On Wed, 19 Aug 2020 10:48:30 -0600, Dan Marotta
wrote:

Remember your high school chemistry (or was it physics?).* Water gives
up 1 calorie per gram per degree C while cooling.* To transition from
water at zero deg C to ice at zero deg C requires the loss of 80
calories per gram per degree C.* That's a lot of heat to be lost!* Sure,
you have a large surface area, but you have a very large volume as
well.* It would take quite some time to freeze a ballast tank.

Bottom line is I never worried about icing the ballast tanks (when I had
them) at sub-freezing temperatures.* Now freezing the dump valves is a
different issue, but not really if you fly your glider all the way to a
stop.* I once landed my LAK-17a with nearly 50 gallons on board and
didn't notice until after getting out of the glider.* Another time, one
dump valve stuck closed and, again, I landed with 25 gallons in one wing
and empty in the other.* I didn't notice until coming to a stop and the
full wing dropped heavily.

.... text deleted

Maybe off topic, but what worried me in past years when I flew in the
New Mexico mountains was not the wing ballast tanks, but the tail
tank.

I always had visions of the tail tank freezing and failing to dump
when I dropped ballast, leaving my CG too far aft.

I usually left the tail tank empty if I was expecting high altitutes.

Bob