Sail performance metrics

Discussion in 'Hydrodynamics and Aerodynamics' started by misanthropicexplore, Jul 25, 2018.

  1. misanthropicexplore
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    misanthropicexplore Junior Member

    A common way to rate rig performance focus on power per area and pointing. (Wingsails and Bermuda)
    Another common way is to rate it by power/sailor effort. (Junk Rig)

    power per pound... the lateen?
    power per ease of self construction? Still the junk rig?
    power per dollar?
    power per ease of use?
    power in light air per ease of use?
     
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  2. messabout
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    messabout Senior Member

    That's a lot of variable criteria. Attaching a value or efficiency component to those categories is not something we can do without considering a whole basket of other
    variables.

    If you mean to determine the best all around rig for your boat, then much information will be needed.

    Way back in the day some research was done by an international agraculteral agency who was interested in figuring out the best or most practical rig for third world fishermen. Among the conclusions that they drew was that crab claw rigs were desirable, simple, and efficient for general use. Many of us would dispute that finding. Just the same, some pretty smart technical people did the experiments and arrived a their conclusions.

    I suspect that one could resolve the issue for his own uses by considering the old wisdom: Horses for courses.





     
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  3. rwatson
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    rwatson Senior Member

    A fascinating topic.

    I have often thought that racing yachts should have their handicap affected by the cost of their gear - like expensive sail rigs.

    If another yacht could get around the same course in double the time, but one tenth of the capital cost - who's the smarter designer ?
     
  4. misanthropicexplore
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    misanthropicexplore Junior Member

    @messabout
    I've heard that about the crab claw, though, yes that does seem to create a lot of controversy. I've never understood how crab claw rig worked better than a Sunfish style lateen.
    I don't have a sail boat yet. I'm still learning what reasonable expectations are before I decide what mine are.

    @rwatson

    Agreed. Though I feel like that would start some actual fist fights at some clubs.
     
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  5. messabout
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    messabout Senior Member

    Misanthrop..... Sail potential is the subject of a lot of good and not so good arguments. If I claim that a full battened monorig is the best, then I must address all sorts of variables to make my argument. Consider sailboard sails for instance. Call them sail A and sail B. It has been clearly demonstrated that some identical sizes and configurations deliver different performances. There are a whole bucket load of variables that we have to address. Sail A has a stiffer mast than sail B....or visa versa. The sail and mast needs to be matched and sure enough if not matched then one will be better than the other. Then we get to the subject of weather. The sail A or B with the more flexible mast might perform better in heavy air that the one with the stiffer mast. In light air the whole deal might be reversed. Then there is the skill of the sailor. Some guys or girls just get better performance than I do from identical sails. Consider the classes of boats that have identical sails by virtue of their rules. The Sunfish with its Lateen for example. The sails are all the same.........well that is not technically true but they are all visually alike and measure the same.. One sail just flat out pulls harder than the next one. Yes of course those are all North sails, laser cut, and all that. So they are presumed to be identical. A quarter inch difference in the panel seams might make a world of difference. That quarter inch of curved seam will matter. It is not easy to get all those seams perfectly and identically sewn.

    The most simple and user friendly sail that I know of is the sprit boom rig and in a close second place is the peak sprit rig. Not the fastest sails in the locker for all around use. But the peak sprit rig might just be superior to some far fancier rigs on a dead run or broad reach. That is a maybe . One of the objections to the peak sprit rig, and in some cases, the lug rig is that they can easily develop death roll when off the wind. Not to say that that cannot happen with a bermuda rig. It does but not nearly so often. On top of that an alert sailor can dampen the roll of a bermuda rig by using some sail adjustment. Not as easy with a squarish sail.

    The most practical plan, if you are new to sailing, is to go sail every boat that you can beg, borrow, or steal. Try some different types so that you can get the feel of whatever boat and rig you might be using. Try not to make up your mind about a specific sail rig in such a way that you ignore other types.
     
  6. misanthropicexplore
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    misanthropicexplore Junior Member

    'And it is also said,' answered Frodo: 'Go not to the Elves for counsel, for they will say both no and yes.' :)
     
  7. CT249
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    CT249 Senior Member

    Is there any evidence that the guys who came to those bizarre findings were smart technical people? Their findings just don't add up. They claimed that a crab claw sail was about 30% faster than a sloop rig. If that was true, you could re-rig a Snipe with a sprit rig and it would go upwind with a 49er (which is around 30% quicker than a Snipe). Or you could re-rig a Hobie 16 with a sprit rig and it would be about as quick as a 25' wing-masted C Class cat upwind. Or you could re-rig a Catalina 22 with a sprit rig and it would beat a J/44 upwind and leave a Farrier F 27 trimaran astern at the rate of 30 seconds per mile. Or you could sort of chuck a spritsail on an original Windsurfer, and it would beat or scare the latest Formula Windsurfers (with twice the sail area and 1/3 the weight) every beat.

    The original crab claw sail came from the Pacific. The only times I know the crab claw canoes raced "modern" sloops was in events in New Guinea. In the only accounts I can find, Fireball dinghies and Hobie 16s left the crab claw canoes well astern, leading one local canoe sailor I know to move to Hobies.

    Either all the aerodynamic experts, all the windsurfer sailors, all the speed record guys, the people who brought us the foiling Moth and the wingmasted C Class, all of the sailmakers and just about everyone else in sailing is wrong, or that one test is. What is more logical? We know that some of the above have tried crab claws and they gave them up. Add the fact that that one "test" doesn't appear to have been peer reviewed or led to any further development of the project it was created for, and it appears that the "test" was a complete load of rubbish.
     
  8. rwatson
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    rwatson Senior Member

    The Crab Claw performance figures are pure bollocks, published by one person, and never verified since.

    It doesn't take an engineer to figure out that it can't be anywhere near the performance of half a dozen other rigs.
     
  9. misanthropicexplore
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    misanthropicexplore Junior Member

    I've read the test conditions for the test, and I don't remember them perfectly, but it was something like this:

    (1.) They used an actual crab claw shaped sail, with deeply hollow leech, not the modern, isosceles triangle shaped ones, but also unlike the historic crab claw, used a somewhat rounded nose. Aerodynamically, I think this would be known as a "parabolic arch", or maybe a "reverse crescent".
    (2.) It was done at scale, smaller than 1" = 1 foot, if I recall.
    (3.) It was done with a rigid piece of plastic/metal shaped to fit, with no scaled booms, or (I think) rigging, just a cambered plate.
    (4.) In a wind tunnel.

    So the results of the test weren't so much "Crab claw is better than Bermuda" as "at low Reynolds numbers, when held stationary in air moving a consistent speed, a low aspect ratio triangle with a parabolic leading edge, has a better lift to drag ratio at high angles of attack than a high aspect ratio triangle leading with the long leg"
     
  10. misanthropicexplore
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    misanthropicexplore Junior Member

    The Balestron rigs I've seen were very high aspect ratio, and I wonder how a low aspect ratio Balestron (say, an equilateral triangle) would compare to a balanced lateen, (like a Sunfish) of the same size and shape. Would the split over the mast give enough performance boost to be worth the bother?*

    *I only ever really wonder about 2000 to 14,000 lb displacement, all weather, shoal draft, blue water cruisers, in FRP over plywood, FRP, and steel. To me those are the sort of boats a workingman can afford, and everything else is sort of like the floating equivalent of of a gokart (dinghy), Class Motor home to mansion (yachts over 40 ft), or Indy car (racing boats): Fun to learn about and watch other people use, but not something I want to invest my personal nest egg in. I should have specified that in the original post.
     
  11. sharpii2
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    sharpii2 Senior Member

    I remember the first years of the pd racer class (8 x 4ft box scows). I started keeping track of the sail rigs used, and I had an itinerary of over a hundred boats then. Just about every fore and aft rig known to mankind was tried, even one, jib only rig. But two rigs continued to dominate. And they steadfastly duked it out for being the most popular. These were the boom sprit and the balanced lug. The next two most popular rigs were the boom lateen and the Bermuda rig. Although they were 2nd tier they came to be affectionately regarded by me as part of the "big four".
    Pd racer sails were rarely made of high-quality materials. They were generally made of poly-tarps and sometimes even visquene. The Bermudan rig works quite well as long as the aft end of its boom is held down. Chinese lugs are not cheap. They need many sturdy battens, and, here in the West, these cost money.
    The boom spritsail was probably popular because it needed very few moving parts, just a snotter, and a sheet line. Most did not have a halyard. But it required a tall mast to get adequate SA.
    The balanced lug rig was nearly as simple. It required only a halyard, a hold down, a parallel loop and a sheet line. The sail-cloth was attached only to the yard and the boom. I've seen some pretty sloppy examples of this sail which still worked adequately (were able to sail upwind), one with a level yard and a down sloped boom!
    I've seen Bermudan rigs with the foot longer than the leech which still sailed quite well.
    IMHO, the Bermudan rig works best as a fractional sloop, if reefing it is part of the plan. The reason for this is changing Horizontal Center of Area (HCA). When a Bermudan main is reefed the HCA moves forward. This can cause a lee helm. With a fractional sloop version, this is less of a problem. The small jib is dropped first. This moves the HCA aft, causing some increase of weather helm. A reef is later put in the main which moves its HCA forward again, which removes this increase of weather helm.
    Boom sprit rigs were almost never reefed, traditionaly. The snotter was usually tightened, which flattened the sail.
    Balanced lug sails were relatively easy to reef. The HCA often moved slightly aft when this was done, if it moved at all.
    I think one must always keep in mind that the mast is usually the most expensive part of the rig. So a rig which can do with a shorter mast is usually less expensive. This is probably why one sees very few high aspect ratio rigs in the days of working sail. The exception to this rule is the sprit-boom-rig because its mast also doubles as a yard. This is because it traditionally doesn't have a halyard, so there is no downward load on it. This makes for a greater taper at the top, which lowers the mast's Center of Gravity (CG).
    I see five criteria in judging a sail type:
    1.) Performance, how much drive it produces per SA, especially upwind.
    2.) Cost. Can it be built for a reasonable price with available materials?
    3.) Durability. How long will it last? Will it still work if damaged?
    4.) Ease of use. Is it difficult to set and/or furl?
    5.) Balance. Does its HCA move a lot when the sail is reefed?
    For racing sailboats the choice is simple. Performance. The devil can have the rest.
    But for the rest of us, these five criteria often clash with one another. And it's up to us to sort out which ones matter most.
    Once these criteria are properly ranked for our individual purposes, we can make more rational choices. If 3, 4, and 5 top your list, the Chinese lug is probably the way to go. If 1, 4, and 5 top your list, a Bermuda rig fractional sloop is best. And so it goes.
     
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  12. DCockey
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    DCockey Senior Member

    Heeling moment can be a fundamental constraint on a sail rig. The heeling moment can't exceed the available righting moment or the boat will capsize. So if the desire is to go fast and sail area is not constrained then the drive / heeling moment is a better metric than drive / sail area.
     
  13. Dolfiman
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    Dolfiman Senior Member

    About extreme sail rig, I had few days ago the chance to see at Nice the 88m Falcon Maltese, a modern version of the classic 3 (to 5) wooden masts with squared sails like the Sea Cloud (also in Nice a few days after), but here sails have some preset camber. Both sail rig are impressive in their kind, how small you feel when you are very close !. Falcon Maltese masts look like to be built in aluminium alloy but actually they are in carbon fibre, height 60 m. The 2400 m2 of sails are furled in the masts. This type of rig is from the Dynarig concept :
    The development of the high-tech DynaRig on sailing superyachts https://www.boatinternational.com/yachts/yacht-design/the-development-of-the-high-tech-dynarig-on-sailing-superyachts--711
    Louez le Maltese Falcon : le voilier le plus moderne. - Viaprestige Lifestyle http://www.viaprestige-lifestyle.com/Moteur/le-maltese-falcon-le-voilier-le-moderne-du-monde/
    IMG1463.jpg IMG1463.jpg IMG1464.jpg IMG1465.jpg IMG1466.jpg IMG1461.jpg IMG1486.jpg
     
  14. sharpii2
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    sharpii2 Senior Member

    This is true. Weight and height of the rig matter even more. This is why taller rigs tend to be more expensive than shorter ones. The mast needs to be light and very strong for its weight. This often means a system of upper and lower shrouds and stays to keep the mast from bending and/or buckling.

    Heeling moment is based on four criteria:

    1.) Wind strength,
    2.) Height of rig Center of Area,
    3.) Depth of keel fin, and
    4.) Lift coefficient of sails.
     

  15. CT249
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    CT249 Senior Member

    I've never seen much evidence that the junk rig is dramatically better in terms of damage resistance. The way the JR fans right about it implies (or states) that a small tear in a bermudan rig will always spread. That's just not the case, particularly with modern membrane sails. I have to admit that I have a few yacht sails with holes in them and there's been no sign of them spreading. Secondly, at least in smaller boats (2 tons or so) you can do an enormous amount of repair work with a few layers of stickyback. Sure, if the leach or luff tears you may have problems, but there seems to be no evidence that the JR is dramatically better.
     
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