2nd: Transformation

Love what can turn up in this hobby.
I think I've just found a chap aging from 36 to 51 between leaving England 3rd Sep and arriving in Montreal on the 15th, via Le Havre.
He and his wife were the only FAIRBAIRNs on the voyage, and the ticket number on leaving England is the same as that arriving in Montreal.
When they left England they were both 36, and he was a mechanic.
When they arrived in Montreal, he was 51, coal merchant and horse dealer, and she was 48.
I was looking, still am, for an Alexander FAIRBAIRN, uncle of the artist Andrew Fairbairn AFFLECK, born 1857 Edinburgh who disappears after 1881 (when he was a Commercial traveller, in Edinburgh).

Any inventive explanations for the aging effect of the sea air?

Wonder if they did a swap in France? Or is it a simple case of bureaucratic bungling?
Anyone interested in the family (James and Ann (WALKER) FAIRBAIRN) may care to look at the Patriarchs page of the DNA Project.