Considering how many CoC scenarios are tied to the sea it's surprising there aren't more resources describing ships from the 1920's. Here are a couple of scans of exactly that. The smaller ones are just profiles, but the largest is the full profile and deckplan from a period freighter working the lumber trade.
As always, click on the pictures here for the full sized version. I haven't cleaned these up at all so you may want to do a little retouching.