# Ships that appear top heavy **URL:** \ **Category:** Factual Questions\ **Created:** [February 9, 2016, 8:38pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649 "2016-02-09T20:38:50Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![snowthx](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snowthx/32/10660_2.png) [@snowthx](https://boards.straightdope.com/u/snowthx)\ **Post date:** [February 10, 2016, 2:49am UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/21 "2016-02-10T02:49:20Z")
> [@msmith537](#): > > Also, keep in mind that just because a ship “looks” topheavy, doesn’t mean it is. The [Oasis of the Seas](http://i.dailymail.co.uk/i/pix/2009/11/02/article-1224504-070E6B86000005DC-422_964x513.jpg)here looks very top heavy. But in the top are passenger cabins, open spaces, restaurants and whatnot that are mostly full of air. Below the waterline you have ballast tanks, fuel and other stores that take up less volume, but are extremely dense. Yeah, I always thought that ship looks too big to sail. 😃 Also, aircraft carriers really look top heavy, but clearly the weight distribution is managed properly (USS Ronald Reagan). ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [February 10, 2016, 5:37am UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/22 "2016-02-10T05:37:47Z")
There have been a few famous cases of ships too top heavy to stay upright. Exactly why the [Mary Rose](https://en.wikipedia.org/wiki/HMS_Mary_Rose_(1510)) sank is uncertain, but top heaviness after retrofitting with more guns was probably a factor. The Swedish ship [Vasa](https://en.wikipedia.org/wiki/Vasa_(ship)) was so unstable it capsized on its maiden voyage. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [February 10, 2016, 6:23am UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/23 "2016-02-10T06:23:40Z")
> [@AskNott](#): > > Keep these things in mind: > > If you could see the part of the hull that’s underwater, a ship wouldn’t look so top-heavy. > > The stacks of shipping containers that make a ship so tall are relatively light for their size, and the dockside crane operators put the heavier ones on the bottom. > > **Cargo ships pump seawater into the bilges for ballast**. They’re supposed to take on and flush out ballast water outside the harbor. At sea, they ride lower than in the harbor. No never. seawater is never pumped into bilges for any reason. In the engine and boiler rooms it is the responsibility of the oiler to keep the bilges pumped dry when at sea. And an AB should be checking the cargo bilges to be sure they are dry. If the bilges were to have water in them as the ship rolled cargo could get wet and damaged. In the engine and boiler room if the bilges are not pumped then machinery, piping, and other equipment and structures would be subject to corrosion. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [February 10, 2016, 7:20am UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/24 "2016-02-10T07:20:41Z")
> [@AskNott](#): > > Cargo ships pump seawater into the bilges for ballast. They’re supposed to take on and flush out ballast water outside the harbor. At sea, they ride lower than in the harbor. Seawater is used as ballast but is pumped into ballast tanks, not bilges. At sea they ride the same as in port generally. The only exception would be if the vessel is going to encounter extreme weather in which case (rarely) a vessel that is lightly loaded or not carrying cargo (described as being “in ballast”) will take on more ballast to lower air draft and increase prop submersion and stability. > [@Snnipe\_70E](#): > > No never. seawater is never pumped into bilges for any reason. Saltwater washdown of holds is the only circumstance I can think of, although of course that isn’t directly to put seawater into the bilges, but that’s where it ends up. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [February 10, 2016, 8:39am UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/25 "2016-02-10T08:39:18Z")
> [@Chronos](#): > > And now I’m wondering if there’s any way to contrive a situation where a floating object has its center of mass below its center of buoyancy, while still being unstable. Sure. Take a stable configuration with CoM below CoB. Then, add a small, dense weight on a _very_ long lever arm to the side of the ship. You can generate an arbitrary amount of torque like this, so there’s some arm length where the ship will tip over. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 10, 2016, 1:11pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/26 "2016-02-10T13:11:49Z")
> [@Dr.Strangelove](#): > > Sure. Take a stable configuration with CoM below CoB. Then, add a small, dense weight on a _very_ long lever arm to the side of the ship. You can generate an arbitrary amount of torque like this, so there’s some arm length where the ship will tip over. I think Chronos might have meant a design that wasn’t quite that unstable. I.e. one that would stay upright until disturbed and **then** flip over, not one that can’t stay upright no matter what. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [February 10, 2016, 2:14pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/27 "2016-02-10T14:14:22Z")
> [@YamatoTwinkie](#): > > Top heavy is fine. The important criterion is that the center of buoyancy always “shifts” more than the center of mass does, during a roll condition. This causes a restoring moment that rights the ship. > > Diagram here: > [10 Tips for Learning New Skills Easily and Efficiently](http://www.learneasy.info/MDME/MEMmods/MEM23041A-busted/fluid_mech/fluid_statics.html) An extreme example is a [floatplane (airplane with pontoons)](https://en.wikipedia.org/wiki/Floatplane). There’s hardly any weight below the water, just empty pontoons. But they are stable, because as soon as it starts to tilt, one pontoon dips deeper into the water, shifting the center of buoyancy towards that side. [Pontoon boats](https://www.google.com/search?q=pontoon+boat&espv=2&biw=816&bih=721&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiEv6-fsO3KAhUEZCYKHTFGBp4Q_AUIBigB#tbm=isch&q=pontoon+boat+double+decker) are pretty top-heavy too. The wide, boxy hulls of cargo ships and cruise ships have the same effect. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 10, 2016, 2:17pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/28 "2016-02-10T14:17:03Z")
> [@dtilque](#): > > There have been a few famous cases of ships too top heavy to stay upright. Exactly why the [Mary Rose](https://en.wikipedia.org/wiki/HMS_Mary_Rose_(1510)) sank is uncertain, but top heaviness after retrofitting with more guns was probably a factor. > > The Swedish ship [Vasa](https://en.wikipedia.org/wiki/Vasa_(ship)) was so unstable it capsized on its maiden voyage. Also the [South Korean Ferry the Sewol](https://en.wikipedia.org/wiki/Sinking_of_MV_Sewol) ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [February 10, 2016, 3:21pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/29 "2016-02-10T15:21:04Z")
> [@enipla](#): > > Also the [South Korean Ferry the Sewol](https://en.wikipedia.org/wiki/Sinking_of_MV_Sewol) Not about buoyancy but surely the most telling comment: “_The company budget for the safety training of the crew was $2 American, which was used to buy a paper certificate_” ---
**Author:** ![Algernon](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Algernon](https://boards.straightdope.com/u/Algernon)\ **Post date:** [February 10, 2016, 3:36pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/30 "2016-02-10T15:36:44Z")
> [@dtilque](#): > > The Swedish ship [Vasa](https://en.wikipedia.org/wiki/Vasa_(ship)) was so unstable it capsized on its maiden voyage. If you ever get the chance, I highly recommend the Vasa museum in Stockholm. It is utterly fascinating, and the ship itself is gorgeous. And to clarify a bit, “on its maiden voyage” might bring visions of capsizing somewhere out in the open sea. However, the Vasa floundered right as she left the harbor. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [February 10, 2016, 3:50pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/31 "2016-02-10T15:50:37Z")
> [@bob\_2](#): > > Not about buoyancy but surely the most telling comment: “_The company budget for the safety training of the crew was $2 American, which was used to buy a paper certificate_” But that’s like 5 billion waung! ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [February 10, 2016, 4:19pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/32 "2016-02-10T16:19:07Z")
> [@dtilque](#): > > The Swedish ship [Vasa](https://en.wikipedia.org/wiki/Vasa_(ship)) was so unstable it capsized on its maiden voyage. The Vasa museum in Stockholm is amazing. If you are ever in Stockholm go see it. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 10, 2016, 4:22pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/33 "2016-02-10T16:22:31Z")
> [@enipla](#): > > Also the [South Korean Ferry the Sewol](https://en.wikipedia.org/wiki/Sinking_of_MV_Sewol) Also the [SS Eastland.](https://en.wikipedia.org/wiki/SS_Eastland#The_Eastland_disaster) ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [February 10, 2016, 4:25pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/34 "2016-02-10T16:25:57Z")
> [@Chronos](#): > > And now I’m wondering if there’s any way to contrive a situation where a floating object has its center of mass below its center of buoyancy, while still being unstable. I don’t think so. The forces want to be at equilibrium. the COB will push upward on the ship while the COM will push downward. A ship is unstable when the COB is below the COM because without enough lateral force to counter they COB and COM will try to switch places and the boat will capsize. ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 10, 2016, 4:29pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/35 "2016-02-10T16:29:56Z")
> [@Algernon](#): > > If you ever get the chance, I highly recommend the Vasa museum in Stockholm. It is utterly fascinating, and the ship itself is gorgeous. > > And to clarify a bit, “on its maiden voyage” might bring visions of capsizing somewhere out in the open sea. However, the Vasa floundered right as she left the harbor. Marine engineering of warships in the age of sail must have been tough - the ships are made of wood and powered by tall sails, yet the heaviest things on the ship - the guns - are best put as high as possible. Instability seems to be hardwired into the very design requirements. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [February 10, 2016, 4:41pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/36 "2016-02-10T16:41:16Z")
Yes, but take a look at this cutaway of [HMS _Victory_](https://farm9.staticflickr.com/8449/8059192290_2ef95452e1_b.jpg). Most of the stores and the ammunition and powder magazines were below the waterline, the decks just had the guns. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [February 10, 2016, 4:58pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/37 "2016-02-10T16:58:40Z")
> [@Dr.Strangelove](#): > > Sure. Take a stable configuration with CoM below CoB. Then, add a small, dense weight on a _very_ long lever arm to the side of the ship. You can generate an arbitrary amount of torque like this, so there’s some arm length where the ship will tip over. But the weight on the lever will move the center of mass. ---
**Author:** ![Malthus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@Malthus](https://boards.straightdope.com/u/Malthus)\ **Post date:** [February 10, 2016, 5:07pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/38 "2016-02-10T17:07:47Z")
> [@AK84](#): > > Yes, but take a look at this cutaway of [HMS _Victory_](https://farm9.staticflickr.com/8449/8059192290_2ef95452e1_b.jpg). Most of the stores and the ammunition and powder magazines were below the waterline, the decks just had the guns. Certainly, it can be done (and was done) so that ships were stable. By the time the Victory was constructed, marine engineers had worked out just how to do it, and had been doing it for some time. Compare with the Vasa, built early in the career of multi-gundeck ships. The Vasa also had the heavy stores in the hold, just like the Victory - but was still dangerously unstable. > **[Vasa (ship)](https://en.wikipedia.org/wiki/Vasa_(ship)#Construction)** > > Vasa or Wasa (.mw-parser-output .IPA-label-small{font-size:85%}.mw-parser-output .references .IPA-label-small,.mw-parser-output .infobox .IPA-label-small,.mw-parser-output .navbox .IPA-label-small{font-size:100%}Swedish pronunciation: \[²vɑːsa\] ⓘ) is a Swedish warship built between 1626 and 1628. The ship sank after sailing roughly 1,300 m (1,400 yd) into her maiden voyage on 10 August 1628. She fell into obscurity after most of her valuable bronze cannons were salvaged in the 17th century, un... The Mary Rose allegedly sank for a slightly different reason: her heavy guns were put low, but the redesign added too much weight; so when she heeled over in a wind, water came in through her gunports, sinking her. Of course, she was a much earlier design even than the Vasa, but compared with the Vasa was a much more successful ship: the Vasa sank right away, while the Mary Rose was in service for years before sinking. > **[Mary Rose](https://en.wikipedia.org/wiki/Mary_Rose#Design)** > > The Mary Rose was a carrack in the English Tudor navy of King Henry VIII. She was launched in 1511 and served for 34 years in several wars against France, Scotland, and Brittany. After being substantially rebuilt in 1536, she saw her last action on 19 July 1545. She led the attack on the galleys of a French invasion fleet, but sank in the Solent, the strait north of the Isle of Wight. > The wreck of the Mary Rose was located in 1971 and was raised on 11 October 1982 by the Mary Rose Trust in o... ---
**Author:** ![UncleRojelio](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unclerojelio/32/3160_2.png) [@UncleRojelio](https://boards.straightdope.com/u/UncleRojelio)\ **Post date:** [February 10, 2016, 5:14pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/39 "2016-02-10T17:14:20Z")
> [@AK84](#): > > Yes, but take a look at this cutaway of [HMS _Victory_](https://farm9.staticflickr.com/8449/8059192290_2ef95452e1_b.jpg). Most of the stores and the ammunition and powder magazines were below the waterline, the decks just had the guns. I seem to recall that both in both the Aubrey and Hornblower books, gun placement is referenced many times. Heavier guns on the lower decks and smaller guns on the upper decks. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 10, 2016, 5:49pm UTC](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649/40 "2016-02-10T17:49:08Z")
> [@msmith537](#): > > A ship is unstable when the COB is below the COM because without enough lateral force to counter they COB and COM will try to switch places and the boat will capsize. This is not true. See my post upthread in which I cite the catamaran as an example of a boat with its CoM clearly above the CoB. A roll will cause the CoB to shift laterally farther than the CoM, causing a moment that tends to roll the boat back toward vertical (see numerous links upthread explaining hull stability). There are also plenty of single-hull boats for which the CoM is above the CoB; the shape of the hull is such that a roll causes the CoM moves laterally so as to ensure stability. Instability happens when the CoM is **too far** above the CoB, such that the CoB can’t move laterally far enough to counteract it. [Previous page](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649.md?page=1) [Next page](https://boards.straightdope.com/t/ships-that-appear-top-heavy/745649.md?page=3)