Rick Spilman

Rick Spilman
Jersey City, New Jersey, USA
March 25

JULY 3, 2012 7:25AM

Of Stabilizers, Stability and Lawyers

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Mississippi lawyer John Arthur Eaves is supposed to be good at his job and is, by reputation, a pretty smart fellow. He recently filed a law suit claiming that the Costa Concordia was “defectively designed,” a “ floating coffin,” had a “propensity … to roll and list” and was dangerous “because of the maze-effect within the vessel…”   I am not a lawyer, but as a naval architect, I can say with a fair degree of confidence that Mr. Eaves does not know the first thing about ship stability.

He didn’t even bother to get the most basic facts straight. He was righteously indignant that Carnival has “the audacity to try and refloat the Costa Concordia which we know was defectively designed. I think it is a dishonor to the families that lost loved ones and to the people that went through this tragedy to try to refloat a boat, put it back out into commerce and put other families and other passengers in jeopardy.”  Of course, if Mr. Eaves had bothered to read the press reports, he would know that the plans are to break the ship up, not to put the it back into service. He also seems unaware that there are five other Concordia Class cruise ships of the same design currently in service.

Unfortunately, regarding ship stability, Mr. Eaves is not alone in his ignorance.  Jim Walker, attorney and blogger at Cruise Law News has been saying some awfully bizarre things, as well.  I have always thought Walker was reasonable and well informed but then I read the following statement in a post defending Eaves’ quixotic lawsuit: “Cruise ships like this depend on stabilizers. But stabilizers are of no help when the cruise ship loses power. Ships like this seem likely to tip over.”  It appears that Walker read a blog post by an uniformed soul which claimed that the stabilizer “is the only thing that keeps the ship upright in any bit of a breeze.”  Really?

At this point, one either can laugh or cry.  Fin stabilizers on cruise ships have almost nothing to do with the stability of the ship.  Then why are they called stabilizers? I don’t know. Why are movie ”trailers” called trailers when they come before not after the movie? My guess is that  calling them  ”gyroscopically controlled  hydrodynamic roll dampening fins” is too much of a mouthful.  Stabilizers, or whatever you might wish to call them, actively dampen the roll while the ship is moving. When the ship stops moving, they have no real function. They most assuredly do not provide any sort of stability to the ship, nor does the ship “depend on stabilizers” for stability. If you want to know more read this:  How Cruise Ship Stabilizers Work

The other topic that is not quite so foolish, but comes close, is the claim that modern cruise ships are too “top heavy.”  There is no question that cruise ships have more decks above the waterline than they used to. More windage is not good for stability but to suggest that the additional decks are adding too much weight largely misses the point. The criticism is invariably based not on facts or stability calculations, but on visual inspection and/or gut feelings.  The facts are that passengers and the decks they occupy are relatively light. The additional space is primarily occupied by air.  Other types of ships also have significant windage, including car carriers and, of course, sailing ships.  Just like cruise ships, with a reasonable distribution of ballast, these ships can be stable as well.

The stability of the ship is not very mysterious. Intact stability is a function of the center of gravity of the ship, the center of buoyancy of the immersed hull, the moment of inertia of the water plane area, the ship’s displacement and the area under the righting arm curve.  None of this is all that complicated but it does not lend itself to snap judgments like, “gee, that ship looks too top heavy.”  And the ship’s stability does not have anything to do with the fin roll stabilizers.  I know that I have said that before, but it seems worth repeating.

Damaged stability is somewhat more complicated than intact stability.  Then there is grounded stability, or more properly the loss of stability when grounded, which has everything to do with the contour of the bottom where the ship grounds.  Any ship suspended on rocky ledges at the bow and stern with the midships no longer supported by the buoyancy of the water, will roll one way or another.  I am not sure how anyone could design around that bit of unfortunate physics. (This applies to all ships, not just large cruise ships.)  I am willing to bet that that is the determination of why the Costa Concordia rolled to 80 degrees.

Why is any of this important? It is important because there are serious issues of cruise ship safety that are not being addressed and silly claims like that a stabilizer “is the only thing that keeps the ship upright in any bit of a breeze,” only serve as distractions.  When there are serious problems, misinformation and Mississippi lawyers don’t necessarily help.

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