Built way back in 1975, the ship is an "open hatch" type cargo ship with two 25 tonne travelling gantries. Built to handle forest products, her holds are built as large square boxes the same size as the hatches to ease cargo handling. The gantries can thus reach all corners of the holds, which are thus narrower than the ship itself. There is dead space between the sides of the ship and the "walls" of the holds making the ship effectively double walled.
The gantries are fitted with hinged outriggers, which swing out over the ship's side to allow the gantry trolleys to pick up or land cargo on the pier.
It is unusual to see such ships carry a bulk cargo like gypsum, but the owners, SMT Ship Management & Transport of Limasssol, Cyprus have, over the years, run a strange assortment of ships through Halifax for gypsum. Included were several former container/bulkers of Belgian origin retroffited as hybrid self-unloaders.
Presumably clamshell buckets are now fitted to the Heron's gantries to permit self-discharging directly to the dock.
The ship is due to sail sometime after midnight tonight.
For a better photo see Capt' Ken or AIS Live.