It may not have escaped your notice that I focus heavily on railways on this corner of the internet. This is perhaps giving you a false impression, if for some reason you use my blog as your only indicator how the world works; much as I would like it to be the case, trains worldwide do not make up the majority of transport, although in places they are significant.
The truth of the matter is that the vast majority of stuff that you buy has to go by ship at some stage. It is worth, before we continue, considering why this might be, by considering the other options.
I have gone on and on and on about the low rolling resistance of trains, and how this makes them ideal for all manner of things. But a train can only be so wide or long before it starts affecting other trains, infrastructure and so on. Roads have all the same issues and also much worse rolling resistance, although the greater freedom of movement is handy for deliveries. Both modes, of course, require there to be land, or some kind of physical infrastructure, which is not always terribly obliging.
This leaves us with ships and aeroplanes. I could get into some tangent about the possibilities for airships, but that is a story for another day. Aeroplanes are a wonderful invention, and are by far the fastest way of transporting stuff. That said, they are not without their issues, not least of which is the limitation on weight; even a very large freighter like a Boeing 747 8F only has a maximum payload of 134 tonnes, quite pitifully small compared with the thousands a train might be able to carry. The fuel consumption is also quite high.
The only real option then is shipping. Ships have huge advantages for long distance transport – no infrastructure outside ports, no worries about the ground being able to support the loads and no worries about allowing freight to pass in each direction.
Since the invention of iron and later steel shipbuilding in the 19th century, ship sizes have been able to increase enormously. Even when sail was still the common method of propulsion, the famous Cutty Sark (and her lesser known, slightly older competitor Thermopylae, which she was suspiciously similar to) had a frame of wrought iron, although everything you can see on the outside is wood.
It is worth here saying something about how one measures the size of a ship. Thanks to Archimedes we know that in order for a ship to float, it must displace the same weight of water as she weighs. This is how a ship’s basic displacement is calculated, as is her deadweight tonnage (DWT), the maximum weight of the ship fully laden with cargo, crew, fuel, provisions and so on. However, you may also hear the term gross register tonnage, or GRT, which is actually a measure of volume inside the ship, each registered tonne being considered equal to 100 cubic feet. Net register tonnage refers to the actual cargo volume inside the ship, and so is just like GRT minus all the engines and so on.
The Cutty Sark and Thermopylae had displacements of around 2100 tonnes. In theory, one could tow the ships on rails on a modern train quite easily. Each could carry several hundred tonnes of tea from China or wool from Australia.
For comparison, a large modern container ship such as the Maersk Triple E class vessels have an empty displacement of 55,000 tonnes, and fully laden the deadweight tonnage is 196,000 tonnes. Since the Ford Fiesta has become something of a yardstick, I have done some quick sums and worked out that the deadweight tonnage is equivalent to the weight of 161,983 and a half Ford Fiestas. In other words, if you tried to make the weight of this one ship out of brand new Ford Fiestas, and you bought every single new one produced for Britain for a year, you would still have to buy every single new one in Britain for another 58 days to complete the job.
Another useful yardstick is the Blue Whale, adults of which weigh somewhere in the region of 150 tonnes, meaning that to make the deadweight tonnage one would need at least 1,306.7 adult Blue Whales. Even assuming the most optimistic estimate of the population, this means that the total tonnage of just this class of ships exceeds the weight of all the Blue Whales in the world.
I admit, it’s a slightly extreme example; until quite recently the size of the locks on the Panama Canal limited the size of many container ships, and this limited size became known as “panamax”. Various other “max” sizes also exist, as ports do not have infinitely deep water or infinitely sized docks. That said, ports are now bigger than ever, and the problem with Panama has now been solved, or at least improved with numerous upgrades to the canal.
But how on Earth are such large ships even possible? Well, the obvious answer is to go on about the structure of such things, like the torsion box that goes around the ship, and how the huge holds support containers stacked enormously high, and how one can’t actually see most of the containers inside the ship. I know, dear reader, that while some of you might find such things interesting, what you really want to know is how you push something that vast along. As usual, I will not get to the answer straight away, and instead meander through some other interesting but only tangentially related topics.
What shape do you think the front bit (the bow) of such a ship should be? Now many of you would simply reply that it needs to be pointy to push water out of the way. Surprisingly enough, this is only half correct, because as a ship so built travels through the water, it creates a bow wave, and a large wake. This wake causes a significant amount of drag on the hull, for complicated hydrodynamic reasons I can’t be bothered to go into here.
In modern large ships, this is counteracted by having a large, blister-like structure just under the water, called a bulbous bow, which creates its own bow wave. As the two bow waves interact, they cancel each other out, reducing the wake and reducing drag, saving a lot of fuel along the way. This only works at certain speeds, since the bow waves are affected by speed, but you get the picture.
The beating heart of these ships though are the diesel engines. The Maersk Triple Es are a little unusual in that they have two engines, rather than one big one, but to give you some sense of scale each of the two diesel engines produces 42,000 horsepower. They are so large, it is actually possible to stand inside the cylinders, and it is absolutely essential to have stairs and walkways around the outside. These drive the ship along via a propeller directly connected to the output, with no reduction gearing at all. Surprisingly enough, each engine actually runs very slowly (less than 18 rpm), to reduce mechanical wear, as well as noise, and these engines are rather efficient, with 50% efficiency being not uncommon.
I will return briefly to our Ford Fiesta comparison here. The most powerful diesel engine ever offered in a Fiesta was a 1.5 litre with 118 hp (now discontinued). This means that you would need to connect about 356 Ford Fiestas to match just one of these engines (in production terms, this is just 27 short of a year’s production for the UK).
You might be wondering why in an age of environmental consciousness, ships still rely on diesel. The answer principally is the energy density of diesel fuel, which is far, far better than a battery or hydrogen or any other alternative fuel. Bio-diesel fuels are not yet available on the scale necessary, and so the only thing that can really be done for the moment (without compromising on the space available for cargo) is to improve the efficiency of the ship and her engines.
And it is these engines, beating slowly in the hearts of mighty ships, that move containers across the world. Containers are such a standard unit now that you, dear reader, may sometimes hear ships described in terms of twenty-foot equivalent units or TEU, the size of a twenty foot container; over 20,000 of these can fit on newer ships (although 40 foot containers are far more common in all fairness).
In these containers come nearly everything you buy, from electronics to clothes, to some food, to consumer products, to virtually every computer, phone or tablet you have ever laid eyes upon.
But this is not the only kind of thing we require to live. These products must be made in the first place, from raw materials, and these raw materials are seldom found conveniently next to where things are produced. Iron ore, for example, is found in many places around the world, but not much in China, despite the fact that most steel is produced there. Even the bread we eat doesn’t last long without going stale; it is produced from grain, which lasts much longer, and this too has to be transported from where it is plentiful to where it is not. And the lifeblood (much as we would wish it not to be) of our modern civilisation, oil, that too must get to where it needs to be used, where pipelines don’t exist.
For such tasks, we need bulk carriers. These ships are much the same as container ships, but optimised to store large bulk cargoes in enormous, cathedral-like holds. Many of these are extremely heavy and unwieldy when they are fully laden, which often necessitates the use of tugs to maneuver these behemoths in port, notably for oil tankers.
These ships and their crews, braving oceans many thousands of miles across, deliver the modern world to you. I am repeating myself here, but it really is true. Even 200 years ago, this kind of global trade would only have existed in the minds of dreamers and lunatics, and yet we all enjoy its fruits now, simply by driving a car (I neglected to mention car carrying ships here, but I did at least remember to mention oil tankers briefly) or shopping in a supermarket.
I do hope, dear reader, I have entertained you at least somewhat, and that at least some of the wonder I feel at the world has been rubbed off on you.