Thanks for some great information and a lot of good ideas.
I know he entered service at age 16 as a ship's carpenter, so I'm guessing he received training before then. I will follow the link you gave for apprentice information.
I've been intrigued by the St. Johns, New Brunswick connection. Until I saw that, had no idea how many Irish emigrated through Canada. He ended up in NYC - I'm guessing the Brooklyn Navy Yard - but have yet to find any of their records.
New Brunswick becomes even more important as I have tried to find out who his wife was. They had three children while living in NYC. After his wife died, he placed a daughter in a convent, sent his sons to live with a family in Dudley, MA, and seems to have gone back to sea as he listed his occupation as 'sailor' on 1870 census. The family he placed his sons with has no discernible connection to him - until I found that the wife was from New Brunswick. I'm theorizing she was the sister of his wife.
Will also check out the Maritime History archives. I have no record of him after the 1870 census. Not with his sons on 1880 census and apparently was not at his son's wedding in 1887. I've searched records for America, Ireland, England. No idea what happened to him.
Thanks for all the great ideas - much appreciated.
Ann