It was my great grandfather's uncle Thomas Laugharne of Dinas Cross in Pembrokeshire, one of five brothers who all died at sea. He took over command of the Colwyn a few months before she went missing on a voyage between Newcastle in Australia and Valpariso carrying a cargo of coal.
Your ancestor Captain Archie Robertson seems to have carried out many similar voyages in the Colwyn and was fortunate to die in his bed. Coal was a notoriously difficult cargo, prone to spontaneously ignite or shift dangerously in rough seas. For more details of the Colwyn's voyages check out
http://newspapers.nla.gov.au/ndp/del/home. Put barque Colwyn in the search box.
I was wondering who the lucky Captain Robertson was who gave up command of the Colwyn just before she went missing. Strange what you find out when you Google a ship's name

Regards Vivien