On a masthead rig, the forward lowers have to be taut, so that, when you add tension to the backstay, they won't let the lower section of the mast move aft. Also, you have to loosen the tension of the aft lowers, so that, when you apply tension to the top of the mast, through the backstay, the middle of the mast is able to bow forward. You should adjust the aft lowers so that they become taut when the mast bends as far forward as you want it to. Properly adjusted, the aft lowers prevent you from over-bending the mast.
You can also loosen the headstay a little, so that, in light air, with backstay tension off, the mast is straight and the headstay has a slight sag, but, when you increase the backstay tension, the headstay becomes taut, the middle of the mast can bow forward, and the top of the mast can bend aft a bit.
If you adjust all the shrouds and stays to approximately equal tension, they won't permit the mast to bend in any direction.
Last edited by Sailormon6; 12-16-2006 at 08:01 PM.