Alternate rig for Shellback dinghy?

Discussion in 'Sailboats' started by Gerrit, May 11, 2006.

  1. Gerrit
    Joined: May 2006
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    Location: Massachusetts

    Gerrit New Member

    A friend is building my family a Shellback dinghy. We like everything about the boat except the suggested 'dipping lug' rig. While the lug sail may be historically appropriate, we would prefer a more conventional cat rig.

    Our reasons are primarily aesthetic, though having a rig that is simpler and the many users are more likely to understand is also attractive. Cost is also a consideration, so finding a commonplace dinghy from which we could get a ready-made sail would be great.

    The lug rig has a very low mast, hence lower weight aloft than a conventional rig (though the lug spar does add extra weight above top of mast). Since the lug sail is more nearly rectangular, with a low peak, the center of effort is quite low (at around 8' above W.L.), and also further aft than it would be with conventional sail.

    The Shellback is 11'2" long, draft 6 1/2" board up, 2'3" board down. It is very light at around 100 lbs, with original sail area of 54 sq ft.

    Can anyone suggest:

    A. Whether a marconi cat rig could work on the Shellback

    B. How much higher the CE can safely be located, and how much more weight aloft we can add (though perhaps we might substitute a metal centerboard to add weight below?)

    C. Whether they know of a sail made for another dinghy which might work with this boat

    D. Whether moving the mast forward to adjust CE closer to original raises considerations other than structural reinforcement, etc. (the structural issues I think our builder can handle).

    Thanks very much for any guidance you all can offer.

    Sincerely,

    Gerrit Stover
     
  2. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    Yes for A.) and no for the rest.

    It is possible to make a 'jib headed' (AKA 'marconi' or 'Bermudan') rig that would have the exact Center of Area (CA) as the old lug had. The only rub is is that the two spars would be considerably longer than they were with the old rig. The mast would be longer than the boat and considerably so.

    The boom would be about 8.5 ft and the hoist (distance between boom ant top of the sail) would be about 12.75 ft. You would probably have to add at least 3 ft more to the mast so the boom could clear your ducked head.

    The mast will now be almost half again the length of the boat. But I have seen this done numerous times on pram dinghy types and it seems to work fine.

    If I were doing it, I wouldn't bother with having a roach (rounded trailing edge), but if you when with that, your spars could be somewhat shorter, but figuring out where the CA is would be a bit more complicated. And getting it where you want it even more so. (but do able, none the less)

    The thing to remember is that the new sail (without a roach) is a right triangle. Or near enough to one to be counted as one. Your CA will be 1/3rd the hoist and 1/3rd the length of the boom (and your area boom*hoist*1/2). You may have to play with the lengths of both spars to get the CA where you want it. Just remeber that having it a little (3" or less) further back than it originally was is better than having it a little further forward.

    I would be surprised, though, if the new sail's CA height ended up much higher than the old rig's.

    Bob
     
  3. Brent B
    Joined: Nov 2005
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    Location: Coopersburg, PA

    Brent B Junior Member

    Marconi Rig implies a main and jib, and Cat Rig has just a main. I assume you want a Cat Rig.

    We have made various alternate sails for the Shellback. Most common is a balanced lug sail, which increases the sail area a bit....desired by some. The cat rig should work too.

    A simple cat rig with a lot of roach in the sail would keep the CE acceptably low. The standard lug sail is actually pretty small for the boat. You might need to move the centerboard a bit forward, or the mast a bit aft...we could figure this out for you.

    Feel free to contact us off-forum .

    Brent
    bensonsails@bensonsails.com
     
  4. usa2
    Joined: Jan 2005
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    Location: Maine

    usa2 Senior Member

    You may want to use an aluminum mast, if possible. I have a shellback dinghy, and it is a very tippy boat. Put in the wooden mast, and it becomes nearly unbearable. Sailing it is a pain, because in no wind it will heel the wrong way quite far, and then when you decide to shift over a little, the mast will cause you to roll further than you intend. Getting hit by a puff is when the fun really starts.

    A cat rig would do much to improve performance, because the lug sail is rather inefficient and annoying to rig. My sail (which came with the boat) looks like a old red tarp(which it probably is).
     
  5. Seafarer24
    Joined: May 2005
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    Location: Tampa Bay

    Seafarer24 Sunset Chaser

    You could easily use windsurfer masts instead of aluminum or wooden masts. These will be made of fiberglass or carbon fiber. You could even use a windsurfer sail and wishbone. You may have to rake the mast aft to get the CoE where it needs to be for balance.
     

  6. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    Another rig you might consider is a boomed lateen (like you see on a Snark or a Sunfish) A 54 sf rig of that type would have a pare of 11ft spars. One for the Boom and one for the yard (the highest point of the yard would be about 5 ft aft the boom yard junction). They would be the longest spars on the boat. The mast could then be 10 ft or less. Maybe as little as 8ft. The beauty of this sail type is that there is only a halyard and a sheet line on it and the yard moves in lockstep with the boom. Also, when you release the halyard, the sail wastes no time comming down. And it needs no agravating tricky gear such as battens (which often have to be removed whenever you furl the sail) and boom vangs. The long yard can be made significantly lighter than the tall mast needed for a jib headed rig. It is probably the best beginner sail ever invented.

    You might even find one from a totalled Snark(r) which would be about the size you're looking for, around 54 sft.

    Bob
     
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