WishBone Sailing Rig

Discussion in 'Boat Design' started by brian eiland, Aug 17, 2003.

  1. sharpii2
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    sharpii2 Senior Member

    I don't completely understand what your goals are.

    Are they to get the mast off the cross beam? End up with a giant jib?
    Or something else?

    IIRC, a Tornado has a 3/4 fractional sloop rig. Such imposes very little stress on the hull structure for its performance capability. The main issue is holding the mast upright and maintaining adequate tension on the jib luff.

    With an 'A' frame mast, you can have a clean luff on the main as well as the jib and, perhaps get better performance. But the long main luff needs to be to be held tight as well as the jib (with much greater tension, due to its longer length). This may end up putting more stress on hull structure rather than less, even with the elimination of shrouds.

    A compromise would be to put ladder rung like spreaders between the two legs and run a much narrower spar up across them, between the two legs.
    To this, the mainsail could be attached.

    Now you have eliminated the long, unsupported, main luff and replaced it with a spar with a much smaller cross section than the original mast. This might provide some performance improvement at the expense of greater top hamper.

    A third approach is to go with a tripod mast, with the main, sail carrying portion, running up from the very bow and canting aft so the mast head is even with the transoms of the boat. Two shorter legs come up from each side of the boat to meet the main leg somewhere near its mid point.

    To the long center leg, the roller furling sail is attached. Viewed from the side, this looks like a very tall lateen sail.

    Now you have eliminated the very tall 'A' frame, the spreaders, the narrow spar between them, and the jib stay. You have replaced them with a thicker spar in front of the sail, giving up some performance, but have reduced top hamper and have all but eliminated sailing stresses on the cross beams.

    Now you have a single sail, which may make up for some of the loss of efficiency.

    The biggest advantage of this rig will be raising it. A block and tackle could be placed at the apex of the two shorter legs to raise the longer center one. These two shorter legs could be set up to pivot fore and aft. Pulling on the block and tackle will cause the two shorter legs to pivot upward and raise the long center leg as well.

    This would be a revelation in simplicity compared to raising the more conventional rig. It could be done safely even in a strong cross wind.

    Most likely, a more conventionally rigged Tornado will beat you in any kind of a race, though.

    I don't think what Brian did would work with your boat. Going with the bipod mast eliminated the need for heavy shrouds very long spreaders, not to mention the downward loads they would put on the wing deck. But he still has back stays and back spreaders to hold the jib mainsail luff tight. No doubt, the wing deck and hulls were designed and built in anticipation of the loads these would impose. Not so with your boat.
     
    Last edited: Oct 24, 2011
  2. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    Just want to point out another advantage of A-frame rig: there's no mast stuffing up the view from cockpit or saloon (see below), and on Catbird Suite, there's no boom either. See

    www.damsl.com

    Barbara likes that at the wheel.
     

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  3. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    And there's no danger of bashing by boom when you poke your head out for an even better view:
     

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  4. brian eiland
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    brian eiland Senior Member

    Alternative Rigs

    High Tacker, you certainly make a good case for alternative rigs.

    And thanks for all those great photos and explainations. I've been a little busy with other matters to keep up with everything lately.
     
  5. brian eiland
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    brian eiland Senior Member

    Masthead Detail?

    One question comes to mind concerning such a rig. Have you experienced any problems with the integrity of the junction at the masthead??

    Those are long lever arms that can excert lots of conflictng forces at the masthead, depending upon the individual movements of their bases at each hull.

    The single-hulled Procyon even experienced some such problems.
     
  6. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    Re: masthead detail photos below

    Hello Brian,

    Not very much ever escaped ol' Malcolm Tennant's attention. See pics below for his solution to stresses at the masthead. Each leg of the A has a sizable plate welded to it at the top, and these two plates are then bolted together. Note that the bolts have advantage of being scattered over some considerable area. I forget exactly how long the plates are, something like 1.5 m. Note that they are quite long relative to mast fore and aft section length. Note also the outline of black, which is the edge of a thick rubber gasket between the two plates to allow flexibility for some motion. Also, the boltholes are slightly bigger than the bolts. Malcolm said that if there was no such allowance for motion, then there would be a problem, stress cracks developing and so on. I think Procyon's problem was that there was a rigid connection at the top.

    Also, for flexibility at the other two corners of the triangle formed by A-frame and boat, the two legs of mast are stepped on pedestals, each pedestal on the corner of two very strong interior bulkheads (one fore and aft, one across). The masts actually are sitting in collars on stainless steel plates that are sitting on the pedestals with thick rubber gaskets providing flex between the plates and the pedestals, and the plates are through-bolted to chainplates on the interior bulkheads (that spreads the compression load, and can also take tension because theoretically one mast or the other could at times be in tension).

    Another allowance for movement is that the bases of the masts have rocker, in other words, the base of each mast tube is cut in a slight curve, so that the masts can actually rock, tilting fore and aft within stainless collars welded onto the base plates and through which collars the masts are pinned athwart ship. Sorry I don't have photos of the mast bases handy, am still traveling. To sum up, there is flexibility at the top and at the bottom(s) of the A-frame.

    To shape the plates at the masthead in the form of a bird, a profile of a catbird, was my idea. The catbird builds its nest in the highest tree around, is a predator who then swoops down on its prey. Hence the expression, to be "in the catbird seat" is to have a very big advantage, like, on top of the world. It is an American bird, and there is a famous James Thurber short story, "In the Catbird Seat". I took some liberties with its profile, gave it more of a hawk's curved beak, whereas a catbird actually has a straight beak. The boat herself has a suite of cabins and a suite of sails (all with pics of Catbirds on them), and she is my symphony, hence the name "Catbird Suite".

    More at www.damsl.com
     

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  7. Bendigonian
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    Bendigonian Junior Member

    Guys,

    One major advantage of the 'A Frame' has to be the possibility of mast lowering and possibly even folding in sections for motoring along rivers. Somewhere or other I found images of an 'A Frame' cat with, what looks like, the rig mounted on raised pedestals to keep it above head height after lowering.
    It's a bit hard to tell, the image is small and low-def, but it does look like there are hinges about 5' up.
    Does anyone know of this cat? My only info is the image name..'Dinghy trip 039.jpg and that it was seen on the St Lawrence.
    It also has what looks like an entrance in the front of the cabin to the foredeck, similar to the South African SMG-50+; another advantage when you don't have a big stick stuck in the middle of the deck.
    Update. I had a note from Phil who took this pic and put it up on BD a while ago, but he doesn't have any more info. Anyone else?
    http://sandhurstpublications.com/AFrame039.jpg
     
    Last edited: Nov 28, 2011
  8. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    Bendigonian,

    I searched my files and have only that same pic, labeled the same. It was sent to me by one of the guys at Dykstra & Partners, the designers of Rainbow Warrior III, along with some other examples of boats with A-frame rigs. I'm waiting to hear back from him about the second round of sea trials with RWIII, so will ask him then if he has more pics of the cat that you're interested in. You mention the SMG-50 and its forward cockpit with no big stick obstructing. In the pics below, it looks like the legs of the A-frame on the SMG-50 may be hinged at the very bottom. If I remember correctly, Procyon's A-frame also was hinged. And I'm pretty sure that Brian Eiland has posted pics of Procyon on this forum, probably on this thread.

    You've probably seen the SMG-50 website, but just in case, here's the link to the photo gallery there:

    http://www.sail-the-difference.com/home/english/gallery/number_one/
     

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  9. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    When we were designing the A-frame rig for my boat, Catbird Suite, the idea of hinging the legs of the A-frame for lowering did occur, but I was put off by the added complication, and cost, of doing it without weakening the rig. Besides, for cruising inland waterways, I'd choose a long, skinny canal boat covered in solar panels, a small wind turbine or two, and electric drive, instead of a big and beamy catamaran with sails. Horses for courses.

    Of course, to be able to lower the mast is an advantage, if that's what you want. Some of the A-frame-rigged boat designers have done that, but I think they've mainly chosen the A-frame for strength to support several furling sails, and the advantage of not having a mast in front of the mainsail, spoiling the air flow. And the catamaran designers among them were clued up enough to realize that with the beam of a cat you don't need booms. But, to my knowledge, all the other A-frame boats still adhere to the conventional, vertical, fore and aft, sail configuration.

    My main consideration in choosing the A-frame was for strength, stepped down through the hulls, to withstand the compression loading of lots of sails on furlers, since I consider roller furling (and reliable roller reefing) to be the single greatest development in sailing in the past couple of centuries. Second only to that was the idea that if some of the sails were on what I call soft furlers (no luff spars), that would open up many possibilities for experimentation.

    Not only does Catbird Suite have a very strong A-frame rig with 4 furling sails (and plenty of room for more), the deck layout allows for a number of unusual and advantageous sail configurations, in addition to the usual vertical, fore-and-aft configuration. I think of her as two proas leaning together. The mention of canted sails, as on a proa, usually brings to mind the boats that are out to break speed records. (See for example, the thread on Sailrocket on this forum.)

    Catbird Suite has a good turn of speed, but she is a big and luxurious cruising boat. And since cruisers typically are more interested in safety and good performance in light winds than they are in setting high speed records, I'd like to point out some of those particular advantages of proa canted sail geometry on a catamaran.

    The mainsail and staysail on Catbird Suite are on soft furlers so that they can be easily moved around and the tacks of the sails attached to different positions on deck, not just on the centerline of the boat as with conventional, vertical rigs. I use them on the centerline for short tacking. But they can be moved and their tacks attached to either side deck so that the sails can be canted into the wind for speed and lift, or canted away from the wind for ease of handling, peace of mind, ideal sail shape with no booms or poles, and good performance in very light airs without the nuisance and wear and tear of the sails continually flopping down in the lulls.

    On a long, passage-making tack, for convenience, safety in high wind speeds, and efficiency in very light winds, I attach the tacks of the mainsail and staysail to the windward side deck, so that, in combination with the genoa attached to the windward bow, there are then 3 sails, all canted away from the wind. The entire width of the boat is then available for sheeting, so that no booms or poles are needed in order to maintain ideal sail shape, all the way from close hauled through reaching to running.

    Cat sailors know that big cats are very unforgiving, i.e., the rig and sails suffer a lot of shock loading in gusts because there isn't the shock absorbing effect of heeling and spilling of wind as with a monohull. With the sails canted away from the wind as described above, the sails are already heeled even though the boat is not heeled, so that there is some spilling of wind in gusts. Of course, with a cat of this size, you don't fly a hull, indeed something would probably break first, but if she ever did start to heel, the spilling from the already heeled sails would be dramatically increased.

    See www.damsl.com and on the welcome page look to your left and click on A-frame Rig and you'll get my longwinded explanation of all the advantages.

    It is also advantageous in very light airs to have the tacks of the sails attached to the windward side and thus the sails are leaning away from the wind so that they set into proper aerodynamic shape by the effect of gravity, whereas, if the sails were vertical there would often not be enough wind to lift them into shape.

    You remember when sailing a little dinghy, when there is very little wind and your sail is just hanging there and flopping, you move your butt over to leeward to heel the boat a bit so that the sail will fall into shape. So in very light wind, as soon as I unfurl a sail, I'm away, while all those vertically rigged boats have sails hanging like so much laundry, all drag, and so are going backwards. Also, my sails don't come flopping down in the lulls; they're already "down" but are hanging in proper shape, and so maintain their shape, ready for the first breath of wind to come back. See the pics below for ideal sail shape in very light airs.
     

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  10. Spiv
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    Spiv Ancient Mariner

    A really good idea; how did you solve the sheeting for so many different tack positions?
     
  11. High Tacker
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    High Tacker Junior Member

    High Tacker www.damsl.com

    In the first photo in my last post above, you can see that the genoa has two blocks on its clew with a sheet around each block, so, 2 double sheets, 4 ends of rope that can be moved around to various pad eyes and tracks on deck, which are bolted through to beams and chainplates on interior bulkheads, as are various tangs for attachment of tacks of the sails, and the tangs also serve as sheeting points.

    All of the sails are rigged with 2 blocks at the clew. Sometimes one of the double sheets is slack when not needed, as in the photo above. Other times, both are used, with one end of each sheet led back to a winch on either side of the cockpit, and the other ends attached to appropriate points on deck. In general, with 4 ends of rope, 4 angles, 4 vectors, to shift around, you can put the clew of the sail anywhere you want in the space above the boat. That is, when the tacks are attached to the windward side so that the sails are always over the boat. If you want to cant the sails INTO the wind, i.e., attach them to the leeward side, it works close hauled without poles, but for reaching, then whisker poles are needed in order to maintain ideal sail shape, because, of course, the clews are then outboard.

    On a long tack, as I said, for convenience, ideal sail shape without booms or poles, safety, and performance in light airs, I usually cant the sails away from the wind by attaching the tacks on the windward side of the boat. An additional safety factor is that with all of the sail area directly over the boat, on a beam reach, for example, there is no sail area way outboard and levering the boat around and tending to broach. Also, all of the gear is reachable from deck, inside my big, trusty handrails. I'm too old to be crawling out on booms.

    It's amazing to me that some sailors still think that booms are necessary, even on a cat. Of course, a monohull needs a boom because it's only half a boat and thus not wide enough. I'll never forget reading somewhere, in my youth, that the force of the boom pushing against the mast is the force that propels the boat to windward. What sheer nonsense! I discovered otherwise when the boom on my little boat, attached to the sail only at the clew, broke. I was able to get home because I had two blocks that I attached to cleats at the corners of the stern, and sheeted to them. So the boat itself became the boom and actually pointed better. That was a borrowed book that I had read, that claimed to be about the "physics" of sailing, and I never bothered to borrow it again.

    And I remember reading somewhere in one of these forums that, when motorsailing, a boom is necessary because you need to pull it to windward on the traveler. Which is also nonsense. No booms needed when motorsailing. Indeed, the flat cut of a furling boomless sail works better than a cambered main for motorsailing, IF you sheet it properly. Some motorsailors think otherwise simply because their jibs don't have proper sheeting points for motorsailing and it hasn't dawned on them that that can easily be remedied.
     
  12. Spiv
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    Spiv Ancient Mariner

    When reaching I have been using a second sheet attached to a block on my spring cleat and adjusting the clew to the optimal position; your system allows even more flexibility.
    Thank you for sharing your knowledge.

    Incidentally, I have seen some interesting boomless rigs in Turkey and posted some pics on the mainless thread. (I hope this link works...)
     
  13. Angélique
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    Angélique aka Angel (only by name)

    It's been 8½ years Brian, but here she is for sale / sail . . . . .

    See the thread - OK... would someone explain this to me? ...

    Cheers,
    Angel
     
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  14. Guillermo
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    Guillermo Ingeniero Naval

    $27000....???
    Perhaps an additional "0" ? ;)

    Cheers!
     

  15. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

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