gaffs, balanced lugs, hoyt offset rig, etc

Discussion in 'Multihulls' started by Anatol, Jun 12, 2015.

  1. Anatol
    Joined: Feb 2015
    Posts: 191
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    Location: los angeles

    Anatol Senior Member

    leading edges, offset rig, shunting, etc

    OK, I did my homework, I read all 10 years of the the sail aerodynamics threads, and more.

    I've asked previously about mast drag, and the efficiency of jib-luffed sails. My current questions are in the same vein, though different enough that it warrants its own thread. Please note, my thinking here is wrt proas. So if you haven't considered the very unusual characteristics of shunting proas, please don't 'help me' with opinions that will only confuse me :).

    If you are of the 'sloop rig is best, so why bother?' camp, it may well be true, but its like saying a Prius is better than a Stanley Steamer. 100 years of intensive technical development will make anything better - you'd hope. The interesting thing about shunting proas is that they're so unlike conventional boats that some conventional wisdom doesn't apply.

    The modern opinion seems to be that the mast, or more correctly mast/sail combo *can* be shaped to add drive. (thanks Mikko). Tom Speer, elsewhere, has explained the "well-known problems of sharp leading edges, though, which form separation bubbles". (Others obviously think differently - see below.).

    BUT - if separation is such an issue - why don't we see 'padded luffs' or other teardrop leading edges on jibs? (ever?)

    In my case I'm thinking about cat schooner rigs. There seems to be a difference of opinion regarding distance apart. Some say far apart to avoid dirty air, some think close for slot effect.

    I was thinking about a couple of provocative pics - Cargo Schooner and Martinique boat with rectangular sails (see below). These both bring the leech of the fwd sail close to the luff of the aft sail, for maximum height. What is the cost of the the added sail area up top? - Especially since heeling is not a big problem on a level-sailing boat.

    Given the current popularity of fathead/squaretop mains: a gaff rig would give me both the desirable close-to-elliptical top, and a near vertical leech for best slot effect (without overlap) for full height of mast/sail. Does this make sense?

    And if so, what of the balanced lug, which some are enamoured of? In my case it may buy me true overlap and some movement of CE fwd (Proas usually have weather helm, often corrected with a small jib - at each end). The fine luff edge leads me back to an idea I was working on for some time, independent of, but rather like Garry Hoyt's self balancing offset rig swinging behind the mast, while negating the possibility of mast drive/mast drag. - I think it has interesting potential for proas.
    http://www.garryhoyt.com/id19.html

    By placing the mast(s) to windward, a balanced sail can swing through nearly 360 degrees, and the fwd projection of the luff can provide some 'slot'.

    So I'm thinking - a pair of almost rectangular high aspect ratio (~3.5: 1) offset balanced sails where- close hauled - the leech of the fwd is very close to the luff of the aft (even slightly overlapping) - might be an interesting experiment.

    Any opinions or predictions? - or historical examples? (I'm imagining some grainy old pics from Catalyst/AYRSS - those guys tried everything :)

    cited-
    chris whites' mastfoil rig
    http://www.chriswhitedesigns.com/atlantic_cats/mastfoil/index.shtml
    "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™."
     

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    Last edited: Jun 18, 2015
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