And in a large break from my regularly scheduled programming, I’ve drafted up a submarine for my upcoming underwater scene:
Used to harvest clams, lobsters, crabs, and other desirables from the bottom of the ocean (near the shore, before it gets deep.) Since the submarine can’t go terribly far without the ship above moving, the propeller is rarely in motion and is mainly used for reversing or for an assist while climbing steep slopes.
Two thin wheels in the back and four legs in the front minimize the damage to the ocean floor.
Upon reaching a good spot for crabs, the boat above lowers the submarine down with three occupants. Half of the metal portion is filled with breathable air from the surface, and the half with the door is a water chamber. Over a few hours, the crabbers venture out two at a time, holding their breath while they harvest for a few minutes, then bringing them back in and re-entering the air portion. The narrow neck of the metal part is a crab jail storage facility.
If you’re wondering why the crabbers have a submarine but not underwater breathing technology, my preferred level of technical expertise in my personal fiction is about Edwardian level (1920s-ish); electric lighting, trains, rudimentary wireless communication (telegraphy and radio), and that’s about it.
I always like to think about why people develop technology in certain ways. In this case, since the submarine technology is being used exclusively by fishermen, there would be no logical reason why they would make a submarine that could operate autonomously a priority. They already have ships, these submarines are just extensions of those ships. In our world, submarines were designed to be autonomous from day 1 for naval warfare. I like to think these fishermen are a bit more insulated from that kind of life.
Also, since these would clearly be very expensive, I imagine there’s just one that a regional fishing community shares, using an honor system and probably some coercive strong-arming to make sure everyone gets a turn with it.
The people inside can communicate with the ship above- nothing high-tech or fancy, just cables and bells. This world would have wireless communication, but putting a receiver on a ship would be bulky and expensive, and generally pointless.
Feel free to share your thoughts 