[Canon] Eta-class Supply Barge

Based on the cargo containers as reference, the ships length is about 31 containers. These containers are roughly 25 meters wide, which is where the 775 meter length comes from.
The 25 meter width comes from the fact that the Zeta-class is states to be 28.74 meters wide, so take off a couple meters for the ship itself and that leaves about 25 meters for the cargo container.