It's an Escape and Life Raft.
These is the only reason about this design. But an escape raft for just one soldier is unrealistic: the royal army must have much money to offer one boat to each soldier!
Indeed, stupid, incoherent set!
Only two more studs longer would be very better as a realistic small boat:
- for another soldier (using the crossbows);
- for place to carry anything else that these weapons which cannot be used;
- for a barrel or weapons to supply the army;
- for a soldier who rows and one or two people he carries, for example to cross the castle ditches or a river;
These two studs = one euro more? not very expensive!