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We will be starting with this program, marine construction and welding. Here, we will actually
look into primarily the constructional aspects of marine vehicles; the constructional aspects
means, or, the constructional aspects will also include your structural arrangements
and their specifics, with regard to the functionality of the particular object or the particular
marine vehicle, and their structural response against the service loads.
So, we will try to look into all these aspects as far as the marine vehicles are concerned;
by marine vehicles here, we mean, primarily the ships and offshore structures, offshore
platforms - we will keep ourselves limited to this. So, that will be one part and the
other part will be the fabrication aspect. In fabrication aspect, we will deal with whatever
things that come after the design is complete; after the design, working details are done
in the design office, then actually, you will have to translate that idea to reality, means,
you will have to have the product; till this time one can say that the things were in a
so called virtual mode, that means, they have been drawn - it is only on paper or may be,
in electronic mode. But for the actual purpose, you need the actual
product, that means, which will give you the service; say, transportation of wheat - you
need a particular kind of vessel, or transportation of trucks, automobiles you need a different
kind of, probably, a carrier. Once the designs are done, that means, your so called preliminary
design, detail design everything has been done, then it goes to the shop floor. Shop
floor will see in sequence what the kinds of activities involved are, and the shop floor
we are talking about here is essentially the shop floor of a shipyard. A shipyard is a
term where - though the name is shipyard, it does not mean that it only build ships
- it builds anything which is in water, more or less; that means, offshore platform also
is build in a shipyard, a submarine is also build in a shipyard; one may name it as an
offshore yard, submarine yard, but the general name is shipyard, that is a conventional.
So, that is what we will do; in constructional aspect, looking in the sequences will give
little more extra emphasis on the joining aspects, that is, the welding; because as
I said - once the design is done, once the plates or the materials have been acquired,
cut to the required sizes and shapes, then you will have to put them together to get
the entire final product: a particular ship, or a particular submarine, or offshore platform,
whatever it is. So, that joining technique used is essentially
welding; we no more do riveting these days, I mean, no bolting as such; long back it used
to be riveted ships, the joining was to be by rivets, now welding has advanced enough,
so we do welding; there again, different kinds of welding techniques are used for different
requirements. So, we will look into those aspects and finally, we will see, once the
welding has been done, you will have to be assured of the weldment quality - the joint
you have made, whether it will serve you the required purpose; the required purpose means,
welding is what? Two pieces you are putting together to make one integral piece, so that
integrity, how good is the integrity? How good is the welding done? Some quality tests,
so we look in to what kind of tests are done. All this we will talk, keeping our focus on
ship building industry; because there are various other methods of welding, there can
be various other methods of testing, but we will only talk about those which are rather
relevant to the ship building industry. So, that is how the entire course will be.
Today, to start with, I thought it will be worthwhile to look into the sort of the products
which we will be dealing with, classification of that; so, classification of that means
- it is essentially types of ships and types of offshore structures.
As far as types of ships are concerned, one can classify in two types: one is the merchant
ships, another is your defense crafts - the naval ships. The purpose of these two are
definitely very different - merchant ships are primarily for purpose of transportation
of cargo, and the defense naval ships are for defense applications.
From the design and construction point of view, there is no difference whatsoever, between
these two types - merchant or naval ships, because both are made of steel or aluminum
or any other constructional material; both are to be welded and both should serve the
same, I mean, similar safety requirements should satisfy and so on, so forth, but the
functional aspects could be different. So, in any guess, we will not go in details
of any of those naval vessels, there are different kinds of naval vessels; we will only talk
about the merchant vessels. There is another kind of vessels also apart from these two,
that is, the merchant vessels - to have them efficiently functioning - you need some kind
of support vessel; so we will talk about what are those support vessels.
Again, another classification can be made - broad classification once again, that is,
sea going vessels, inland vessels, I mean, within the gambit of your merchant vessels
- there can be sea going ones, there can be inland ones; within the inland ones, again,
you have small cargo carrier, passenger carrier. There can be another division which is from
the pressure tourism point of view, pressure craft - crafts necessary for tourism purposes;
that is another class. On top of that again there can be another classification of high
performance craft; something called high performance craft or high speed craft.
Broadly, I think we can go like this - if we just look into the merchant vessels, I am just giving the name merchant vessels
for all kinds of vessels apart from the defense ones - naval ones; so, in this - there will
be seagoing, there will be inland, there will be support vessels, there can be what is referred
to as high performance vessels. This, we are basically talking to make you
aware that what all kinds of vessels are there. Obviously, in the entire course, we will not
be taking each one of them and talking about them, definitely that is not feasible; but,
the basic principles of design, the basic principles of construction, the basic principles
of welding, all remain essentially same. But, once you will become a naval architect,
it is expected that at least you will have awareness of all these types of vessels. So,
that is how we could divide this merchant vessels in these four categories; of the seagoing,
we will have further sub division; there can be many types of seagoing vessels, but we
will concentrate primarily on these ones: the first and foremost can be referred to
as general cargo carrier -
a particular type of ship, as the name suggests, it carries general cargo - cargo of any nature,
any type. Another one is referred to as bulk carrier
- that is essentially, cargo in bulk. For example, you are carrying wheat, say, forty
thousand tons of wheat, you will have to import from Australia. So, what could be the means
of this transport of this wheat? It can be - either pack them in bags, those gunny bags
or whatever, pack them in bags, load it in a ship and bring it; if it is done that way,
then possibly, it will be brought in a general cargo carrier; but if you have a ship wherein
you have big holes like this room, say for example, even bigger, much bigger than this,
wherein you just put the wheat in lose condition and bring it - that is bulk carrier, that
means, you carry the cargo in bulk. Obviously, the second option is much easier,
or much more efficient than the first option, because otherwise, unnecessarily we will have
to use so many carry bags wherein you have to first load, stitch it, and take it; so,
not only it is additional work involved in loading each bag, stitching the bags, it also
adds to the weight - a fictional weight of those bags itself. Instead, you carry the
whole thing in loose; but if I put the wheat in a general cargo hold, then again may not
be very convenient to carry, because that is not designed that way, functionally it
is not designed. So, the bulk carrier come in to being because of this bulk trade; so,
this bulk trade is going to exist; as long as mankind exist in this world, this bulk
trade will exist. That is how, this type of vessels developed
over the years depending on the requirements - that is what is a bulk carrier; we will
look into this in little more detail later, when you talk about bulk carriers, automatically
implies - it is a dry bulk carrier. Next comes, possibly we can mention the oil
tanker - this is also a bulk carrier, but it is a liquid bulk carrier, so give a different
name, oil tanker - there you carry oil. Primarily, by oil tanker, we mean the crude oil tanker
- crude carrier, because there is huge straight of crude petroleum, crude transportation.
Obviously, there are vessels which carry the refined oil also, that means, the petroleum
product, we are not going in that; broadly, we will talk about the oil tanker which is
a crude carrier. Then comes container ship; container ship,
what is it? As you can see the name, it carries containers - what are those containers? You
may have seen on roads or on rails those huge rectangular, cubical boxes - huge ones.
Instead of carrying the cargo in general form, in loose form - in general cargo carrier,
you can carry anything; but anything means? Suppose the furniture of this room is to be
transported and if I lift each chair individually and put it in a ship hold - that is the way
a general cargo carrier is loaded, that means, each unit cargo is individually handled - so
imagine, if I have to suppose transport these chairs and I transport one by one, that amount
of time it takes for loading and unloading; whereas if I have a box wherein I pack all
the chairs and I just transport the box it becomes much faster.
That gives, I mean that particular aspect gave rise to this concept of containerization
or container ships, because you know everything is eventually driven by economics - that is
the bottom line. So, what people found, that a general cargo
carrier - the loading time and the unloading time may extend to the period of two to four
weeks; that means, it calls on a port first, it unloads whatever product it brings and
then it loads. The entire process may continue for four weeks - that means what? That four
weeks is total wastage as far as the ship owner is concerned - he is not earning any
money; rather he is paying because the four weeks he is staying in the port, he will have
to pay the port dues. Instead, if he could have had cut it down to, say four days of
stay in the port, then what happens - he pays less; not only that, he makes more number
of trips. When the ship runs in the sea, when it cruises,
then only the owner actually earns; he is spending when the ship is sailing, definitely,
because the fuel cost, the salary, etcetera; but that is an earning phase - because he
is taking somebody’s cargo and he will be paying. So, he would like to make more number
of trips; how to make more number of trips? One way would be - increase the speed, another
way would be - decrease the down time, it means, the ship is stationary - not sailing.
Increasing speed could be option, but that comes at a cost - very high cost; you will
learn later in your other courses that speed of the ship and the power required to deliver
that speed - it increases exponentially. From, say, 15 naught to 16 naught, it is not
a linear sort of increment in the power requirement, it is exponential; so, there is a limitation
- you cannot go on increasing the speed because power requirement increases, means, your fuel
consumptions increases, your cost increases; that also you cannot go on infinitely increasing
because there is a cut-off somewhere, beyond which, you put more power - the ship weight
increases, it does not deliver the speed. Because speed is also related to the weight
of the bulk, the ship, so that is not an option; good option - to increase the number of round
trips; so, one of the best option is to cut down in the port time, that can be done if
I can cut down on the cargo handling time, that is the loading-unloading time; so, that
gave birth to the concept of containerization.
So what happens here? The containers are loaded on-board the ship; containers themselves come
loaded from the consignee; whoever is, suppose sending some product, some machine equipment
or whatever - he will take containers to his factory premises, load the containers and
the containers are delivered to the port - and containers are put into the holds; same thing
on the destination ports - containers are taken out, put on trailers and, goes to the
port of I mean goes, straightaway goes to the customer for whom the cargo has been assigned.
So, what happens, in the process, since the containers are of identical size, standardized
size, so you can have the enterprise of loading and unloading mechanized - it becomes very
fast; so that is how, the concept of containerships came.
But, as you can see, as we are coming from general cargo, bulk carrier, oil tanker, container
ships, basic purpose is same - transportation of cargo; but the functional requirement is
changing because we are transporting different kinds of cargo, so that way, that has a bearing
on the design of the vessel; we will see later how the design changes.
Another very popular important trade is import-export of automobiles, that gave rise to a particular
type of a vessel, which is referred to as - ro ro vessel or ro ro ships, because, in
global trade, automobile is one of the commodities which is very heavily, sort of, imported and
exported. For example, one of the biggest consumer of
automobiles is U S A, so they themselves are manufacturing many cars, many automobiles,
but they also import many from Europe, as well as, from Japan; so, there is a huge trade
in this. How do you transport these automobiles? You can put them in a container, but not all
kinds of automobile may fit in a container; so, putting in a containership may not be
very viable; of course, in the bulk carrier, does not arise question of keeping the automobiles;
by this automobile, I mean, it can be trucks, it can be passenger cars, which are self-propelled
by themselves. In a general cargo carrier, again it will not be very convenient.
Here, what we will have to see in ro ro vessels or an automobile carrier is, that how easily,
again the same question, how easily you can load the cargo and how easily you can discharge
the cargo and in between stage after loading and discharging is the safety of the cargo
demats? So, how to do that? Since the automobiles can roll-off themselves, so that is why, they
are called roll-on roll-off ships - that on and off I have deleted, and I said ro ro ships
in short; actually, the ro ro - that name was derived from roll-on roll-off.
That means, the car rolls on the vessel, docks itself there, wherever it is assigned; when
the vessel calls in the port of destination - it rolls out; so that is how, your loading-unloading
becomes very easy, very convenient. So, that is the functional requirement of
this vessel, that the car - the cargo, will roll on the vessel, will keep it stationary
during their entire voyage, and again unlock itself and roll out; so, the functional requirement
- based on that, you will have to design accordingly.
Immediately one thing comes to the mind, that this kind of vessel should be a multi-deck
vessel; several decks should be there, because in each deck there will be several cars. In
a bulk carrier, you do not need decks because entire cargo is put in bulk; in oil tanker,
you do not need decks; so, the functional requirement automatically gives you clue - how
the internal structural arrangement should be.
Also, you can see a bulk carrier or an oil tanker, the port through which you will put
the cargo and the port through which you will take out the cargo again, will be different
compared to a container ship, will be different compared to an oil tanker or a ro ro ship;
so, that means the functionality, that is why I am saying externally it may look all
identical, but because of the functional requirement, internal arrangement will be different. We
will look into those structural arrangements; so that is ro ro vessel.
Then possibly, you can talk about the passenger ships or passenger carrier or also referred
to as, passenger liner. As you know, long back when this aviation industry did not mature
that much, passenger transportation - also used to be, you cross a continent - it used
to be by a ship; that means, the cargo was passengers.
Today, of course, passenger liners no more as such, serve that purpose, but again it
is becoming gradually very popular in the tourism sector - that means, for holidaying,
for sort of leisure purpose, people go in this passenger liners for spending some good
time. Well, these are also huge vessels; obviously,
here the cargo is the very delicate cargo – passenger, human being, so accordingly,
you will have to provide facilities. In other cases, the cargos are not that delicate yet;
in oil tanker some delicacy is there - you will have to have proper vent mechanism so
that fire hazard. In ro ro vessel cargo is again delicate from other point of view - cannot
afford damage to any car while handling, there cannot be any single scratch in the body - that
way it is delicate; as well as, they are rolling-on and rolling-off, means, they are on their
own engine power within a confined space. So, question of ventilation is very important
because the pollution, say, a ro ro vessel with capacity of 2000 vehicles; so, 2000 vehicles
will come inside a very confined space, each will have fractional amount of C O emission,
you can imagine the polluted environment in that; so, the driver of the last car, when
he parks the car and goes out, he may get fainted, because it is already so much heavily
polluted inside; so, all those aspects are there.
Passenger liner is the most delicate cargo, so obviously, you will have to provide for
him the best possible comfort, and all those other aspects, because here we will have to
keep in mind, the passenger line as primarily being used for leisure purpose; so, comfort
of the highest ordered is needed. Obviously, safety in other vessels is also needed, but
here the safety requirements are still more stringent because here many more human lives
are concerned; so, that is the passenger liner. Probably, it will be worthwhile to mention,
there is what is referred to as LNG LPG carrier; LNG and LPG carrier. You have any idea of
what is this LNG - Liquid Natural Gas, similarly, Liquid Petroleum Gas. So, there is also some
bit of trade, intercontinental trade, in this particular product. If you have to transfer
a Liquid Natural Gas or Liquid Petroleum Gas, obviously, none of the above mentioned vessels
are suitable.
What is the fundamental difference in this particular product compared to all other products
above? That is the requirement; I am saying - fundamental difference of the product, that
is, the requirement of product’s storage; or product’s storage is the fundamental
difference in the product. Liquid, it is not gaseous; there is another
liquid also, oil tankers; so, could I have taken it in oil tanker - definitely not; so,
what is the fundamental difference? Fundamental difference is - fundamentally,
this cargo is a very low density cargo, even in the liquid form also - it is low density;
and second, the temperature of the cargo. These are the two very fundamental aspects
- the temperature of the cargo and its very low density.
So, what is happening in the process? You know, in ships, there are some requirements
of, what is called, load line requirement; load line requirement means that you are not
allowed to load a ship beyond a certain loading point, beyond a certain capacity; beyond a
certain capacity means what? Means, you have designed the vessel and you will have to,
sort of, define the full loaded draft; that means when the ship is, say, a particular
ship is designed of carriage of ten thousand tons cargo, that means, in the departure condition,
the maximum weight of a ship is when, at what point of time you have the maximum weight
of total weight of the ship? This weight of the ship is referred to as what - displacement.
There is a term called displacement. We do not say the weight of the ship, we say, displacement
of a ship. Why this term has come, you know? Can you guess? It displaces the water, equal
amount of water; that is how this term is used - displacement.
Can you tell me when a ship will have its maximum displacement? During departure, loaded
departure; there are various stages: loaded departure, loaded arrival. These two are different,
there will be difference in weight, because in loaded departure condition you will have
the entire fuel stock, you will have entire fresh water stock, you will have the entire
provision stock, everything is full. Loaded arrival - many of these things have depleted
to a bare minimum level; so, this loaded departure condition - at that condition, the ship should
be floating at a certain draft, which is already predetermined.
You may have empty spaces available in the ship, but you cannot load further cargo; then
what happens - the ship will sink beyond that line which has been prescribed, that is the
load line, also referred as Plimsoll line. Why? Because from the safety aspect, there
is a requirement of what is called, freeboard. These are, of course, you will learn all these
elsewhere also, but I am just, may be it is worthwhile to mention.
That what I am drawing is just a section at the mid length of a ship; externally you can
see like this, so this is your, let us assume, that this is my LWL - Load Water Line at the
loaded departure condition; so, this distance - the distance from the deck at side to the
load water line, this is referred to as freeboard. There is a specific requirement that the freeboard
could be less than so much. There is something called SOLAS - Safety of Life At Sea. There is SOLAS convention
- this particular convection outlines or gives the guidelines of various safety features,
safety aspects, which are mandatory, which we will have to follow while designing, while
operating and all that. Because human lives are at stake, so this
SOLAS convention prescribes freeboard - that for a particular type of vessel, this must
have to be the minimum free board, it cannot have less than that. When it may become less,
suppose I have loaded - I over loaded; so, over loading is not only a problem of structural
point of view, but it is a problem on the safety point of view, so that is not permitted.
Anyway, so what happens in case of higher density cargo? You load to a certain extent,
I mean, that way you design and your vessel very easily attains the load water line, or
it may sink to the required draft; but in case of LNG and LPG carrier, it hardly sinks
to any draft unless until, you really load a huge amount of the cargo, because the density
is very less - of the order of 0.5 or so. So what happens, LPG LNG carrier? Here I have
drawn, only little bit is above the water, major part of is below water, but in LNG carrier
it can be otherwise - much above will remain; that means, there freeboard is no problem,
there is other kind of problem coming in to picture - there is too much of exposed area
above water level, means, too much of wind force will be working; so, that I can give
another design problem. Then, of course, the cryogenic temperature
- low temperature means, it is literally, substantially subzero temperature. Cryogenic
temperature means, accordingly, you will have to have all those required thermal insulations
and containment systems; so, that is how they classify itself as very sophisticated vessels
and it needs special attention, obviously.
So, broadly we can say, the sea going merchant vessels can be classified - in this probably,
we have done it in six different heads. Let us take a quick look at the other ones - the
inland vessels. In the inland vessels, we have the river crafts, what are they? The river
launches, the launches for small time - for ferrying of passengers across the river, or
along the river; then, through inland water also we transfer cargo, so we do not name
them as cargo ships, but we name them as barges, barge; we call them as barge.
So, these barges could be self-propelled or could be dumb barges; that means, it can have
its own propulsion mechanism - so it becomes a self-propelled barge - that is, a miniature
version of ocean going ships, a cargo ship; then, dumb barges - dumb barges means, it
does not have any propulsion mechanism. It has only cargo holds where to load the cargo;
so, you will have to have another prime mover or an order vessel which will push it or pull
it through these dumb barges, those come under the support vessels; so, in inline - primarily
these two, launches and barges.
Then we come to support vessels
which provide for, I mean, helps in the proper operation of the sea going vessels, inland
vessels etcetera; they provide support. We started with the merchant vessels, naval vessels;
naval vessels - it is a very specific function; merchant vessels primarily trade – primarily,
transportation of cargo. All the sea going vessels, what we have just now talked about,
all are basically cargo transportation; inland vessels also, we have talked about, is cargo
because launches - passenger cargo, barges - general cargo.
Support vessels - they are not for any so-called cargo transportation purpose, but for facilitating
this process. So, first and foremost, support vessel could be referred to as tugs - tug
t u g. The function of these tugs are, like I said, that if we have a dumb barge - it
can be a one dumb barge or there can be couple of them put together, there can be various
configuration of barges put together - and one tug pushing it, we call it a pusher tug;
so, this is a kind of a support vessel, that means, it moves there. Another support this
tug can provide is - when a big ocean going vessel enters a port, you will have to berth
the vessel, means, parking of the vessel alongside the bank, which is called quay or the berth,
because it has to be on the shore side, such that, your unloading loading can be done easily.
So, how to move that big vessel? Say, a hundred thousand tonner bulk carrier is coming. If
it operates its own propeller, own propelling equipment and maneuvers it to come to that
position, it may not be able to do so, because, you must realize, that the breaking mechanism
is not as efficient as compared to the surface vehicles. With that inertia, it goes and hits
the quay - that will break, also this ship will be damaged, so what is done generally?
The vessels are maneuvered with the help of tugs; so, another support the tugs provide
apart from pushing the dumb barges - they help maneuvering the vessels in the port area.
So, a configuration like this, what I have drawn is - these are the tugs, this is a big
vessel, in comparison the tug will be this form; so two tugs pulling the vessel from
the back side, another tug pulling it from the front, so that to keep the right course
and slowly takes to the desired destination, wherever.
So, that is how I have classification - as a river tug, which is essentially pusher tug
for barges; then you can have harbour tug; that means these tugs, their primary function
is to maneuver big vessels within harbour. There can be now ocean going tugs; what is
this ocean going tugs? The first two tugs we have talked about, they will be operating
in sheltered water - river is also sheltered water, harbour is also sheltered water; but
when you go in an ocean, it is not a sheltered condition - you will face the ocean conditions.
So, this is a different class of tugs which are referred to as ocean going tugs. For some
purpose, you need to pull a vessel right up to the ocean, or for rescue purpose also you
may need; some break down has taken place, a tug goes out in the ocean and pulls it back;
by this ocean it does not mean really a mid-ocean. A tug is not necessarily supposed to go to
mid-ocean, means, thousands of miles away from the coast; not that way, but definitely,
in the ocean atmosphere to be capable; so that is an ocean going tug.
Then you have firefighting tug; by firefighting tug means - all the above three tugs can be a
fire fighting tug - that means, tugs along with having the facilities of firefighting;
there is a fire in a vessel, the tug will go and douse the fire. So, that is one of
the support vessels. The other support vessels are - there is something
called dredger which dredges; the name, very name dredger means, for example, like the
harbour or the port is little inside from the sea that is connected by means of a river
or canal or channel; so, we will have to always maintain the required draft in those channels
or the rivers, such that the designated vessels or the required capacity vessels can sail
through that; as you know, there is always a sort of this phenomenon continuous, that
is, siltation. Because of various other factors, siltation
of rivers takes place, siltation of canals takes place. Because of this siltation, the
draft availability or the navigability of the rivers or canals becomes poor; means,
if we do not have the required draft, a vessel cannot move, so we will have to clean that
silt physically - have to grab, take the silt up, and throw it elsewhere. So, that is been
done by vessels called dredger which dredges. The dredging operation is basically digging
up the silt and removing it, so have a support vessel called dredger.
Another support vessel is pilot vessel; this is nothing, but the pilot travels from the
port to the ship. When a ship enters the port area from the oceans, at some designated point
pilot takes over from the caption of the ship; he guides the vessel to the port because he
knows this canal or the channel through which the vessel will sail and enter the port; because
as I said dredging does not mean that the entire river geometry
Say, the river bed is something like this, everywhere you do not have the sufficient
draft; a certain region, probably, you are maintaining navigable. It cannot go on tracing
the entire width, so in navigable - within the river or within the channel, a navigable
canal is maintained that the pilot knows very well.
So, he takes over, he guides the ship through that navigable canal, why is this so important?
You have any idea, why is it so important? Because if you do not do that, the vessel
may get grounded; a term used - grounded, means stuck in the silt; stuck means, it will
sit on the silt suddenly. Suppose, the draft is less, it goes and plows in the silt.
So what is the problem? It is not only the question of coming out, it may tilt and capsize
immediately, why? That we will learn later, because its floating condition has changed;
it was stable when it was floating; a ship has to be stable. It is in a stable equilibrium
condition- that mean - if some disturbance is given, some tilting force is given, it
comes back to its original position, that is, stable equilibrium. When the external
force is removed it will came back to its original applied condition; so that happens
when it is in the floating condition.
But the moment it touches the ground, then the floating condition changes; all those
parameters changes, it becomes unstable and may capsize, so that is very important. So
that is what a pilot vessel is - the pilot travels. What is so important about it? Because
it is essentially ocean going vessel; because it will face the wrath of the ocean when the
vessel is waiting out at the ocean, not in the slitter water. So, this is one of the
support vessels and there is other type of supporting vessel, which is referred to as
supply vessel. Supply vessel which is used to supply provision
and other equipment to offshore platforms.
So there can be some more other support vessels, they are the general ones. High performance
vessels, which are they? They are essentially the planning craft, referred to as, planning
craft; another one is referred to as hydrofoil craft; there is something called SES - Surface
Effect Ship; there is something called ACV - Air Cushion Vehicles or hover craft; so,
these are some of the high performance crafts. What is the difference, why I have classified
them as separate? Well, because they are high performance; what does it mean - high performance?
it means - no, speed is a relative term; in case of ships we talk about speed length ratio
v by root over l; that comes from the float number v by root g l, g being constant, v
by root l; so, that is what is referred to as speed length ratio. Depending on the length,
for a given speed, it may fall in the high speed zone; it may be classified as a high
speed vessel. So, in high performance, primary difference
is that they are very weight sensitive vessels - that is number one. Their mode of operation
is not only the buoyancy force which is acting, which is holding them in water; rest all the
vessels which we have seen: the sea going vessels, the inland vessels, the support vessels,
all are supported by buoyancy force only - they are floating, they are following that great
Archimedes principle. But the high performance vessel, when they are performing, when they
are cruising, part of the weight is supported by a lift force - something equivalent or
something similar to that of aircraft. The aircraft does not float in water, it is
supported by a lift force in air; it is not because of its buoyancy it floats; same thing
in high performance vessels, this planning craft or hydrofoil or ACF or ACV, all these
- some kind of lift force, apart thrust is generated in the hull, thereby the weight
of the vessel is fully or partly supported by the thrust - that lift force, and rest
supported by buoyancy; that is how, they are called high performance vessels.
So, what is the great fun about it, what is a big deal in this? The big deal is, the moment
it gets supported by lift force means, the entire thing is not supported by buoyancy;
that means, the vessel is much out of the water - lesser part of the vessel is touching
the water, that means, lesser frictional resistance; the moment you have lesser frictional resistance,
for the same power, you have higher speed, simple; that is how we attain a high speed,
that is how the aircrafts fly at so high speeds, because the frictional resistance is very
nominal - it is only the air resistance. That is the way we will find, there is all these
aircrafts, they are trying to go up, as up as possible - 30000 feet, 38000 feet, where
the air is less denser, lighter - the more lighter it is, lesser resistance - so it tries
to pick up the highest altitude, as fast as possible, and then cruise though, it attains
higher speed or lesser fuel consumption. So, that is what is this high performance vessels,
of course, in detail, you will learn in later courses.
Another fundamental difference here till this point - seagoing inland vessels and support
vessels, all are so called displacement craft, they are referred to as displacement craft,
why? Because they are supported by buoyancy force and so, thereby we see that they are
not generally weight sensitive; the weight is not a very important criteria - it is important
criteria, not very important - but in case of high performance vessels, they are very
important because if your weight becomes little extra, it will never come up, the lift force
will not be able to push it out of the water.
So, thereby one will have to take care of the constructional material of this. It cannot
think of using steel or such heavy dense material for building of such craft, you will have
to use a lighter material; so, that is how we see that this is the primary classification
of the merchant vessels of the ships. So, we will continue in the next class.