I once lost an expensive anchor when anchored in a very strong current around 3 knots when the tide changed but was lucky enough to be awake at the time and save the vessel. I learnt to tie d shackles then (about 1980). New laws in Oz are addressing trailer d shackles and banning the common d shackle, so many accidents must have occurred when safety chains were not properly fixed to the vehicles. inproper walk around?