Jud:

I would make one out of concrete and tow it out with your Catalina to set it. Use about 3 sacks of dry concrete mix and place it in a square plywood form on a nearby dock. Put a bent piece of rebar in the middle to attach your mooring chain. After it cures, hook up a chain and toss it overboard. Hoist it up off of the bottom a bit with your Catalina's genoa winch (it should weigh 300 lbs) and some turning blocks. Tow it out where you want it and drop it in place. If you use a decent scope, say 4:1 it should hold your Catalina in anything short of a gale. If your scope is limited go a few hundred pounds heavier, but then it gets to be unwieldy to handle and tow.

David