DynaRig MotorSailer, ala Maltese Falcon

Discussion in 'Motorsailers' started by brian eiland, Mar 9, 2007.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    With a fully-battened sail on a rotating mast, the batten leading edges could be attached to the mast. This would allow the use of mast rotation to modify the batten shape, and perhaps optimize the profile and/or sail twist.

    Has anyone experimented with this idea? The biggest problem might be establishing batten stiffness: this would likely be optimized for light winds where efficiency would be most desirable.

    Like a rigid wing, there is likely no way to reef such a sail.
     
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  2. AdvShipbuilding
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    AdvShipbuilding Junior Member

    Your idea is good we also went that way..
    In my wingsail the wing is twisted partly by being fixed to the mast. It also can be riged by use of a much larger chariot. The sail is fixed in X to the chariot which is fully around the mast. By means of a rail the round chariot can move up and down but not around the mast which allows the sail to tense when it is puched by the wind around the mast. The effect received is exact with your idea. The problem I had within the study is that with the changing of windpower the battons don't keep a good angle. The system needs a secundary pully system to finetune. We drew the chariot system to allow reefing but we suspect it will need some testing and adjustments before it is fully operational. My father wants to build a reefable wingsail for his 45 foot catamaran so even after my thesis ended (few weeks ago), we'll keep working on building a usable good system.
     
  3. ancient kayaker
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    ancient kayaker aka Terry Haines

    if the basic concept works, perhaps the next step would be to use inflatable battens so their stiffness can be adjusted to suit wind pressue.
     
  4. AdvShipbuilding
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    AdvShipbuilding Junior Member

    It is possible but maybe not very reliable in every day use. It would offer opportunities to finetune but inflating would require every batten to have its own air supply. In that case too many hoses would have to go in the system. In a fixed version it is possible but leakage and damage by wear and storm would be a problem in sails. Best case use kevlar for the tubes to minimize. Feefing would be made very difficult. I think too many problems in usage would make it not applicable in every day yachting. Maybe in the racing tests can be made.
     
  5. brian eiland
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    brian eiland Senior Member

    Camber Spar Yards

    Sorry I don't have time to elaborate at this time, but one thing I had been thinking was how to marry the idea of a reversable rigid 'camberspar' in place of the yards of the square rig :idea:

    Camber Spar
    http://www.freedomyachts.org/viewtopic.php?f=16&t=8583
     
  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    Brian, I'm not sure I fully understood that article. It seems to be describing the use of a wishbone sprit on the jib. I tried a double wishbone sprit on a leg-o-mutton sail but it was clumsy and was getting too elaborate so I gave up.

    I have been trying to conceptualise a reversible Dynarig-type spar to eliminate backwinding when changing tack but haven't been able to come up with anything that would work. One problem is, the sail needs to move to the other side of the mast without rotating the mast 180 deg. About the only thing that would allow that would be an A-mast, but that would be virtually impossible to rotate.
     
  7. brian eiland
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    brian eiland Senior Member

    Camber Spar Dynarig

    Hi Terry (Ancient Kayaker),
    I can see from your contributions to this discussion and contributions to this other subject thread, ‘Square Rig Variation’, that you have a great interest in this subject matter.

    I do as well, but unfortunately at the moment I’m working on the opposite end of vessels…a propulsion drive leg design rather than the sailing rig ;)

    I knew this fellow Dave Bierig, a sailmaker in PA, who developed this Camberspar idea. It was right about the same time that Freedom boats were introducing their wishbone booms on their freestanding mast, and here was a concept that required only a half of a wishbone boom. It was contained in a pocket built into the sail as opposed to double arms ‘around’ (external) the sail.

    I’ve often thought of other applications where this camberspar idea might be utilized, including the mizzen sail and the inner foresail on my mast-aft concept. Perhaps it was this posting of yours #20;
    ..that prompted me to think of possibilities of using the Camberspar concept on a Dynarig design. I have a bunch of ‘doodles’ on various napkins and pieces of paper, but I’ve never gone through a development process.

    My basic thought was a round freestanding mast that has external tracks down either side 180 degrees apart. These tracks would allow the a ball-ended ‘camberspar yard’ to ride up and down the mast, and these camberspar yards (half yards really) would be able to rotate over 180 degrees in the horizontal from one camber of sail to the opposite camber. This rotation of the camberspar yard (better described as a ‘flop’ from one camber to the opposite) would occur within a pocket built into the sail panel. This sail panel pocket would be horizontal on its bottom edge such that the camberspar yard would rest in it at full camber when on either tack. The sail panel’s pocket would be exaggerated in dimension at its outer edge in order to allow the tip of the camberspar yard to flop over on the opposite tack (camber). Perhaps some sort of ‘leech line’ internal to the sail would be needed to facilitate the ‘flopping’ of the camberspar yards. Naturally you would want both ‘halfs’ of any one camberspar yard to rotate onto the new tack in unison, or you might end up with an ‘S’ shaped sail aerofoil rather than a full camber foil shaped sail.

    That nice round mast might have two cambered panels bonded on either side, that project out at each end to form a small slot that allows the camberspar yard and its sail to exit the mast’s slot. These two panels would act to make the mast appear as an elliptical aerodynamic shape at the center of the cambered sail.

    I know this is an incomplete thought process, but it was my idea for using the camberspar concept as a yard for the square sail ‘dynarig’ configuration. It harkens to your call for a “one piece sail with pockets for each yard instead of separate sail panels”, and could “form a full aerofoil profile on either tack” while requiring very little mast rotation.

    (I'll try to add a sketch in the next few days when I get a chance)
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    I was thinking of the same thing, more or less, but rejected the idea as being too complex and likely to cause excessive sail wear. I believe the essential thing about the Dynarig is the vertical tension that the spars impose on the sails to maintain them in a smooth curve. To create that tension there would have to be an outhaul or somesuch to move the spar at the end of its travel after each change of tack. Sounds like a lot of work. Also there would be continuous tension at the edges of the sail which would be applied at the ends of the spar(s), leading to a tendency for them to jam. I have to admit that I don't like the idea of the camberspar itself for the same reason.

    re-reading my own earlier post, it seems what I was really thinking about was a wingsail.
     
  9. brian eiland
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    brian eiland Senior Member

    I don't know that I follow you here? The sail is tensioned on the camberspar just like a full batten in a mainsail. That batten can flop from one tack to the other without any readjustmet of the tension. The camberspar can as well.

    Have you utilized a camberspar jib before? I installed one on one of our Firefly trimarans for a gentleman who sailed singlehanded all of the time, and tacked a lot out of his creek on the Chesapeake Bay. He loved it.
     

  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    I don't think I understand how it works: I have not been able to find a picture.
     
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