The manual for many single seat gliders state that a parachute is part of the certification basis.
The CG arm for the pilot commonly assumes a parachute.
Gliders commonly specify minimum weights for the pilot and if you happen to be that light and are not wearing a parachute, the CG is too far back -- and if you do not pay careful attention to the CG the first time, you will find out very quickly when you lift off on tow
