(Oxford English Dictionary)
dock-walloper (U.S.), a casual labourer engaged at docks and wharfs
1860 BARTLETT Dict. Amer., *Dock walloper, a loafer that hangs about the wharves. New York.
1879 Lumberman's Gaz. 15 Oct., Dockwollopers are paid 40 to 45 cents an hour.
July 1841, Arcturus, A Journal of Books and Opinion (New York), pg. 130:
The sunny weather has brought out the loafers, and the codgers, and the dock wallopers again, in all their glory.