High Tacker (www.damsl.com)
Hello to all, especially Brian Eiland and philSweet,
I'm a newcomer to the Boat Design Forum and first of all want to thank Brian for his references here to my A-frame rigged boat Catbird Suite and her website
www.damsl.com. And it's good to see that quite a few members recognize some of the benefits of an A-frame rig with all sails on furlers.
In particular, the reference above to the good upwind performance of the SMG-50 catamaran is informative because usually the first question sailors ask is whether she goes well to windward. I can say yes for Catbird Suite and am glad to hear about SMG-50. But there are many other benefits in an A-frame rig, especially with furling sails whose tacks are movable.
With respect to philSweet's comments re the geometry of some of my sail configurations, it is correct that the heeling moment is reduced when the tacks of the sails are attached to the windward side of the boat, effectively "heeling" the sails, re-directing the heeling moment downward and also allowing for some spilling of wind in gusts. And, heeling moment is further reduced if sails are attached to both sides of the boat.
With respect to the racking moment, I want to point out that with main, staysail and genoa all tacked down to the windward side, every sail (and on all points of sail) in its entirety is over the boat and within the cage of the rig, i.e., everything is inboard, as opposed to the conventional configuration in which, during reaching and running, substantial portions of a mainsail and a big jib are outboard, exerting leverage on the boat. In my sails-tacked-down-to-windward configuration, on a beam reach or broad reach, the luffs and leeches of the sails effectively amount to a rig within a rig, almost doubling the strength of the standing rigging, and without a boom putting a bending load on the mast in addition to racking the rig.
Most of the time, there's no need for sails on both sides of the boat. Mainsail, staysail and one genoa total some 2100 sq. ft. of sail, and having those three sails attached to the windward side of the boat allows the entire 30-ft. width of the boat for sheeting, eliminating the need for booms, and thus that old bugbear the accidental jibe becomes a non-event. And having the total sail area directly above the boat greatly reduces the tendency to broach.
See
www.damsl.com for more details on the advantages of unusual sail configurations accommodated on a catamaran with A-frame rig and furling sails whose tacks are movable. The rig of course also allows for the straight up and down, fore and aft conventional configuration. Uh, perhaps we should call that the square configuration.
I would also like to answer some comments about weight and windage. It is a fallacy to assume that two legs of an A amount to two times everything, far from it. If designed properly, an A-frame rig, in comparison to a single-masted rig that would support the same total area of furling sails, has superior ratios of strength to weight, strength to complexity, strength to cost, and strength to windage.
Again, see
www.damsl.com for detailed explanations. See the photos and notice how slender the mast sections are on Catbird Suite.
Cheers, Tom Bradshaw
