On Tuesday, May 2, 2017 at 9:00:41 AM UTC-4, wrote:
"Could you tell us about glider type, CG, weight and tow speed, especially
in relation to manufacturer recommended tow speed? "

Ventus B, 15M with winglets, dry. CG at 56% of range, 740 pounds, 60 Knots, Flaps +1, Spoilers closed.

Better double check that W&B, because the behavior you describe suggests a CG close to or behind aft limit. There are probably a few Ventus Bs around with undocumented tail weight added. That was sort of the fashion in the 1980s.

If you are indeed at 56%, then there is some other significant issue.

best,
Evan Ludeman / T8