Mike,
You said that poor handling during low speed towing is mainly felt by newer standard class racing ships. This is probably correct if we accept Andreas’ explanation that downwash interaction (requiring higher AOA which leads to tip stalling) is the root cause of the poor handling problem, as flaps would allow a lower AOA than with a standard ship. However, a look at section 4 of several pilot handbooks showed that the 15/18 m ships have higher minimum tow speeds:

Ship, dry min tow, wet min tow
D2, 54 kt, 65 kt
LS-8, 54 kt, 65 kt
Duo, 54 kt solo, 65 kt dual
V2, 65 kt, 70 kt
ASW-27, 65 kt, 70 kt

Do you know what the 15/18 m pilots experience when being towed below 65 kt?

-John, Q3

On Tuesday, November 5, 2013 1:32:35 PM UTC-5, Mike the Strike wrote:
The Discus 2 exhibits the same behavior. It's a problem mostly seen in newer unflapped racing ships because of the angle of incidence of the wing. This results in a nose-up attitude at low speeds and on aerotow this results in a downward pull on the nose from the towrope. This down-pull has to be counteracted by up elevator. With ballast, I run out of up elevator around 60 knots or so, and I have had my glider sink into low tow a couple of times with a slow tug and have had to release a couple more. In free flight, the glider will stall at its placarded speed and handles fine. Tows below 60 knots have very poor aileron and elevator control.

There may be other things going on, but I suspect the relative angle of the towrope to the fuselage on tow is responsible. Flapped ships alter their pitch and hardly suffer from this effect.

Mike
Discus 2b