For any fixed wing aircraft the max L/D speed (or minimum sink speed,
for that matter) changes with the square root of the difference of the
mass ratio. Assume that a glider and pilot weighs 700 pounds and has a
max L/D at 50 knots. Now add 400 pound of ballast for a total weight of
1100 pounds. 1100/700 = 1.57. the square root of 1.57 is 1.25 - so your
new best L/D speed is 50 x 1.25 = 62.5 knots.

Tony V.