Metal chains would rust.
This is how the writer patches the hole in the tie-in novelization. Not to, y’know, ski, but he uses his whip to tie himself to the periscope.
Speaking of Indiana Jones movies (and all “I know it’s just a comic strip movie” disclaimers in place), the bit that drove me nuts when I saw it in the theater was the circular staircase that collapsed in the German castle. While it is conceivable there could be such a think, consider how much horsepower would be required to reset it- you could hook up 20 tanks with chains to that thing and it would still be a bitch to “reset” it once it was dropped… and yet the secret mechanism to do this was to recline a metal chair.
Can you imagine the medeival baron who built this castle and how much he must have blown a gasket everytime a cat jumped in that chair, dropped the staircase, and then he had to sprend the next three growing seasons roping peasants and oxen to the thing and having them heave-ho it back into position, only for it to be dropped again when German Duke Jr. decides to show off for his visiting friends: “Look what happens when I lean back in this chair!”
Even in keeping with the spirit of the movie, it would have made much more sense to have a hidden staircase, which actually do exist, that Sean could discover under said chair or whatever. (Of course the same movie depicts Hitler misspelling his own name, dirigibles crossing the Atlantic several years too late and three Crusaders who built a boobytrapped Boggle board to protect the Holy Grail but were really anal about the letter “j”.
“How are we going to get there? Plane? Boat?”
“Easier: dotted line.”