water ballast

Ballast and downwind. Is the goal to simply glide as far as you possibly can after the last climb? If so, then no ballast is better than ballast. Unless, of course, you get a boost in L/D max due to higher reynolds number for the ballasted flight.

Generally speaking, ballast lets you have the same glide ratio at a higher speed and thus at a higher sink rate. You won't stay in the air as long, but you would cover the same distance in no wind, with or without ballast (see above possible exception). Since the airspeed for the same L/D is higher with ballast, headwind will have less impact on the distance you can cover. For the tailwind case, you won't be in the air quite as long, so the wind won't "push" you quite as far.

If the thermals are big and strong enough to support carrying water, you are always better off carrying water, whether going upwind or downwind. Until that last glide at the end of the day, where going downwind, you can get a little extra time aloft and wind drift by being dry.

Steve Leonard