The article on launching and retrieving a trailer boat in the Summer issue of PBO reminded me of the frustration I suffered years ago when I first tried to recover my Sailfish 18. I used a rope tied onto the car tow hitch in order to get the trailer far enough into the water, but found that when pulling it out it was difficult to keep the boat properly positioned due to the trailer bouncing around as it ran over irregularities on the slipway surface.
I replaced the rope with a winch, suitably mounted onto a length of steel channel so that it can be hooked onto the car tow hitch (see photo). This allows a slower, more controlled pull as the winch is cranked, and allows the position of the boat to be checked and adjusted as it comes out of the water.
Before winching the trailer out it is a good idea to chock the car wheels to ensure it cannot move down the slipway.