It takes a big man to admit when he's out of his depth, and I'm a very big man indeed. I've tried three times to figure out what on Earth I should be doing in the Sail Simulator 5 demo, but all I do is flap around in circles, and then try to ram a boat. By the looks of it, someone who knows their jib luff from their main tack might be able to fathom it. Or someone who reads the instructions.
In the demo you can play some online multiplayer, much around wtih the Stentec Laser dinghy (which sadly doesn't include firing lasers), and enjoy sailing around Treasure Island (which sadly doesn't include any treasure). It has very pretty, if someone repetitive, sea. And that's my expert opinion. You can get the full version here.