Thjs works too.

http://thmarine.com/z-launch-watercr...unch-cord.html

Or even simpler. Back down ramp, boat not in water but whee's right at edge of water. Undue winch line and chain safe line. Attach 30 foot rope to bow cleat. Take balance of 30 foot line and drop in pickup truck bed, the attached end of line to truck bed cleat. Back in , give it a nudge, boat floats off trailer, pull truck forward till boat beaches. Done