Decided to try and model and print a submarine to mess around with in my pool possibly with my 4yr old nephew. I picked the seawolf fast attack submarine due to ease of modeling essentially a perfect cylinder. created a rudimentary connector between the 3 main hull pieces so that it is essentially watertight (which works pretty well but mileage may vary).
Printed mine with everything in vertical direction (for perfect circles) at about 30% infill, but feel free to experiment with that, mine floats way to high so maybe more infill would help but not certain. I had to fill the hollow space inside with water and a small aluminium bar to get it to be at the right waterline and be stable moving around. For supports I would make them only work from model to build plate to make removal much easier.
IMPORTANT INFO to get the connectors to work, a bit of sanding is definitely required on the outer cylinder of the bow and stern sections and on the little ridge inside the connector. I got my bow and center to be perfectly snug, however my stern wasnt sanded enough and snapped and broke the center piece connector as well, so had to glue it. Sanding is also required on the prop connecting piece, though you can always just glue it on. (also recommend 100% infill on prop shaft to make it stronger for sanding, first one broke on me while sanding.
Feel free to give it a try, it survived and entertained a 4 year old in a pool for most of a day and came out far better then I imagined my first attempt would, however there is room for improvement but some people asked for the STL so im making it available as is so user experience may vary.
Prop section was printed at 100%to not break during sanding and fitting.