Had you paid more attention, you would have realised it's not the classic riddle, but an already tweaked version that makes it impossible to solve, hence why it is interesting.
I'd give them full credit if they noticed that, but I was also wanting to see if, given the unstated assumptions (one thing in the boat, don't let anything eat anything else, etc) they'd realize it was unsolvable.
This variation of the classic puzzle is unsolvable. If you have a solution, let me know.
“What is heavier, 20 pounds of lead or 20 feathers?”