You might get a high risk, Lloyd's of London policy on the hull, (less the
value of the engines), and that could be supported by survey. Just because the
boat doesn't have operable engines shouldn't mean that it is without value.

I'll bet the insurance coverage the marina is looking for has more to do with
liability than with replacing your hull anyway. What happens if your boat
spills fuel? Catches fire and burns a few other boats or part of the facility?