Tuesday, January 24, 2012

Why Mega Cruise Ships Are Unsafe: Opinion

Many of you will have by now seen multiple photographs of the stricken Costa Concordia. Just as surely as many of you will have seen photographs of the Concordia's stabiliser and dismissed it as just that, a stabiliser.

But it is far more than just a stabiliser, it is the mother and father of all stabilisers, it is simple enormous. And it is enormous for reasons other than to stop passengers honking up their foie gras when the ship experiences inclement weather.

It is the only thing that keeps the ship upright in any bit of a breeze.

Although I might be in danger of wearing out my own analogy, the one where I describe the Costa Concordia as a plank with a block of flats stuck on top, there is no better one that I can offer up, the thing is quite simply, a naval architect's nightmare, and quite frankly, I personally wouldn't cross the boating lake on the thing.

Before we address the design factors of the Costa Concordia, let's take a look at the way ships should be designed, and what better example given the subject of this post, than the infamous Titanic. If we look at the ratio between draft, the amount of ship below the waterline, and that of the air draft, the amount above the waterline we see a vessel of reasonable and safe proportions.





Now let us look at the Costa Concordia. What you see regarding draft, (the plank) is what you get, about twenty foot of it, there isn't but a few foot more than what's visible.



And air draft? (the block of flats) a good two hundred feet of it, generically referred to as top hamper. Now I don't think you need to be a naval architect to appreciate that things look somewhat amiss. There is an old saying in boat building, if it looks right, it is right. Something we can never accuse the Concordia of looking. To really put things in true perspective, just compare the size of the people on the stern of the vessel in the second photograph. The amount of draft is equivalent to four of those people. Scary; very scary indeed.




So what we have so far is a vessel that, although it must have passed some kind of inclination test, doesn't exactly fill one with confidence regarding its seaworthiness. Enter the stabilisers.

With a vessel of such air draft comes one thing, windage, lots and lots of windage. And the only thing combating that windage, preventing the ship heeling at an alarming rate, is the forward motion of the vessel and the deployment of the aforementioned monster sized stabiliser.

The photograph below shows an unnamed cruise ship, just getting underway leaving Charlotte Amalie harbor in St. Thomas, US Virgin Islands. There is no sea running, the wind is offshore and is striking the vessel on its starboard quarter, not even beam on. And if I were to make a guess, the wind would be approximately force four, about fifteen knots, judging by the ripples on the water. But as you can see, she is struggling to keep upright in this breeze.

She too will be fitted with similar stabilisers, and you can bet the farm it's doing all it can to try and pull the ship back on an even keel. As will the port side stabiliser; it will be set to try and fly, whilst starboard side is trying to reach the sea floor. That is why they are so huge, they need to be effective as soon as the ship lets go and gets underway at low speed.

So basically what we have, is a ship that is inherently unstable that has to rely on oversized stabilisers to make a passage.

As long as they don't go wrong, and as long as the ship doesn't break down. And don't forget, a ship that is dead in the water will invariably lay across the wind, side on if you will, presenting her windage to whatever is blowing at the time.




Update: From the comments, and unchallenged by me. But that's not to say these things don't lean like a sonofabitch in a wind. And if they were dead in the water, the leeway they would make would be alarming. But I still stand by what I said about how the stabilisers would be set in the picture above.

Please be aware that the Princess Cruises ship ("getting underway leaving Charlotte Amalie harbor in St. Thomas") is not leaning because of high wins but because it is turning - this is completely normal behaviour, no reason for worries at all and results from pure physics ... centrifugal force.




Italy wanted to relax safety standards before Costa Concordia

.....As is almost always the case after a major maritime casualty in European waters, the commission will now launch a review of existing passenger safety legislation. As it happens, a revision of passenger ship construction rules was on the commission's work program prior to the Costa Concordia grounding. The body has, however, until now not considered major changes to the way cruise ships are designed and built.

"Gargantuan" cruise ships such as the Costa Concordia are "not safe, terribly unstable" and start listing in the wind as soon propulsion is cut - according to John Kuehmayer, chairman of the Austrian Marine Equipment Manufacturers.

"The only vessel designed for yearlong passages across the North Atlantic is Cunard's Queen Mary 2. All the other cruise ships have to be cheap money-making machines", he says. If the commission engages in a serious review of cruise ship safety, it might not like the evidence it uncovers. Significant changes would be opposed tooth-and-nail by the multi-billion dollar industry. The commission scored a significant victory over Italy on passenger safety. Taking on the cruise industry would be a battle of a different magnitude. Full story publicserviceeurope.com


A bit extra found on the web. "block of flats on a barge" LOL.

One of the things bothering me most is the sudden loss of initial stability leading to the rapid, and ultimately fatal, listing. I have dug up some numbers that might shed a bit of light. The original Queen Mary is 1,019' 6" long, 118' beam, with a 40' draft. Gross Tonnage is listed at 81,237. The air draft (distance from water line to the top of the forward funnel) is 181'. Passenger capacity listed at 1,957 with 1,174 crew. 3,131 total.

Compare this to the Queen Mary 2. Length, 1,132', beam, 135', draft, 32' 10" air draft 236'! and 151,400 GRT. Passengers, 2,620, crew, 1,253. Total 3,873. The Costa Concordia is even more extreme. Length, 951'. Beam, 118'. Draft, 26' 10"!!. 114,500 GRT. Air draft 215'.! Passengers, 3,570. Crew 1,068. Total 4,638.!! The purpose is to illustrate that modern naval architecture has a much greater portion of the ships volume and weight above the waterline. this is compensated in part by wider beam but mainly is accomplished by computer controlled ballast and fuel stowage.

Costa Concordia has 14' less draft but 34' more air draft and 33,000 more GRT in a 68' 6" shorter hull. Consider that the Titanic, with a similar gash type damage sank more slowly and for practical purposes the decks remained level albeit down by the head. They would have had time to launch many more lifeboats had they had them. This sudden loss of stability is a scary issue. In fact, passengers have been injured in modern cruise ships when a steering malfunction caused a sharp turn and a severe list from the turning forces.

Perhaps safety standards will be modified and the "block of flats on a barge" style of naval architecture will have to revert to a more "seagoing" style of ship. One thing for certain, there will be repercussions from this. Had the ship had this sudden loss of stability in deep water, I fear the results would have been much more terrible.

http://cruiseforums.cruisecritic.com/showpost.php?p=31972708&postcount=43

Here is a ferry that came to grief a bit nearer home, virtually on my doorstep as it were. And for all my saying, that I wouldn't cross the boating lake on such a vessel, I have in the past, bummed a ride on this thing. Never realising of course, just how shoal drafted the thing really was. Story



59 comments:

Anonymous said...

I fully agree with this article. Lightening the superstructure by using thinner steel plates to in conjunction with use of stabelizers is another way of compensating for the air draft.
These cruisers also have their superstructures all the way from bow to stern to gain more revenue generating accommodations, but it also adds the extra weight and windage further reducing ship stability. After all, cruising is all about the Benjamins from cruise ship designs to cruise ship operations.

Himself said...

Noted.

And I've learned a new word.

http://www.urbandictionary.com/define.php?term=benjamins

Anonymous said...

Me too, thanks. M

Anonymous said...

What they need is:
- Bigger draft (more underwater decks)
- Higher watertight compartments
- More watertight compartments
- Horizontal watertight isolation
- And double hull.

It's the only way to say that a ship is safe. But i don't think a company would want a ship like that. This construction needs more money, beast engines to move that boat, more fuel for these engines, and the most important why they wont (and they have small drafts) the ship will not be able to dock if they use these safe proportions, they going to need 30 meters deep port.

Anonymous said...

Excellent article Himself, thank you.

Found your blog via http://www.cruiselawnews.com/
2012/03/articles/sinking/are-
cruise-ships-dangerously-top-heavy/

Himself said...

Why thank you.

Though I am only a "small boat" man as opposed to a "big ship" man, the physics are the same. Just as physics are the same on Mars as they are here on earth.

Physics is physics.

As with common sense, it's worth all manner of brains.

H

Himself said...

The role of physics in the sinking of the Titanic

http://www.sciencecodex.com/the_role_of_physics_in_the_sinking_of_the_titanic-88979

Franz said...

Please be aware that the Princess Cruises ship ("getting underway leaving Charlotte Amalie harbor in St. Thomas") is not leaning because of high wins but because it is turning - this is completely normal behaviour, no reason for worries at all and results from pure physics ... centrifugal force.

Himself said...

Noted and credited, see post.

Himself said...

Franz

http://onlyinamericablogging.blogspot.com/2012/04/channel-4-documentary-disasters-at-sea.html

Anonymous said...

Stabilizers are used to reduce the ship motions in heavy seas to make the ride more comfortable to passengers, not increase the overall stability of the vessel. They are not "the only thing that keeps the ship upright in any bit of a breeze". The ships can withstand much more from the winds and waves than the people in them, especially in case of cruise ships with thousands of non-mariners onboard.

I don't understand why people see the Titanic, which was built over 100 years ago (and sank!) as the ideal design for modern ships. Get over it and learn some modern shipbuilding.

Also, increasing beam is a more effective way to increase the initial stability of the vessel than increasing draft. That's why Oasis of the Seas is so stable - it's freaking 47 meters wide!

Anonymous said...

Comparisons of draft to air draft are totally meaningless without reference to naval architecture and an understanding of ship stability. Anon post is correct, stabilisers keep the passengers comfortable and play no part in the stability requirements. This blog has no scientific background or basis. Nice pictures though!

Himself said...

A naval architect I ain't, but I will say, these vessels are design safe just like a nuclear reactor is design safe.

When it goes wrong, it goes wrong with a vengeance.

If the stabilizers went kaput in a gale of wind or the vessel was dead in the water, it's the last place on earth anybody would want to be. Yourselves included.

Anonymous said...

John Eaves, an American lawyer who represents more than 150 passengers from 10 countries, said he hoped the investigation would lead to sweeping improvements to safety drills, training, and ship design in the cruise industry.

"The ship was top-heavy. It only sat half as deep in the water as the Titanic but it carried more than twice the number of passengers. The captain made a horrible mistake but we need to change safety standards in the whole industry."


http://news.yahoo.com/costa-concordia-pre-trial-starts-captain-tripped-defense-151012032.html

Himself said...

The big one is still yet to come, can you imagine the death toll if the captain hadn't run her aground?

I still find it inconceivable as to why anybody would want to be crammed into a floating box with thousands of other people. (Whose idea of a good time is to be crammed into a floating box with thousands of other people.)

Himself said...

What a difference a day makes, it was like Cape Horn yesterday looking out of my window. Today it's like Lake Como.

Anonymous said...

The Titanic's halves did land right side up after sinking. It did have other flaws like the compartments having no watertight ceilings but a big enough gash will sink ANY ship but an iceberg.

Here's a fun forensic experiment like CSI. Take a cruise ship made useless when an engineroom fire causes a days long blackout like Carnival Triumph. (Carnival Epic Fail?) and makes it so stinky as to make it "totalled".

Try this. Install a guidance system and make it a drone ship. On an April 1, launch the Epic Fail to the north Atlantic to sideswipe an iceberg with telemetry and a chase ship.

Then see if the 2 halves end up upright or on their side. THAT'LL tell the story better than any calculations. And make Carnival foot the bill for the experiment.

Himself said...

That's quite a bizarre proposal, LOL but I know exactly where you're coming from.

We have yet to see the biggy, be it a fire of Biblical proportions or trying to abandon ship in a gale of wind.

Which will reduce lifeboat capacity by half, because they will never launch them on the weather side with any success.

Anonymous said...

OT

http://www.guardian.co.uk/uk/2013/apr/03/offshore-secrets-offshore-tax-haven

Terry Tuggle said...

Why not just have a fin say about half way down the hull. The middle third of the ship would be enough for roll stability. About three foot wide angled to 45 degrees from the water line would create enough surface area to stabilize the roll. A second fin on the back of the ship parallel to the water line would dampen pitch; preventing the stern from dipping so much as the bow rises.

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Anonymous said...


OT. It's about the benjamins. (25 January 2012 10:56)

http://www.dutchnews.nl/news/archives/2013/05/dutch_firm_exported_chemicals.php

(...)Suggestion to the government: stop all weapons sales to all countries, or at the very least, all non-NATO members...but you know they won't 'cos it's all about the benjamins

Anonymous said...

A fascinating post, but essentially I think it is very wrong. It seems to be based on opining rather than fact.

Modern cruise ships all look top heavy, but this is an illusion. The weight (engines, generators, fuel, food supplies, water etc.) is deep in the heavy steel hull. Ships like 'Oasis' have upper decks made of light Aluminium. If you laid them on their sides, they would pop upright like a ‘weeble’.

There is a myth that the great Ocean Liners (you mentioned the Titanic) were very stable with there deep draft and modern ships are not so – this is untrue. The regulations about stability are much more stringent than they ever used to be. Tank-testing and computer modelling for sea -keeping/stability are much more advanced.

Deltamarin who are designing the Titanic II face the problem that they are trying to build a ship than looks like the Titanic, with similar looking hull design/shape. However they cannot replicate it exactly, because in computer tests is not stable enough for the modern regulations. The hull will HAVE to be modified to be mores stable - probably a shallower draft.

The original Queen Mary (1936) has a reputation of cutting through North Atlantic storms like a knife through butter. In reality she had the habit of rolling badly and 45% was once recorded. This would not be acceptable now.

Because of the improved understanding of stability and tighter regulations, many older Ferries and ships have been required ‘sponsons’ added to increase stability.

I believe the 'Queen Mary 2' is actually twice as stable as the 'QE2', although she is rather special ship.

I believe stabilizers have NOTHING to do with increasing a ships stability in terms of ‘safety’. They reduce ‘pitch and roll’ to make things more comfortable for the passengers.

Modern ship all have a shallower draft, but this does not make them unstable. They also have flat-bottoms so they can sit easier in dry docks.

Unfortunately, Concordia had a very big hole put in her hull. No ship could have sustained that kind of damage.

I’m not a navel architect, just a ‘layman’ who reads ship stuff, so those with knowledge please feel free to challenge me.

Malcolm

Anonymous said...

This blog is complete rubbish, written by someone with no knowledge of ship stability or the rules that these ships have to pass BEFORE they are allowed to put to sea. Absolute rubbish.
Ship stability is dependent not on the height of the vessel but on the position of the centre of gravity. As long as the major weights are contained low down, you can build as high as you want.

Don't worry all ships that sail to and from british waters have to meet stringent rules.

Stabilisers such as on the Concordia will never in themselves keep a ship upright.

Himself said...

Malcolm 20:12

I thank you for your comments Sir, and interesting they are.

It seems to be based on opining rather than fact.

I rather thought my title made that clear, for like yourself I'm no naval architect.

But as a single hander, live aboard, for a dozen years or so, rightly or wrongly, I think I'm entitled to that opinion.

And opine again I shall.

When the big one comes, and it will; just as sure as there is a nuclear instillation at Fukushima, it will come.

Then and only then, after the event of course, all recriminations coming after the event as they do, might people question the wisdom of cramming so many folk on the still proverbial, block of flats on a plank analogy.

Dead in the water in a good blow, across wind and waves, rolling like a bastard, and making leeway like a lost beach-ball, would you fancy your chances of abandoning ship safely?

That's to say nothing of how close under your lee, that shore might be.

I don't think I even need to add fire to the equation, do I?

It is only by sheer coincidence that I know what happens when a ship looses its stabilisers.

Taking passage, on the then smallest vessel on the Atlantic run, and I add, the last vessel down the St Lawrence for that season, the Stefan Batory lost its stabilisers in a blow.

Rolly? You might say that, the ensuing panic among a good portion of the passengers testified to that. Or so I was informed the next day at least.

Me? I was in my bunk full of Gordon's, and adopting Australian philosophy: She'll by right mate.

Peace.

Himself said...

Anonymous 15:01

Go and fuck yourself.

Anonymous said...

"..rightly or wrongly, I think I'm entitled to that opinion."

Yes Sir and me too! ;-)

Malcolm

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Anonymous said...

Then and only then, after the event of course, all recriminations coming after the event as they do, might people question the wisdom of cramming so many folk on the still proverbial, block of flats on a plank analogy. - Himself
25 September 2013 16:07

Well said. Mx

To name a thing is easy: the difficulty is to discern it before its appearance. - Pierre-Joseph Proudhon (1809 - 1865)


Anonymous said...

I do not wish to spoil the party, but in my opinion modern cruise liners are extremely stable, simply because the lower superstructure of the ship is built with heaver material such as steel and the upper sections with lighter material such as aluminum and as a consequence the ships stability due to height is not compromised.

Anonymous said...

i just want to know are cruise ships hulls as safe as transatlantic container ships

Himself said...

Straw man, container ships, ergo . . .

A container ship doesn't carry 7,000 souls.

Wide beamed ships = snappy roll.

Try launching lifeboats and evacuating 6 or 7,000 people in gale of wind and dead in the water.

You would never get the weather side boats away, and I wouldn't be too sure about the leeward ones either.

Throw an onboard fire into the mix and a crew that have no idea what they are doing.

What could possibly go wrong?

Paladin said...

I share the same concerns as the author. The largest ship I've sailed on was 1000 ft long, and carried 2800 passengers, and crew. Never again. I will not go on any ship that carries more than a thousand pax, and prefer smaller ships with 500-800 pax, as we might just get into a lifeboat if something went wrong. The Oasis of theSeas has sufficient lifeboats, but they each hold 345 pax. Can you even imagine how long it would to fill one of these boats, let alone the entire pax, and crew. Amazing that only two of these boats could hold the entire pax, and crew of any of Regent cruise fleet. Oh, and one more thing, you are going to have to beat the crew to the boats, otherwise, like the Andrea Doria which only could use half of its boats, the crew took most of them, and then were turned away by the rescuing ships, until they went back and filled them with passengers.

Anonymous said...

Gentle Folk
At the end of the day I would rather take my chances in a cruise liner that was in difficulty than an aeroplane that was in difficulty at 35000 ft

Himself said...

Paladin

I thought for a minute you were talking about the Oceanis.

http://www.oceanossinking.com/

Himself said...

16:21

Why anybody would want to cram themselves, along with 5,000 others, on to a floating petri dish, in the first place, is beyond my understanding.

At least with an aeroplane, the captain stays aboard. What?

Himself said...

A brief history of SS Andrea Doria

https://simple.wikipedia.org/wiki/SS_Andrea_Doria

Anonymous said...

In 1957 my family and I crossed the North Atlantic in a traditional ocean liner. We sailed thru a hurricane for 5 days...the boat went up forty feet and down forty feet and rolled from side to side for 5 days...that was the last time I set foot on another ocean going vessel..they even had a life boat drll during that time...

Anonymous said...

What frustrates me the most is this article was obviously not written by a professional seafarer or by someone with any knowledge of marine architecture

In their upright hydrostatic states cruise ships, lines and all ships are very stable rolling to very large angles before their stability disappears

The reason the Concordia sank is the same essential as the Herald of free enterprise, free surface effect basically a liquid causing an increasing and perpetual angle of list until the ships stability it's gz becomes negative or in the case of the Concordia it finds a new equilibrium

The bigger argument is why passanger vessels have not adopted the dubbed hull approached pioneered by tankers and now used on almost all new vessels over a certain size.

Also stabilisers are only for passenger comfort and not designed to be an aid to stability or even an integral part of it.

Jack Holland said...

As an old Navy man, I thought ship stability was all about the Metacenter and Center of Gravity.

Anonymous said...

Doing the same thing over and over and expecting a different result “cruise ship insanity” it was only a couple of hundred Korean kids that had to die this time or they really might consider changing they designs. As the great America poet Cyndi Lauper once said “Money Changes Everything” As long as the industry can legally bribe our congress things ain’t changing.

Himself said...

Jack Holland. You are quite right Sir, as I do acknowledge in the article. (inclination test)

But by the same token, old navy man, how would you fancy your chances of evacuating 8,000 aged souls under a worst case scenario?

Himself said...

Anon When it comes, the big one, and it will, wait then for the gnashing of teeth and wringing of hands.

Oh, and the bleating. Whodathunkit? well I never, blah blah blah.

I used to have a few tunes of Cyndi once over. Peace.

https://www.youtube.com/watch?v=KpwTUO5IsGk&list=PL99BC3E5D7377FB14



Anonymous said...

You should read a naval architecture text on ship stability before wasting your time writing this nonsense. Your argument comparing total height and draft is fundamentally flawed. The dimensions of the ship are not the only thing that affect stability. The location of the centre of gravity relative to the centre of buoyancy and the shape of the hull affect stability. Furthermore, very few ships are designed to maintain stability in a damaged condition where flooding occurs over more than about 15% of the length (this doesn't only apply to cruise ships).

jdonalds said...

The reason I googled and found this blog is we just returned from an Alaskan cruise aboard the Island Princess and I wondered how stable the ship is.

I was astounded by the ship, but what kept going through my mind was the amazing amount of weight in wood, glass, ceramic tile, marble, and other materials. I also noted the 25' draft on a 200+ foot high ship and wondered if the ship was top heavy.

I tend to believe the bloggers comments and would worry if winds were high or the sea swells were large. We encountered nothing over four feet in wave height during the week trip

Himself said...

Thanks for your input.

It's been my experience and observations, that when things go wrong at sea, it is rarely one cause or one event. When they go bad, they go bad in a big way due to accumulative problems.

But might I ask you a question?

Although you say it was calm, how would rate your chances of getting off the thing in a big blow/on fire?

And the Island Princess doesn't appear quite as extreme as others.

http://bit.ly/1pePjca

Other. http://twitpic.com/b0ql9j

Anonymous said...

We crossed the Atlantic in 50+ foot waves in the Norwegian Epic. The storm lasted 3 days and the ship was rock solid. I was surprised how well she handled the rough weather.

FTSuperintendent said...

Sir,
An interesting but somewhat inflammatory initial comment, easy to understand, however wholly misleading.
No 'modern' cruise ships (sic) have come to grief as a result of inherent stability problems.
The stability of these vessels is nothing whatsoever to do with active stabilisers and is not some subjective judgement.
The stability curve ( ie. the graphic illustration of how much righting moment, in foot pounds, it has at any given degree of roll.) is very accurately calculated prior to, and during, construction.
After launch, ultra accurate, and irrefutable, 'righting tests' are made to confirm their accuracy.
In any case, this ship sank solely as the direct result of an incompetent decision made by her master, effectively causing maritime suicide by driving her up against a headland outcrop at increasing speed.
Leave the poor old designers out of it.
Best aye
Rob V

Anonymous said...

As a retired USN MCPO who served as a repair locker chief on an aircraft carrier, my questions concerning cruise ship safety is related to firefighting and damage control What type of training and qualifications in firefighting does the crew possess? The one and only cruise ship I was on in 2007 looked like it had enough flammables aboard to burn like a torch. I'm not confident the crew could of handled a fire of any consequence.

Anonymous said...


A fin stabiliser only 'damps' the roll of the ship. It will lessen the dynamic roll angle in a seaway and generally enhance comfort for passengers. The stabiliser fin can be retracted - this will not affect the static stability of the ship.

Anonymous said...

I share the concerns regarding the impossibility of safe evacuation from a large cruise ship in distress. About four years ago a cruise ship broke down in Drakes Passage and I remember seeing video of appalling motion as the ship wallowed in mountainous seas. It did not capsize, which rather confirms the views expressed by those naval architects who have written in, and so this event might be regarded as a practical test. However, any other mishap on board, such as water being admitted through a broken side hatch and sloshing about, might have been fatal for everyone on board. I am currently on a seven year old small cruise ship and I am impressed by the sophiscation of the fire prevention and watertight compartmentalisation built into the ship. Rather like travelling at 35,000 ft in a modern airliner, a passenger nowadays has to trust the design, reliability, and safety systems of the craft, and NOT count on being rescued if the craft (air or sea) fails. It is still nice to have the illusion of a safe evacuation, in the form of lifeboats on a ship and slides and life jackets on an aircraft, but by the time they are needed one's survival chances are less than 100% and maybe approaching 0%.

Oregonian said...

Could a naval architect explain the significance of the center of buoyancy as the pivot axis of roll, rather than the center of gravity? I would think that the deeper the center of buoyancy, the less roll might be expected in proportion to overall hull width. In terms of structural integrity, growing hull dimensions will depend ever more on structural systems designed to distribute loads more like an aircraft rather than a building. In planes and boats, there is no ground to anchor load carrying elements to, but weight is still a big internal issue. Materials strengths have increased somewhat over the last several years, but systems must still be designed to balance loads, and I imagine there is a tendency to lighten structure accordingly in the direction of failure i.e., the Tacoma Narrows bridge.

lakeeriesailor said...

To get it out in front: I'm not a naval (or "navel")architect, but to the eye, the modern cruise ships have too much what used to be called "top hamper." I can also tell you that I was a U.S. Navy sailor many years ago, on the light cruiser, U.S.S. Oklahoma City, CLG-5. She was in the yards for many months for various modifications, and considerable weight was added topside for one thing or another. When we went out for sea trials, the ship rolled to about 40 degrees in moderate seas, maybe 12 to 15'. Back to the yards we went, and the superstructure was relieved of some 30 tons. For the record, the Okie City (nickname) was about 11,000 tons, approx. 600' long and DREW 27'! Air draft, as it's referred to in this blog, was probably no more than 40' - draw your own conclusions. However, I do know this: flat-bottomed craft have high INITIAL stability, but when that is exceeded, it's bye-bye. "Anonymous" said that you could lay a cruise ship flat on her side and she'd pop up like a "weeble." No, she wouldn't. That vast area of glass on her topsides would cave in from water pressure, she'd then downflood, and that, as is often said, would be that. Other commenters have also cited all the dock-side testing and tank testing that is done before a cruise ship can be launched. Could I gently point out that these tests cannot predict what would actually happen in very heavy seas. And in any case, as someone famously said, whatever can go wrong, will. See analogy by another commenter re Fukushima.

Anonymous said...

As said before, those fin stabilisers have nothing to do with the stability of the vessel. And even less with the damage stability as in case of Costa Concordia. Height of the superstructure increases windage area and raises center of gravity, and thus decreases GM, but the significance is much lower than it may seem. If you are really interested in ship stability, you may want to check 'Ship Stability for Masters and Mates' by Barrass & Derrett. It is pretty basic stuff and you don't have to be a naval architect to get an idea. PDF can be found by googling it.

Emman Esguerra said...

I believe they are still safe like NSMS in the Philippines.

Jay said...


In terms of Stability the greater the momentum Arc (Think of a lever with a longer haft) The greater the stability. By creating light aluminum superstructures and wide beams the ships are not likely to roll over. Couple of things to think about. Aluminum is rated by the national fire association as a flammable material. THe ships movement creates some grinding and that makes aluminum powder. They put aluminum powder in rocket fuel because it burns at 6900F , The entire ship runs on Vast amounts of electric power. Electric fires have been caused by aluminum wire in houses built in years of 60;s and 70[s and once it's burning that hot It's not going to be contained

THe problem on today's ships are that they are overcrowded because volume increases by a cube function with size and surface area increases on a squared function hence fights for deck chairs on the upper deck.

The biggest danger with these consumer temples is fire fighting and crowd control. So imagine you are in a giant flammable aluminum box with 6000 people and a third world crewman with limited English trying to keep order in the face of a serious fire--not pretty.

I had the chance to take a cruise on a real oceranliner converted for cruising the deck was close enough to the water that you got the feel of being at sea.

In my opinion the new ships might as well be attractions on the las vegas strip for all the feel of being at sea they provide. Complete with long lines and choke points---no thanks

Anonymous said...

This article does not consider the Aircraft carrier not equipped with stabilisers but having a great big runway welded on top but surely stable enough as aircraft have, and will continue to, land with regularity. These vessels also cross teh Atlantic and other oceans, surely not only in fair weather.

Fin Stabilisers are only useful when the vessel is under way, think of an aircraft's wing, useless without forward motion. The notion that Stabilisers add to the stability of the vessel is completely wrong, any vessel that relied on stabilisers to meet stability requirements would not be permitted to put to sea EVER.

Much has been made of the height of the vessel above water but the few mentions of beam or breadth of the vessel have been largely ignored. As mentioned by some of the contributors the beam plays an enormous role in the stability of the ship, consider placing your aforementioned plank on a flat surface against the stability of a knife balancing on it's sharpened edge, or the back even. The plank is significantly more stable.

The people that design and certify these vessels are smart enough to know that if one of these vessels were to sink because it did not meet stability criteria then they would be responsible for the deaths of a grate many people and subject to prosecution and other legal action.

I submit that your article needs a bit of a rework following a chat with people that really know ships and stability of ships.

AugustaB said...

Stability in ship design is related to what is known as metacentric height. The metacentric height is the distance between the metacentre, which is the centre of buoyancy when the ship is perfectly upright and the centre of gravity of the ship.
Ships in which the centre of gravity coincides with the centre of buoyancy are called submarines.
In cargo ships the metacentric height is usually of the order of 1 to 2 feet, whereas in passenger ships the metacentric height is lower.
Having a large metacentric height means that the righting moment when the ship heels (tilts) is greater and the ship recovers faster from anything that makes it heel. Cargo ships can roll quite severely but remain perfectly stable. This is a condition called "stiff".
Passenger ships with their lower metacentric height tend not to roll as violently but are nonetheless less stable as the righting moment is lower and they will recover less quickly from a heel. This is a condition called "tender".
Stabilizers slow recovery from a roll and are also effective in reducing rolling but they are not as such a source of stability.
True stability lies in having the centre of gravity below the centre of buoyancy.
I have been told by insiders that the metacentric height of some cruise ships is of the order of 3 inches. This means that the righting moment will be small, perhaps dangerously small.
On the plus side these ships are very large and when carefully commanded should not be excessively affected by heavy seas.

American Rambler said...

I found this interesting to read as I have been looking at the ability of vessels to recover themselves in situations where they get knocked over (rolled) or pitched length ways to to internal or external conditions or forces being imposed on them. I am not by any means trained in ship design, operation nor construction so am not any kind of expert. I have looked at videos of ships moving around in bad weather and sinking or breaking up after receiving considerable damage. I find the proportions of the current mega ships to put it bluntly pretty ugly and lacking in gracefulness that a number of popular ships of the past have had. Ships like the SS France/Norway, HMS Queen Elizabeth, and SS United States for example. Regulatory bodies have over time forced or codified design and safety improvements which most of us are not even remotely aware of. We have all benefited from that. Many get all excited about things when we have a spatacular failure like the Costa Concordia, Exxon Valdez, or Sinking of MV Sewol (Korean ferry) happen. The MV Sewol became the disaster it is due to a spactacular case of bad seamanship and serious modification defects performed which seriously reduced the stability of the ship. The crew jumped ship and then made the passengers stay in their cabins until it was to late to escape. A competent crew would have been able to save the passengers relatively easily. Even after the massive cargo shift that caused what evolved into the fatal capsizing. The negligence leading to the Exxon Valdez was mitigated a lot by designed in safety features of the ship in spite of it not being double hulled and by response activities which followed even though it received a lot of negative publicity. The ship stayed in one piece and most of the cargo recovered. The Costa Concordia is a whole new level. If I remember correctly, certification requirements mandate demonstration that the passengers are able to be evacuated from the ship by lifeboat within 30 minutes. Policies and procedures were in place requiring shipboard water tight doors be closed and ship speed reduced when operating in shallow coastal ares, the captain purposely violated almost every rule, refused to initiate evacuation procedures in a timely manner, and was one of the first to jump ship. If the ship had been buttoned up as required by the regulations, and been operating at a slower speed as also required, even though it would have been severely damaged, initial flooding may have been reduced significantly. As such, more time would have elapsed and maybe the outcome as well. I have been looking for more detailed information on the actual damage done by the initial reef strike and how the ship flooded. I find the roll to starboard prior to the final grounding interesting due to the fact that the ship was holed on the port side and would like to know and understand what happened to allow that. I would also like to find out what design features played a roll in preserving the ability of the ship to reach the island and preserved it's power and function for as long as it did. I noticed the ship had power for quite a period after the final grounding. Tall relatively shallow draft ships have demonstrated good abilities to survive what would be disaster conditions. I point to the example of the MV Cougar Ace, a very tall boxy automobile carrier that flopped onto its side in the North Pacific near Dutch Harbor Alaska in July 2006. It had flopped over so far that the entire keel, rudder an screw was out of the water. The capsizing caused by a water ballasting procedure gone wrong. The ship continued to float and was recovered by a salvage crew who righted the ship using a portable pump by re-ballasting and balancing the ship to restore its stability. The ship was repaired and re entered service.
I am continually fascinated with how things that look unstable are in point of fact quite stable. Ships are the best visual representation of that.