There is a magic point when you forget about heading and focus on flying a hull (it was about 7kts on the Inter 17, and I have no idea yet where it is on the F16, but I'm sure it's lower), heading downwind will come when the speed builds, the hull flys and then you have to bear off.

90deg is probably a good target for when you are moving real slow, once the boat is starting to drive, it might be tighter than that.

I'm still very very much learning my F16 - but it's Fun <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />