Thanks for posting this; I haven't run across it before. The first verse does have some typos that are easily corrected (see CAPS below):

On a winter's night OFF Plymouth Sound
We were setting a course for the Nancy Jane
Steering by A LIGHT from the Eddystone rock
When we ran aground in fathoms ten.

I'm not convinced it's traditional but there are not a lot of "wreaking" or "salvage" songs out there that I'm aware of.