Course was in an unheated swimming pool with a wave machine turned on, designed to simulate the North Sea.
Offshore Survival Centre | Blackpool and The Fylde College
Was quite a while ago, but I think we were wearing t-shirts, swim shorts and life jackets.
It was obviously not aviation focused and the rafts are bigger (as you can see in the pic) so your test was probably more representative, but I'm still surprised at 0% success of your test subjects!
the final test had us doing it in the dark with simulated rain, panicking "passengers" and involved an 8 meter (I'm guessing) jump off the side of a "ship" into the water...
great fun!