Graham, thanks you for your reply & interest.
I have made several searches whilst in Liverpool Records office as well as paying for research at the City of London Records office only to find they have no record of voyages for the period 1891-1897.
As you found the Captains log for earlier years does include ships which I have traced but not for the period around his death - real disappointment.
I then went and checked all the Liverpool Street directories 1891-97 and he is recorded as Hugh Duncan, Master Mariner , living at 235 Crown Street Liverpool - the same address as on the Census for 1891 which just has his wife Elizabeth + children.
I then found a website for British Nationals born in Agentina including the records held at the Anglican church St Bartholomew's in Rosario Santa Fe but no records for a Hugh Duncan in 1897.
My plan is to trace ships sailing out of Liverpool 1896/7 to Argentina , but that might be a long slog to find his name on a crew list unless there are any other routes to try?