It’s a midwinter morning in Hobart, after the longest night of the year.  White frost covers the grass.  The air temperature is 2 °C.  The sun’s not even up yet, because it’s only 6.45 am.  So why would people be driving, walking, and riding their bikes down to suburban Long Beach and assembling near the water, dressed in whatever clothes are the warmest things they own?  There they stand, in track pants, uggies, down jackets, scarves and beanies, casually chatting and laughing.  I join a small group.  We’re stomping our feet and rubbing hands together to keep warm.  Organisers, dressed in black, are bustling around near a black tent.  Gradually, things happen.  People line up casually, collect towels and caps, have a number drawn on their hand.  There’s a safety briefing.  Over to the (vaguely heated) change room.  Out we come in our white towels and red caps, down to…