I have raced (a Dart 18, it was a long time ago) in what I would call 'Icing' conditions and the problems are numerous.

1, Sailing up wind, the spray (it was about F4-5) was freezing on the tramp/ mainsheet and sails, the only way to sheet out was to kick the multi-block system at the back of the sail.
2, Tacking was very difficult as when the crew came in from the wire, there was a real danger that they would just slide out the other side
3, The traveller line was icing up too
4, Spray was icing on the sails, each tack resulted in the ice cracking and sliding onto the tramp/crew.
5, Gybing close to other boats was dangerous as the ice would fly about 15 feet as the battens popped.

I was actually not [too cold, but I was wearing :

Thermal underwear
Silk socks
Skisocks
Polartec 200 Ski-pants
Cotton T Shirt
Cotton sweatshirt
Polartec 300 fleece
Bull dry suite
Spray top and trousers (and of course life jacket
Sailing gloves.

Some of the people with high-tec boats could not go out becasue they could not get the dagger boards into the hulls as the slot tape was freezing back up as fast as they could thaw it out.

Low tec is good sometimes