At 07:48 PM 3/20/2006, Alan Brooks wrote:
Thanks, Dave, I always wondered what the 'spreaders' were for. I always assumed they simply added stiffness, not that they were a control mechanism.
Well their function is indeed to add stiffness -- by applying a force perpendicular to the mast against the direction the mast is bending. But they are a static control mechanism; they can be "tuned" in terms of how much stiffness they add, and in what direction. For instance:
* Unlike a structural beam -- say, the mast or a golf shaft -- the bending of a RIGGED mast (with stays and spreaders) doesn't have to have the same flexibility to both sides of a plane. Remember that the stays are wires; they are very strong and stiff in tension, but flop completely slack in compression. So spreaders (and, in some cases, un-spreadered stays) can apply a force when the mast bends in one direction that are not equaled when it bends 180* the other way. Completely unlike a golf shaft.
* The force the spreader exerts on the mast depends on the tension on the stay and the angle by which the spreader deflects the stay. So you can adjust it either with a turnbuckle on the stay or the length of the spreader. In practice, a spreader may have a series of holes (actually, slots that can be closed off) through which the stay is passed. The further out from the mast the hole with the stay, the more force the spreader exerts on the mast.
* The boat I raced had a very simple stay-spreader arrangement. But even it had a "secret weapon". The spreader was attached to the mast with a limited-motion hinge so that, if the mast bent in such a way as to move the spreader aft, then it applied more force to resist the bending. But if the mast bend moved the spreader forward, it would hinge forward freely, allowing the mast more bend. (It has been 30+ years, and I don't remember exactly why this was desirable -- but I was convinced it was.)
Cheers! DaveT -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.385 / Virus Database: 268.2.5/284 - Release Date: 3/17/2006
