Why Are Big Ships Bendy?

The Little Captain is available from the Casual Navigation store:

✩ABOUT THIS VIDEO✩
In this video we explore hogging and sagging, and learn that it is completely normal for massive ships to bend and flex.

✩ABOUT CASUAL NAVIGATION✩
I am a former maritime navigational officer and harbour pilot, with a passion for animation. My hobby is presenting educational stories and interesting nuggets from the maritime industry and sharing them on social media to keep them freely accessible to everyone.

✩SUPPORTED BY PLUS MEMBERS✩
Thank You to all Plus members on Patreon. Your support helps keep these videos freely accessible to everyone across social media.

✩WITH THANKS✩

✩DISCLAIMER✩
All content on this channel is provided for entertainment purposes only. Although every effort has been made to ensure the content is accurate and up to date, it remains the responsibility of the viewer to determine its accuracy and validity. The content should never be used to substitute professional advice or education.

[CasualNavigation]

The Little Captain is available from the Casual Navigation store:

[peterrollinson-lorimer]

My Father was a great lake sailor in the 1920s. One of his ships was just a few years old but nicknamed "the hunchback" due to a permanent bend in the hull from a bad storm.

[Kenionatus]

In metrology (the science and craft of measuring things), there's the saying that everything is rubber. Even solid granite measuring plates have _some_ sag when supported at the ends. The trick is to keep the deformation of your measuring setup so small that it doesn't matter for what you're measuring.

[wormyboot]

Today I realized that I no longer consider myself "most people" about nautical stuff anymore because of how much this channel has taught me. I've learned a lot here.

[davidpawson]

There's a video taken by a crew member during a storm on a large freighter of some type showing an unnerving, to me anyway, of the flexing of the ship in a passageway that runs the length of the ship. It's actually kind of terrifying.

[MrHegemonie]

That's actually how most torpedoes work nowadays : remove water from underneath the keel and let the beam sag beyond limits. Works especially fine with sub, and you don't need to be too accurate to produce massive effects (ie, even if you don't hit the target, it's likely to be damaged)

[NigelMelanisticSmith]

I feel like "motion of the ocean" was used in this video more than normal for this channel lol

[MxCraven]

Hearing you say "motion in the ocean" is something I didn't know I needed in my life

[terryboyer]

I saw a vid of a Great Lakes bulk freighter hogging and sagging in a storm. Quite impressive. And scary!

[statelyelms]

Hogging is basically what I assume happens in the Dreadnoughts song "Roll Northumbria" (fictional ending of the British supertanker Esso Northumbria; in reality she was scrapped, fearing this would happen, since she was apparently a straightforward scaled-up version of a smaller tanker with not much consideration for the behaviour of larger vessels at sea and so cracked her hull often for her short life). She rides above a rogue breaking wave, her hull can't handle the compression and the cracks finally split her open.

"-for atop a wild breaker, the cracks in her frame
spilled her black guts all across the wild main
she limped away through an ocean of flame
Roll on, Northumbria
Roll, Northumbria, roll"

Actually, would love to see a video on that ship someday.

[OttoMatieque]

'little captain' and 'motion of the ocean'
for a second I thought this video was going to go from nautical to naughty

[DCTriv]

If you ever get to go on such a ship in bad weather and look down a long corridor, you'll see the length of the corridor flex up and down, and a little side to side. It's pretty unnerving the first time you experience it, but is a cool phenomenon.

[nickt]

Reminder: its the motion of the ocean AND the size of the ship.

[robinwells]

This was an issue with the early liberty ships where the prefabricated sections were welded together but sadly poor construction tolerances lead to the keel sections and other strength members not always lining up at the adjoining bulkheads which you can imagine reduced overall hull strength considerably. Couple this with poorly normalised steels and welding temperature control issues along with cold Atlantic waters and you had a fatigue nightmare. The construction tolerance issue was quite difficult to eliminate and examples appeared well into post war decades worsening as overall hull dimensions increased with bulk carriers.

[Bird_Dog]

Now for the really scary part: Metal that is repeatedly flexed back and forth experiences an effect called work hardening.
The flexed part gets harder and more brittle with every motion. Given that in a ship's hull the flexing takes part over a great length, this takes a long time to become relevant, but it inevitably will weaken the structure.
So, no matter how well you take care of your ship's hull, it's days are numberd.

[CTCTraining]

Thx for another fascinating video. Just wondering if you are keeping abreast of the changes being trialled on cargo ships (wind wings, methanol, batteries etc) and it would be interesting to hear if any of these changes are presenting extra challenges for the captain and crew. Keep up the great work 😀👍

[DomyTheMad]

1: it's a fysical object. everything bends.
2: "i mean we can make it bend less? but trust me it'll snap in half like 100x more often"

[rob]

And the hogs belly sags, a bit like mine! lol. Seriously though, my respect goes out to the crews of container ships. What a complex job they have on their hands, travelling the worlds waterways so we can all get our goods without any appreciation or even a second thought.

[runedahl]

When calculating ships seaworthiness and draft you figure out several variables. Draft and trim is obvious but also the vessels stability The stability is defined by the distance between the meta center and the center of gravity (GM). We also used to calculate on what angle of list the vessel would capsize. In addition we would calculate structural conditions like hog and sag. In addition you also have the shear forces that also have to be taken into the equation. On every ship the limits for hog and sag and for shear forces are clearly defined. One for port conditions and one for seagoing. The limitations for seagoing are naturally stricter. Before the days of computers you had to calculate this by hand but there were devices that could help you speed up the process. On the devices you set the weights and the device would in a clever way tell you if you were within the limits.

[TrassseB]

Here I was all my life thinking the sea was boring & shipping was stupid…
3 videos in I’m hooked 😅