THE BRITISH THREAD II

I believe the engineering term of art for the key measure of a ship's roll stability is the "metacentric height" which, if memory serves, is the vertical separation between the ships cernter of gravity (or mass) and the center of bouyancy ( the point at which the distributed bouyant force can be said to act). The metacentric height is the lever arm for the restoring moment when the ship rolls for any reason. Unfortunately the center of bouyancy , determined by the underwater shape of the hull, and draft - or draught you write it) moves , almost always reducing the metacentric height, when the ship rolls. Ultimately that determines the maximum roll from which a ship can recover at all.

Modern cruise ships (and some container vessels when they are loaded) have extremely high freeboards (vertical height above the waterline), making them very vulnerable to wind forces during stormy weather. A sustained 40 Kt wind directly on the beam could easily induce a constant list oif roughly 15 degrees in such conditions. ( A crosswind could also have been a factor in drifting the ship onto the rocks). The extensive vertical mass also raises the center of gravity significantly, requiring equivalent ballast (concentrated mass near the base of the hull) and almost always yielding a reduction in the metacentric height and a reduction of roll stability. I stringly suspect this and some crew errors are the key elements of this accident.

Interestingly the Italian cruise vessel didn't sink: it simply stabilized at a 90 degree roll angle. That pretty clearly indicates design shortcomings and/or errors in the ship's actions to contain and control the damage by quickly sealing the punctured compartments and/or counter flooding.

There is no such thing as a completely safe ship, aircraft, vehicle or machine of any kind - even in today's world. We can (and routinely do) identify the salient risks attendant to any design and take measures to reduce their effects. We also identify typical operator errors and add design features to reduce or mitigate them. Unfortunately neither are perfect and the added design complexity can also create its own increased potential for unforseen consequernces.

An interesting angle mentioned on our news channels this evening:

The rock which did the damage "should not have been there". Well no ****, Sherlock.

But it might have been the result of recent seismic activity thrusting a portion of the seabed up.

So there you are. The accident was caused by the demand for cruising.

No cruising--no accident. Cruising --risk of accident with 4000 dead.

And I know about crossing the road ****. That is necessary. Cruising isn't necessary. In fact one look at the sea from the Islay ferry put me off goodstyle.

Why should us stop-at-homes pay to rescue them silly sods?

because one of them might turn out to be your solicitor?

I've now read some of the news reports and looked at a sequence of photos all widely rerported. I doubt seriously that there was an uncharted rock near the shore the ship approached so closely - the photos of the rocky shoreline strongly suggest the natural presence of other rock formations close off shore - and the ship passed very close indeed. The captain was reported as saying "the rock shouldn't have been there" or words to that effect - and in his mind that may well be true, but the available facts suggest it was his perception, not the rock, that was at fault.

Apparently at least 30 minutes elapsed between the initial grounding and the moment when the ship began to list badly and eventually turn on its side. This very strongly suggests some combination of inadequate design and inadequate actions to limit the consequences by quickly sealing affected compartments and counter flooding to correct the list.

Some years ago a U.S. Navy aircraft carrier drove over a charted, lighted sea mount at about 28Kts at twilight during flight operations off the southern California coast. The event made long (50M +) deep cuts in both sides of the hull, penetrating 3 M at some points within the ship. They quickly isolated the affected compartments, counterflooded to conrol the resulting list, and returned to port without additional damage or injury - or even much reporting by the news media. (The captain was quickly relieved, however.)

Navy doesnt take to captains running over the undersea beds.
I have a question George. Do the cruise ships not have transponders in their front as well as amidships for depth cross sectioning? Id think that since I (who had a boat 40'loa , had several transponders both fore and amidships, Id think that it would be a no brainer for something like a cruise ship which is always traversing shoaly areas and areas whose shoals change.

Also, wasnt there a pilot on board they were in some kind of channels?

I don't think that they needed a pilot there, since they've been in a 'normal' (though coastal) region

I knew the carrier captain in that case very well. He was then regarded as the most proficient carrier captain in the Navy (but that didn't save him). He was also a bit arrogant and abrupt with people. On reconstruction it turned out that the ships position was plotted correctly and only person on the bridge who didn't know that the dim light ahead was Bishop's Rock was the captain, ... who was conning the ship at the time. The others were either sure he knew and had a plan, or were afraid to tell him. This happened just a few months before I took command of Carl Vinson, and was a lesson I kept in mind always.

I suppose you are referring to sonic depth finders. I'm sure the ship had them but, depending on their orientation, they only tell you the depth in a small area below the hull. This ship is very large compared to the field of view of a depth finder and the proximity to the rocky shore very close. If one is fool enough to approach an obviously rocky and steep coastline within a beam of the ship, devices like that won't protect you - It appears they drifted on to the rock that penetrated the hull somewhat from the side.

Walter's chart above makes it clear to me that the captain here took a significant risk, and for a small return - a tradeoff I would never have knowingly accepted. The news reports suggest it had been done before, but taking a (say) 5% chance of losing the ship so passengers can get a better look at the coastline isn't good odds.

I don't think any of us need a lecture on it not being the rock's fault George. I know what the lecture is all about mate. It's about you strutting your stuff as a maritime expert so we all take you seriously and bow to your judgement in other matters.

Well I don't. The creation of the demand for piss-balling about pompously preening the persona caused the accident.

What caused that is a bit more complicated.

Who besides Spendi could conflate boob jobs with high speed rail systems. Ya gotta' love him.

Let's just say that I really am expert in the subject of ship operations, based on a lot of relevant experience, and that I addressed the matter with a far greater economy of words than those with which you so abundantly devote to subjects about which you know very little.

The gash in the hull seems to be above the waterline now, due to the ship's list. Although we can't see what's underneath, the ship was reportedly travelling sideways at the time, so maybe what is visible is all the damage there is.

Is it possible they could weld some steel plate over it, pump the ship, and recover her that way?

No, having seen fresh pictures this morning, this is daft.

There are too many windows under the waterline now. It will not be possible to make the ship watertight.

Neither do I. Has he blamed it all on the British Empire yet? If he hasn't, it's only a matter of time.

Hey, leave it out, you two. George has been informative, interesting, and restrained.
If you want to pontificate about something you've got to establish your fona bides first, and George has done that, and no more than that.

They could pump the bilge full of ping pong balls, thatll refloat it.
I found out last night that the captain boogied before the ship was even emptied of passengers. He was arrested and detained pending possible manslaughter charges.

George--under what "rules of the road" would these criminal charges be brought, is it the country in which the ship is traversing?

I wouldnt want to be that guy. He seems to have really "compounded a felony or two"

I don't doubt that you are an expert on ship operations George. I don't think the US Navy would have allowed you to take command of the Carl Vinson otherwise.

But, as you said, there will be accidents at some point.

I am something of an expert on the creation of the demand for cruise ship operations and without that demand being created, contra Goethe, accidents would not happen to cruise ships. The design of cruise ships and their operations are obviously fairly minor aspects of the creation of the demand for them as without that demand the design and operation of them are unnecessary and there would be no cruise ship problems like this one or those associated with disease or terrorism.

As I don't see the relevance of the incident at Bishop's Rock to either this thread or to the accident off Italy I can only assume it's use is merely to once again parade your puissant chutzpah before the poor sods who make up the membership here and whose destiny has not included being in command of an aircraft carrier. Which is to say milking the accident.

I seem to remember you telling us of the grounding of a ship off the coast of Africa on which you were in a position of responsibility.

I am also an expert on the design and operations of the Good Ship Venus but I allude to that subject on rare occasions and even then only tangentially.



If you would be so kind as to tell me what it is you are referring to there I will endeavour to provide an answer.

If, as you rightly say, accidents are inevitable with cruise ships then an exclusive focus on their design and operations seems to me to be a tacit approval of the future accidents which will inevitably occur and provide further opportunities for experts on the design and operations of them to strut their expertise.

Focus on the demand for cruise ships does have a chance of preventing future disasters.

The last post on the "Quote of the Day" thread--



And there a lot more people sitting quietly in their rooms than there are sailing on cruise ships.

I presume he is an expert on the design and operation of ships.

How many ping-pong balls would it take fm? Could they be filled with helium?

How many holes would it take to fill the Albert Hall?

I'm not too convinced about this, fm. You propose the deadweight of this giant vessel should be balanced by a wodge of ping-pong balls, acting upwards against the floors? Good luck.

Where can I buy ping-pong ball shares?