on a river or lake? currents or tide? what about if there was a flood and the lake/river filled up much higher to completely cover said boat house?
Just some questions ... example Lake Georgetown (corp lake) filled well beyond expectation several years back which covered all the public parks including all the covered picnic sites and restrooms. They had to close down all access due to septic in the lake & underwater electricity ... once the lake went back down, there was a whole lot of repairs needed to the structures & electrical systems.
although I see your point ...