cruise ship rolling in big seas

[leaotis]

http://www.metacafe.com/watch/503533/rough_cruise/

comments are interesting

[TimH]

I wonder who was on puke detail...

[Bob (oh, THAT Bob)]

It appears to be rolling almost all to starboard, quite severely. I think the wind and waves are from port, otherwise I would think it was taking on water to starboard. I would think that in those seas they would turn into the wind and waves. They'll be waves over the deck, but even on a cruise ship I would imagine that they can batten down things enough to tolerate it. As cruise ships go, that's not a very big one, but still good sized, that's a pretty big blow. I've seen some very tall-aspect cruise ships anchored in Miami (usually designed for the Caribbean cruises), this ship does not appear nearly as tall, but I've always wondered how the tall ones behave in a beam wind.

[Thorne]

http://news.bbc.co.uk/2/hi/europe/4264661.stm

http://www.metacafe.com/watch/503533/rough_cruise/

Plates and bottles went everywhere when the ship was brushed by the waves. The deck master said everything would be fine. I thought "I don't care" I wanted out of there. It felt as though the ship was jumping and pitching. The deck master was almost thrown to the floor. We were almost victims of the blue sea.
Jim C. Korn, Halifax, Canada

I was laying in my bed sleeping off the excesses of the night before watching the cabaret dancers and downing pints of Cinzano when the whole ship lurched to the left sharply. I dashed into the corridor and found fire-extinguishers dislodged from their mountings rolling alarmingly down the corridors. The Captain came over the intercom and quickly reassured everyone, but it was many hours before we were on our way again. The cabaret dancers entertained both customers and crew throughout the day though and Cinzano supplies were not effected!!
Mark Dowle, Abingdon, UK

[Three Cedars]

Whoa... definitely top heavy .... makes me wonder if adding water ballast in the hull ( with bulkheads ) would have hepled.

Probably trying to stick to schedules .... pushing it ...

[Bob (oh, THAT Bob)]

Whoa... definitely top heavy .... makes me wonder if adding water ballast in the hull ( with bulkheads ) would have hepled.

Probably trying to stick to schedules .... pushing it ...

My thoughts as well, ballast definitely helps, but the righting moment due to ballast doesn't start to kick in until it begins to heel over, it may not go as far, but the geometry is working against it; lots of tall lateral windage to push on, and it appears a relatively flat bottom (perhaps not, tough to see) for the waves abeam to torque on, so much so that it looks like it was catching air under the port side of the hull, splashing aside water as it came down. Not the kind of behavior you want to see in a blue-water vessel. I am no expert in this field, but on a much smaller scale, Derek Hutchinson recommends narrow, rounded hulls versus wide and flat for sea kayaks that will be operating in surf and swells, as they are more easily able to maintain upright attitude and respond to control inputs. Wide and flat is stable for calm water, great initial stability, but works against you in swells. (Not sure if this is completely analogous as most kayaks don't have ballast, though I added some to mine.) But for the same displacement, rounded/deeper hulls have deeper drafts and thus reduced port accessibility.

I'd like to see John Hardiman's comments, he seems to have more than a bit of knowledge...

[Ocean Spray]

It must have been tough in the pool that morning!

[JimD]

It must have been tough in the pool that morning!

I guess you could say it was a wave pool.

[sandingblock]

Wasn't there something on the forum a while ago about about waves from a certain angle causing ships to roll severely.

It looks like this ship is rolling to starboard as the wave gets under it's port bow, and then when the wave gets over to the starboard quarter it's rolling back the other way.

If this effect was in time with the natural roll period of the ship it could get ugly.

[leaotis]

water on the dash disabled the engine controls??

[outofthenorm]

It looks like it has almost zero way on. Engine issue of some kind? At close-to-zero speed, any stabilization system would be useless and the waves would take over. Sure would be hard on a hangover.

- Norm

[hansp77]

Crab Boat in Bering Sea getting pounded by waves.
http://watch.break.com/294254/Deadliest_Catch__Waves/

[John E Hardiman]

John,

Your presence and knowledge is requested at the following post

http://www.woodenboatvb.com/vbulleti...ad.php?t=65291

Cheers,

Bob

Looks good to me, they'll still be serving in the bar.

She's not making headway in a 20-30' seaway, ~ 30 knts, with a cross swell and barely rolling 30 degrees total with a good period. Fine piece of design work. I wonder what happened to get her like that, most likey an engine failure as someone stated one the blog, otherwise she whould have way on and missed the weather. (Checked the WIKI, between the Balearics and Sardinia in winter, so of course it would be steep and cross seas).

There were some comment here and in the blog that show some people do not understand stability and ballast, what they are, how they are different, why they are needed, and what effects they have on design. The NA that did that vessel was good, and it shows.

[Bob (oh, THAT Bob)]

Thanks John, I guess things there were not as bad as they looked. I guess to the untrained eye (like me) the roll seemed unusually large for the size vessel, but perhaps not. As far as the knowledge of myself and others, umm, well, yeah, that's why we called. At least we're that smart.

[John E Hardiman]

Thanks John, I guess things there were not as bad as they looked. I guess to the untrained eye (like me) the roll seemed unusually large for the size vessel, but perhaps not.

Remember, it is the relationship of the vessel size to wave size that sets the physics. So ship to sea, boat to lake, rubber ducky to bathtub; the physics is all the same. What's important for safety is the relative rates of motion. That is why I looked at the period, vice the amplitude.

As an example, would you rather roll through 30 degrees on a ship deck or pitch through 10 degrees on a 40' sailboat?

[brian.cunningham]

Top heavy or too light?
Looks like it too far out of the water to me.

[Thad]

Might be great with some loads but not great with a load of people, especially in the upper decks, almost like murder.

[John E Hardiman]

Top heavy or too light?
Looks like it too far out of the water to me.

The misconception that modern cruise ships are top heavy is broadly held, but poorly founded. Most modern cruise ships have a lower CG than old liners and better motions. The main reason is the lower freeboard forward that most ships now have (due to reduced route speed requirements in North Atlantic storms) signficantly lowering CG. It is this lower freeboard that makes them look "high"

For a comparison


RMS Queen Mary (1936)
Decks =12 (2 non accomidation)
Decks above stemhead = 5
Height = 181'
Length OA = 1018'
Beam = 118'6"
Draft = 38'9"
Depth of Hold = 68'5"
Gross Tonnage = 81237


Freedom of the Seas (2005)
Decks =15 ( 3 non accommidation)
Decks above stemhead = 10
Height = 207'
Length OA = 1115'
Beam = 126'7"
Draft = 28'
Depth of Hold = ?
Gross Tonnage = 154,407

Since most of an accomodiation deck is air, and all of the heavy stuff, engines, stores, and tankage is low, it is easy to see that that it is only the preception of the number of decks that leads to the idea of top heaviness. Because of SOLAS, modern cruise liners are much more stable than the old ones.

[Bob (oh, THAT Bob)]

The misconception that modern cruise ships are top heavy is broadly held, but poorly founded. Most modern cruise ships have a lower CG than old liners and better motions. The main reason is the lower freeboard forward that most ships now have (due to reduced route speed requirements in North Atlantic storms) signficantly lowering CG. It is this lower freeboard that makes them look "high"
....

Since most of an accomodiation deck is air, and all of the heavy stuff, engines, stores, and tankage is low, it is easy to see that that it is only the preception of the number of decks that leads to the idea of top heaviness. Because of SOLAS, modern cruise liners are much more stable than the old ones.

Interesting, those were my (mis)perceptions exactly. I can understand about the reduced freeboard now. I thought all those high stacked staterooms added a lot of mass, but perhaps like you said, not very dense with respect to lower decks. I would still think that windage is a stability issue, but perhaps not, as it is not like it is as high as a proportionate sail for that size vessel.

I still would like to see the CG heights for the two compared vessels at worst case loading (I would expect near end of cruise with plenty of passengers but some fuel and stores depleted). But only because I am a stickler, it's not like I doubt you in this area. Interesting, I'll have to talk about the above with my dad.

That appears to be the QM2 in the background behind QM? Looks like more decks of rooms up top but the hull appears to be old school (in terms of freeboard height), unless my eyes are playing tricks. Other aspects of the hull are noticeably different though; flatter sides and shorter waterline vs. overall length compared to the older QM?

[brian.cunningham]

And the upper decks are usually aluminum, much like a double decker bus. But the CG changes if it's not loaded properly. It also changes if the ship was reconfigured later. Remember that Italian ferry that had decks added to it, and then sunk later?

[outofthenorm]

... modern cruise liners are much more stable than the old ones.

Okay, but they're sure not as pretty.

- Norm

[ahp]

The "Queen Mary had widows in her foreward superstructure smashed in one Atlantic storm. The Liner "France" had a 10 x 30 ft hole punched in her foreward superstructure in one March N. Atlantic gale.

[John E Hardiman]

Interesting, those were my (mis)perceptions exactly. I can understand about the reduced freeboard now. I thought all those high stacked staterooms added a lot of mass, but perhaps like you said, not very dense with respect to lower decks. I would still think that windage is a stability issue, but perhaps not, as it is not like it is as high as a proportionate sail for that size vessel.

I still would like to see the CG heights for the two compared vessels at worst case loading (I would expect near end of cruise with plenty of passengers but some fuel and stores depleted). But only because I am a stickler, it's not like I doubt you in this area. Interesting, I'll have to talk about the above with my dad.

That appears to be the QM2 in the background behind QM? Looks like more decks of rooms up top but the hull appears to be old school (in terms of freeboard height), unless my eyes are playing tricks. Other aspects of the hull are noticeably different though; flatter sides and shorter waterline vs. overall length compared to the older QM?

You still don't get it. (BTW CG, or more correctly KG, is meaningless by itself. As I pointed out earlier there is a big difference between stability which is the interaction of KG,KB,and BM; and ballast/weight which only effects KG and KB.

Old passanger liners were required to carry passangers across oceans as cheaply and quickly as possible. This meant as many small compartments as possible were croweded into every deck. 8'x12' with 4 bunks and an en suite head was common, very similiar to a Pullman car suite which was the expected land based equlivant. The decks were consequently heavy with structure and ,more importantly, piping and cableing. Modern cruise ships are mostly destnations, an end unto themselves, a moving hotel. Conesquently, the compartments are larger because more time is expected to be spent in them (7-10 days vice 4-5). This reduces deck weight because there is less structure (i.e. fewer partition panels) and more importantly less services.

Additionally, outside rooms can command a premium, which equates to more profit as the initial cost is already sunk and upkeep costs no more. Therefore the idea is to get the most outside rooms, which means more decks. Normally, this would be a problem in two ways; a) the increase in weight high and b) the loss of profit on the unsold inside rooms which are a sunk cost. Modern cruise ships solve both of these problems in one feature; the atrium. 20-40% of most "decks" is air and only air...there is literaly nothing there. Modern decks are 1/2 the weight of a classic liner deck even before we begin to use lightweight cored materials.

Finally, a cruise ship is a moving hotel, not a passage maker. This allows the ship to go slower and pick it's weather, which allows it to be wider and shallower than liner. That means machinery can be placed lower which lowers CG, it raises a deck out of the water which increases profitable outside rooms, and that stability is better because a 10% increase in beam equates to a 30% increase in BM.

The argument a passangers toppling a properly maintained and laden ship is bogus. The Freedom of the Seas carries 5730 souls and even at 300 lbs apiece that's only 767 tons (more likely 175 lbs/447 t) ; i.e. about 1% of her true displacement (~71,000t) or about the amout of fuel she burns in 2 days. In most capsizings this cause is unengineered modifications (rasies CG slightly) and gross overloading (again rasies CG slightly) mostly coupled with a casualty that puts free water on the decks (greatly lowers BM). There are exceptions, such as the MV ROCKNES which exposed a blindspot in the rules, but mostly I would fear fire more than a capsize on any well found ship.

[George Roberts]

"The argument a passengers toppling a properly maintained and laden ship is bogus."

I agree.

I guess we could compute the "worse case" wave/loading that would capsize a cruise liner, but I suspect the case is easily avoidable.

[John E Hardiman]

I guess we could compute the "worse case" wave/loading that would capsize a cruise liner, but I suspect the case is easily avoidable.

As you know, there is always some small, real, risk in any seaway and/or situation. The operative idea here is to work into the design features that keep it manageable from an underwriters point of view...like less than the odds of getting struck by lighting or being in an aircraft accident while flying to the cruise port.