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