There are three possibilities:
1) Hobbler was slang for a dock labourer.
2) Hobbler, hoveller, huffier, rowed or sculled small boats in docks and rivers in which he acted as an unlicensed pilot or did odd jobs.
3) Hobbler to a dock pilot who rowed dock pilots from point to point as required.
From The Times 23rd. July 1912.
Court of Appeal, Workmen's Compensation.
........... Between October 15, 1910, and February 2, 1912, he worked as a 'hobbler' i.e., in mooring and un-mooring vessels in dock at wages ranging from 12s. to 14s. a week............
From The Times 28 May 1877.
Our Canal Population.
.........in loading and unloading, the auxiliary hobbler found on all
navigations would be obtainable.......
Stan