Yeah I remember having this realization after I ran the numbers. A canal with a massive ship beats rail easily on throughput. So much for my idea to have ships plug into a maglev railway and fire their containers to the other side.
I don't think your math works out. Let's assume you want to move 3000 containers along a 3000 mile path. Let's also assume 1: you can stack containers one high onto the railway at the rate one container per minute, 2: the containers will move at 300 miles per hour and 3: the ship moves at 20.
On thenship all 3000 containers arrive at once and the total time to move them is 3000miles / 20 = 150 hours.
On the rail the containers take 50hr to offload. Hence the first container will arrive at the other side in 3000/300 = 10 hours. The _last_ container will arrive at 60 hrs 0 minutes. At one minute per container in the 150hrs it took the ship to arrive you could have delivered 140*60 = 8400 containers to the other side.
Not that the ship is only 15 times slower than the railway.
The governing factors on your railway are the ratios for distance to travel vs the offload time. Or put another way the delay bandwidth product.
I've seen these in action many times and called it 'techno-ballet'. Rather impressive. I guess meanwhile there are even more advanced ports, but I didn't track that development.
https://news.ycombinator.com/item?id=38992104