Overboard...edit .0000001 brownlie

[Brownlie]

The wildest seas had risen up the night that Donny died. -- You might be able to "delete" had and "that" "The wild seas rose up the night Donny died."
Close running to the western gales and on an awkward tide, -- Think prepositions can be deleted. Like "on an awkward tide"
the Gina Belle had tumbled on -- Do you need had? 
her stern was low, her going gone. 
The tumult turned her round and round, -round and round is redundant. You only need round IMO.
in waves that broke on jagged ground --Not sure about jagged ground. Sounds like a cliff. 
no more than half a league away. -This is sort of like the Edmund Fitzgerald song 
 
The bladderwrack flew in the spray as Donny fought the wheel.
The grounding shook her, jarred her straight, pinned her by the keel; -- For the rhyming, should the line length or meter be consistent? 
Again, again, again she skewed
until her timbers cracked and flew -- Do you need cracked and flew?
in shards that rained upon the deck, - can you get rid of that, in and upon?
or what was left, until she wrecked
upon the heartless granite shore. -- Not sure about the word heartless here. 
 
Donny had thrown into the swell, unhitched his line, made free. --Don't need had IMO, unless maybe Donny is still in the throes of the swell.
Down deep he dived in to the rage, in hopes of calmer sea; -- Don't need down and deep. Deep = going down already. 
he swam below, some distance gained,
then burst for breath while wreckage rained
around him, crashing everywhere.
The anchor hit him hard and square 
and Donny died a sailor’s death. -- Don't like died xxx a death.[b] Died a sailor (without the word death) or faced a sailor's death or something better than those two options. [/b]
tectak
2017

This is really understandable, which provides a nice break. Even if you have to change the rhyming words, I'd clean up the style and delete unneeded words.