bleak

[Tiger the Lion]

Hello TM. I feel like this piece is primarily rhyme driven. That isn't necessarily a bad thing, provided it doesn't come at the expense of clarity.

There are tumults in the ocean, "on" would be more relevant than "in" if your sailing
but the ship must sail,
it cannot sink.

I must reach the port, I would strike "the" - for word economy and metrical movement
I cannot sleep, with the repetition of "must/cannot" from L2 and L3, this line becomes ambiguous. 
not a wink. then a cliche to clinch the rhyme
All that said I think you'd do fine to simplify this strophe and tie up your rhyme at the end, 
when times are hard more cliche
and light is bleak, "light" and "bleak" are almost opposites. You might make the light "weak" but you don't even need the rhyme here. 
sea is the paper,
and tears are ink.

I'm only nitpicking because you choose an important, but old sentiment that can't be puffed up with forced rhymes and  
tired cliches. Weaving a real, living experience into your core metaphor would improve the piece more than any lazy rhyme.
Good luck with it,
Paul