If I remember correctly it used one of the HFM 590 bulb keels, removable of course! If I am right it had a steel bar within it which was about 25mm diameter and about 100mm long, this was roughly 125mm below the hull, on a 590 that is. I assume the same applied to the barge.
Await some better answers, I am trying to remember something I had 25 years ago!!