What's with the Bulb? - Part Two

If you haven't read the Part-One, click on the it to get a very brief introduction about the bulbous bow. 

In the following part we shall be discussing about how it helps in reducing drag and what are the requirements to have a bulb.

To understand with the working of the bulb we need to know about the various types of waves generated by the ships.

There are generally two types of waves generated by the ship,

• Divergent Waves: originated at the sides of the ship and have crests inclined in relation to the symmetry plane of the ship.

• Transverse Waves: originated at the ford and aft part of the ship and have crests perpendicular to the symmetry plane of the ship.

The interference between these wave systems originates the characteristics humps & hollows as a function of the ratio (Vs/Lwl) of the ship. This is where the Bulbous Bow comes into picture, the wave system generated by the bulb interferes with the wave system of the ship resulting in ideally no waves, practically smaller bow divergent waves. The length of the bulb defines the phase of interference and its volume determines the width of its bow system.

                           

However, the efficiency of the bulb lies in that narrow range of speed for which it is designed for. At low speed a Bulbous Bow will trap water above the bulb without forming a low pressure zone to cancel the bow wave. This leads to increased drag and loss of efficiency. Each design has what is known as most efficient hull speed, or often just hull speed. This term refers to the speed where the shape of the hull is acting on the water in such a way to produce minimum possible drag.

The ideal hull speed may not be the top speed of a ship because at some point the lower pressure zone created by the bow features become larger than necessary. A zone of lower pressure water that is larger than the hull is insufficient and leads to reduced rudder response.

Ideally the cone of lower pressure will collapse just before the propeller and this would lead to a phenomenon of cavitation, this leads to reduced efficiency of the propeller, sluggish steering, and excessive wear of hull and drive components.

Now the biggest question arises Who Can and Who Can't?

It is generally observed that vessels under 49 feet(15 m) do not have enough wetted surface area. The structure of bulb also increases drag and at a certain point the benefits shrink to zero. Conversely, larger ships with a high proportion of waterline to frontal area use the bulbous bow most effectively. Another factor that determines the use of bulb is the cost to benefit ratio. LSD

                                  

Article By: Tanumoy Sinha

Author's Note: This article is the second part of the topic 'What's with the Bulb?'. It expounds to us about the working of the bulb and what are the favorable situations to use the bulb effectively. In the next and the final part of the series we will be discussing about the various sections of the bulb, few design factors and followed by advantages and disadvantage of having a bulbous bow.  I have written this article based on my experience and technical knowledge on the same as a Naval Architect. The picture used above does not belong to LSD, and full credit for the same goes to their respective owners. If you have any queries or doubts, write to me at learnshipdesign@gmail.com

Ship of the Week - Green Dolphin 575

BACKGROUND BEHIND THE DESIGN

Of late the demand for bulk cargo trade in the intra asia routes have shown a constant elevation in graphs, triggering the requirement of handymax vessels. Handymax ships have this potential to compete against larger tonnage vessels as in they can carry wide range of cargoes and their optimized size make them suitable for easy handling within ports and terminals. The concept design has been devoloped by joint collaborations and research activities of DNV-GL and SDARI (Sanghai Ship Design and Research Institute). 

WHY IS GREEN DOLPHIN 575 UNIQUE?

FUEL AND ENERGY EFFICIENCY: 

• Main particulars have been optimized by systematic RANS CFD analysis and resistance tests to obtain a better speed and less fuel consumption.   

• To be specific, the design is capable of a 10 to 14.5 knots speed with fuel consumption of only 22.8 tons/day. This is the lowest ever specific fuel oil consumption rate among ships of the same class till date.
• The best part - Naval Architects must forget making it a rule in their minds about the effect of bulbous bow. The bulbs don't always increase hull efficiency and performances. Green Dolphin 575 was tested for better performances in realistic sea states 'without a bulb'.
• Fuel efficiency at low steaming speeds was further elevated by its adaptation with Watrsila's W5X62 long stroke main engine, driving a large diameter and low RPM propeller. That too, the propeller would be incorporated with a duct in front of the cap fins to reduce propeller hub vortex. The design is also capable of being operated at the same efficiency by MAN 5G60ME-C9.2

AVAILABLE VERSIONS:

SINGLE HULL STANDARD VERSION:

• Has a traditional bulk carrier cross section.
• It is compliant with the IACS Common Structural Rules.
• Higher cubic capacity than ships of similar class.
• Most suitable for free flowing type of cargo. For example: grains.

DOUBLE HULL OPEN HATCH VERSION:

• Double hull cross section enables box shaped holds.
• Wider hatch openings than the standard version. (Compare the top views of the standard and double hull versions)
• Made suitable for transporting packaged cargo.
• Three holds donot have hopper and wing tanks, enabling stowage of project cargoes and steel coils.
• Easy clean cargo holds.
• Container loading enabled on hatch covers, with lashing equippments.
• Packaged cargo loading enabled on hatch covers.
• Timber cargo loading enabled on hatch covers.

OPERATION FRIENDLY:

• Designed for widespread range of heavy bulk cargo.
• Dimensions optimized for operation friendliness in most ports.
• Designed for alternative loading wuring heavy cargo carriage.
• Holds equipped with compressed air supply, Carbon dioxide fire-fighting systems, and portable wash water systems on covers.
• GRP pipes for ballast and bilge lines, prevents corrosion.
• Tank tops are designed for stowage of heavy weight cargo like steel coils.
• 30 Ton energy efficient derrick cranes with variable frequency drives and 28m outreach.
• Prepared for cold ironing operations.

Alternate loading layout on Green Dolphin 575 with Holds 2 and 4 empty

THE MOST ROBUST BULK CARRIER DESIGN TILL DATE:

LSD

Article By: Soumya Chakraborty

Author's Note: This article is the first of its type at LSD. The core value behind the initiation of this series (Ship of the Week) is to share the technologies and devolopments made on ship design. The images are not owned by LSD and full credit goes to the owner of the images. There shall be an article under this series every week.  I hope they help you knowing about one new ship every week. Do visit the links tagged with a few terms in this article. It would only increase your knowledge and not take away your time. Thank You for reading. If you have any queries or suggestions, please comment. You may also write to learnshipdesign@gmail.com

What's with the Bulb? - Part One

Shipping has always remained the backbone of world trade contributing over 90% of the total trade. The world economy would collapse and it would be impossible to transport the vast quantities of food, raw materials and manufactured products without shipping. As the economy prospered the demand for long range cruisers increased and so did the requirements to enhance sea keeping and efficiency. Lots of money was spent on research and experiments to find out that one innovation which would promise to save money and improve comfort at sea.

In the late 50's and 60's research was undertaken to reduce drag on large commercial cargo ships. With the development of Naval Architecture came efficient model testing, this along with advanced knowledge of Hydrodynamics led to the creation of the Bulbous bow which was formulated typically to provide 5% reduction in fuel consumption over a narrow range of speed and draft. This was significant for a large ship crossing vast oceans at the time when the price of fuel was rising. As the market for displacement ship opened up, Naval Architects began to innovate the design of the bulbous bow to provide more efficacy.

Although available in various shapes and sizes, generally the bulb looks like a section of a pipe with large diameter with a domed end sticking out of the bow of the vessel. Today, it's a very rare sight to find a large ship without a bulbous bow. Their results have been proven over a countless number miles in all kinds of weather by all kinds of vessels. LSD

 For Part-Two click on the following link http://lshipdesign.blogspot.com/ .

Article By: Tanumoy Sinha

Author's Note: This article is the first part of the topic 'What's with the Bulb?'. It gives us a very brief introduction about the need of a bulbous bow followed by a general description of it. This article was written keeping in mind that the reader has a very little knowledge about the bulbous bow. The up coming articles would focus upon the various types and hydrodynamics of the bulbous bow. The picture used above does not belong to LSD, and full credit for the same goes to their respective owners. If you have any queries or doubts, write to me learnshipdesign@gmail.com.

Know A Ship - RoRo Ships- Part One

Ro-ro is an acronym for Roll-on/roll-off.Roll-on/roll-off ships are vessels that are used to carry wheeled cargo.The cargo could be anything from your car or private helicopter to a train carriage antique like the dining car of "The Orient Express".Today this vessel has grown from its humble origins of that of a Train Ferry to the New MV Tønsberg, the largest car/truck carrier, a video of the same has been included below this section.

RO-RO VESSELS HOW AND WHY?

It is not just size that determines how these vessels have evolved through the years to fit certain standards and practices but other factors play a crucial role too as although automobiles are highly traded commodities,cargo of other kinds are also sometimes taken along-with on board.This introduces certain variations in design and corresponding structural characteristics.

The cargo-carrying section of the ship is a large open deck with a loading ramp usually at the aft end or bow or sometimes both ends to facilitate faster loading/unloading process.The cargo may be driven aboard under its own power or loaded by carriers with straddles or fork lift trucks.

Here is picture of a Ro-ro vessel with a bow ramp and door.

  

  And Here is one with a stern ramp and door.

A SLICE OF HISTORY:                                                                                                                          The first ships of this type were the Ferry, equipped with railways to allow the transport of train carriages between the margins of the rivers that were too wide for bridges.One of the first ferry ships,the Forfarshire was built in 1861.

The use of the Ro-ro concept in merchant ships started in the late 1940’s, early 1950’s, mainly in short-sea routes.

Today,these vessels contribute to many sea going trade purposes and military operations.They are even being considered on being introduced in the luxury market currently dominated by cruise liners and yachts.

Dynamic Positioning System - Part One

Unlike olden ages when ships were only used for cargo trades and passenger transport purposes, the present era has a lot more to do with ships. Ships are now not only used to transport cargo, but operations like mid-ocean research activities, underwater pipeline laying, dredging, sea bed drilling have also found themselves on the priority list. The offshore industry has also evolved rapidly from the primitive jacket platforms to the present day SPAR Platforms, Tension Leg Platforms, Semi-submersible platforms, Floating Production Storage and Offloading Vessels (FPSO), etc. Among these, certain category of ships and offshore structures are required to operate at conditions in which their movements and stability in maintaining positions at even the roughest seas must be controlled to the highest precision. 

You must have seen a helicopter hovering over an area, without gliding either way from its position. Well then, how is that done by ships? Dynamic Positioning System- A technology that was developed in the 1960s, which is designed to assist a vessel or an offshore structure to either maintain perfect station keeping or precisely follow a predefined path at sea; even at the roughest sea conditions where wave heights may rise to 21 meters. 

The dynamic positioning is a computer controlled system that uses a combined operation of underwater tunnel thrusters, propellors and rudders to assist the structure in maintaining its position or track. The entire system is controlled by a combined action of sensors, GPS, and mechatronic systems onboard. The range of operations carried out by vessels equipped with DP is wide today. Some of them are:

1. Gravity Coring.
2. Drilling (Oil Exploration)
3. Oil Production Drilling
4. Diving Support
5. Pipe and cable laying operations
6. Flo-tel Services
7. Hydro-graphic survey purposes
8. Survey of wrecks at sea
9. Dredging
10. Underwater rock dumping
11. Heavy lifting operations
12. Platform supply
13. Shuttle tanker offtake operations
14. Oceanographic research activities
15. Underwater mining practices

The only reason why DP systems are used is their efficiency and redundancy. Efficiency in the sense, DP systems are precise to the orders of few meters (50 meters of precision at open sea is equivalent to a precision in micrometers in brain surgery). The redundancy of DP systems is sufficiently reliable; that is, if one computer control system fails, there are three more backups to keep the operation running without a single glitch.  

In this article various applications of DP systems have been explained with appropriate examples to ensure the realization of the necessity of dynamic position in the modern day operations at sea. The original article is divided into parts. Each part would deal with a couple of DP System applications in different ships or offshore structures.

• Dynamic Positioning in Cruise Ships:

Ever wondered how does the captain of a cruise ship manage to dock the monster vessel with centimeters of precision in spite of the space constraints at the port? That's correct. Dynamic Positioning is also used in cruise ships for counteracting the challenges faced during berthing at shallow draft ports. Not only that, it improves the flexibility of the ship and avoids the requirement of anchoring in areas where the sea bed is sensitive. Note in the video below, how the Queen Mary 2 berths precisely at ports using its DP System.

• Dynamic Positioning in Pipe-laying Ships:

Subsea pipelines and cables are layed for transfer of gas, oil, and communication lines across oceans. With today's cutting edge ship design it is evident that ships are well built to carry out the laying of these pipelines and cables on the sea bed. These operations are highly risky with big money at stake. Any damage to the pipeline or the vessel itself during the process can jeopardize the entire operation. To understand why such a vessel would require a DP system, it is important to first know how pipelines are laid on the sea bed. 

Subsea pipe laying operation

Pipe segments are welded in a weld assembly line within the pipe laying vessel at then passed on to the sea bed through the aft of the ship. The pipe emerging out of the assembly line is supported at the aft by a steel structure called the stinger. In spite of being made of stainless steel, the pipe is nothing but a strand of thread when lowered into the ocean. Thus, it forms a curved shape right from the end of the stinger to the touchdown point, where it touches the sea bed. As the ship moves forward, the pipe is laid on the sea bed. Due to a pre-designed map of the pipelines, the ship is required to follow the track exactly without any room for error. If the tension in the entire line is lost, the pipe would buckle at the touchdown point and the entire operation would shut down. Precise calculations are done to predict all the parameters before the operation is commenced. 

One could wonder what would possibly have happened if a strong wave hit the ship at the time of operation. Or, what is the ship failed to follow the predefined track along which the pipe was to be laid? Once the pipe is laid, it is almost impossible to lift it back up. The saviour here is again Dynamic Positioning System onboard the vessel which keeps the ship constrained against any sway or yaw motions, maintaining a predefined surge (forward movement of the ship is called surging motion). The DP system also controls the movements of the ship according to the tension in the emerging in the pipeline, resulting in overall dynamic control over the entire process. 

You can read the second part of the series here. Note in the following video how the world's largest pipe laying vessel MV Solitare uses its Dynamic Positioning to lay pipes in the worst sea conditions. LSD

Article By: Soumya Chakraborty

Author's Note: This article is the first part on Dynamic Positioning Systems. Prime focus has been laid on basic understanding of DP systems and two applications of the same have been depicted with videos and illustrations. I have written this article based on my experience and technical knowledge on the same as a Naval Architect. The videos and the figure donot belong to LSD, and full credit for the same goes to their respective owners. The second part of the article would deal with how dynamic positioning is used in Drillships. If you have any queries or doubts, write to me learnshipdesign@gmail.com

Marine Industry- How INNOVATIVE?

What do you think is the biggest difference between the ship building or design industry and any other industry in the world? Size- that's what your answer would be. Correct it is! A ship is indeed the largest man made self propelled structure ever constructed by the human civilization. Let alone size, you see there is another departure from the kind of practices this industry indulges in, which sets it aside from all the others. Innovation. To be more specific, it would be better to put it this way that the rate of innovation required for this discipline to keep facing challenges is way higher than what is required in the aviation or let's say, the electronic and IT industries. 

The score of questions in your mind now are to be answered by this example. Think about how design and production goes on in a laptop production company. Once the design for a laptop is laid out and approved, it is finalized that a certain number of products pertaining to that design would be produced in bulk. In case of the automobile industry, it goes the same way. Yes, modified versions are designed based on neccesities of innovation and renovation, both. But it is certain that a successfull design in every industry would correspond to a bulk of products. Well, that doesnot work in the shipping industry. Here, every ship sailing at the sea has an unique design of its own. When a ship is ordered by an owner, the ship is not produced from an existing design of an already sailing vessel. That is simply not done. The reason is really simple. Every ship in this world is designed specially for its type of cargo, the sea routes it is supposed to follow, the sea states it is likely to encounter, the time for which the ship can sail continuously without docking, and the list is longer. This gives rise to a requirement for extensive modification and renewal in design of every new ship that is being built. 

So innovation in this industry is the key to its survival against the challenges of nature. Every ship sailing at the seas not only has something new in its design but also lack certain design aspects which are taken care of while designing a new ship. It is a constant innovation and feedback based improvement process. If an owner places an order for three ships of the same kind, you are wrong if you presume all three would have the same design. Well, then what is it? The layout below depicts how, the feedbacks from the operational results of the first model would be used as basis for innovative steps in the devolopment of the second model. Note the overlap in the time spans for production of each model helps in keeping up the neccesary innovations for the upcoming model.

Design and Production Layout in Shipbuilding Industry

It means, the shipbuilding industry is constantly in the verge of changes, powered by rigorous research and devolopments that are carried out by various Research organizations and Companies all over the globe. The ethics and needs of this discipline subject proffesionals like naval architects, ocean engineers and hydrodynamists to challenges forever. Ship Design and Construction has changed since the first ship set sail and with the magnitude of research and technical devolopments practiced in this field, the tendency of constant changes is probably never ending. LSD

Article By: Soumya Chakraborty

Author's Note: This article has been written on the basis of analyses made on the trends of the ship design and ship building industries. LearnShipDesign is coming up with many more articles pertaining to every aspect related to maritime technology and the industry. I encourage you to read them and most importantly, share them with students and budding engineers. In case of any queries or feedbacks write to learnshipdesign@gmail.com

Our Vision

Ships have been, and still are the most efficient machines facilitating trade in the world. Ever since the first wooden boats transformed their efficiency and size into steel ships, the design of these marine structures have been evolving every now and then, based not only on the varying amount of trade, but also depending on technical obstacles faced in the available designs. Design, Operation and Maintenance of ships and marine structures require a blend of a wide spectra of engineering disciplines, coupled with economic and market analyses. It is due to these widespread applications in the process that the profession of Naval Architecture has evolved from being focused in the architecture of ships to a conglomeration of mechanical, civil, structural and hydrodynamic engineering along with disciplines of engineering economics. 

Today, Naval Architects are the most important people responsible for the design, production, operation and maintenance of ships, offshore structures, submarines and other marine structures. That is because, professionals in this discipline have practiced the art of blending technology with economics and ergonomic needs.

Education and Research in this discipline is practiced in universities all over the world today. With more challenges already piling up on the list, it happens to be the budding Naval Architects, Marine Engineers and Hydrodynamists who will be the minds behind the best innovations in the sphere of marine technology.

Learn Ship Design is the world’s pioneering initiative of a dedicated team of Naval Architects to share and bring to light the technological aspects of the maritime field. Today, a kid knows less about ships than he would about planes, space crafts or robots. Not because students don’t like to know about ships or because planes whiz through the air and that robots can help make their morning drinks. It is due to a lack of sharing of knowledge, facts, technology and possibilities that one could find related to the technology on the seas. We know less than two percent about the space, and guess how much have we known about seas and oceans? Lesser.

At LSD, we try to share everything one would want to or possibly afford to know about marine technology whether it is related to ships, submarines, offshore oil rigs or the behaviour of the oceans. We encourage passionate children, students, budding engineers, and professionals to not only learn from this but share the same.