A Cheer for Samuel Plimsoll

Roman Mars (RM): This is 99% Invisible. I’m Roman Mars

“O a cheer for Samuel Plimsoll…”

RM: If you look at the outer hull of commercial ships, down by the waterline, you might find a painted circle bisected with a long horizontal line. This simple marking is called the load line or, as I prefer, the Plimsoll Line. And not to oversell it but this elegant graphic design has saved thousands of lives.

Tristan Cook (TC): This is one of my favorite examples of design because what I really like in the world is when you can find a massive problem that definitely needs solving and with some thought you can solve it with something as simple as a circle with a line through it. I just find it amazing. That’s what I’d like to do with my career.

RM: That’s Tristan Cook

TC: And I’m a human factors engineer. So that means that I look at the way that people interact with their environment, and figure out how that will affect their behavior.

RM: Tristan also curates an outstanding blog called Humans in Design. So anyway, the massive problem that needed solving in the 19th century, that Tristan is referring to, was the huge number of British ships sinking in the ocean because they were overloaded and in disrepair, sending hundreds of merchant seamen to a watery grave. The problem was so widespread these vessels became known by another name—

TC: Coffin ships.

RM: Coffin ships. Now overloading ships has certainly happened since there have been ships to overload, but it was the introduction of insurance that created the coffin ship.

TC: It’s still a colloquial term for ships that are overinsured–so they’re worth more money, to the person that owns them, at the bottom of the ocean than they are afloat.

RM: So ship owners would purposely overload older ships with cargo, thinking that if the ships made it, they hit the jackpot. But if the ships didn’t make it–they still made a lot of money on the insurance claim.

TC: Early days in insurance, so people weren’t quite aware of the idea that by insuring something you’re going to change and affect people’s behavior.
RM: This is called a moral hazard- when people engage in risky behavior because they are not fully accountable for the consequences.

TC: You’d assume that insurance is going to keep everything the same, but it doesn’t. When something is insured, your behavior may become more risky, or you have a different incentive to do something.

RM: And the unintended consequence of insurance was that ship owners had an incentive to sink their own ships and send hundreds of souls to the bottom of the ocean.

TC: The most famous one was one called the S.S. London, that had 230-something people on board.

RM: It was leaving from a place–and I’m not kidding–called Grave’s End in England. Theoretically headed for Melbourne, Australia

TC: But it was overloaded with a whole bunch of railways parts and things like that. That was in the mid-1800s. That sank as in a storm like when it tried to turn back towards a port.

RM: This is where our hero British MP Samuel Plimsoll–and the Plimsoll line–comes in.

TC: Just after that happened, a guy called Samuel Plimsoll got elected to the British Parliament. And he wanted to pass a bunch of new shipping safety laws based upon his knowledge of this disaster.

RM: But passing these safety laws was not easy for Plimsoll—because it just so happens that murderous, regulation-hating, immoral capitalists and their friends sometimes serve as elected officials.

TC: A lot of people in British Parliament owned ships, so they were the owners that didn’t want extra regulation, so yeah he had a fairly large amount of trouble getting through. It didn’t sail through, it had very little support in Parliament.

RM: So Plimsoll took his case to the people.

TC: Plimsoll wrote a book called Our Seamen, which was really championing the issue. And that went really wide.

RM: And eventually, due to widespread public support, the Merchant Shipping Act of 1876 was passed. It required the simple, elegant graphic I described earlier, a circle with a long horizontal line through the center, to be painted on the outside of the hull to show the maximum loading point of’ the ship. The mark let a third party know plainly and clearly when a vessel was overloaded and at risk of sinking in rough seas. If you see that horizontal line above the water, you’re good. If you don’t, well, you could be sunk.

TC: It’s kind of really pretty looking, to look at. That’s what drew me to it initially. It’s very geometric.

RM: And some form of the Plimsoll Line remains on ships to this day.

TC: There’s just a slight modification so that in different waters, or salt waters or fresh water or with different sorts of ships you’re allowed to load it to different levels. So there’s a couple of different levels on the outside. Personally I think it’s amazing. With boats these days, there’s all these different safety measures that have been implemented. There’s GPS, boats drive themselves halfway though everywhere. But, when it gets down to it, the thing that is most importantly keeping a boat afloat is still just a circle with a line through it on its hull. Just a bit of paint.

RM: There have been numerous poems written and songs sung about Samuel Plimsoll, but over time his name has faded even though his mark on the world lives on.

TC: It’s actually less known as a Plimsoll Line and more of a load line, but at the time, it was definitely known as a Plimsoll Line.

RM: But if I’ve done my job today, you, dear listener, will only call it a Plimsoll Line, because it seems like the right and honorable thing. And besides, if there’s an opportunity to use an eponym, use the eponym, it’s just cooler!

RM: Our tars upon the ocean he struggles to defend /Success to Samuel Plimsoll for he’s the sailors’ friend.

RM: 99% Invisible was produced this week by me, Roman Mars, with help from Tristan Cook and Tom Nelson, who curate the blog Humans in Design. This program was made possible with support from LUNAR, making a difference with creativity. It’s a project of KALW 91.7, local public radio in San Francisco, the American Institute of Architects in San Francisco, and the Center for Architecture and Design. To find out more, including a link to the blog Humans in Design, go to our webiste–it’s 99percentinvisible.org.

Comments (6)


  1. Nicolette Jones

    Glad to see your interest in the immortal Mr Plimsoll.
    Warmest wishes,
    Nicolette Jones, author of The Plimsoll Sensation: The Great Campaign to Save Lives at Sea

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