The Boston Sea Ranger was one of two ships built in Selby for Boston Deep Sea Fisheries of Lowestoft, and was lost off the Cornish peninsula with five of her crew, pretty much as the song details.

On the night in question, the Ranger came in from sea to the outer wall at Penzance harbour, waiting for the lock gates to open so she could come in and land some old mackerel. Inside the harbour, her sister ship "Boston Sea Knight" was waiting for the gates to open so she could put to sea. The dock crew decided the swell was too great to risk pumping out the ballast to open the gates, so the Knight remained locked inside, and the Ranger had to put to sea again.

The picture of the Ranger mentioned by another poster is rather odd, because it is in the Fleetwood website, and I do not recall the Ranger ever going there. Link follows

http://www.nettingthebay.org.uk/gallery/deepsea/twlr75.htm

The Sea Knight is still around, and I found a link to a recent photo of it, now serving as a safety vessel

http://www.shipphotos.co.uk/pages/covexbrilliant.htm

I am glad that someone has thought enough of the Ranger's crew to write a song about them, for years it has been just one of many small (and not-so-small) fishing boats lost while working around our coasts.

Strangely, after 25-odd years, I cannot remember who of the five the song must be written about. The one person who springs to mind didn't even sail on the Ranger, and I don't think I met him until several years after the event. Memory can be an odd thing though.