The loading of container trains

I was stood today on Barking station at the end of the platform waiting for my train to Southend when a container train came through. Not unusual in itself but I have always wondered about how the containers are loaded. I see maybe ten loaded wagons then 20 empty then 12 loaded, then a gap of maybe 5 then another 10 then another gap and maybe a series of 15 consecutive wagons loaded with containers.

How does this work?

Is it there are different rakes within the train with one set of wagons bound for - I dunno - let's say Wembley - and another set for Daventry. Does that rake of wagons stay together permanently or is something else going on? Are there multiple destinations on container trains or is there just one and the person loading them just loads them at random. Genuinely puzzling stuff and I would like to know the answer!

Steelman said:

Is it there are different rakes within the train with one set of wagons bound for - I dunno - let's say Wembley - and another set for Daventry. Does that rake of wagons stay together permanently or is something else going on? Are there multiple destinations on container trains

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It can be a bit of these, depending on the exact flows.

Steelman said:

or is there just one and the person loading them just loads them at random.

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It's definitely not random.

Steelman said:

Genuinely puzzling stuff and I would like to know the answer!

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Several things will impact it:
- Terminal operations: Busy ports run on tight schedules and containers have very specific places to be in their storage yards and on board the ships, so they must be loaded and unloaded in an order that doesn't get them out of sequence but also doesn't require the crane to run half a mile from one end of the train to the other inbetween each lift.
- Container and wagon type combinations: for rail gauging, it is vitally important that each container is placed on the correct type of wagon otherwise you will get a very unhappy freight customer and bridge engineer! The routing of the train, availability of wagon types, and sizes of containers to be shipped all impact this.
- Combinations of goods: for safety reasons, certain types of goods need to be kept far enough apart from each other to prevent fire or explosion. Less of a risk on a train as containers can only be at a maximum of 2 faces rather than all 6 on a ship, but still something that may need to be considered.
- Air turbulence: to minimise drag, it is best to have containers in a line as close to each other so there is minimum gap between each big vertical 'barn door' of an end.
- Wagon suspension: it's designed to cope with the max weight of the containers that might be loaded on it, so when not loaded the suspension can sometimes be a bit lively. to keep the suspension under control it is best to have the weight of the containers distributed along the train.
- Coupling tension & brake force distribution: the weight distribution along the train can have an impact on couplings being slack or too tense, and a loaded wagon will have different braking charachteristics.

All of these combine to produce a detailed loading plan that leads to the containers being loaded as they are.

See also this youtube video about Ship logistics:
DISCLAIMER: I am not a freight expert by any means and everything above is probably subject to some level of correction, and I'm sure I've missed many things out as well.

Good summary from zwk500.

Where I am it used to be the loading terminal would have their list of containers to load and would load at random using their own knowledge and experience unless given verbal instructions from the train preparer. These days its much more controlled and aligned and each FOC produces their own load plan based on their standards that the loaders *should* work to. Trains are generally planned so they are loaded front to back but there can be a number of reasons why gaps appear in the middle. Usually a case of booked containers not available, wagon restrictions, run out of time or terminal crane/ops failures.

This was true of 4S47 last night from DIRFT. Largely loaded, but with some empty wagons in the middle.

MarkWi72 said:

This was true of 4S47 last night from DIRFT. Largely loaded, but with some empty wagons in the middle.

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If I tried doing that on my Hornby train set the unloaded wagons would fall over inwards when going round a bend !

Some good answers, thanks the replies!

Thanks very much to "zwk500" for the video - really really useful. There is one puzzle I have had for years, and which doesn't actually apply to our UK trains - how do the stacks of containers get locked together on "doublestacks" and on ships. I am assuming there are locking brackety type things which lock together the upper and lower boxes on a doublestack, but who actually places them in the slots ? I imagine it is quite a potentially dangerous operation unless you don't fear being squashed, but also, the slots are potentially up to 9 feet off the ground, and I cannot imagine a guy walking around a dockside with a stepladder. I have actually asked Sal Mercagliano this question and not really got a conclusive explanation.

Wyrleybart said:

Thanks very much to "zwk500" for the video - really really useful. There is one puzzle I have had for years, and which doesn't actually apply to our UK trains - how do the stacks of containers get locked together on "doublestacks" and on ships. I am assuming there are locking brackety type things which lock together the upper and lower boxes on a doublestack, but who actually places them in the slots ? I imagine it is quite a potentially dangerous operation unless you don't fear being squashed, but also, the slots are potentially up to 9 feet off the ground, and I cannot imagine a guy walking around a dockside with a stepladder. I have actually asked Sal Mercagliano this question and not really got a conclusive explanation.

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There are several designs of twistlocks, some of which can operate semi-automatically (they lock on contact, but then need somebody to unlock them). https://en.wikipedia.org/wiki/Twistlock
According to wikipedia, the operator can insert the twistlocks on the bottom castings as the container is lifted, and then they engage automatically when the container is lowered onto the container below.

Example of a semi-automatic Twistlock in use:

There are also fully automatic Twistlocks, which are released by the force of the crane lifting the container:

On container ships, side lashing bars/rods/poles are also fitted into the container corner fittings for extra security: