The Mercator is definitely with full sail and is underway, not moored. Some how, as mentioned, he shared his negative or someone shared theirs with him. A remote possibility was that many years ago, you could buy negatives of things like postcards in shops and maybe he purchased the negative. Is your negative framed in cardboard or is it just a strip of film?Another response: "What if it was some significant event and the reporter and his father were on the same dock taking a picture of that ship at its mooring at about the same time?"
So, yes, knowing him, I'm now thinking his ship may have been in port when the Mystery Ship was in port, he attended some event and that's where the posted pic came from.
Does this sound logical, given what we now know about the pic I posted?"
One significant event that the Mercator was part of in the 1930's was that in 1936, she had the great honor of bringing home the remains of the Flemish missionary and apostle of the lepers, Pater Damiaan, from Molokai island. He was later known as St. Damien of Molokai after he was canonized on October 11, 2009 by Pope Benedict XVI.