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.
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