Chris White Atlantic 47, MastFoil

Discussion in 'Multihulls' started by bearflag, Nov 21, 2011.

  1. bearflag
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    bearflag Inventor/Fabricator

    The Chris White Designs MastFoil™ (patent pending) is a unique combination of modern rigid airfoil technology with proven soft sails. The basic concept is not new and you can see examples of large rigid wings and soft sails in the current America's Cup catamarans.

    However the MastFoil has some critical differences. The main difference is that the MastFoil is a small part of the overall sail plan and can rotate 360 degrees around the load bearing mast which allows it to be feathered on any point of sail and in any wind velocity. Left alone, the foil will continuously feather if the control is set in that mode. Without this critical ability to feather on any heading, a rigid airfoil would typically not be suitable for use on a cruising boat. Another important difference is that the foil does not carry any of the mast compression loads. This enables the foil to be lightweight, structurally simple and rotate easily around the mast.

    Why eliminate the mainsail?
    Most sailors agree that the mainsail, particularly the large roached, full battened mainsail combined with the aft-led-shroud, no-backstay-configuration that is used in most catamarans today, is by far the most troublesome sail to hoist, reef/unreef, furl and cover. In addition, mainsails create significant safety liabilities because they cannot be easily or quickly reefed or furled when sailing downwind. In violent squalls this feature has caused more than a few capsizes. The conventional catamaran mainsail can also be somewhat risky to gybe in a blow.

    For all the trouble associated with the mainsail, what do you get? Per unit of sail area, the mainsail is the least efficient sail on the boat. Sailing upwind, the mast - at the aerodynamically critical leading edge of the mainsail - robs a great deal of its power. Sailing downwind, the shrouds prevent easing the sheet enough to unstall the sail. Also the large roach area of the sail contributes to significant weather helm which slows the boat and can make steering more difficult.

    At the other extreme in sail handling is the modern roller furling jib. You don't need to hoist and drop the sail every time you use it. It reefs easily on any point of sail. It furls completely in seconds. Couple these attributes with a rugged self tacking set up and there is not an easier to handle or more efficient soft sail.

    In the quest for simplified handling and improved safety, let's just do the obvious. Get rid of the mainsail. And in its place substitute more jib area combined with a super efficient MastFoil™.

    ...​

    [​IMG]
     
    Last edited: Nov 21, 2011
  2. CatBuilder

    CatBuilder Previous Member

    What the?!?

    I can see the self tacking, double head sails, but does that foil actually do anything?

    It looks so small. I wonder what lift it provides compared to the headsails.

    Do you think that Atlantic 57 capsize a while back has him thinking this way - to lower the center of effort by using double headsails rather than a big main?
     
  3. Doug Lord
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    Doug Lord Flight Ready

    It appears to be a very high aspect ratio two element wing sail. Can't tell if it has a slot or not.... Not much info. Somebody posted about this here or on Boat Design not too long ago and no better info showed up I don't think.... It's also on SA-haven't checked that thread today again.
     
  4. bearflag
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    bearflag Inventor/Fabricator

    Last edited: Nov 21, 2011
  5. Doug Lord
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    Doug Lord Flight Ready

  6. CatBuilder

    CatBuilder Previous Member

    They both have an extra "http://" on them.
     
  7. Doug Lord
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    Doug Lord Flight Ready

  8. catsketcher
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    catsketcher Senior Member

    Mainsails are efficient

    I don't get where Bearflag gets his data that mains are inefficient. The most efficient boats in the world are either ice boats, C class or AC 45 cats or similar. They have no or only small jibs. In the classes where only total sail area is measured - like 16ft skiffs and NS 14s they have big mains and small jibs. 16s don't even have rotating masts.

    I don't mind the idea of a cruising cat with a large jib for downwind work but the loads involved in winching large genoas in and out going to windward is much higher than a small blade and a main with a traveller, vang - or wishbone.

    The main aint dead yet and as it is more efficient than the jib upwind - especially if you don't go the ketch design as in the first post - it will be around for some time to stay.
     
  9. catsketcher
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    catsketcher Senior Member

    Sorry Bearflag

    I am gobsmacked - I really like Chris White's book and some of his designs but I find that Bearflags post is straight from White's site. I can't believe a good designer could write such silly stuff - "the roach contributes to weather helm". Cmon Chris - the roach actually reduces tip drag and makes the sail more efficient and often reduces side loading due to an increase in lift to drag - See Dashews book on a few retrofits. Any reasonable designer will calculate the total sail area including roach in their design and then incorporate this into the balance calcs. To attribute weather helm to roach only is certainly not standard yacht design practise - think of the many boats with lots of roach that sail very sweetly - Farriers etc. I can also tell you of many monos with little roach that have terrible weather helm.

    I know I have designed only one sailing cat and he has designed heaps but still he is putting stuff up on his site that isn't up to intellectual scrutiny.
     
  10. bearflag
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    bearflag Inventor/Fabricator

    I copy and pasted it from Chris White's site. The "relative" inefficiency of a non rotating non wing mastedmain sail without a headsail is fairly well known. Of course there are several caveats there. Of course what efficiency means itself is a mixed bag.
     
  11. CatBuilder

    CatBuilder Previous Member

    Agreed. I still think this has something to do with Anna, that Atlantic 57 that capsized. It pretty much capsized due to insufficient reefing of the main and an inability to get to the sheet to let it lose in time. It had all that nice roach way up top, which contributed in those conditions.

    I seriously think he is a little gun shy in his designs now because of it. Look at how low the COE of those sails are in the picture. A gale would hardly put a dent in reserve righting moment. :D
     
  12. brian eiland
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    brian eiland Senior Member

    Mainless Rigs

    I came to some of these same conclusions LONG ago....get rid of the traditional mainsail and put on some efficient jibs....and lower the aspect ratio & overturning moments...

    Only I did it with a more simplified single mast arrangement :idea:

    http://www.runningtideyachts.com/sail/

    http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-7.html#post198605

    Regards, Brian
     
  13. bearflag
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    bearflag Inventor/Fabricator

    Agree with CatBuilder on this one; however, that isn't to say this plan isn't without merit, if you read his page he says it is for safe handling cruisers and singlehanded sailing.

    I cross posted it on Brian Eiland's aft-mast page even though it is a "ketch" because it seemed to borrow a few of the things he has been addressing in his thread.
     
  14. pool
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    pool Junior Member

    keep it simple !

    that looks all pretty complex to me, the twin masts on a 47' cat as well as the standing rigging on the aft mast
    all you need is an A-frame mast with a boomless rollerfurling main and full vertical battens, and you have an efficient, safe and simple rig layout for a small crew on a big boat.
     

  15. brian eiland
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    brian eiland Senior Member

    Ketch Rig

    I think Chris has 'reconsidered' that ketch type rig he liked so much at one time. I addressed that here in this posting:

    Ketch Rigged Catamaran
     
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