Yeah they are the beasts I remember, spent most of my time dodging them, as i was a sailorman, when in the docks used to moor a lighter alongside at night, because those swimheads used to ramp up inboard and take out your rails rip hatch cloths etc. Remember in Tilbury docks in the canteen having a meal when I saw a empty lighter blowing down the new dock with a gale of wind. It hit a big solid caste steel ship mooring bollard, it snapped off level with the ground and rolled a good 50ft. The lighter was unaffected. But those tug masters and the old lighter men knew their trade well, seeing them line up a barge let go of the tug and watch it run up nice into its berth on the river front.