Wings for Early Supercat Catamarans

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Bill Roberts
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Wings for Early Supercat Catamarans

Post by Bill Roberts » February 19th, 2019, 9:03 am

In the early days of SC development, mid 1970s, Bill Roberts and Steve Edmonds experimented with a wing, a sail with thickness, that could be raised and lowered like a sail. This required a mast with two sailtracks. A mast and wing were fabricated and tested. The wing was identical to a H14 sail in every aspect, area, aspect ratio and plan form, except for thickness. The idea was to isolate the benefit of airfoil thickness, a wing, relative to a sail.
In testing vs a H14 with standard sail, the wing was slightly faster in max boat speed in all winds tested. The place where the wing was outstanding relative to the standard H14 sail was in tacking. As a sailboat begins turning into a tack, the sail begins to luff and continues to luff until the angle of attack on the new tack is sufficient to fill the sail and forward thrust is established on the new tack. During this coasting time, sail luffing and no forward thrust, the boat slows dramatically. This occurs during roughly 45 degrees to 60 degrees of turning with no thrust, actually sail drag, out of a 90 degree tack.
With the wing it produces lift/thrust at much smaller angles of attack. So going into the tack the wing produces lift/thrust for an additional 15 or 20 degrees of boat turning/tacking where the sail is luffing causing drag. Coming onto the new tack the wing produces forward thrust 15 or 20 degrees sooner than a sail and the boat doesn't come to a stop and accelerates away from the tack. The wing cut the H14 tacking time roughly in half.

Why no SCs with wings? Safety was number one. If the boat turned over, it could not be righted by the sailor or sailors. Cost was another.
The complete US Patent on the wing Bill and Steve built and developed and tested can be found at HERE and is also available for download below.
By the way, the wing Roberts and Edmonds developed is somewhat similar to today's, 2019, America's Cup Wings.
Attachments
US4064821.pdf
Roberts_Edmonds_WingSail_Patent
(816.47 KiB) Downloaded 39 times

T Peterson
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Boat Make/Model: Supercat 17
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Re: Wings for Early Supercat Catamarans

Post by T Peterson » February 23rd, 2019, 12:33 pm

That is an impressive design. I could even understand most of the patent!

If the sail provided more forward thrust during tacking, it would seem to me that it would also point higher. You didn’t mention that so I’m also assuming that even if it did point higher, the loss in speed more than offset the higher pointing.

Bill Roberts
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Joined: November 17th, 2003, 7:13 pm
Location: Stuart, Florida

Re: Wings for Early Supercat Catamarans

Post by Bill Roberts » February 23rd, 2019, 5:36 pm

T Peterson,
Wing powered sailboats do point higher and go faster than sail powered boats.
A big name in the spar making business who sails A Cats did make a Carbon
wing for his A Cat. When sailing this wing powered A Cat against other A Cats,
it was slower. Within the A Cat class, wings are slower than sails according to
some A Cat sailors.
You are reading too much into the pointing angle vs boat speed situation.
The base boat from which we were working was not a pointing machine.
That is the result of an optimization study which was never done.
As soon a Steve and I realized that the wing complexity and safety situations
were not for the general public, all further development efforts were stopped.

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