Container ship construction

jamesgpobog
18th March 2012, 22:44
This pic got posted here in the gallery. I know zero about this type. It looks to me like what is shown is the ship completely empty, the decks being the 'foundation' that the containers are stacked on and fastened too.

My questions are, what is under these decks? Are all container ships built this way? How are they ballasted, because it looks like this would give a high center of gravity.


Picture Clicky (http://www.shipsnostalgia.com/gallery/data/510/MV_Karma_050312_004.JPG)

Andrew Craig-Bennett
18th March 2012, 23:19
What you are seeing are pontoon hatch covers, which are lifted off and placed ashore in order to access the containers stowed in the holds under them.

Containers in the holds are held in cell guides; containers on deck are lashed. There will be alternative positions for 20', 40', and maybe 45', 48' and 52' boxes.

The ship's cranes can handle the hatch covers using the container spreader.

Designers have usually sought to minimise the GT by having a greater proportion of the cargo on the hatch covers, rather than under deck; this also assists stability of course.

Ballast water is carried in the DB tanks in the usual way and container ships are also fitted with a heeling tank to maintain the ship almost exactly upright during cargo work. In more modern ships fuel is not carried in the DB tanks but in tower tanks at the ends of the holds.

C of G varies with the load condition, of course, but in general container ships are more at risk of being too stiff than of being too slack.

Spurling Pipe
18th March 2012, 23:55
[QUOTE=Andrew Craig-Bennett;584659
C of G varies with the load condition, of course, but in general container ships are more at risk of being too stiff than of being too slack.[/QUOTE]

Don't quite understand this. Please explain.

jamesgpobog
19th March 2012, 00:10
What you are seeing are pontoon hatch covers, which are lifted off and placed ashore in order to access the containers stowed in the holds under them.

Containers in the holds are held in cell guides; containers on deck are lashed. There will be alternative positions for 20', 40', and maybe 45', 48' and 52' boxes.

The ship's cranes can handle the hatch covers using the container spreader.

Designers have usually sought to minimise the GT by having a greater proportion of the cargo on the hatch covers, rather than under deck; this also assists stability of course.

Ballast water is carried in the DB tanks in the usual way and container ships are also fitted with a heeling tank to maintain the ship almost exactly upright during cargo work. In more modern ships fuel is not carried in the DB tanks but in tower tanks at the ends of the holds.

C of G varies with the load condition, of course, but in general container ships are more at risk of being too stiff than of being too slack.
Thanks. That makes sense and is why I was confused. As you seem to indicate, I had imagined the ships to be built sort of like bathtubs...

John Cassels
19th March 2012, 07:29
Don't quite understand this. Please explain.

Yep , don't get it either !.

Michal-S
19th March 2012, 08:22
The vessel depicted is actually multipurpose general cargo vessel suitable for carrying containers, not a pure container-ship. Hatch covers are not lifted-on pontoons but hinged lids operated by hydraulic pistons and rolling on wheels to the fore and aft part of hatch-way. Capacity of the vessel will be ca.700 TEU-it means 700 x 20 feet (6-metres long) containers, without regard for stability and permissible stacking weights. Capacity in terms of full (standardised measure is 14 tonnes/TEU) containers will be around 500 TEU. Under hatch covers there are cargo holds-in form of box-shape, it means with flush sides and all curves (especially in the area of bow and stern) worked into boxes facilitating stowage of containers. Bottom of holds (aka tanktop) is equipped either with flushed or raised fittings for stowage of containers. Such a vessel may also be fitted with 40 feet spacing cell-guides for fast and secure positioning of containers and to avoid additional securing inside cargo holds. There may also be serviving platforms for connecting and fitting reefer containers, but it is not common for this size and type of the vessel and rather met on bigger ones. Box-shaped effect is achieved also with distribution of miscellaneous tanks: ballast water (including heeling control system) situated mainly in double sides and double bottom, fuel tanks-either in double sides or (more popular and ecological) between holds in form of deep-tanks and separated from ship's sides and bottom by ballast tanks to prevent pollution in case of hull failure. Fresh water and/or diesel-oil tanks are usually situated in aftermost hold adjoining engine-room bulkhead and form box-shapes as explained above. Keeping this type of vessel ballasted properly is very difficult, when no cargo on board. Empty vessel tends to have large trim aft (up to 5-6 metres difference between stern and forward draught readings can be observed in such case) and high GM (metacentric height value). It is necessary to add ballast water to put her as close as possible on even keel remembering about submersion of propeller, rudder and bow-thruster as well as about longitudal strength of the hull-particularly empty hull. At the same time GM value, high already, is being raised even further-up. It will cause a great stiffenes of the ship that will roll every 6-8 seconds, from side to side, encountering bad weather. Add to that high noise and vibrations caused by propeller turning just at the water level and resonance from empty holds.

More can be found in Google search under: "container vessel general arrangement plan"

Spurling Pipe
19th March 2012, 13:25
C of G varies with the load condition, of course, but in general container ships are more at risk of being too stiff than of being too slack.

Andrew, would really appreciate your explanation.

Thanks in advance!

jamesgpobog
19th March 2012, 14:01
@ Michal-S That was quite a post. Thanks. I have a question about something that you mention, a ship's 'trim'. I was on a USN oiler (T3-S2-A3 type) that had been jumboized to 644 ft. I remember that after extended deployments on station, we would get very empty, to the point that the bow was almost out of the water while the stern was almost at a normal level. What effect does this have on the handling of the ship? This pic is of a sister ship and illustrates the condition, though this ship is not quite at the extreme of the condition, it still has a few feet to go.


http://navy.memorieshop.com/Waccamaw/AO-109.jpg

Klaatu83
19th March 2012, 15:08
One difference between container ships and unrep tankers is that box-boats don't usually do extended deployments at sea, they operate point-to-point. Draft and trim are scrupulously checked as soon as the ship docks, and immediately prior to sailing, and stability is also calculated prior to sailing.

Tankers are usually fairly stiff (excessively stable) when they're loaded, because the weight is concentrated down low. However, you usually don't want a box-boat to be overly stiff because then it will tend to snap-roll. If that occurs then, if the cargo inside the containers hasn't been properly secured (a circumstance over which the crew usually has no control), then there is a possibility that the cargo could shift inside the containers and become damaged. I once witnessed steel plates break right through from inside a container. On another occasion, steel pipes began rolling around loose on a flat-rack container stowed on the fifth tier above deck, too high for the crew to reach it, and we had to return to port in order to have the container removed and re-stowed. (It is also worth noting that, unlike an unrep tanker, most container ships are operated by a total crew of 20 or less, so there aren't a lot of people available to carry out damage control, anyway.) Also, although it's never happened to me, in really heavy weather it has been known for container ships actually to lose some containers over the side.

Over the years I sailed as a mate on quite a few box-boats. Incidentally, I also spent some time as AB on that same Waccamaw depicted in the photo you posted, though it was "USNS" then. Though I can't actually say I ever sailed on her, I did spend several weeks on her in the shipyard after MSC first took her over from the "Regular Navy". Apparently, the "Regular Navy" crew had been aware for some time that the Waccamaw was going to be transferred to MSC, so they deliberately stopped carrying out any maintenance on her. All I know is that, when we our hands on her, she was a real mess. That photo gives a pretty good idea of the size of the crew when the Navy operated the Waccamaw, but there were only seven of us (not counting the Bos'n), so you can imagine what a job we had on our hands! I considered myself fortunate when I was transferred off and promoted to a Third Mate's berth on anther ship before the Waccamaw left the yard.

jamesgpobog
19th March 2012, 16:29
Very interesting, Klaatu83. Small world. It may have been another post of yours, but I heard that about maintenance here before from someone.

I don't know if you read my other posts about this but I think I figured out a small bit of trivia about the jumbo oilers. There were a total of 8, but 3 of those were significantly different in that they had enclosed well decks and no external deck/walkways on the forward deckhouse. The 3 all do have double rudders though.

The other 5 all looked pretty much the same. I had heard that one had kept it's original single rudder and the others had been fitted with double rudders, but I noticed that 2 ships had no what I had always thought were prop guards. Turns out the 2 with no guards, Navasota and Waccamaw both have single rudders, and they were the first and second ships jumboed. Guess they handled like crap...

Derek Roger
19th March 2012, 20:03
Too stiff would mean a very high GM ; a low GM would make a ship "tender " ; I think that it may also be refered to as "slack ".

Spurling Pipe
19th March 2012, 20:31
Too stiff would mean a very high GM ; a low GM would make a ship "tender " ; I think that it may also be refered to as "slack ".

Thanks for that Derek.

Spurling Pipe
20th March 2012, 14:20
Andrew,

I see you are on line.
Would you mind clarifying 'C of G varies with the load condition, of course, but in general container ships are more at risk of being too stiff than of being too slack' in your post No.2 as it seems at variance with what Derek has suggested and I am confused.

James_C
20th March 2012, 15:14
I rather suspect that what Andrew was getting at is that it's undesirable to have an excessively "stiff" box boat with many tiers of 'on deck' containers - for obvious reasons.

Spurling Pipe
20th March 2012, 15:28
No Jim, that is not what he is saying. He is saying that they are at more risk of being 'stiff' rather than 'tender'. I would simple like to know how he arrives at that conclusion as it is contrary to my thinking and possibly Mr Cassells who has also queried it.
I am would have thought it was common courtesy to respond after my repeated requests..

Dave

John Cassels
20th March 2012, 19:49
Andrew and I have had previous discussions on similar lines and we have
agreed to disagree. In all my many years of experience of these type of
ships ( both afloat and ashore) there was more of a risk of being on
minimum GM than the other way around.

Spurling Pipe
20th March 2012, 23:48
there was more of a risk of being on
minimum GM than the other way around.

Exactly! Andrews lack of response speaks volumes.

jamesgpobog
21st March 2012, 00:13
I rather suspect that what Andrew was getting at is that it's undesirable to have an excessively "stiff" box boat with many tiers of 'on deck' containers - for obvious reasons.

OK guys, it ain't obvious to me, I know jack squat about this....

So, first, what is GM again? And why is a loaded ship undesirable to be excessively stable?

Andrew Craig-Bennett
21st March 2012, 00:19
I have only just spotted this thread. I was searching the site for some information on Ballin's passenger ships.

I am not quite sure what I am being accused of by whoever hides behind the name of "spurling pipe", but I find his courtesy rather underwhelming.

Andrew Craig-Bennett
21st March 2012, 00:25
I rather suspect that what Andrew was getting at is that it's undesirable to have an excessively "stiff" box boat with many tiers of 'on deck' containers - for obvious reasons.

Right.

Modern ships have been optimised for shoal draft, low fuel consumption and small GT.

This leads to a barge shaped hull form which, in the larger sizes, tends to be very stiff, unless well laden.

Obviously if well laden it won't be.

But in these days the main trade lanes are essentially one way - my own outfit takes one laden box out of the UK for every ten we bring in.

A large GM imposes a higher loading on the lashing system.

Hope I have made myself clear.

Andrew Craig-Bennett
21st March 2012, 00:29
The vessel depicted is actually multipurpose general cargo vessel suitable for carrying containers, not a pure container-ship. Hatch covers are not lifted-on pontoons but hinged lids operated by hydraulic pistons and rolling on wheels to the fore and aft part of hatch-way. Capacity of the vessel will be ca.700 TEU-it means 700 x 20 feet (6-metres long) containers, without regard for stability and permissible stacking weights. Capacity in terms of full (standardised measure is 14 tonnes/TEU) containers will be around 500 TEU. Under hatch covers there are cargo holds-in form of box-shape, it means with flush sides and all curves (especially in the area of bow and stern) worked into boxes facilitating stowage of containers. Bottom of holds (aka tanktop) is equipped either with flushed or raised fittings for stowage of containers. Such a vessel may also be fitted with 40 feet spacing cell-guides for fast and secure positioning of containers and to avoid additional securing inside cargo holds. There may also be serviving platforms for connecting and fitting reefer containers, but it is not common for this size and type of the vessel and rather met on bigger ones. Box-shaped effect is achieved also with distribution of miscellaneous tanks: ballast water (including heeling control system) situated mainly in double sides and double bottom, fuel tanks-either in double sides or (more popular and ecological) between holds in form of deep-tanks and separated from ship's sides and bottom by ballast tanks to prevent pollution in case of hull failure. Fresh water and/or diesel-oil tanks are usually situated in aftermost hold adjoining engine-room bulkhead and form box-shapes as explained above. Keeping this type of vessel ballasted properly is very difficult, when no cargo on board. Empty vessel tends to have large trim aft (up to 5-6 metres difference between stern and forward draught readings can be observed in such case) and high GM (metacentric height value). It is necessary to add ballast water to put her as close as possible on even keel remembering about submersion of propeller, rudder and bow-thruster as well as about longitudal strength of the hull-particularly empty hull. At the same time GM value, high already, is being raised even further-up. It will cause a great stiffenes of the ship that will roll every 6-8 seconds, from side to side, encountering bad weather. Add to that high noise and vibrations caused by propeller turning just at the water level and resonance from empty holds.

More can be found in Google search under: "container vessel general arrangement plan"

Absolutely right; I was replying in terms of a generic containership rather than the particular ship illustrated, because the question was generic. Folding covers on multipurpose ships fitted for containers should be "non-sequential" i.e. you should be able to open either cover without regard to which one must be opened and closed first. This avoids the need to double handle boxes.

Andrew Craig-Bennett
21st March 2012, 00:41
Exactly! Andrews lack of response speaks volumes.

Look, chum, if you want to get someone's attention, send them a PM; don't go mouthing off in public if they don't see something on one particular thread.

I have a fleet of ... container ships... to operate and was just idly scanning the site at lunchtime for some research of my own on Edwardian passenger ships.

Cisco
21st March 2012, 01:37
But in these days the main trade lanes are essentially one way - my own outfit takes one laden box out of the UK for every ten we bring in.


Thats what I, who has never sailed on a container ship, would have thought..... same as general cargo....full cargo of wool.... tender..... big load of steel products....stiff......
makes sense to me....

Spurling Pipe
21st March 2012, 09:36
Look, chum, if you want to get someone's attention, send them a PM; don't go mouthing off in public if they don't see something on one particular thread.

I have a fleet of ... container ships... to operate and was just idly scanning the site at lunchtime for some research of my own on Edwardian passenger ships.

Look, Chum I suspect your delay in response was due to you seeking advice. Your not a mariner are you?

James_C
21st March 2012, 10:50
Your not a mariner are you?

So what?
You've made it quite obvious on this thread that you've been impatient to attempt to prove yourself "superior".

Andrew Craig-Bennett
21st March 2012, 12:50
To illustrate:

http://www.shipsnostalgia.com/gallery/data/513/medium/Cosco_Felixstowe.JPG



http://www.shipsnostalgia.com/gallery/data/513/medium/Cosco_Hong_Kong.JPG

Identical sisters, the first pic is at the last port in the NW Europe rotation and the second pic is at the first. Not much difference in the slots occupied; big difference in the draft. The Felixstowe is full of empties - notice the bulbous bow - it can be hard to get a sense of scale but you can estimate how far out of her design draft she is by looking at the barges alongside.

The Hong Kong is full of revenue cargo.

Container ships are designed around the assumption that they will be carrying a fairly constant load; in this they are very different to bulkers and tankers. This assumption can be tweaked a bit - to take two extremes, this ship:

http://www.shipsnostalgia.com/gallery/data/513/medium/HIGHLAND_CHIEF_1712x1123.jpg

was designed for a trade in which heavy twenty footers are the norm - she was actually designed around 20T/ TEU homogenous, so much so that her hatch covers are "all across" twenty footers, and in Duncan's picture you can see her down to her marks with just the cargo she was designed for.

Conversely, the ships above, designed for the East-West trade, are designed around 11T/TEU homogenous. Their beam is 39.8 metres, LOA 280 metres, and whilst their deadweight at the moulded draft is 69,000 tons "everything" is actually worked around the "design" draft, known in Germany as the containerdraft, of 12.5 metres, at which point the deadweight is around 10,000 tons less.

Now, if your ship for some reason has to depart a long way from those parameters, things are going to happen.

There are a lot of things that you can tweak but you really really don't want re-stows, whilst at the same time you need to observe such things as sf and bm...

Cisco had an excellent picture, taken from his own bridge, in which he had snapped a boxship between ports on the Australian coast with most of the deck cargo off and a few solitary "pillars" of boxes on deck...needless to say, a few hours later, the inevitable happened.

That's why I say, whilst taking the point that a big deck cargo reduces the GM, that the "problem" is more likely to be too big a GM than too small a GM. You can increase the GM by doing the obvious things with stowage, such as putting the heavy stuff at the bottom, but reducing it, whilst avoiding restows, can be tricky if you don't have enough cargo to play with.

Container ships are built to carry a lot of deck cargo; the chances of the stowage planners at a modern terminal, or the Mate of a small ship using her own gear in small ports, getting the GM too small are rather limited, with the excellent software programmes now in use, but it can be rather easy to get it too big.

See also posts 6 and 9 above.

Andrew Craig-Bennett
21st March 2012, 18:35
Thats what I, who has never sailed on a container ship, would have thought..... same as general cargo....full cargo of wool.... tender..... big load of steel products....stiff......
makes sense to me....

Fred Drift (but SN relevant):

CNCo bareboat chartered, then bought, the Wanstead and sisters because of their big tweendecks, which were ideal for wool.

Penny just drops - one reason why Richard Woodget kept screwing more and more wool into the Cutty Sark was that it made her stiffer.

Duncan112
21st March 2012, 18:56
Maybe slightly off topic but...

I was Chief Engineer on a geared container ship running between LA/ San Fran and Papeete and Samoa, basically consumables West Bound and pick up tinned tuna and clothing in Pago Pago with the balance of empties. Due to sail about 21:00 so the Master and I went ashore for lunch with the agent to Sadies. Come back and the Filipino Mate is in tears on the quay, the stevedore approaches the Master and informs him that:

"Your ship is unsafe Captain, the only way I can keep it upright is by hanging containers outboard on 2 cranes"

On further questioning it transpired that the Tuna and garments which were to be stowed in the bottom tiers of the holds had been late arriving so, unbeknownst to all the stevedore had taken it on himself to stow the empties in the lower hold and put the tuna in when it arrived. The Mate found this out at about 13:00 and remonstrated with the stevedore to no avail, only to be roundly insulted and told:

"One port discharge, it's ok you B... Flips know F all"

Needless to say, the Master took rather a dim view of the stevedores attitude, but could do little, save order the ship to be unloaded and stowed to plan, as there was only one stevedoring firm in the island, run by the islands Paramount Chief. Still we got another night in Sadies.

It would appear that some years earlier a ship was chartered in whilst ours was in dry dock and improperly stowed, loosing stability and capsizing on the West Bound passage.

John Cassels
21st March 2012, 19:13
Andrew , I'm sorry to say that your answers , attitude etc are starting to fall
short from what should be expected from someone with your standing.

Rather dissapointing.

Andrew Craig-Bennett
21st March 2012, 19:17
@ Duncan - Cue terminal Fred Drift about how a standard logger ordered from an IHI subsidiary yard, to be fitted with cell guides, ended up being built at IHI itself because the yard that designed her could not cope, so IHI had to do it all again at a huge loss - and then she came back for lengthening... I can picture Hiroshi Iwamoto almost crying into his pint in the Still and Star with John Newton even now!

Andrew Craig-Bennett
21st March 2012, 19:26
Andrew , I'm sorry to say that your answers , attitude etc are starting to fall
short from what should be expected from someone with your standing.

Rather disappointing.

If you would not find post no 24 in this thread offensive, if directed at you, you are a much better man than I am, John.

In the light of what you say, though, I have removed a remark from my post 26.

As you say, we have discussed this before. It depends, I suppose, on how you view it.

In my experience, people are seldom trapped by the obvious; it is the things that are not obvious that come up and bite us. The dangers of insufficient stability, in any ship with a deck cargo, are obvious; people tend to overlook the dangers of excessive stability.

I can only recall two cases of inadequate stability of a boxboat causing trouble at sea, one being the one that Duncan mentions and the other, years before, concerned a little British ship some of whose crew members come here so I won't name her.

John Cassels
21st March 2012, 19:49
Andrew , then I guess our experiences are very different.

As ch.mate , I was always being asked to sail with minimum stability with
maximum stresses. I don't ever remember having such a large righting
lever that I had to worry about moments of inertia acting on the deck containers and their lashing systems.

Guess this is just the difference in our various experiences - isn't it ?.

Cisco
21st March 2012, 20:08
Look, Chum I suspect your delay in response was due to you seeking advice. Your not a mariner are you?
You're new around here aren't you...........

Andrew Craig-Bennett
21st March 2012, 20:11
Andrew , then I guess our experiences are very different.

As ch.mate , I was always being asked to sail with minimum stability with
maximum stresses. I don't ever remember having such a large righting
lever that I had to worry about moments of inertia acting on the deck containers and their lashing systems.

Guess this is just the difference in our various experiences - isn't it ?.

John it must be so - forgive a wild guess, but did your experience by any chance include Canada, conbulkers and OBOs?

jamesgpobog
21st March 2012, 20:25
Andrew...your mailbox is full...

Andrew Craig-Bennett
21st March 2012, 20:30
Thanks James - I've restowed it now.

randcmackenzie
22nd March 2012, 00:00
I did 3 years transatlantic container ships in the seventies, but never did sail too stiff, though some tricks had occasionally be pulled to get her stiff enough.

But these were very finelined (C of F about .55) and quite narrow compared to the much more boxy hulls Andrew describes.

And if the C of F is increasing to maximum at load draught, then the water plane area is also maximum, and the GM increases too.

Best Regards.

Andrew Craig-Bennett
22nd March 2012, 07:54
Randmackenzie makes a really good point; the shape of containerships has changed.

Containerships began by looking like the breakbulk liners that they replaced; over the past forty years they have become wider and flatter with less freeboard. Feedership designers are concerned to reduce GT; mainline ship designers don't want to increase the draft as the ship gets bigger.

Michal-S
22nd March 2012, 09:44
@ Michal-S That was quite a post. Thanks. I have a question about something that you mention, a ship's 'trim'. I was on a USN oiler (T3-S2-A3 type) that had been jumboized to 644 ft. I remember that after extended deployments on station, we would get very empty, to the point that the bow was almost out of the water while the stern was almost at a normal level. What effect does this have on the handling of the ship? This pic is of a sister ship and illustrates the condition, though this ship is not quite at the extreme of the condition, it still has a few feet to go.


http://navy.memorieshop.com/Waccamaw/AO-109.jpg

A problem of excessive trim on cargo vessel will be associated mostly with her sea-keeping abilities. Theoretically it is that aft trim gives us better course stability and reduced manoeuvrability but in the open water the effect is negligible. We will be more concerned about wave encounter from head-on directions and phenomenon of bow-slamming, i.e. impact of waves on bow's bottom surface. Apart from obvious inconvenience of vibrations caused by the slamming we will experience speed reduction, fuel consumption increase and possibility of damage to hull's plating.
Referring to this thread discussion concerning container vessels being too stiff the problem lies mostly with cargo securing (as mentioned)-whence vessels are designed to carry more and more containers on deck (I could see up to 8 tiers of high cube-9'6" or 2,9 m-boxes stacked on deck) container securing equipment and cargo securing manuals are designed within some limitations of metacentric height and related accelerations and forces acting on that. In general, as a rule-of-thumb, GM should not exceed ship's beam/13 but there are more accurate and scientific methods applied for lashing forces calculations, taking into account: ship's size, speed, position of the cargo on board (lower hold, upper hold, lower deck, upper deck-approximately and fore, midship or aft distribution).
Another problem related to high GM value is parametric rolling phenomenon-especially known to large container vessels with high areas of bow and stern hull overhangs/flares and in ocean crossing. To see full explanation of the problem please search for "parametric rolling" and description of accident of m/v "APL China" in the Pacific Ocean in 1998.

Andrew Craig-Bennett
22nd March 2012, 10:11
Thanks, Michal, for another excellent explanation.