Ask Sail: Why The Bombproof Mains?

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There are a number of reasons why this Outremer catamaran has a burly mainsail

There are a number of reasons why this Outremer catamaran has a burly mainsail

Q: This past winter I did a bareboat charter aboard a 38ft cruising catamaran. I was once again impressed by how heavy and massively built the mainsail was. Why does this always seem to be the case on multihulls? (The headsails seem to be pretty much the same as those on monohulls.) Also, what is it that makes the mainsails on mulithulls so bombproof-seeming? Heavier-weight fabric? Multiple fabric layers? Some other construction technique?

— Ann Connolly, Chicago, IL

BRIAN HANCOCK REPLIES

Multihull sails are built stronger and therefore heavier than a sail for an equivalent length monohull because of one simple fact: multihulls don’t heel. When a puff of wind hits a monohull, it heels over and some of the load is taken off the sails. However, this is not possible aboard a multihull. Instead, when a puff of wind hits the load goes directly onto the sails. Therefore they need to be built a little stronger. This might include using a heavier fabric, but will definitely include having larger reinforcement patches. In addition, because multihulls are wide there is also often no need for a backstay to support the mast. This in turn means they can be rigged with square-top or square-head mainsails, sails that work better with full-length battens, especially up high, which also adds to the overall weight and bulkiness of the sail.

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