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  • So, today we will continue with the mid ship sections, discuss about the container ship,

  • container ship mid ship section.

  • Well what is a container ship basically? As the name, you can see that it carries containers.

  • Containers are somewhat of this type, somewhat means, they are essentially a rectangular

  • container. As you can see, the dimensions are they have a cross section of 8 feet by

  • 8 feet, and length either 20 or 40 feet, they are in feet; this is the universal standard,

  • means all the containers which are used in the container ships, they will be either 20

  • feet long or 40 feet long. One nonstandard in between is there, that

  • is 35 feet long. But not a very, I mean, that is not used very commonly or popularly for

  • the simple reason. Here you can see it is a multiple 20 or twice that 40. So, in place

  • of 140 feet container, I can load 220 feet container. That is possible, but if I design

  • it for 35 feet, then I have problem. Any ways so these are the two most widely used.

  • The whole concept of containerization came as I think. So, we have already talked about

  • it is essentially to implement or to have minimum port time. What does that means, very

  • efficient loading as well as unloading of cargo because a ship owner will not only like

  • to have a very efficient vessel I mean high dynamically designed so that it consumes minimum

  • power such that your fuel bill is minimum. At the same time, you would like to have systems

  • or facilities such that he can load the required amount of cargo as well as unload it at the

  • minimum possible time. Because this process of loading and unloading they are actually

  • not a revenue earning time for the ship owner. It is actually a expenditure kind of thing

  • for him because he is in the port; longer he stays in the port, more fees he pays to

  • the port. And not only is that he just kind of idling.

  • Had he been moving means he is taking the cargo to some destination; he earns revenue

  • that if he earns. So obviously, one would like to have it a loaded unloaded as fast.

  • Now you have seen the general cargo ship all cargo are individual a piece of cargo has

  • all kinds of shape size and weight. So, loading unloading will be very tedious.

  • Instead, if you can think of a system where in we pack the cargo in a box of standard

  • size, then the loading and unloading become very easy.

  • So, that is how the concept of this containerization came. In fact, in container ships, essentially

  • carrying a general cargo in the container. Instead of piece by piece in loading and unloading,

  • I will just handle one container whatever items are there inside, they may have different

  • shape, size, and weight.

  • So, that is what the basis of container ship is. So, in the process what happens, we have

  • seen general cargo carrier, bulk carrier, we have talked about carrying capacity in

  • terms of tons, dead weight; how much dead weight. How much cargo it can carry in terms

  • of tons 12000 tons, 60000 ton like that. Whereas in container, we talk in terms of T E U 20

  • equivalent unit. That means, in container ship that carrying

  • capacity is referred to as in the form of T E U. I have written here 12000 T E U what

  • does that mean? That means, a vessel can carry twelve thousand such containers. Twelve thousand

  • 20 feet long containers or could be six thousand 40 feet long container or mixture of that.

  • So, this is what is the kind of unit T E U, which gives you the idea of how many containers

  • it can carry. So, here while doing the container ship design, we will have to keep in mind,

  • if the owner want to say 6000 T E U container ship means you will have to make provision,

  • you have to design the vessel in such a fashion that 6000 such containers can be loaded in

  • the ship and obviously, this containers are not only kept in the hold, also they are kept

  • above the hatch covers. Also they are kept above hatch cover that

  • of course, depend on design how many tiers of container will keep above hatch cover means

  • open in the air. It is in any guess. So, that is what is container ship. So, what we see,

  • the very typical feature of container ship what it would be; it would be as we go on

  • increasing the capacity of container this 12000 ton T E U is not a very common container

  • ship. Commonly we have well in the range of I would say I mean so called ocean going container

  • ship could be in the range of 2000 to well may be 6000.

  • This 12000 and all that is a very ambitious kind of container ship possibly one or two

  • have been built. They are huge they are really huge. By huge what do you mean. We mean the

  • length could be very big. So, as the length is becoming bigger, what is happening? It

  • is becoming more slender, your bending movement is increasing terribly and also slender.

  • And for we have talked about we have containerized the cargo because of easy loading and unloading.

  • So, if you have to do that we will have to have a mid-ship section something like a open

  • section means fully open. Till now all the vessels we have seen, if I just make a comparison

  • here, we can say the all the other vessels had a hatch opening like this; be it a general

  • cargo carrier or a bulk carrier. So, something like this. So, what do you see

  • here is that almost half of the deck approximately not necessarily, you have the deck plating

  • and then you have an opening. But in comparison to that if I see a container ship, these are

  • irrespective of capacity. If the general cargo carrier a say a small general cargo carrier

  • say 3000 ton of general cargo carrier, or 10000 ton of general cargo carrier, you will

  • have sufficient amount of deck plating and then a hatch opening.

  • Similarly, with bulk carrier, but a container ship whether it is a small container ship

  • or a big container ship, its hatch opening would be in comparison like this.

  • If this entire three are of the somewhat same so called external dimensions, same load carrying

  • capacity, here you can see the hatch opening is much bigger. For the simple reason, that

  • unless you do that we cannot have my loading and unloading or so smoothly operated.

  • Because the containers will be like this, it will be vertically loaded and vertically

  • unloaded. One after another it will go. So, I will have to have the hatch opening as big

  • as possible such that I do not waste any space in the side. Because if I have a small opening

  • like this in case of bulk carrier or general cargo ship, then I have to lower the container

  • and shift it laterally, lower the container and then shift that laterally which is definitely

  • not a worthwhile proposition. So, it is done this way and this continual handling is done

  • fully automated in properly automated ports where you have facilities of handling container

  • ships. They are automatically done means without any fully automated system, the containers

  • are lifted and kept on the dock and from there it is I mean well send to the destination.

  • So, as the size of the container vessel increases, we have the length increasing thereby giving

  • raise to increase bending movement and where whether it is a small one or a big one, you

  • have a huge hatch opening; means with increasing length, it is not only becoming more slender

  • and your bending movement is increasing. Your torsional strength is decreasing drastically

  • because it is becoming a case of open section. This is what an open section is and somewhat

  • equivalent to an open section in case of open section just the opposite of it is what? Obviously,

  • close section and oil tanker. This is a close section and that is what the oil tanker is.

  • So, we can see when those huge super tankers were built; of course for some other reason

  • this days those super tankers are no more build the super tankers means of their carrying

  • capacity of around half million tons of crude, half million ton is 500 1000 tons of crude

  • the vessels could carry, vessel length of the order of 400 meter huge.

  • But today even making a 12000 T E U container ship is much smaller than that, but still

  • we say it is a very challenging business; a challenging job to build a vessel having

  • 12000 T E U capacity a container ship. For the simple reason it is open section.

  • Torsional strength becomes a big problem here well. So, that is the basic of it. Now how

  • this torsional strength is taken care; that is the major thing here. Till now we have

  • seen we have designed well again the same thing from the functional requirement, we

  • will have to have a huge hatch opening. From functional requirement we had wing tanks in

  • bulk carrier from functional requirement, we had lower deck in general cargo ship.

  • Why lower deck because for segregation of cargo in general cargo ship. It is called

  • a go anywhere type of ship. So, it can carry any cargo to anywhere, any place. It has its

  • own handling facility. It does not need any port facilities. It should have enough draft

  • so that it can park itself. It has its own cranes derricks to load unload cargo and so

  • for segregation of cargo, you provide a lower deck certain things we will have to unload

  • from there, certain from below. Any way functional requirement wing tanks functional requirement

  • here functional requirement is a big hatch opening.

  • A big hatch opening and that is leading to the other things there we did not have any

  • structural problem. Here you have a strength problem, torsional strength that takes precedence

  • I mean that becomes more important than longitudinal strength.

  • So, one we will have to look into the aspect of torsional strength. How that has to be

  • taken care of. So, here you can see the kind of the deck well these are all same or so

  • called Bul work and you hatch what you call, hatch coming.

  • So, the deck is very small how small well; obviously, it has to be enough such that it

  • gives a good working/walking space because you will have to probably work/walk from the

  • fore end to the aft end all that and plus well it can be just the single skin of the

  • hull. So, there will be stiffeners inside. So, that much space. So, it could be as less

  • as 1.5 to 2 meters even. Anyway. So, what is done is this particular

  • arrangement as you can see, at the top it is called, this is primarily this full thing

  • taken together this is referred to as box girder.

  • It is something like you have observed the I mean for domestic use the tumblers I was

  • talking about. What you see in tumbler. Just to give it the necessary torsional strength,

  • they are generally of this shape.

  • If I keep the edges without any stiffening, it does not have any torsional stiffness.

  • Just to provide stiffening this is bent like this. Those plastic tumblers, domestic tumblers

  • that gives you the strength. So, here imagine the case, instead of I mean we are just simplifying

  • it trying to draw equivalence. This and instead of turning out side say I turn inside I also

  • have the same stiffness. And obviously, here in case of a tumbler,

  • it is a quite a small thing, but in this case it is a long, much longer object. So, this

  • rigidity is required all around. So, what is happening? This box girder I mean

  • this stuff is extending all through or in other words like here in that case of the

  • tumbler, just by turning the edge I could achieve the required stiffness. Now here obviously,

  • stiffness is going to be much higher. So, I am not only turning the edge I making this

  • heavily constructed.

  • How heavily what basically is done? If I just enlarge that part of the box girder, it is

  • nothing but such enlarge section of the box girder. This is your box girder. This is the

  • side shell plate. Here you have as usual the Bul work and or railing whatever. You have this hatch opening here; this is the

  • hatch coming. So, only this much is my deck then rest is full open. So, what is done is

  • this is your side shell. We will just take a look how it is done in other vessels.

  • Say general cargo ship once again, you have the deck opening. So, stiffening of this was

  • done by means of a hatch side girder and then stiffening of the deck you had those deck

  • longitudinals etcetera. In case of a bulk carrier what we did, stiffening

  • was done by also a vertical plate; I am no more calling it as a girder, but the function

  • is same. Here I had this girder, here I am having the vertical plate which is slopping

  • bulkhead. So, this is providing the necessary stiffness.

  • Now, here what is happening? Bringing a same plate vertical plate or a girder and in addition

  • having a fully horizontal plate thereby completing a box like thing. And this is now stiffened.

  • These are my so called deck longitudinal. This part of the side shell is also longitudinally

  • stiffened. Again for the simple reason that a longitudinally stiffened system gives me

  • best buckling strength. It provides me I mean it is not only good in case of I mean it is

  • good in case of structures which is subjected to longitudinal bending and when a structure

  • is subjected to longitudinal bending, in the event of compression it suffers buckling.

  • So, what is important is buckling strength. Now if longitudinal framing system is adopted,

  • then it will give you a better buckling strength. A better buckling strength means your critical

  • buckling stress will be higher. So, due to longitudinal bending it would not buckle that

  • is what is important.

  • So, here again the same thing. We are providing longitudinal framing system because of the

  • reasons I just talked about thereby this will behave perfectly as far as the longitudinal

  • strength is concerned and also we have said that if we go on increasing the number of

  • a container the length is increasing, bending movement will increase. So, you need more

  • longitudinal strength. So, this is how. So, this box they are the total box it is referred

  • to as box girder. The word girder means essentially a heavy stiffening member.

  • That girder can be a just a t section or girder can be a box like a thing. In this case it

  • is not only a box, it is a stiffened box. It has all kinds of stiffness inside like

  • we can see again within this box you can see that it is the weight has been done it has

  • a sufficient strength longitudinally, but again the same issue.

  • This longitudinals are running all along the length. So, you will have to have support

  • in between, in between transverses are needed because well you have the bulkheads. When

  • you have this, whatever that concept of bulkhead that remains because one thing you can see,

  • this transverse sub division bulkheads they are a must; whatever be the ship type they

  • are must. Why must? Because that gives us the so called required safety aspect from

  • the safety point of view that in the event of any accident or damage, this will provide

  • me quite a substantial level of safety before the vessel really sinks.

  • So, bulkheads are there. So, in the process what happens, if the bulkheads are there like

  • here I have drawn in red. So, this longitudinals in the box girder in that case will be running

  • from one bulkhead to another bulkhead. So, this again becomes a quite a huge span. So,

  • again from the same logic, we will have transverses in between like we had the deck transverses

  • in the general cargo carrier or bulk carrier.

  • So, same logic is there. So, here the transverse means what; means essentially a plate here,

  • a plate there. So, together it can be one plate which can have a like in bulk carrier

  • we had the transverse in the top wing tank. Same thing; this is a transverse having a

  • flanged. This is joining a double line means I am showing that the edge, there is a flat

  • bar welded to the edge which provides which functions like a phase plate. This cross section

  • is nothing but we have the plate and there is a flange welded a flat bar welded. So,

  • this is a transverse and now once this is a transverse means well those same things

  • those scallops, those cut outs will be there. So, thereby we see that this transverse. So,

  • this is a transverse. Again the same thing; this transverse will be spaced every three

  • to four frame space. So, as you can see that entire structural arrangement whatever be

  • the ship, the method of arranging them, the deployment of stiffening members; all follow

  • the same principle because at the end of that their purpose is such that there is no part

  • of the structure attains a stress level beyond permissible limit. That is a final purpose;

  • in all service conditions no part of the structure should attain a stress level beyond permissible

  • limit. Now, only variation of the structural type

  • etcetera is coming because of functional requirement. You need here the torsion becomes more important.

  • They are the well the bending becomes more important and so and so forth.

  • So, that is how this is what is the box girder construction. So, this provides we can see

  • a quite a heavily stiffened structure right at the top of the I mean at one end of the

  • entire hull structure.

  • So, this provides you a sufficient strength towards torsion as well as longitudinal; obviously,

  • as well as longitudinal, but this alone is a I mean much less stiffening would have been

  • required if we would have calculated only on the basis of longitudinal bending; bending

  • longitudinal strength, but this is provided to provide called additional torsional strength

  • as well as your side shell stiffening. So, we can see the side shell here again is

  • transversely stiffened. You have heavy transverse framing on the side shell.

  • So, that it is may be this is side shell going and this is a part of the transverse frame

  • which is now which will be suitably bracketed; that red line is the part of the bracket is

  • being shown, the blue line part of the side shell frame is being shown as you can see

  • here.

  • Yes bottom side we have not provided because you see the construction. In the bottom side

  • at every frame space this frames are coming and they are bracketed to the bottom plate.

  • So, bottom plate is stiffened by these brackets.

  • Rightly pointed out that this side plate or the deck plate as well as this side shell

  • plate are stiffened by stiffeners; longitudinal stiffeners longitudinals whereas this bottom

  • plate is not stiffened as such, I mean we are not seeing any stiffener here. What is

  • happening; this is getting stiffened from below by this bracket because a huge bracket

  • is being welded at every frame position. So, this bottom plate is stiffened by this

  • bracket itself. Like these plates are stiffened by this longitudinals, here these are stiffened

  • by these brackets. Because this side shell frame; this is a side shell frame; this side

  • shell frame will be there at every frame position. This is a side shell frame. So, what you see

  • that the side shell is transversely stiffened. So, transverse stiffening or transverse framing

  • arrangement is taken in the side shell. Why? Had it been longitudinal framing system then

  • again the case of those two big transverses would have had come. Some it could have at

  • enclosed in the cargo space, boxes would have I have to shift more, some space more space