: Hi Mike,

: I had a 1/2"x10' piece of copper tubing laying around ($20 now) I paid
: about $3 and I mangled it pretty good trying the experiment using steel
: cable. It didn't act like I thought it would and go into a bend curve.
: Don't know why. I'll try one more experiment using rope. The old siege
: guns of the Middle Ages used rope twisted to get their power so I figure a
: twisted rope could dial in the any curve wanted. Your idea of a wood core
: is as good as any and would have reverse tension. I can buy 10 feet steel
: tubing very cheap, it's not all that heavy and wouldn't fail, but the best
: looking crab-claw sails have a curve on the spars and that is partly what
: I was trying to get at. If I made a sail curved where the spars go and put
: in stiff strait spars the sail would turn into something baggy it would
: seem.

Hi John,
Those twisted ropes seige engines used were a slightly different application to what you need. Plus they had a habit of exploding regularly. Modern rope should prevent that problem. Hey, what about a mini trebuchet for harpoon launching?
Steel tubing might work for curved booms if you can get a stable curve in it.

: What was your impression of the crab claw" Did you like it? Did you have
: problems going up wind and was it superior going across the wind on a
: reach?

: John

I liked it, less lines to fiddle with. As a 'flying rig' it isn't as close-hauled as a bermudan rig, that's with three lines connecting. With an extra line for hauling the lower boom closer to the mast, it tightens up a bit better.
On a reach or run, it flies. Letting the rig fly a bit, lifts the bow a bit almost like planing. It's similar to using a fixed point kite for sailing.
It does need a bit more attention to it to get the best out of it, but not much more than a bermudan.
This was on a 12' sailing dinghy I borrowed from my brother-in-law. A short term loan.

There was a wind-tunnel tests done on different rigs in 1985 by MacAlister Elliot & Partners, Lymington. "Design Factors Affecting Sail Power Based on Wind Tunel Research into Rigs Used for Fishing Vessels." This may be available through a Library service or University database.

Tony Marchaj and Jeremy Howard-Williams were involved in this. Howard-Williams' book 'Sails' Sixth Edition has mention of this and has fair comment on this rig type.
Quote from this book. "Initial results showed it to be 25% better than the best of the other rigs [1], being particularly efficient on a broad reach. Further tests, however, have shown that both wind gradient and airflow distortion by the hull cause deterioration in th crab claw's lift (partly because they make the vortices curl along the yards asymmetrically)."

[1] The rigs tested were: Bermudan, Lateen, Sprit, Gunter, Dipping Lug and Crab Claw.

My thoughts on this point. The airflow distortion may have been due to the use of a western style monohull in the tests, on sometinng like a kayak or a multihull, this may be moot.

Hope this helps,
Mike Savage
South West Cork