I am not very familiar with your location but here in Wisconsin lets pretend someone wants to steal my boat.
1) Probably couldn't get it started, if they did and wanted to untie and head out then..
2) They would get "swarmed" by helpers, someone would notice something was not right and the event would either be stopped or tracked
3) If they got away from the marina where would they head? South to Green Bay? Maybe across the Bay to Sturgeon Bay then Milwaukee or Chicago? No fuel gauges on my boat, would they make it anywhere?
4) So say they make it to the big city (Chicago) what now? Sell it ? For the little it would bring on the "hot" market it would only pay the theif or thieves a few hundred dollars a day for their effort.
5) Part it out? The engine is the only thing worth anything, the average thief wouldn't know I just spent $20,000 on the rebuild, How do you get it out of the boat? More work!
6) How about the stuff on board? Used clothing, worthless, Used electronics, nearly worthless. Ive got some nice binoculars on board but really, that's about it. Wouldn't cover the transient fee at any marina.
I guess the only reason to steal my boat would be because they want a boat and can't afford one. They sure wouldn't steal mine, it's not as shiny or new or pretty as many boats within 20 miles of mine.
Besides, the get-a-way would look like O.J. Simpson in his white Bronco, Slow Motion...
pete