When I put a strap on the T3XXX winch, I thought that, well the whole trailer is only 22 ft, and I'd never gone more than half way, so 20' is enough, even giving me a goodly number of strap wraps. and I have a roller trailer, so I can just run the boat up on the rollers, right?
And I was proven right for the first 3-4 launches, in San Diego and St Paul. Then I had to haul out in Dubuque, Ia, with the Mississippi river running low. I buried the truck and the strap just barely reached, with Judy and I pulling the boat on the trailer for all it's worth. That was a looong winch. So, the length of the strap/cable/rope is not for the normal launches, but the weird ones, like Dubuque or anywhere in San Francisco Bay (Sausilito, San Rafael, for 2.) My apologies to Dubuque and San Francisco, in advance.
Now there are different ways of getting the boat up on the trailer, all of which require less cable than I use. However, if the strap/wire/rope is too short, you're at a ramp a long way from home, you probably don't have a cable stretcher with you either. So my new rule of thumb is 30' min, off the drum. For those who launch at a ramp they know, less is probably enough.
And Bob is absolutely correct on tying down the back of the boat. The first time I did it, on a 22' sailboat, it kept me from dumping a boat on top of a house in Ensenada, Mexico. The only time I've ever done something in advance that saved my rear. NEVER leave home without a strap across the rear of that boat. Here's a place you can get a good strap cheap:
USA 2 " Tie Down Strap. Get the cheap one, the others are too complicated.
Boris