Hello, Joelrio,
My reading & understandng of the 1891 census for William Sturla & family on the vessel Argnum is this.
The heading on the census is for Argnum Ice Hulk, probably more like a barge moored in dock in Polpar so is not an ocean going vessel. This is probably why William Sturla's occupation is classifed as Shipkeeper & not Master, meaning his job was more of a live-in manager with his family. Enumerator's often listed wives & children as being, i e shipkeeper's wife or daughter, this does not mean they were employed as such.
I am not too sure of this, perhaps someone else can help here, but I think it was the custom to bring ice into London docks where it was stored in straw for distribution to hotels, restaurants & large houses.
Meliora