Our bonus boat is out of the rafters. Looks like some sort of a one-person (or maybe one-child) shallow rowing shell, but the ends are very rounded, not like the pointy shells you see racing on the Charles. There are two foam inserts, presumably to help it float, at either end, and the narrower end seems to have a metal piece. I did google various permutations of "photos of one man rowing shells with rounded ends", but no apparent matches.
The sides are coming apart, so I don't think this baby is headed back to the water anytime soon.
And, just in case you were worried that we wouldn't have a way to get around in all the remaining boats, there's a stash of oars in the lower level rafters, I'm sure there are one or two that will work.