I agree with Don
Rick:I am 14 years old, but I consider myself a pretty good sailor considering that I sail very often with my Dad on his O'Day 28, and my mom's friend's Catalina 22. As far as your Question goes, the topping lift is to keep the boom at a 90 degree angle to the mast when your sail is down; so it needs to de disconnected via a small clip attached to the aft stay. The boom vang, However, lets u tighten the sail when sailind to windward, and keeps the boom from lifting up when sailing down wind, and allows u to tighten the sail to get maximun efficiency. I would keep the boom vang somewhere between medium and loose tightness, to all free movement of the main and boom. (it usually doesen't need to be messed with) But your topping lift deffinately needs to be disconnected from the aft stay ( or just loosen it, if it is the type that connects to the top of the mast) while under sail. -BenP.S: If u have any other Questions, E-mail me at Lyman57@hotmail.com