Sunday, 29 March 2015

Basic Ship Terminologies- Part 1

You don’t really need to think about ships to come up with terms related to them, anything discipline in Science and Engineering, Economics, Finance, Fine Arts, etc. has its own myriad lexicon. Well, just imagine what would it be like if a designer of a car was completely alien with even the simplest of its terms and parts?

So, let us get to some of the basic terminologies associated with any ship:


Hull is basically the main structural component of a ship. It is a watertight component and supports the deck, and the superstructures. It is nothing but a structural beam providing the ultimate mechanical strength to the ship. The part where it meets the water surface is called the waterline. It is comprised of transverse and watertight members called bulkheads, intermediate members called girders, stringers and webs. Also, it has minor structural arrangements called stiffeners, which are used to increase the strength of the hull steel plating. 

The shape of the hull is chosen to strike a balance between cost, function and requirement and other hydrostatic and hydrodynamic considerations. Hulls can be of fine form and fuller form, monohull and multihull, displacement type, semi-displacement type and planning type, etc.


It is the basic structural foundation at the bottom most part of the hull that runs along the ship’s length. It acts like a backbone of the ship. When dry docked, the ship rests on wooden blocks in the dock. It is the keel, which takes up most of the loads in that case. It not only contributes to the global longitudinal strength of the ship, but also takes up local loads. A ship with a weak keel is a design failure.

They are primarily of two types- “flat keel” and “bar keel”, the former being the most common type and the more stable ones , the latter being the ones meant for smaller vessels like trawlers and tugs.


It is the forward-most part of a ship. Well, if you have seen a ship you must have unmistakably noticed the protruding front section of the ship. Bulbous bow (read our advanced article on bulbous bow) is the bulb-shaped or pear-shaped bulging part of ships. It primarily helps in reducing the power required by the engines to propel the ship.


It is the posterior end of a ship. It is located at maximum length of the aft. The design of a stern also affects the efficiency of a ship’s propeller (which you will learn in an advanced level).There can be various cross-sectional shapes of stern. There are two main types of stern designs used in the shipbuilding industry as of now:
  1. Transom Stern
  2. Cruiser Stern

Port and Starboard Sides

Viewing the ship from the aft, the left side of the ship is called the Port side, and the right, is called the Starboard side.

Superstructures and Deckhouses

It is that above-lying structure above the hull which essentially runs from one extreme side to another. It is placed above the two extreme bulkheads horizontally. A deckhouse is similar to a superstructure, except for the fact that, it does not run across the extreme ends of the ship. A deckhouse terminates somewhere within the extreme sides of the deck.

Length Between Perpendiculars (LBP)

Length between perpendiculars or LBP is the measure of the distance between the forward perpendicular which coincides with the intersection of the stem and waterline and the aft perpendicular which passes through the rudder stock.

Length of Waterline (LWL)

The distance between the extreme forward and aft points of the ship, where it intersects the waterline, is called Length of Waterline or LWL.

Length Overall (LOA)

The length between the extreme ends of the ship is called Length Overall or LOA.


A propeller is the component fitted at the aft of the ship, and it helps in propelling the ship forward. It is driven by a shaft, which in in turn driven by the ship's engine. A ship may have one or more than one propellers depending on the type of the ship, and its functionality. Designers and ship operators should always be careful in ensuring that the entire propeller is always immersed below the water surface, in order to be able to operate at its maximum efficiency.


A rudder is the equipment which helps to steer the ship. It is always placed behind the propeller. If you cut a rudder plate along it's length (from forward to aft), you will notice that it is an aerofoil section (like the wings of a plane). The reason behind using an aerofoil section, is that it generates a lift force when any fluid (water or air) is incident on it at a certain angle. This lift force is used to turn the ship.

What comes up in Part 2?

In the next part (read Part 2 here) we shall get acquainted with newer terms that are more fundamental to a designer, and are of utmost important in deciding on the principal parameters of the ship.LSD

Article By:- Subhodeep Ghosh

Sunday, 15 March 2015

Design of Ocean Research Vessels: A Perspective

Research has often progressed with the development of the technology to observe details more minutely than ever before and so has surveying. However, when it comes to oceans covering a vast portion of the earth’s surface, the mammoth scale says it all- there is still a lot to know about them and so discover a lot about ourselves from the enormous timescale of their existence on planet earth. You might be familiar with the programs working towards making humans settle on mars, but still underwater habitats, their study and the plethora of knowledge to be gained from such endeavours might not have equal appreciation from you yet. Trust me, the oceans are worth looking forward to.

Scientific research expanded beyond geographical barriers and we needed a better look at the vast outer space and of course, the oceans, a sizeable part of life on earth still remain undiscovered today. The search for fossil fuel reserves, everything other possible human necessity grew, and so the Ocean Research Vessels came in to being. Depending upon need, the earliest ORV’s did hydrographic surveys, assessments of fish stocks, primitive study of properties of water at varying depths, deploying buoys, etc. before the advanced vessels of today which can do a lot like these and more:
  • Study of the marine flora and fauna: this is an area of extensive ongoing research, especially with the discovery of new species every now and then.
  • Study of the interactions with the atmosphere: this receives a lot of attention today especially with the growing concern with climate, the data from such research is invaluable. So, it goes without mention, the study of pollution and adverse anthropogenic factors on marine life are imperative.
  • Study of wave phenomena, sea states, and seismic research: these become important, especially when setting up offshore structures for the extraction of resources.
Oceans are arguably the biggest reserves of moisture on earth and also store and release energy more efficiently than land.

Now, how does the mission shape the design? An ORV houses advanced scientific equipment taking down observations, often having delicate sensors and components. The components may be either heavy or lightweight. The ship should be able to optimise between cruising time and working time as the latter is crucial. Again when cruising, the marine environment within its radius and the season of operation is important. The cranes and winches for lowering/deploying the scientific devices and their loading conditions and strategic positioning should be taken care of.

Here I am trying to give you a standpoint to approach the problem with. When given the task of designing an ORV, you should first fix the vessel parameters, generally all ORVs require reasonably very good stability in the sea states of their operation which calls for an appreciable length/beam ratio. The sea states take into account the maximum wave heights possibly encountered and so you would have decide the speed in each sea state, given that your equipment which would be exposed on the deck are not affected in a large way. 

Speaking of deck area, ORVs have large exposed deck spaces for container labs (if any), special frames called the A-frames and deep sea winches with their extensive cabling for lowering and retrieving equipment. However the length of the ship puts constraints on the equipment it can carry and the endurance (i.e. period of operation- the crew and scientists aboard also matter) of the vessel. However a vessel of intermediate size (around 100m) can house all the ones mentioned above. Then there are other factors like having advanced manoeuvring capabilities and the ability to operate around ice. Ocean Research Vessels often have Twin Screw Propulsion owing to its enhanced manoeuvring capabilities.

ORVs should also necessarily be ‘quiet’ ships. This means both external and internal noise should be minimum. External noise components are reduced by proper fairing of the hull shape. This shape when optimised to allow smooth flow around it ensures minimum external noise and subsequently, hull vibrations are reduced. Another source of external noise are the propellers and they subsequently need to be minimized.

Fig. 1:Innovations in hull design have been incorporated into the newer generation of ORVs like in this case, the Ulstein's X-Bow concept (Courtesy: )

Sources of internal noise are reduced in many ways in these ships by the use of motors instead of direct-drive diesel propulsion. Other methods are the use of Hull Dampening and Bulkhead Insulation. We can discuss that another day.

It is observed that such ships have conventional 12 kHz, and 3.5 kHz echo sounding systems and provision for additional systems as needed. Something worth considering here is the use of multi-beam echo sounder which is a modern technology and an improvement over single beam and earlier lead line techniques as it can provide a better area of coverage while covering a fraction of the surveying length.

Most advanced ORVs have Dynamic Positioning Systems (a standard on many vessels today) which develop a numerical model of the ship and based on the response from waves, are able control the rudder angles, propeller operation, bow thrusters in a combined manner allowing the ship to hold its position or course automatically with high accuracy. They require Global Positioning or some sort of position sensors, gyro compasses, etc. The vessels operating in Polar Regions have extra-strengthening (ice-class vessels) for the ice cover they are about to encounter. Sagar Nidhi is our very own Indian ORV with both of the above features as we would see later.

Research vessels necessarily require laboratory spaces and stores for scientific equipment, these are exclusive to them only. Laboratory spaces cover a substantial part of such designs. Laboratories have to be fabricated using uncontaminated materials and a good design would allow maximum lab cleanliness among the furnishing, cabling, hatches and fittings. Proper ventilation network with fume hoods is essential. Laboratories on board are often broadly divided into wet labs, dry labs and electronic labs if they are present separately from dry labs. Access between laboratories are usually such they are convenient and at the same time do not act as general passageways.


Some of the equipment commonly used on such vessels are:


Normally on many ORVs. Used for basic Conductivity, Temperature and Depth measurements. Used single or in cluster arrangements called ‘rosettes’ and lowered into the water normally using an A-Frame.


Collection of sediments from the ocean floor. Information from the soil several layers deep helps in understanding past history and also for climate changes, weathering phenomena.


Other than the CTD apparatus these equipment's are also used for detecting presence of biological life, nutrient content and dissolved oxygen. Limited to small parts of the ocean area and is time consuming.


Underwater analogue to topography of sea bed. Use of side scan SONARs, single beam echo sounders, these reveal the underwater morphology and geological history.


Use of acoustic waves at certain frequency ranges which generate 2D and 3D representation of the data of the ocean floor with depth. These are reasonably accurate.


Measuring the transparency of the water body. The scale is chosen as per depth at which the disk when lowered into water using a rope ceases to be visible.


Collect planktonic organisms. The size of plankton to be caught can be set by changing the size of the funnel shaped net used aboard the ship for the purpose.

Some Champions

Here are a few ORVs which have served towards knowing our oceans, the environment, and the planet as a whole.

Fig. 2:ORV Sagar Nidhi
Courtesy: )

ORV Sagar Nidhi

ORV Sagar Nidhi is owned and operated by the National Institute of Ocean Technology, India. This vessel is state of art with ice class capabilities. Accommodating 30 Scientists with a crew of 24-25, this vessel can do a variety of Underwater and Oceanographic Research procedures. Provided with Diesel Drive Propulsion and DP Systems. This ship houses excellent navigation systems with an Integrated Bridge and can hold live communication with the shore which will soon be enhanced by the introduction of a VSAT within the system.

Fig. 3:ORV Sagar Kanya
Courtesy: )

ORV Sagar Kanya

This vessel is owned and also operated by the Indian National Centre for Antarctic and Ocean Research. This vessel was delivered by Germany in 1983 to the Ministry of Earth Sciences, India. This vessel conforms to the class requirements of Lloyds Register of Shipping and the Indian Register of Shipping. Like ORV Sagar Nidhi, it is fully automatic diesel electric with type twin screw propulsion and on board DP systems. Both vessels have endurance of around 45 days continue to be workhorses for the service of their organizations.

Fig. 4:ORV Sagar Kanya

Aurora Australis

Currently owned by the British shipping and Logistics Company, P&O Maritime Services, this vessel is an icebreaker built and launched in 1989 and in service since then. This vessel was originally designed as a multi-purpose research ship. The crew on board the vessel is 24 and this vessel can carry up to 116 passengers. Ship houses laboratories for extensive oceanographic and meteorological research. The ship can allow the operation of up to 3 helicopters from the helideck. The ship is frequently used by the Australian Antarctic Division (AAD) and has been used Department of Defence of the Royal Australian Navy among others mainly for research and supply purposes.LSD

Article By: Sudripto Khasnabis