Oldie:
Every time the clew gets even a little bit down into the water it wants to go further. Last Sunday I was out at the train and this happened, it's a royal B*TCH to get the sail back out of the water. I think what happens is that the wind blows the top surface of the water downwind, while the water underneath stays still... this means that you're trying to twist the sail against the current. Unless you're Hercules this is difficult.
So every time the sail was the wrong way around I flew it facing whichever way it was facing, then did the almost waterstart trick, flipping it over when it passed the eye of the wind. Then it would end up in the right position, ready for a waterstart. The whole operation, once it gets out of the water, took me about 5-10 seconds, and I did this about 10 times, it worked really well, and didn't require incredible strength.
Sure, try the Boards method but whenever I've tried it it's taken forever and sapped strength I'd rather use when upright