Captain William Bligh was not, as it happens, the tyrant that pop culture tends to paint him as, and certainly Fletcher Christian was not all that great. Also, Bligh’s sailing a 23-foot launch for about 3600 miles and actually finding his target is considered one of the great feats of seamanship. In short, Donald Duck, Aquatic Sociopath, is no William Bligh. He does manage to avoid being eaten by a roaring shark in this short, but I’m not sure that’s a good thing. And even in the various other shark movies I know of, the hero doesn’t just punch the shark.
Donald is being Donald, only at sea; he’s traded his in ordinary sailor suit for the fanciest one he can lay his wings on. Complete with an ornate hat covered in, well, you assume it’s not feathers. Lambswool, possibly? Anyway, he’s trying to make his three nephews crew a large sailing ship, and that goes about as well as you’d expect. Donald gets mad at them for not being able to do what they’re supposed to and ends up in conflict with a green, roaring shark.
It’s a rare Disney cartoon that makes reference to bird droppings, I have to say, but Donald’s so proud of that hat that we actually see him move out from under a seagull. As a child, I personally never thought about such things, even though I doubtless saw this cartoon many times then. But, yes, while it’s never actually shown, Donald’s pride in that hat starts with avoidance of a seagull. Or at least after he looks at us at the beginning and says, “Some class!”
Another “when I was a child” reflection here is a series of camps I looked at as a girl. I can’t remember if it was actually Girl Scout camp or these things for gifted kids we went on, but there was one I desperately wanted to do but wasn’t old enough (and frankly we probably couldn’t have afforded it anyway) on a sailing ship. Now, that ship was bigger than this one, but you would’ve learned how to crew it, and there were spots for a couple of dozen kids. Yes, larger, but still. Donald’s trying to crew this ship with his three nephews, as I said, and this is one of those shorts where they come across as literal children, perhaps ten years old in human years.
Okay, so the answer to this is, as it so often is, “because Donald.” I get that. I’ve certainly written about him enough times to give up seeking logic in his antics. But the difference between Disney and Warners, especially in 1939, when this was made, was that Disney cartoons were a little closer to realism. This is ridiculously implausible, that I grant you; I mean, even leaving aside that we’re looking at a talking duck. However, Disney cartoons start from a place where asking the plot to make sense isn’t an entirely stupid idea. Though asking Donald to make sense sure is.