to the deck as possible to reduce drag. Since the wishbone on my system is not being used like a "normal" wishbone it still needs a vang which is actually a double vang with lines diagonally from the mast base to each side of the wishbone. Another variation incorporated in this system is a midboom mainsheet connected to a carbon tube fixed between the two sides of the boom. When a sailboard TYPE rig using camber inducers and a square top planform is adapted to boats such as the Moth (and the new Hoot) it has to be different in that it must function over a much wider range of windspeed than a typical sailboard sail-but the sailboard designs have and are inspiring a new look at main only rigs particularly on very fast boats.
    I've experimented a bit recently on a small camber induced rig for an rc model but it doesn't work well yet- it IS ,however, an area very much worth working in for fast rc boats particularly when combined with a square top planform and modified wishbone that allows a practical deck sealing main.
    Are you considering a sailboard type rig on your new model?
    --------------------
    Here is the aeroSKIFF14 sailplan-note that the boom appears to be a normal boom but the forward part of the sail actually comes down thru a wishbone boom; on the proto,the F100 and my personal boat the portion of sail that comes thru the boom down to the deck would be about double(back end twice as far aft) what is shown here:
    Address:http://www.boatdesign.net/forums/attachment.php?attachmentid=5297&d=1141571544 Changed:10:12 AM on Sunday, March 5, 2006
     
  4. Andy P
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    Andy P Junior Member

    I've used a sailboard rig for testing purposes on my IC ( int Canoe ), but it's not really suited to the boat.
    The advantages are low drag, easy handling, especially in stronger winds, but there is lack of power in light winds.

    There is low righting moment from a sailboard sailor, so the sails are tuned for depowering early, but staying controllable.
    Sailboards usually select the sail size for the conditions, so the sails are generally only suitable for a limited wind speed range.

    On a dinghy ( when one sail has to cope with 0 - 25kts wind ) with much more RM, the sail opens the leech too soon, and is underpowered and wont 'point'. ( no leech tension )

    My new IC rig is similar to board sail in that it uses camber inducers, pocket luff, but is stayed, with conventional boom ( like int moth sails ).
     
  5. AleX`G
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    AleX`G Junior Member

    Yes doug I am very interested in these modern aproaches.
    I like the wishbone boom.
    I am just concerned about how diffficult it will be to make a model with the correct shape.
    So does the sail actuall act like a tensioner on the boom and pull it down. and then you can adjust the camber with the outhaul?

    Any help you could give me especially on the model side of things would be greatly appreciated. Im going to try and get some proper designs drawn out when i move into my new house next week.
     
  6. CT 249
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    CT 249 Senior Member

    Andy P is the closest to my experience.

    However, there's a tendency to think all sailboard rigs are pretty much the same, when it seems there's actually maybe as much variation between them as there is between a 470 and a 49er (or more?). A "normal" sailboard sail these days is probably a slalom/freewave cut (in the smaller sizes) and a Formula cut (in the larger sizes). These are designed strictly for planing conditions in a situation where actual area is not measured (and people pay by size not by performance) and where people change sails for the wind and always try to be overpowered.

    Therefore they are big and flat (for the windstrength), they twist off enormously, have an amazing feeling of low drag and sideforce (which is vital in boards which have a high top speed and depend on small-ish fins for lateral resistance), have a high top speed, and are utterly gutless when it comes to low-end power and pointing.

    Longboard sails, on the other hand, are cut with much more depth and less twist (although less depth and more twist than they used to have, because people pump these days). They are designed for a larger wind range, and actually work OK in terms of pointing and light-air pace. Upwind in light winds on a longboard they seem to be competitive with "normal" windsurfer sails of 1-2m bigger. In strong winds the smaller sail gets you round the course when the big-rig guys are swimming.

    Put a Longboard sail on a slalom board and you'll go quick in marginal planing conditions (for the sail size) but have a low top speed and really struggle to get upwind because of the higher drag and sideforces overloading the fin. It's a really graphic way to drive home the relationship between drag and upwind sailing.

    The boom doesn't sail doesn't pull the down much, just out. The wishbone acts as a vang, which is actually a pain at times because you sometimes wish you could induce twist while keeping the outhaul tight, as you can in with a conventional rig.

    The camber is adjusted with the outhaul, and with the downhaul. The downhaul acts like a 49er's downhaul, using compression to induce bend that flattens the sail, especially in the head. Much of the depowering seems to be about keeping the centre of effort stable so the back hand doesn't get overpowered, which is largely irrelevant in a boat.

    I don't know how much the lift from the sail affects the board. A good longboard starts out-performing something like a seahugger Moth in conditions when the rig is still vertical and the amount of lift is negligible. I've had coaching from a world champ and Olympic medallist who tells me to keep the rig vertical as much as I can, rather than raking it, and some FW sailors do the same thing. Then again, the ex Olympic team member who beat me in one nationals sails upwind in a big breeze leaning back at 40 degrees or so and he goes like stink!

    Moths and Renjolle and Canoes have been trying pocket-luff fathead/squarehead sails that were effectively camber induced for decades. One of the guys involved in the Moths was a scientist of international renown (although not an aero), so the theory was probably OK. However, the rig was dropped for simpler designs, and the modern CI rig apparently only has a small margin. The windsurfer style sails also suits the Moth style of boat, as the top Moth sailmaker says it doesn't really work in the same way in planing hulls with a big "hump" and a hunger for more power.

    In summary- can perform OK in dinghies if you get a longboard racing rig. Cheap second hand. Can be hard to get the rigged rig in the dinghy. Shortboard sails are designed for totally different purposes. I'm still not sure whether they are actually the massive advance over dinghy rigs some windsurfers say. Underlining that is the fact that in the sort of stuff dinghys sail in (light or fluky) the "Mk2" version of the original Windsurfer (mylar 6m with just one full batten and two short battens) can often beat the modern Olympic RSX with 8.5m of monofilm, battens and camber inducers.

    The sailboard rig really does well in some conditions, but to say it's inherently better seems to be a bit like saying a Formula 1 car is better than a World Rally Championship car; one has a higher speed in perfect conditions but can't even look at getting around courses the other does quite happily.
     
  7. gggGuest
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    gggGuest ...

    That really is a no-go n the dinghy style rigs. Its been tried time and time again and the truth is that you just don't have enough control over the leach with the combined outhaul/vang etc. Its one of those things that you really think ought to workfor the simplicity and everything else. but just doesn't.

    Loads of concepts and ideas are transferrable both ways between sailboard and dinghy rigs, and these concepts and ideas have been transferring both ways ever since sailboards started (and for that matter to and from microlight aircraft which also, in their soft wing incarnations also have a lot to offer). Plenty of sailors and sailmakers do both after all. There's this big myth that sailboards and sailboats are entirely different worlds with no relationship, but it's just that, a big myth.
     
  8. AleX`G
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    AleX`G Junior Member

    Well i think my boat is going to need quite a large displacement.
    Min weight = 2kg
    max sail = 2000cm2
    those boats on the wyliecat site looks so good though

    Im just trying to go through every possibility for my model boat and hopefully gain some knowledge on the way.

    Are there any advantages to twin masted boats.
    I heard alot of the lift comes from just behind the leading edge so it would make sense to have 2 masts to maximise that edge.
     
  9. frosh
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    frosh Senior Member

    Hi Alex, you will strike a dead end trying to adapt a wind surfing rig to your model deep keeler. I don't believe that any forum members will give you encouragement to pursue this path either. It is a bit like trying to fit a Jet Ski propulsion system to a small heavy trailer sailer. It is just not going to work. Why don't you decide to stick to what you seemed to like before, the rigid wing sail with articulated flap? BTW two rigs are much less efficient than one if the maximum sail area is restricted. :)
     
  10. AleX`G
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    AleX`G Junior Member

    Because lots of people were saying it will be way to hard to control.
     
  11. Doug Lord

    Doug Lord Guest

    sailboard rigs

    Alex, a careful reading of what has been posted here will show you that there are certain elements of a sailboard rig that may be adapted to rc sailboats. The value of such a system will depend on many factors including Reynolds numbers. However, there are many elements that we know work at this scale: square top mains(and their automatic gust responce),adjustable upper outhauls, getting the sail as close to the deck as possible and a wishbone boom(used a little differently as explained earlier). Since a camber inducer helps hold a sails shape it MAY have benefits in models as well if solutions can be found to "popping" the battens. Many experimental rc rigs have explored sock luffs and also precise gaps between the back of a round mast and the leading edge of the main(see Lesters site).
    I think a camber induced ,sock luff , rectangular planform rig with relatively high aspect using a "gaff" (as I showed you earlier), and using a wishbone to allow the sail to be brought right down to tbe deck will prove to be a fast main on any type of rc raceboat that allows it. The camber inducers are the only question right now-at least for me: I haven't been able to make that part of the system work well yet.
    In light air you'll definitely benefit from a jib but a square topped jib(attach the forestay to the"gaff" about 25% aft but have this point adjustable) with adjustable upper outhaul works and should be considered as should getting the sail as close to the deck as possible and using a "radial jib fitting"(or JPT-jib pivot traveler) that keeps the forestay on the centerline(improves pointing compared to "normal" rc jib attachment).
    Depending on your time available you can experiment(with a camber induced system and square top jib) or just go with the modern improvements to a typical rc rig that we know work at this scale as mentioned above.
    Highly Experimental Square Top Jib on my 16' hydrofoil rig:
    Address:http://www.monofoiler.com/images/aeroskiff_trial009.jpg Changed:11:06 PM on Friday, October 31, 2003
     
  12. AleX`G
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    AleX`G Junior Member

    To be honest i like both systems (flexi sail like dougs designs and solid sail wing designs)as they both represent cutting edge in both fields.

    With a wingsail the sail could vertually touch the deck as no main sheet would be required. Also i like the way with the wing sail that you can alter the camber in the race without having to adjust lines. You could also set the desired twist before the race. The only downside is how dificult to control the sail would be on a model. And the build difficulty.

    Dougs idea alows lots of adjustment pre race which would allow efficient settings to be set. And also have the wing tip gust response. Also its easier to build and more forgiving in a remote controlled race.

    Bearing this in mind it boils down to this question.
    What is going to be fastest in ideal conditions
    and what will be the most reliable system in terms of power in varied conditions.

    I would say the wingsail has the speed advantage in better conditions on things that i have reaad but the gaff style rig is probably more reliable.

    Time will also be a limiting factor so i feel i am heading towards the flexi sail for ease of build although i expect it will be nowhere near easy. As Id rather get more practice in thean less due to my lack of sailing experience. Also practising adjusting the settings. Doug would you mind sharing some of your actual construction methods with me If you do not wish to do so publicly you could PM me. Id definately give the square top main and wisbone boom a go. But what exactly is the benefit of square top jib.
    Or is it just the same as the gaff style main to allow more adjustment of the camber?

    Now I really have to focus on final design and planning my time and setting targets for myself. You really can go on for ever with these discussions :)
     
  13. tmark
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    tmark Junior Member

    I'm curious Alex, how is your project progressing? Have you got any pics / drawings that you may to share?

    Regards, Trevor
     
  14. AleX`G
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    AleX`G Junior Member

    Yes I am writing this from schooln where im meant to be making the boat ;).
    I have constructed a test wing for the wing rig. It is a balsa rib type job like model plane. I am planning to cover the leading edge with fibreglass or CF.

    But on the final version i will probably make it out of foam.
    I would have done this in the first place but the school just bought a new wire cutter so i can cut the foam fast and accurately.
    I have also made the flap. And a small program which worksed out the shapes of the ribs.

    I would post some pictures but i have 56k at the moment at home and the school wont let me upload stuff.
    I plan to start making the hull at the end of october.
    The pivot point will rpobably be some kind of bearing out a drill or rc car.


    Thanks Alex
     

  15. frosh
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    frosh Senior Member

    Hi Alex, good stuff. Remember we discussed the solid foam wing with articulated flap quite a while ago. If the finances allow it, sheath the foam on one layer of CF but fine stuff, not the readily available 200 gsm weight. I think that around 80 gsm is available, except it is expensive; but hey you dont need much, as it is only a model. Good luck, and may the best yacht win. :)
     
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