I sail at Thunderbird regularly and don't have any issues with them telling me I can't use the beach. I launch my Inter 20 from the beach at Sailboat point. Which is on the other side of the marina from where you describe.
I have also used the ramp at the Zoom beach area. I typically roll my boat down the ramp on the beach wheels, then pull it over to the beach.
Bill Etchieson
Yep, no problem launching there and as a matter of fact I would say it's the best spot on the lake. One of the bonuses is watching the power boaters and jet ski clowns try to back down the ramp. We have sat there with a few beers and rated them on single attemps, multiple attemps and changing to qualified driver. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" /> I have some great stories.