If we ever get Batfish off the ground (whether floating or propped up), we'll have to look into getting props made for her.
Back to the earlier discussion of becoming seaworthy, I think the only way that the Navy MIGHT allow a boat to motor out to sea would be if the holes at the bottom of the hull were welded shut and the dive plane transmissions were rendered inoperable. Basically, this would ensure that she stays on the surface and there's no accidental dive, even if the ballast vents are accidentally opened or one has a bad seal. Otherwise, if the boat could dive, all it takes is one bad seal on a door, exhaust port, induction valve, etc., to sink the boat permanently.
I think that would be a pretty popular attraction, if people could take a short cruise on a WWII sub.