1/4" poly rope is between 1000 and 1200 lbs breaking strength when new,
not 1/2" which is much too strong. Note that the breaking strength will
reduce with use, so you would not want to use 1/4" poly to tow a double
seater or motorglider with water ballast.

Stewart Kissel wrote:
There was a recent thread on this topic...a search
of the archives should turn it up. FWIW 1/2' poly
typically is 1,000lb strength new, which allows it
to be used here in the USA for most gliders without
weak links.