rig like some marbleheads have, to much curve in your mast can lead to other problems when you go to ease the sails out for a reach or run! How do I do Pre-Bend? It might sound a little gruesome if you have just payed out a lot of money for a piece of lightweight alloy tube, if I suggest to you pick it up and bend it over your knee! But that is basically what you will have to do to pre-bent it. It really will have to be trial and error with you if this is the first time you have done this, as I cannot really tell you how much effort to put into this bending of the mast over the internet! Best under do it I think to start with. What you are attempting to do here is to put a permanent bend in your mast in a forward direction, so you must be sure you have the fore and aft line correct on your mast before you start this operation.  You will not want much bend down low, maybe none, start about halfway up and bend it just ever so slightly from mid point right to the very top first time around. If you have got it right you will have maybe two or three inches of forward bend in it and it will look cazy but this is what you will need. The more you bend it forward the more tension you will be