After having webbing straps fail on me in the past, I now have a 10mm Dyneema (Kevlar) rope, spliced onto a stainless 3/4 tonne hook. I have a safety chain fastened to the trailer which goes to the bow eye. The winch is braked so I can control the boat once it starts rolling off. The winch handle is removable to stop broken arms & smashed teeth if it all goes tits up. Here's the drill:-
Reverse to bottom of slip (in low box
Take weight off safety chain with winch & remove safety chain.
Remove winch handle
Give boat a shove & control descent using winch brake.
Recovery is a reversal, I always make sure the safety chain is attached to the eye before pulling up the slip.
Once the boat is off the slip, it's secured to the trailer with 3 ratchet straps, 2 at the stern through the towing eyes & 1 at the bow through the bow eye. The safety chain & winch strap play no part in holding the boat down. If all the straps failed or some numpty forgot to put them on
the safety chain would allow the boat to roll about 50mm back off the trailer & then stop it.