I took the time to list commodities hauled over the Murray Bay Sub in the late 70s. In fact, I only bothered about the five selected industries served by the local switcher. As you know, we won't be bothering modelling the Charlevoix parts, which, except its incredible scenery was the most boring part of the line with very little variety in industries (a paper mill, a LPG dealer and General Cable in Clermont).
There was a few other industries as well between Limoilou and Beaupré, including two sawmills, a Sico Paint plant and a Shur-Gain grain elevator, but we won't bother about them. Un fortunately, we don't have any place to spare for them and, except one of the saw mill, most of them weren't rail-served by the earlu 80s.
I came to the conclusion about 51 car spots were shared by the five industries. Also, the yard can hold 51 cars (50ft car to be precise). That means there should be about 50 cars on the layout at any given time. Also, the shortest siding is at Beaupré. It can take 10 cars, 2 locomotives (a pair of 4-axles engines) and a Pointe-Saint-Charles caboose.
At this rate, five operating different trains are needed to replace all cars. A lot of action for a small layout! Once again, selecting credible rail-served industries show us you don't need a thousand tiny clients to make a layout busy, but a handful of good clients. The smallest industry have 4 spots and the largest can hold 18 cars into 5 different spots. It's good to know that if you spot 5 cars under a coal tipple, it only counts as one spot.
The week was also extremely busy trying to figure out typical operations at St. Lawrence Cement plant. Mr. Stéphane Mélançon was a big help in that matters. His uncle, an former employee from 1963 to 1968, was kind enough to recall his memories of that time. It's quite impressive to try to understand things from 50 years ago when you never actually saw them. Thanks to him, we now have a better understanding of the works behind a large cement plant.