Wonder why ships don't tip over?

[JohnsPrincess]

This is a total fear of mine. Our last cruise was this past Christmas with Disney and I could feel the ship rocking side to side and I was Freaked out. My husband told me all the above and tried to calm my fears but all I could picture was it rocking more...and more...and more and eventually just turning right over!!! Lol. Of course, we're booked on the Legend in Aug so I obviously know somewhere in my brain that we'll be fine.

[mboatman]

I do. I remember when ships had heavy, deep keels as ballast. Their draft was so deep they couldn't get into shallow ports, (remember the Cunard France always anchored outside St. Thomas bay?)

It is my understanding that newer ships have more of a flat bottom instead of a pointy keel (and they draft shallower), then huge water holding tanks inside the hull act as ballast. These are controlled by computers to keep the ship level and up.

Anyone knows more about this?

Same reason weebles wobble!!

[dan40]

I do. I remember when ships had heavy, deep keels as ballast. Their draft was so deep they couldn't get into shallow ports, (remember the Cunard France always anchored outside St. Thomas bay?)

It is my understanding that newer ships have more of a flat bottom instead of a pointy keel (and they draft shallower), then huge water holding tanks inside the hull act as ballast. These are controlled by computers to keep the ship level and up.

Anyone knows more about this?

 

 

Your question contains the answer, BALLAST. The deep hulls of ocean liners were for riding the oceans rough waters, not for ballast. They had to carry tons of ballast the same as cruise ships do. The shallow draft flat bottoms are so ships can use unimproved shallow harbors of tourist destinations.

Remember a ship with 90,000GRT or 220,000GRT has NOTHING to do with its weight. Each will weigh millions of pounds, much of it ballast.

[Brewzz]

I've sailed through lots of very rough seas, and left a lot of footprints on the bulkheads, but never worried about tipping over. As a few others have said, modern ship are designed so that only a small percentage of the ship's weight is above the waterline.

[LHP]

I think it is probably related to the concern that Congressmn Coleman made in a Congressional hearing a few weeks ago about the possibility of Guam tipping over because it would become too populated if we enlarge our military base there. The cruiseships are not islands so I'm sure they wouldn't tip over.

 

That was going to be my answer....

 

because they are not Guam... :D

[glrounds]

I do. I remember when ships had heavy, deep keels as ballast. Their draft was so deep they couldn't get into shallow ports, (remember the Cunard France always anchored outside St. Thomas bay?)

It is my understanding that newer ships have more of a flat bottom instead of a pointy keel (and they draft shallower), then huge water holding tanks inside the hull act as ballast. These are controlled by computers to keep the ship level and up.

Anyone knows more about this?

 

Fixed ballast, very wide beam, high cube design, water ballast, are all elements that combine to give a very stable ship with a draft of less than 26 feet in most cases. The deepest draft ship running until recently was the old Regal Empress which drew at least 32 feet. She was built in 1953, so that makes sense.

 

Although any water stowed onboard is obviously kept in the lower sections of the ship, but even better the incredible amount of steel, all the diesel engines, electric motors, pumps, compressors for the refrigeration, air conditioning, lighting and for air pressure, food storage, etc. which is much more dense than water would be the main "ballast" giving the ship its stability. All this is kept at the absolute lowest point possible on a cruise ship. Cabins and public areas above the waterline are also made of much lighter materials. Additionally, stabilizers are used to keep the ship from pitching from side to side.They are hydraulically operated to quickly send out an "uplifting wing" under water whenever the ship starts to pitch to one side.They're fast and, for the most part, while at speed, very effective. All this lowers the center of gravity which is at or near the waterline.

As another poster has stated, the real problem with these ships is when they are in port with limited speed and manuverability and are struck by high winds as one of the videos showed. The high slab sides of these modern day ships makes an excellent sail ! ! :) I think most recently high winds while in port were responsible for several Carnival collisions (low speed of course) and a couple years ago caused a Princess ship in open seas to heel over for quite some time. These ships are incredibly safe from capsizing. It would take a super high wind or a freak sea wave to capsize them.:)

Try to keep in mind, the Poseidon was a movie ! :D

[oncruisecontrol]

- Here is a video of very rough seas with a cruise ship.

 

I also dug up this realic from the past http://boards.cruisecritic.com/showthread.php?t=154578

 

 

A harrowing experience for the passengers, I'm sure. But, the ship in the video appears to be drifting (as in engines not running): A different situation than what occurred today on Carnival Ecstasy.

[noblepa]

As others have mentioned, all the really heavy stuff, like the engines, water tanks, fuel tanks, etc. are in the bottom of the ship, below the water line.

 

Although it does seem counterintuitive that a ship with perhaps 30 feet below the waterline and 100 feet above would not be top-heavy, they aren't.

 

In order for a ship to capsize, the center of gravity must cross the waterline. Because of all the weight below the water line, the center of gravity is only a few feet above the water line. A ship would have to list well over 45 degrees to capsize. Even the worst case of listing that have been reported are usually only 15-20 degrees. I'm sure it feels like the ship is going over, but it really isn't.

 

As a result, its almost impossible for an undamaged ship to capsize. Now, if the hull is breached or too much water is taken aboard, due to heavy seas, the geometry of the ship changes and all bets are off.

 

What I've always wondered about is if the ship IS damaged and begins to list even a moderate amount, say 15 degrees, that may be enough to make it impossible to launch the lifeboats on the "uphill" side, effectively cutting the number of lifeboats in half. Now you're in a Titanic-type situation, in which you don't have lifeboat seats for everyone on board.

 

Paul

[waiting4acruise]

What the reason I think those on the Ecstasy yesterday were glad it did not capsize when it did a manuver to avoid a bouy.