My history here is very sketchy, but I seem to recall the two earliest antennae were loop antennae and dipole antennae, both of which predate the turn of the century. That may well be a diamond loop antenna.
As far as wireless adoption goes, it was adopted militarily by about 1900-1905, and before WWI, most higher-end ships (passenger liners, mail ships, etc.) were equipped with wireless as well. After WWI, cheaper radio sets spread wireless down to even the poor men of the seas, the tramp steamers, rusting freighters etc. but this still took some time.
If it's 1919, it's easily possible that a tramp steamer could afford a wireless set, but that's early enough that only the more diligent tramp captains would invest in such a thing. They really weren't ubiquitous until the 30's.