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On a sailing vessel, a backstay is the piece of standing rigging that runs from the mast to the transom of the boat, counteracting the forestay and jib. The backstay is an important sail trim control and has a direct effect on the shape of the mainsail and the headsail.

Types of backstays

Sailboat diagram. The backstay is identified by the number 15.

There are two general categories of backstay: The permanent backstay is attached to the top of the mast. The running backstay is attached about two-thirds of the way up the mast (sometimes at multiple locations along the length of the mast). In general, most modern sailboats will have a permanent backstay and some will have a permanent backstay combined with a running backstay. Backstays are not always found on all vessels, especially smaller ones.

A permanent backstay is attached at the top of the mast and may or may not be readily adjustable. In a mast head rig, tensioning the permanent backstay will directly tension the forestay. This control is used to adjust the amount of "sag" in the headsail. In a fractional rig, tensioning the permanent backstay will have two effects: First, the forestay is tensioned (controls sag in headsail) and second, the mast bend is increased, particularly in the upper one-half to one-third of the mast. Increased mast bend tends to reduce the draft (camber) of the mainsail.

A running backstay always attaches to the mast at a point below the top of the mast and is generally used in conjunction with a permanent backstay. Running backstays are found on both masthead rigs and fractional rigs. There are some rigs for which running backstays may be used without a permanent backstay. This occurs most often where the mainsail has significant roach. Gaff rigged boats invariably have running backstays with no permanent backstay. In both of these cases the mainsail extends aft of a line from masthead to stern, and so a permanent backstay would interfere with the operation of the sail. As a direct consequence of its attachment point (below the top of the mast) a running backstay is always adjustable, because it must be manually engaged and disengaged during every tack or jibe. Adjusting the tension on the running backstay has two effects: First, the forestay is tensioned (controls sag in headsail) and Second, mast bend is reduced (the mast becomes straighter). The overall effect of tensioning the running backstay is a deeper mainsail (more camber) combined with a reduction in headsail sag. If the running backstays leads to the mast where the forestay attaches, the effect of tensioning them will be as follows. Again the forestay is tensioned reducing sag in the headsail and second, mast bend is increased with flattening of the mainsail as a result. Both effects are desirable as the wind increases.

Backstays are generally adjusted by means of "block and tackle", hydraulic adjusters or by lines leading to winches.

Backstays as antennas

On modern ocean going yachts, the backstay is also commonly used as an antenna for Marine SSB radios and/or an amateur radio, accomplished by placing structural backstay insulators at either end of the backstay.[citation needed]


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