The design of soft wing sails for cruising

Discussion in 'Boat Design' started by David Tyler, Jan 19, 2014.

  1. David Tyler
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    David Tyler J. R. A. Committee Member

    Only off-topic insofar as hard wings are mentioned, but everything else might apply to soft wings for cruising, so:

    There are now several catamarans with a rig in each hull, and they sail well, but two rigs in each hull? Sounds like a major trimming problem to me, that can only be solved with an electronic control system. Walker wingsails come directly to mind, as an example of a failed attempt to get that to work satisfactorily in all respects.

    Bearing in mind the comments I've read about the AC wings - the work on optimising the shapes has all been done, the hard part now is to get the controls right so that the crew is trimming them to the optimum all the time - I wouldn't want to go there.
     
  2. P Flados
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    P Flados Senior Member

    With 4 wings, the self trimming type would seem to be very needed, but I am not sure that you would have the clearance to pull it off.
     
  3. groper
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    groper Senior Member

    heres the latest news from Rob Denny regarding a biplane rigged catamaran in another thread in case you guys here missed it;

    Here is a vid of the catamaran discussed above before its masts were chopped down to 12m;



    The point is, the rig proved to be extremely powerful - why? Because it is very efficient (good L/D ratio) and generates alot of horsepower per unit of sail area. Therefore it doesnt need to be very large. Now if you continue this improvement in efficiency to better still L/D ratio and better still lift coefficients of a 2 element wing sail rather than a single element, then the size of the sails could be half again for the same power.

    This brings up the next point worth discussing, how to engineer a 2 element sail with minimal fuss and complexity? The lastest omer wing sail is just about there from what ive seen, its still a single element with adjustable camber by the looks of it, but it doesnt look like much effort to change what they already have and turn it into a 2 element sail. I suspect they are already looking at this and will be in their next design rendition...
     
  4. groper
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    groper Senior Member

    Came across these today aswell... anyone seen these before?

    Soft Wing sails by matinbleu;
    [​IMG]
     
  5. Will Fraser
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    Will Fraser Senior Member

    My experience in designing aircraft has taught me that the "simple, elegant solution" is almost never apparent at the beginning, but is the result of iterative refinement after mixing and matching many different more complex solutions. Only once a good variety of solutions (however complex they might be) are available, the terms "unacceptable complexity" and "acceptable trade-offs" are defined and used as a criteria to cull or modify the solutions.

    So to start, first identify the various parameters or variables that need optimising and then start fiddling with ways to achieve that.

    The use of a headsail is - as I understand it - primarily for increased lift for a given total sail area, but it comes with a drag (and L/D) penalty. Thus its use is constrained by the boat's available righting moment, wind strength and point of sail.
    Apart from slapping a more efficient wing mainsail behind the standard jib, I would imagine that the following could all play a roll to some degree:

    Jib AoA tolerance
    Jib sheeting angle
    Slot control
    Overlap

    So here are just a few ideas to get the ball rolling:

    AoA tolerance: #1 - what about a battened luff pocket for the jib? #2 - Or even a full-chord airfoil section with articulating battens like Tystie's mainsail?

    Sheeting angle and slot control: Looking at the #3 "balanced" boom of the Harry Proa (that carries the jib tack to windward) and the articulating "boomlet" employed by Beneteau to control wing camber - #4 - now what if such pivoting boomlet was used on the headsail of the Harry proa? #5 - Combine this with sliding pivot points and you can even control overlap while you are at it. #6 - Now add a zipper along the jib leach and main luff to seal the gap completely when not required (such as to delay the need for reefing when going to windward in strong winds) and you might just have the Ultimate Efficient Sail.

    Now the quest for simplicity:

    Even though this complex solution is completely impractical, it might still be possible to use some of the ideas on their own or in various combinations with each other.

    Let us assume the addition of a conventional headstay is not acceptable because of the additional mast loads or whatever. We also limit the number of additional control lines associated with the new headsail element to two (just as an example). That means ideas 1 and 2 cannot be applied in the obvious sense, i.e. the jib foil battens sliding up and down the headstay.

    It might still be possible to use it in the following way:

    Create a headsail element by rather splitting the existing junk-type wingsail into two (much like the modern slotted junk-lug rigs that use the area ahead of the mast as some sort of "jib"). The front element can self-tack around a tensioned luff-haul parrel that is first led to a block an extension of the lowest batten (i.e. #3) such that the LHP runs parallel to the mast. This limits the height of the headsail to the lowest batten attached to the LHP, but you retain the incremental reefing attributes of a junk, while reefing the main and headsail in one go. The two lines assigned to the headsail can both be used as sheets, one at the foot and the other somewhere higher up. I think the pic attached will illustrate it better.

    It might by no means be a practical solution yet, but shows the principle of how a solution "evolves".
     

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  6. David Tyler
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    David Tyler J. R. A. Committee Member

    Also, in the Hauraki Gulf, there's Cool Change, a larger cat with a similar biplane rig. That's probably as far as you need to go with a large cat. Cool Change cruises up to the islands regularly, and was in New Caledonia for the austral summer, so is ocean-proven.
     

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  7. David Tyler
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    David Tyler J. R. A. Committee Member

    I came across Matin Bleu in Polynesia in 2007, and had a look at the rig. It was quite similar to the one that Beneteau's designers are working on, from memory. There's a clearly visible process of evolution going on there.

    Not for me, though, with rotating masts and booms that are quite a piece of engineering. Also lacks the quick and easy reefing that is an essential element of my design brief.
    There was a language difficulty, my schoolboy French not being up to technical discussions, but it was an interesting boat to look at, with many original ideas.
     

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  8. Will Fraser
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    Will Fraser Senior Member

    Please explain the difference in reefing - it looks so similar to your old rig.
     
  9. David Tyler
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    David Tyler J. R. A. Committee Member

    You're having some interesting ideas, Will. You may not be aware of the work of a fellow JRA member, Paul McKay (pic attached). Please go on with the brain-storming.

    For me, though, this part of the process is over. As a result of starting this topic, I'm confident that I have a suitable foil section and a sensible planform that is appropriate to my need.

    I have earmarked March and April to construct this rig, and now I must get down to the work of the detail design of the battens and their tooling, and the sails.
     

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  10. David Tyler
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    David Tyler J. R. A. Committee Member

    Principally - it doesn't employ chinese sheeting, which looks after the reefing as well as the sheeting angle. It has a rotating mast, and with all such rigs, you go to the mast to reef. This is anathema to me. I pop my head out of the Hasler pramhood, ease the halyard and trim the other lines, and go back below out of the cold and wet.
     
  11. Pollen
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    Pollen New Member

  12. David Tyler
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    David Tyler J. R. A. Committee Member

    Merci beaucoup pour l'opportunité de le voir! Les similarités sont expliqué!

    Some things I noticed:
    1. Conventional slab reefing, with 5 reefs.
    2. A very wide boom that will be acting as an end plate.
    3. The sail will not fully self-furl; though it comes down most of the way by gravity in light airs, it will not do so in a breeze.
    4. The head of the sail is horizontal, and will foul lazyjacks as it is hoisted; the first part of the hoist must be done head to wind, unlike a junk.
    5. The halyard winch is underneath the boom, which is awkward; though I think I heard that they were trying to find a way to put it on deck.
    6. The foil seems quite thin, and the camber not very great; probably enough power for that boat, though.
     
  13. Will Fraser
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    Will Fraser Senior Member

    Good luck, please remember to post some pics of the progress.

    Just one last thought regarding the section shape: unless dictated by some practical constraint, consider tapering the thickness of your section on the top battens to remain as close to the original as possible (14%). Generally, beyond 15% the Cl-max starts to suffer.
     
  14. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    David,
    I don't want to change the topic of this thread, but I am curious about Tystie. How well does a junk rigged, shoal draft, internally ballasted boat handle ocean voyaging? (Well, I assume) Do you have a web site which describes her?
     

  15. David Tyler
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    David Tyler J. R. A. Committee Member

    Well, for the over 80,000 miles sailed thus far. CE marked in Category A, ocean. You'd have to join the JRA at www.junkrigassociation.org, only £7 pa, and read Newsletter no 38, and many subsequent references.
     
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