I love the visuals. I was a little disapointed that I couldn't stop on the islands and rescue people (or kill them if I'm a pirate). The curse was a bit simplistic with just the clouds so it would be good to add more variety if you expanded upon it. 

I think you could have extended the level further. Maybe do something procedural instead with increasing difficulty, rather than having an actual 'end'. That would increase playability, something like a high score (distance travelled). Also having such a tall map made me wonder wether going forward was actually the right direction. I think you could probably shrink it to fit everything within the height of the monitor (flappy bird style?).
The boat is really cute and the movement was satisfying.
I think you could have done something more creative with the theme than black clouds. Maybe canonballs or randomly generated whirlpools, sea creatures or enemy ships that try to kill you. I dont know whats in the Kenney packs but im sure you could find something cool.
Good job overall!