You might have noticed that cruising catamarans don't have backstays. The reason they can manage without this common feature on monohulls comes down to their design.
First, catamarans are wider. Their significantly wider beam allows the shrouds (the wires supporting the mast from the sides) to be attached much further apart and often further aft. This wide stance provides the necessary stability that a backstay offers on narrower boats.
Second, catamaran masts are designed to be quite stiff to resist bending. Sailing downwind with a gennaker or asymmetrical spinnaker generates large forces on the mast to the forward and to the side. The wide base of the shrouds described above goes some way to handling these loads. However, the mast itself also requires sufficient fore-aft stiffness to resist bending. This is one reason why catamarans of a given length often tend to have shorter masts than cruising monohulls of the same length, since for a given section, shorter masts are stiffer than long masts. This inherent stiffness, combined with the wide shroud base, reduces the need for a backstay to counteract forward forces.
An additional advantage of the backstay-free design is the ability to have mainsails with squarer tops, i.e., less triangular in shape. Such “roachy” sails have an increased sail area for a given height, which makes them more powerful, particularly when sailing on reaches and runs (as shown in the top photo). The wider head can also improve the overall aerodynamic efficiency of the sail by reducing vortices at the tip of the sail that creates drag.
Therefore, the absence of a backstay enables a squarer, more powerful mainsail on a shorter, stiffer mast. This shorter, stiffer mast, supported by widely-spaced shrouds, in turn reduces the necessity for a backstay – a truly efficient design!
OVER.
Comments
Post a Comment