Thank you so much! This is perfect, and includes a lot of relevant information. I was unaware of the first series of barges mentioned in this text, but it fits nicely in with the evidence I have.

The Concrete Barge located at 51.45388, 0.28371 has no superficial resemblance to the other FB-series, which has stumped me previously, but I can now identify it as a St.-series barges produced in the area.

Br.
Erlend Bonderud