bend is increased (the mast becomes more bent). The overall effect of tensioning the running backstay is a shallower mainsail (less camber) combined with a reduction in headsail sag. If the running backstays lead to the mast where the forestay attaches, the effect of tensioning them is to reduce sag in the headsail, increase mast bend, and flatten the mainsail as a result. Both effects are desirable as the wind increases. Backstays as antennas On modern oceangoing 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. References Sailing rigs and rigging