Good explanation of the self-unloaders.
I sailed for a brief period of time on the Ontario Power in the winter of 1968-1969. The owners, Upper Lakes Shipping, decided that year to take her out on the Atlantic Ocean for the winter. I was first a Watchman, then quickly was promoted to Wheelsman (those are the terms used on the Great Lakes ships).
She was a wonderful ship, with a crew of a little more than 40 men, I don't remember exactly. The Wheelsmen also operated the boom when we were unloading. I don't know if the procedures have changed nowadays. There is a cabin at the base of the boom, elevated above the deck and right in front and below the bridge, where all the controls to maneuver it are located. It was quite exciting to have that responsibility. At first, we tended to be too nervous with the trim and we would send too many signals to the men operating the gates down in the tunnel. That would drive them crazy. But we quickly learned to be more circumspect with those bells.
Unfortunately two First Mates were badly injured in quick succession that winter, and Upper Lakes Shipping tied up the ship in Philadelphia for the rest of the winter.
I remember vividly those two accidents but will not relate them here. I would be interested though to hear from other crewmen who were there that winter.
After that I sailed on one of the Gypsum ships, also self-unloaders, but sea-going ships nevertheless and engaged in foreign trade. Those ships had a somewhat different unloading system: same tunnels under the cargo holds, same hydraulic gates, same belts, but no boom above deck. Rather there were two large doors in the hull, right in front of the engine room, one on each side of the ship and which were opened when in port, through which a shorter boom extended over the docks or hoppers ashore. On the Gypsum Princess we also carried an extra length of boom that we rigged and swung from two large masts on the stern, to extend the range of the unloading conveyor belt.