There's a song by an artist called Sail North, and one of his songs sounds GLORIOUS to throw into a campaign (please listen to it so you get some context). I've got some ideas. When someone takes the helm, they go completely blind and gains a blindsight of 60ft, everyone else makes a DC 20/25 (depending on how I feel) Dex save. On a save,they evade the ship's attempt to grapple them, must escape the ship or must make continuous Dex saves. On a fail, they are grappled and restrained (DC 20 to escape), and take 2 damage dice (still trying to figure that out 2d8? 2d10? 2d12?) and three turns to escape or be strangled to death.

Those are some of my ideas, feel free to modify them, add to them and give some of your own, I'm still kinda new, so tips would be on encounters (relevant or irrelevant to the song, idc) on the way would greatly appreciated.

For anyone wondering, below is the video that inspired this. If you click "view on youtube" and open the description it has the full lyrics. The guy makes pirate-themed shanty-like songs and they're good but this one is definitely the best in my opinion. Definitely has the campaign-style feel. 

I think this is like a one-shot. You meet the blind captain, he tells this tale, but you think you're better so off you go to follow suit. You would have some encounters on the sea itself, and finally you find the The Shadow and manage to get on board. Then when you take the helm there's a Con Save to see if you go blind, the ship's rigging comes alive like from Animate Objects and maybe some Undead appear? 

Definitely something that gets the creative juices flowing.