From The Cliffs.

[tectak]

The mainsail died, they heard it ripNot much wrong here, billy. "they" is a little impersonal, even for you. It is usually better to tell us who "they" are before dropping the identity. You could even give one or two "characters" names. " The mainsail died, Seb heard it rip...." Your poem
dread ran like scurvy through the ship. Again, fine but scurvy isn't contagious. As far as I know it is a vitamin C deficiency.....maybe that can still run. Pedantic...sorry
They cut the rope that held the cloth Then "He cut the rope that held the cloth(Seb?)" I think one man would cut a rope, more than one (they) would cut ropeS. Strangely, sails are tethered by "sheets". I don't think they are called ropes. I'll check
and dropped the tatters to the froth;
all white and roaring o'er the deck,"all" is a known. Maybe " Spumed white and roaring o'er the deck. A misplaced foot, a broken neck." Or something.
a misplaced foot would break a neck.

The anchor lost, the boat's heart broke
upon the granite, splintered oak.
Some jumped too late, some leapt too soon
their buckled bodies bent and strewn this is a fine stanza and I am loathe to offer up suggestions. Aw, the hell with it....buckled and bent seems a near duplication. Stick pins in my effigy
across the knife-edged rocks they lay
all cut and bloodied in the spray."All" sticks out as an overused filler."broken and bloodied in the spray"

There are grammar issues but I am tired! Overall, this is a seafaring tale to be sung in three part harmony with one hand cupped over left ear. I commend it. I have googled it. A rope holding a sail is called a "sheet".
Best,
tectak