If they were all under roofs, there must have been a lot more roofs, the Athenian navy was huge. Of course, a good many of the structures may not have survived, or been scavanged for building materials after the fleet was scrapped after Athens was defeated by those Spartan pederasts.
They give the full count in the video. Keep in mind that some portion of the navy were always on sea duty, so rotation must have been in effect much as at Norfolk. But the total number of boat house given was staggering nonetheless.