"With thankful regards, K. Vandesande, Captain, Mercator."
I'm not sure the captain's name is accurate - that's what it looks like to me after comparing
this signature with the one he wrote on the back of the photo.

"Panama, 1st April 1935

Dear Mr. Cooke,
Thank you again, most sincerely, in name of the officers of the Belgium training
ship Mercator, who had the priviledge of visiting the Leper Settlement, for
your kind attention and hospitality.

Trusting you are doing well, and with our best wishes, we remain dear Mr. Cooke

Yours very sincerely
K Vandesande (?)
Captain 'Mercator'"