Sail Plan Optimized for Acceleration

Discussion in 'Sailboats' started by Earl Boebert, Nov 4, 2013.

  1. Earl Boebert
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    Earl Boebert Senior Member

    I sail a small class of model yacht (RG65) in winds that are often very light and highly variable within that limit. So going to windward can look like "sail into a hole, stall, get a puff, sail into another hole" over and over.

    So I am seeking opinions on what a sail plan optimized for acceleration (assuming such a thing exists) might look like. It's a sail area limited class, so do people favor masthead over fractional, big jib, little jib, or what? Anything from scientific results to SWAGs would be appreciated.


  2. sharpii2
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    sharpii2 Senior Member

    I think this is more a matter of sailing technique than sail type.

    The problem is the sail loses its shape as soon as it runs out of wind.

    It takes time to recover its shape when the wind returns.

    Typically, the boat is deliberately heeled to leeward, so the sails will better hold their shape when the wind quits. This is probably not an option with a model keel boat.

    Very flat cut sails have little shape to lose, so they might do better.

    A taller rig might do better, as there is usually at least slightly more wind higher up than lower down.

    I imagine a tall fractional rig with a fat head main may be the best you can do.

    It will have a very high aspect ratio (AR), which will make it more efficient. It will have its sail area higher, which will get it at least slightly more wind. And it won't be handicapped by a tall mast, as there is not much wind to begin with.

    In windier races, this rig might be outclassed by shorter rigs, as they will have less top hamper (shorter mast) and and have a lower Center of Area (CA) and, therefore, be able to carry more SA in a given amount of wind.

    The taller, higher AR rig might not do well if the water is at all choppy, as the pitching of the boat might cause frequent, drastic changes in the apparent wind the sail experiences.

    My recommendation assumes smooth water with light winds.
  3. Doug Lord
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    Doug Lord Flight Ready

    Ribbon jib

    I used to sail with a fleet of EC 12's and they are an excellent light air boat.
    I built a 50" cat with an experimental rig where I tried a "ribbon jib"-it was a mast head "Jib" with a luff of about 65" and a chord of 2". I light air it was amazing-allowing the cat to outsail an EC 12 on every point of sail while going
    faster.The cat was a dog in those conditions with a conventional rig and could never beat an EC 12! By light air I mean when its virtually glass and the air is as you describe.
    In moderate to heavy air the sail didn't work that well but the cat could fly a hull and zoom...
    I think the ribbon jib is sort of like a "slat" high lift device.

    Attached Files:

  4. Skyak
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    Skyak Senior Member

    Light wind condition is lift limited as opposed to righting moment limited, so a deeper camber gives more power but the sail should not depend on wind for it's shape. This is easier on a model than a full boat. A high aspect sail with more sail up high sweeps more wind with it's limited area. A masthead rig with a fractional (shorter) jib would avoid the backwinding that happens where the jib reaches the mast -but shape and the slot are more important.

    I don't remember what they were called but the rigs that have the boom extend around the mast to the base of the fore stay have a big advantage downwind and are easy to build and manage on a model boat.
  5. messabout
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    messabout Senior Member

    Skyak, modelers call that layout the "swing rig". It is best rigged on a free standing mast but shrouds can be made to work if necessary. The swing rig has the unique feature of a tight forestay and vang combination.

    When running free there is less weather helm tendency because the jib is swung out to windward opposite the main, thus less turning moment by the main. Less slamming force when jibing too. The boom is pinned to the mast and allowed to pivot up or down but not side to side.

    Not sure that class rules will allow this on the OPs boat.
  6. Skyak
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    Skyak Senior Member

    Thanks. Doug's post slipped in while I was typing -a more highly developed version of what I was thinking -swing booms top and bottom. I guess a picture can be worth more than a thousand words.

    I don't know what the rules are either.
  7. mij
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    mij Junior Member

    Earl, would a super light weight material be an option for days with light winds. I'm imagining something a bit "crinkly" that holds its shape once pushed into position. Something like a very light weight cellophane?
  8. messabout
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    messabout Senior Member

    MIJ modelers are already using such a material in many cases. The material is a clear plastic, possibly mylar, with a matrix of some sort of strands. It is available in several different weights. It is called "Trispi". The stuff is durable and very flexible and it does not stretch much. A nicely cut sail of this material will hold its shape admirably well. The only problem is that it is more difficult to see the sail shape and trim when the boat is at a distance.
  9. michael pierzga
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    michael pierzga Senior Member

    Upwind, When boat speed exceeds windspeed..a hole..there is not much you can do trim wise.

    Fast boats hold course, hold trim, sail thru the hole and resume sailing.

    Hard to do with a remote sailboat because you have no feel.

    Down wind in light conditions with a swing rig is equally challenging.

    The rig wont jibe or ease out
    Perhaps there are tricks.

    Its been years since i raced models.

  10. gggGuest
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    gggGuest ...

    I suspect dynamic behaviour of the rig in terms of spring rate etc would be an area to consider. I sail full size dinghies on a raised reservoir where the wind becomes much more disturbed and inconsistent as you approach the windward mark, and I find it worthwhile to change rig settings for the final approach in certain conditions, notably letting the sail twist more.
    Bethwaite found that whilst sophisticated stiff masts with little dynamic movement were faster in steady wind, in variable and unpredictable wind an over flexible. highly responsive mast worked better even though in theory it was aerodynamically inferior.
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