I have been attempting a little research into the origin of the term 'Captain's Tiger'.
The SOED has the first recorded use to describe a Captain's personal steward as being early 20th Century.
However, Tiger to describe a person was used much earlier:
Before 1400 it came as the term 'Fen Tiger' - A savage or bloodthirsty person; a person of great energy, strength, or courage specifically a native of the Fens.
In the Mid 18th Century Tiger was a slang term for an overdressed person, also a hanger-on or parasite.
By the early 19th Century it became a usually liveried boy acting as a groom, footman, or other servant.
But, by the mid 19th Century Australian slang had it as a person engaged in menial employment; more specifically, a sheep-shearer.
If we go back to the idea of a late 18th Century liveried servant, often overdressed to suit the whims of his employer, and look at the typical livery of the time it is easy to imagine how the use came into currency - Contrasting and distinctive braid in an often striped pattern.
If we transpose this to the type of rig which the late Victorian Captain would probably insist upon being worn by those stewards serving at dinner etc and we have the combination of a 'footman' or Butler in 'extravagant attire' - which would hark back to origins which would have been in living memory then but are forgotten now.
This etymology is a contrast to many words which start at sea and are adopted ashore without care of their origins. This one seems to have made the reverse journey.