Hehe well I believe it's sort of the point for this story to be "horrible" not in the sense that it's bad but rather that it's sad. I'm pretty sure the MC is suffering from severe depression so that's where that's coming from: the boat, the sea is metaphorical of his inner struggle and the way he deals with it all. It's just the way things are with people suffering from stuff like that, you feel me? They rarely get the luxury of a happy ending.
Alternatively if the mental illness angle isn't your cup of tea the story can be read under a purely supernatural lense too, like a mysterious entity dooming this voyage, it can be interpreted as a horror story that way.
It's a story that plays its cards close to its chest, never giving definitive answers, and that leaves it open for multiple takes on it