Boats that use net drums and powerblock net haulers
The drum has 2 ( either chain or wire ) fairly long cables with a G quick connector at the end. When the net is hauled the initial sweeps ( called bridle in the diagram above between the door and the net ) go onto the winch and has an o connector which the G link goes into ( the end of the bridle/sweep has a G connector in it ). The winch then slacks back until the net is hanging on the net drum cables which are then hauled up , once the wires from the winch are up to the boat they are then disconnected and the net then hauled up onto the net drum.
Once you get about 75% of the net up onto the drum the powerblock ( the big roler on the end of the crane ) is used to scoop the net and take it to the side of the boat so the rest is hauled by hand through the block before the cod end is hauled aboard and emptied.
following images hosted on Trawlerphotos and linked to here using img tags
Twin rig trawling uses a 3rd trawl wire which is used to tow a heavy weight called a clump between the nets. In this method instead of 1 net its 2 and its the same procedure as above except for having one more wire and the clump to connect to.
Some boats using white fish trawls haul the net right up to the blocks using the winch , having 2 connectors on the wires which makes hauling the net onto and off the drum a lot faster ( not got 25 or 30 fathom of wires to haul before the net )
couple photos of model trawls in a flume tank to show how a net looks on the bottom