By the way, at our lake with a very nice, long, reasonably moderate slope concrete ramp, we routinely launch and retrieve 4.5' draft fin keels like Impulse 21, Santana 20, and J/24. This is usually done with a 25' tongue extension that is carried on the trailer and slides out. Most are actually alongside the regular tongue, with brackets attached to frame members such that the extension can slide out. Some people pull it in and out with the car, but I kinda like sliding it by hand if it's lined up well and smooth enough. A suitable jockey wheel is necessary - the bigger the wheel and softer the better. Eg. if it's a hard plastic wheel, bigger is better, or pneumatic wheel. The best jockey wheel I've seen was on a custom Triad trailer built for a Beneteau First 235 fin keel. It pivoted down, and was a nice sized pneumatic tire. Rolled nice and smooth... With a nice jockey wheel like that, strap launching is just about as easy. Nice and high keel guides REALLY help get everything in position.