If you don't have a tongue extension...
You might try this trick if you can't get the boat deep enough to float the boat and your tow vehicle is about to develop a deep and meaningful relationship with the water.1. Back down the ramp until the trailer wheels are about a foot away from the water. Chock them securely. Unhitch the trailer, drive forward about 10 feet and set the brakes.2. Grab your 30 ft piece of 2-inch manila or polypropylene rope (Home Depot sells it), tie one end securely to one side of the tow hitch on your vehicle, run down to the trailer receiver, drop the line through the frame, bring it back to the other side of the tow hitch and tie off securely to make a bridle.3. Get back in the vehicle and drive forward a couple of feet to take up the slack in the bridle and pull the trailer off the chocks. Set the brake and remove the chocks.4. Back the trailer into the water as you normally would; gravity will keep the bridle tight and the trailer will go straight down the ramp. You can back the trailer in as deep as you need to float the boat free and your tow vehicle will still be high and dry on the ramp.5. Once the boat is off, pull the trailer up out of the water, chock the wheels, reattach the receiver to the ball and drive away.6. To retrieve the boat, do everything in reverse order.This also works on weedy or slick ramps, especially if you don't have a 4WD vehicle, because it will keep your vehicle on a surface with good traction. If you are worried about unhitching your trailer on the ramp, rig the bridle before you get on the ramp so you always stay connected to the trailer.Some people use only one line, tied to the trailer and to the hitch. I prefer the bridle because it offers a little more control on the ramp and if the trailer ever gets hung up, I can untie the line at one end and retrieve it without having to go into the water. Resist the temptation to use steel cable. Poly line is great stuff. It is plenty strong (I have used it to free pickup trucks buried to the axles in muck). It also has more "give", and will give you plenty of warning if the trailer ever gets hung up. Cable will snap. Happy trailering and sailing!!PeterS/V Raven