Question 1 :
... if you have an F16 and plan to be racing it sometimes as sloop and sometimes as unirig, is it necessary (or advisable) to have two different mainsails?
I would say "not necessary"; I think it will only pay off when you are already finishing in the top 3 (or top 5)of decent sized fleets regulary. If one does not then effort is much better spend on sorting out your tactical or trimming mistakes.
About it being advisable, well I can't see that having two specilized sails will hurt, but I really don't see that much in it as well. I doubt wether the extra expense is worth it unless you are getting really serious about racing.
I really think it is one of those things that sailors needlessly work themselfs up over. Often they fuss about a perceived technical advantage while throwing away a multiple of it by applying bad tactics on the water.
Question 2 :
... if you are buying an F16 and you are going to be sailing it half the time as a unirig and half the time as a sloop rig, which sail cut would work best for both?
This is easy, a sloop cut main will work best in both setups by far. Simply because you can always depower a given mainsail but never power it up beyond what the sailmaker cut into the sail. Ergo a sloop main can be made to work (well) as a single handed mainsail, but a cat-rigged (singlehanded) sail can often not be made to work well as a doublehander sail by virtue of insufficient curve/draft (lack of power to compensate for the extra crew weight).
So when in doubt get a sloop cut main. Actually I would advise everybody to get a sloop cut main that is optimized for your expected doublehanded crew weight and then just trim into a good shape for singlehanding. Most inexpensive option with overall the best results and the most flexibility. Only when you are really serious in racing singlehanded or some A-cats are giving you a hard time then maybe decide to get a specialized 1-up main IN ADDITION to your 2-up mainsail.
But I wish to underline again that skill and hours practising are always the way to the top no matter what you are sailing. This can't be overstated, simply because skill is so much more dominant in the final outcome then small changes like this. That is when assuming that the boat is dialed in correctly, afterall a small change to my jib did result in a noticeable difference but that was because my jib wasn't working as intended. (It fluttered and collapsed when pointing)
Wouter
