Actually ; 1-up means sailing solo as in only 1 person on board. 2-up means sailing doublehanded (2 persons on boards or even more)

Pretty much this means, when looking at the F16 class rules that 1-up = main + spi and 2-up = main, jib, spi.

However ! I must be said that the F16 rules allow any crew to sail "with less" then allowed under the rules. So if you want then you can sail F16 1-up with only a mainsail. You won't be very competitive in most conditions, but that is only your disadvantage, not one of the other crews who are using all that is allowed.

But when I talk about 1-up or 2-up in these F16 forum post I'm actually refering to the setups that are fully maxed out under the F16 rules and that means

1-up = solo with main and spi.
2-up = doublehanded with main, jib and spi.

Wouter