Gromit -
I agree, and got pretty close to our nurse shark friend when I was investigating to find out exactly what s/he was doing under there. However, neither for love nor money would I have gotten in that dinghy while our shark friend was under it.
Yeah, that's what I didn't really understand about the story. If I saw a shark under the boat, I would get far away from it, not climb inside. Especially if the boat was made of rubber!
By the time our friend's mind had processed what he saw, he had removed fins and snorkel and was halfway in the dinghy. It was too late and he had to commit. Besides, turning on the motor would have solved the problem, but for some reason they just sat there.