Thanks for your answers. I think the tight fitting clothing is definitely a big one, I generally get cramps when I wear a wetsuit. I've only got one sail for the moment, a 5.8m and so I'm overpowered occasionally and have nothing to rig up instead. Was sailing with the Futura 93l in 25-40 knots but also with huge lulls, it was pretty ridiculous, hardest chop I've ever experienced, mast high swells, but at least I was back on my board.
Got a couple of cramp spasms again whilst water starting (kicking with my legs) but thankfully they didn't lock up.
JP Super-X 106l, North F8 Ram: 5.8m,