Back in the old days, before God invented beaches, we always launched our 20x10-foot Shark catamaran with a hoist.
Every sling we have ever used has been 4-point -- attached basically at the ends of the main beam and the rear beam. Usually attached to the beams just inside of the hulls. You can install strap eyes on the beams or, if you have space at the ends between the trampoline and the decks, you can put loops of line around the beams at each point.
Then you experiment with balance. Probably best to use some non-stretch line. Bring the four lines together at the lifting point that is going to hook onto the hoist hook. Use the hoist to lift the boat a little bit at a time to see which way it is going to tilt. Keep adjusting the lengths until you get it right.
Then measure the lengths of the four lines, so you won't have to go through that whole process again.
You can either use the rope sling that you start with, or some people use the measurements to have a sling made out of cable.
It's an easy and effortless way to launch the boat. The only drawback is that you have to raise and lower the sail on the water rather than on land.
Once you have your sling, you could probably also use it to support a makeshift tent for camping on the tramp, by holding the top of the sling up with the halyard. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
