They're called "boatels" or "dry stacks. Never seen sailboats stored in one, but they're popular with owners of ski boats, bow riders and "pocket cruiser" powerboat owners 'cuz they don't have to trailer it and and launch it themselves and it's considerably cheaper than a slip. You call ahead and set an appointment to launch your boat...it's (supposed to be) waiting for you at their courtesy dock when you get there. The only major downside: they close at 5 or 6 in most places, so if you want 'em to put your boat back in its rack you have to get back in time.