These boats were equpped with 9hp Petters because they were intended to work singly. If the river was high they would hang onto one of the tugs or hitch a free tow behind a tanker. They had enough power for normal river conditions. Remember, Josher's 9hp motors worked on the Trent, Soar and Weaver
I don't think anyone, except the designer, can explain the reversal of the traditional position of the cabin and engine room. The boatmen disliked it and it was clearly unsafe if the crew had to exit the cabin quickly in an emergency. The long holds were usual in all S&C boats to provide maximum hold space for timber and other light, bulky cargoes.
The last of these boats in use for carrying could take 23 tons up the Shropshire Union as against 20 tons on a Josher.
The two bought by Ballinger carried 23 tons of crumb between Frampton and Bournville. Tonnage was limited by the bulky nature of the cargo. They would probably, even in 1960 have carried 25 or 26 tons of heavy goods on the W&B.
On the subject of BCN gauging, I had two boats weighed at Tipton and can confirm that weights up to 24 tons were placed in the boat and the rest was done by calculation.
.