Nice porthole that's 100% a porthole and not anything else. ;)
Awesome concept! It felt kind of like a mix between FNAF and Iron Lung. Genuinely creepy atmosphere and good immersion. I feel like it would have been even cooler if the inside of the vessel were the same 3D art style as the environment with the same dark and moody feel.
I unfortunately found myself staring at the left wall for the majority of the experience because it was the easiest way to control everything important. It would have been awesome if the gauges and power switch at least were on the front wall with the porthole so you could see more of the cool environment as you descend.
I played the web build and didn't experience any issues other than the initial intro scene which seemed to use a shader or something that produced a garbled mess.
The tentacle section took me longer to figure out than I would care to admit even though I had already listened to the tapes, but I still made it to the end with 50% hull integrity. I'm very thankful it was forgiving in that regard!
The ending itself certainly caught me off guard so well played and great job overall!