Blackmagick sails
Tuning the Rig
It's so very easy to focus all your attention on the sails, because this is what we are looking at mostly as we are sailing your boats. One can tend to forget about the mast which is holding every thing up there for you to see, and if the mast is doing things it should not be, well, mostly so will your sails! To start with we shall look at the two most common ways a mast can bend and whether or not it is a good idea to have it do so.
Sideways Bend!
OK we'll start with this one, sideways bend, two schools of thought here! Some suggest a little sideways bend is OK! it helps open up the slot between main and jib when looking front on at your yacht. This could be a good idea, but how much is too much? If you allow your mast to bend sideways you are infact turning your mainsail inside out, try it sometime, rig up your boat, put the mainsail on and just gently bend the mast sideways a little without the sidestays attached, or with only the weather side attached, watch what happens to the mainsail and you figure it out if it is a good idea or not to have sideways bend in your mast! That aside if the mast bends anywhere but backwards it will be allowing the forstay to sag or go soft on you, making the jib fuller at just the time you don't want it that way, in a breeze! So if you have decided you don't want any, how do you stop it from bending sideways?

Generally the higher up the mast the attachment point of your sidestays the less chance your mast has of bending off. Spreaders placed at approx. half distance between deck and upper sidestay attachment point also help prevent this sideways movement. The spreaders do not have to be overly wide, they can be only as wide as the gap between mast and sidestay, just holding the wire in line between deck and upper attachment point. Once again there are many schools of thought here but best not make them too wide I feel. A stiffer mast also helps, but stiffer usually means heavier, do we want weight up high on a racing yacht?
Fore and Aft Bend
Once again there are no hard and fast rules here, some like a soft mast that they can bend aft quite some amount right through it's entire length, others prefere to sail with a straight mast most of the time, bending it only ever so slightly aft in a breeze. Whatever you decide you want, if it is to the extreme ends of this scale you had better discuss it with your sailmaker, because if you are going to bend your mast aft to a greater degree you will need more luff curve cut into your mainsail and unless you know what you are doing you can get into all sorts of trouble setting your sails! I would suggest if you are fairly new to all this just go with a stock set of sails and only use a very moderate amount of mast bend aft in a breeze. A well cut stock set of sails should be fairly easy to get to set right with the minimal amount of fiddling. A little aft bend is recomended in a breeze to flatten the sail through the top sections and help the leech twist of a little up high. You will however usually have to tighten up on the kicker or boom vang when you bend your mast in this fashion, as the leech will fall off mostly to far without some correction. The lower portion of the sail (main or jib) can be flattened by pulling the foot tight, or tighter, as discussed elsewhere.
I see mostly straight masts here, but this is light weather sailing, and it doesn't mean they are all correct in their thinking either. Sometimes doing things differently makes the sport more fun, be adventurous if you wish to win, copy until you are as good, then start thinking for yourself! 
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