February 26, 2020

Merchant Ships - Introduction

While warships are the public face of sea power, they are in many ways a secondary manifestation at best. Ultimately, the purpose of naval power is to allow use of the sea while denying it to the enemy, and the users of the sea are generally merchant ships. As such, it's worth taking a look at the use of the sea for trade, resource extraction, and leisure.

A model of a Roman grain ship

The sea has always been the easiest way to move large volumes of cargo about. Historians estimate that it was 20 times cheaper to ship a given cargo by sea than overland in the Roman Empire, and as a result, Rome was kept alive by grain imported from as far away as Egypt, while areas less than 100 miles away overland focused on lower-volume products like wine because of shipping costs. Even rivers, although only a quarter as efficient as sea transport, offered a tremendous advantage over the primitive roads and animal draft required to move cargo where there was no water route. Over the next two millennia, improvements in shipbuilding gave sea transport an even greater edge, until the invention of the railroad finally opened up the interiors of the continents.

But the substance that powered the railroads - steam - also provided the opportunity for great improvements in the economics of merchant shipping. Between the periods 1820-24 and 1845-49, the volume of seaborne commerce entering British ports expanded 195%, despite a growth of only 40% in the British merchant marine. Not all of this was down to steam,1 and it wasn't until the last quarter of the 19th century that steam engines reached the levels of efficiency required to replace sail on the major trade routes, and sailing ships made up 60% of the British merchant marine as late as 1880. It was then that merchant shipping as we know it today began to take shape, the form I will investigate throughout this series.

Container ship Ever Conquest, in the Port of Los Angeles near Iowa

The vast majority of merchant ships are in the conceptually simple business of moving something from one piece of land to another. It could be grain or oil or cell phones or people, but something is being shipped across the sea.2 For centuries, all of these were carried by the same vessels, with cargo loaded aboard in man-portable packages and passengers often given a piece of deck and expected to see to their own comfort and even food. This changed in the early 1800s, first as dedicated passenger liners began to operate, designed from the start to carry people instead of goods, and then as the increasing specialization of transport saw the dawn of refrigerated cargo ships, tankers, bulk carriers, container ships, ro-ro vessels, and so on.

In the course of this series, I've taken a look at a number of different roles, where the type is today, and how it got there:

Next time, we'll start with passenger ships.

1 One major contributor was improved charts, which gave captains a better sense of where the winds were likely to be. This slashed voyage times by a quarter in some cases.

2 Some exceptions exist, most prominently fishing vessels and tugs, which have other roles; but these will be dealt with in due course.


  1. February 26, 2020echo said...

    Really looking forward to this series. Guns are fun, but my inner moneygrubbing economist has an autistic fascination for shipping and ports.

    The river vs sea trade efficiency difference sounds astonishing to me--I thought rivers and canals were on par with railroads, given thousand-year-old cities like Paris being over 200 miles inland.
    I guess local wealth and strategic importance can overwhelm shipping costs?

  2. February 26, 2020bean said...

    Note that Rome is quite a ways inland, too, and that grain from Egypt came up the Tiber. My numbers came from acoup.blog's post on transportation infrastructure around ancient and medieval cities. As for rivers/canals vs railroads, remember that the arrival of steam helped inland waterways, too.

  3. February 26, 2020Lambert said...


    Tl;Dr: The Romans were kind of bad at boats, especially because the med is seafaring on Easy Mode so French cities ended up on important parts of the road network.

    The Romans also built British cities on important bits of the road network e.g. Canterbury, London, Verulamium, Dunstable (of all places), Towcester (all on Watling Street) but urban life was much more heavily disrupted by the Migration Period than in France. Once whatever renaissance you consider to be the real one got underway, we were better at faring the North Sea, Atlantic and rivers so port towns became the dominant cities.

  4. February 26, 2020Eric Rall said...

    Before railroads, major cities were generally either coastal or positioned along a navigable river. Paris is on the Seine, which is readily navigable. Enough so that Vikings tried to raid Paris by sea at least twice. The Seine is a little over 30 ft deep when it passes through Paris, which is a little shallow for a modern ocean-going container ship, but was plenty deep for any sailing ship up to and and including an 18th century Ship of the Line (not that that came up much, I expect: French Ships of the Line probably had better places to be, and enemy Ships of the Line would probably have been stopped by shore artillery quite a ways before getting to Paris).

    Tangentially, most of the state capitals in the US Eastern Seaboard are located at the Fall Line, an escarpment along the western edge of the coastal lowlands. This happened because the Fall Line is the inland limit where rivers stop being navigable, so a port on the Fall Line is going to be the best transport hub for anywhere to its west for some distance.

  5. February 27, 2020Doctorpat said...

    This may be anticipating a subject already in the pipeline, but to what extent did steam power increase the productivity of sailing ships because of tugs? All that "waiting on the tide" to leave/enter port etc. didn't matter any more.

  6. February 27, 2020bean said...

    I don't have numbers for that offhand, and that one is way down the list. This is going to be much more like, say, the Riverine Warfare series than the ones where I drop all the parts in quick succession. It was significant, although there were limits to how much, because you generally get two tides per day, and voyages were measured in weeks. Now if the wind is blowing the wrong way, that's when you get the big gains in time.

  7. February 27, 2020Doctorpat said...

    I'll also note that one thing Bean's work has done a lot of is moving snippets of information from the "I have heard of this" category to the "yes, I understand how this fits into a cohesive world view" category. Often this moment of insight is a particularly well chosen photo. There is a photo in one of the battleship articles showing literally hundreds of sailors walking up gangplanks loading stores onto a WW2 design ship, and the comment that this just sucked up so many resources (man-hours, plus also ship-hours and dock-hours) whereas a more modern design would allow, I presume, forklifts to drive right in, if not load in entire shipping containers?

    Anyway, that was a warship that needed enough supplies for the crew. For an actual cargo ship, multiply that by orders of magnitude.

  8. February 27, 2020Doctorpat said...

    Hi @bean,

    Oh, you're online.

    Yes, I also imagine that there are a lot of ports where you just plain get congestion. If 100 ships want to launch today, and there is 30 minutes of the best conditions, that is going to probably mean someone misses out.

  9. February 27, 2020echo said...

    the cost advantage of water transport over land transport increased considerably from the Roman era to the Middle Ages... during the Middle Ages towns in Britain were roughly two and a half times more likely to have coastal access – either directly or via a navigable river – than during the Roman era.

    Wow, interesting. I'd assumed the relative costs were much more consistent, but obviously different peoples had very different technology, infrastructure, and institutional skills.
    But it certainly makes sense when you think about who was conquering around the North Sea after the Roman era.

  10. February 27, 2020Doctorpat said...

    @echo, Yes. I would also have guessed that it would be near constant relative values, but I suppose that the Romans were famous for roads. While the English are famous for their sailing.

    The Greeks were more of a maritime civilization than Rome.

    Now let's not get into whether the Byzantines were Roman or Greek.

  11. February 27, 2020Lambert said...

    Containerisation was the big change in loading/unloading.
    The London Docklands became a ghost-town in the 70s, when loading loose cargo manually onto cargo ships became obselete.

    RE inland waterways:
    'One man one horse one cart one tonne of goods. One man one horse one narrowboat 50 tonnes of goods.'
    —Canal Museum volunteer

  12. February 27, 2020Alsadius said...

    One book I can't recommend highly enough here is The Box, by Mark Levinson. It's about the advent of the shipping container, and while that might sound boring, it kind of blew my mind. It seems like half the modern economy is based on this. China couldn't give us all of our plastic crap if we needed longshoremen at both ends - it would rapidly stop being economical.

    Also, in the pre-modern era, there's another obvious disadvantage to inland cities. Silting. They didn't have effective dredging systems, so you saw gigantic metropolises(for their day) like Bruges just dry up totally when the canals and rivers got too silted for cargo ships to get in and out safely. Bruges has less population today that it did in 1400. (Estimates are 125-200k then, down to 50k in 1900, and up to 118k today)

  13. February 27, 2020Alsadius said...

    Lambert: Interestingly, the reason London dried up wasn't so much the loose loading. It's that British longshoremen were heavily unionized, and the union rules prevented container shipping. The one place they could find on the island of Great Britain with a legally-organized port but no such union restrictions was the microscopic Felixstowe, which became the busiest port in the UK by far as a result of this.

    The busiest ports in most other countries are in basically the same places they always were - Los Angeles Rotterdam, Shanghai, Singapore, Antwerp, Hamburg, Mumbai, Piraeus, and so on. It's mostly just the UK that switched due to containerization. (Mind you, the nature of those ports changed massively in the container era, but their locations didn't)

  14. February 27, 2020bean said...

    First, I should say that discussions of ship loading and containerization are in the pipeline, with all of the juicy numbers you could want. So I'm mostly going to stay out of that to avoid giving away my material early.

    Re the Romans being bad at boats, how do we know it's not that they were particularly good at roads (universally agreed to be true) and that just made boats relatively uncompetitive by comparison? Unfortunately, I wasn't able to track down good analyses of this in the time I had. Also, statements of Rome's non-maritime nature are usually overstatements. The Romans made extensive use of sea power, most notably during the Punic Wars.


    I’ll also note that one thing Bean’s work has done a lot of is moving snippets of information from the “I have heard of this” category to the “yes, I understand how this fits into a cohesive world view” category.

    That's one of the nicest things anyone has ever said about this blog. Thank you.

    Re loading of supplies on warships, it's mostly forklift pallets. Containers are a bit larger for that, although they are used as the basis for the Stanflex system.

    If 100 ships want to launch today, and there is 30 minutes of the best conditions, that is going to probably mean someone misses out.

    This seems unlikely, for exactly the reasons being discussed elsewhere. For 100 ships to want to launch, 100 ships would need to be loaded within 12 hours of each other, and that's basically never going to happen.


    That's only half the story. Container ports take up a lot more flat space than non-container ports, and that space is hard to find at the center of a city. As a result, many container ports are not where the original port for a region was. LA is an exception, as the city center was never near the port, but the main port activity in the New York and San Francisco areas moved to Newark and Oakland respectively. Rotterdam got their territory through land reclamation, and I don't think that port was all that big before containers.

  15. February 27, 2020Chuck said...

    I honestly can't wait until we get to the pallet. One of the most underrated inventions of the 20th century.

  16. February 27, 2020bean said...

    I'm not really talking about pallets as such. Containers, on the other hand, are going to be highly praised.

  17. February 27, 2020Chuck said...

    No pallets? Then look for me to add in my $0.02 in the comments.

  18. February 27, 2020bean said...

    Absolutely. I'm focusing on marine transport, and not on revolutions in transport in general, to avoid a complete change in my scope and to keep the time investment down, not because I hate pallets.

  19. February 27, 2020Alsadius said...

    @Bean: Interesting. Hadn't thought of the land-use aspect - I thought the main reason for the ports leaving the old city centres was the elimination of the factory-to-ship direct loading scheme, with a new focus on intermodal rail loading and shipping things to and from inland areas. I guess it makes sense that both would be true.

  20. February 27, 2020Lambert said...

    How much of 'good at roads' is about the actual road and how much is just having a bunch of legionaries garrisoned nearby ready to fight off any bandits/warbands?

  21. February 28, 2020Doctorpat said...


    A fair number of ancient Roman roads are still in use. I'd guess they were actually pretty good at roads.

  22. February 28, 2020Grant said...

    Re: Roman Roads The Roman Roads are really good for military and administrative use, but weren’t intended for large scale trade. They tend to follow the high ground, which is militarily advantageous, but makes for inefficiency in hauling heavy cargo. They also are optimized for foot and horse traffic rather than heavy wheeled vehicles, as the weight is borne by the road structure itself rather than transferred directly to the underlying soils. During the medieval period, commercial traffic often used local roads that followed terrain contours, even when a Roman road was available. So they were good at roads, but primarily for military units and messengers, rather than commercial haulage. Source: Lander, The Field and the Forge (sorry, no page numbers)

  23. February 29, 2020echo said...

    Considering that Rome sourced much of its grain from Northern Africa by the Imperial period, I agree with Grant that the road network's Vale for trade is probably overstated.

    Found this map of urban amenities that seems to show population clustering around seas and rivers (although other maps show Britain in particular as having lots of landlocked fort-cities).

    My guess is that a lot of Roman city locations determined by garrison camps or Iron Age hill forts required expensive "last mile" grain transport from nearby rivers. But I'd guess most of the grain-miles were still covered by boat or barge.

    Like at Old Sarum, settlements eventually moved to better locations once economic concerns trumped tactical ones.

  24. March 01, 2020Lambert said...

    settlements eventually moved to better locations once economic concerns trumped tactical ones.

    And then back again as the Empire declined. They say that many of the rocche in Early Medieval Italy were on the site of old Etruscan hillforts. (Likewise with Verulamium/St. Albans)

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