Thanks bbart. That link works.
I am a member of Findmypast. I must make more use of their newspapers. I did look up his father Thomas Threlfall. In 1851 he was accused of the murder of Henry's mother, 19 years after she was found floating in the Leeds Liverpool canal in Halsall. There was a deathbed witness to the alleged murder but Thomas was acquitted. I was just following up on Henry's future life when I came across the link to becoming a Merchant Seaman. Now I have two stories, a murder, and a shipwreck !
Chris