happened to my mate on the way back from a fishing trip, we were both towing small tinnies and he had an F150 and you could not even see the trailor behind, I was following a few miles behind and I came across his boat with winch post still attatched sitting on the road, a quick call on the mobile phone (cell to you folks) and he did not even know it was gone, it turns out the tie down strap had come unhooked somehow and was dangling on the road and got hooked on what we call a cattle grid, which is a series of railway track set about 1 foot apart on the road to stop cattle roaming along to the next farm, anyway it was still hooked to the line and the tinny had been yanked off the trailor along with the winch post, it had got caught around a rowlock and caved in the side of the boat as well, sorta looked like a big aluminium banana, still laugh about now, but not too funny at the time, for him anyway, oh and did not do the motor much good either.