Are cruise ships safe for the marine environment?

by Charles Roring

Cruise ships are beautifully designed to attract prospective passengers to go on voyages heading to a number of destinations such as the Caribbean islands, the Great Barrier Reef of Australia or to Alaska. In recent years, the passenger carrying capacity of cruise ships is getting higher. Ship designers or naval architects tend to construct ships that are bigger from year to year. The reason behind this is the economy of operation. Ships whose carrying capacity is high can lower the operational cost thus bringing more profits to the investors or the ship owners.

Newly designed Carnival cruise ships can carry up to 5,000 people each. This number is the same as the population of a village or a small town. From the technical point of view, such ships will have at least 2,500 rooms to accommodate the passengers.

These passengers need food and water during the voyages to their destinations. After the food and the water is consumed or used, they will become waste. Such huge amount of waste needs to be processed and released from the ship. This waste is a problem for the marine environment.

In addition, for the efficient operation of the cruise ships, the underwater hulls of the ships have to be kept clean from fouling. Usually, shipbuilders apply anti fouling paintings which are chemical substances that are dangerous for the environment. Although less toxic paintings have been introduced to the market of shipbuilding industry, they are still toxic which are harmful for the environment.

So, the challenge which we have to face and solve is making the cruise ships that are safe for the environment. Also read: The Speed of Ship and Propeller Pitch

Is traveling with cruise ship still an attractive adventure?

by Charles Roring

Traveling with ships is still attractive for people who are not busy or racing against time. In my previous article about traveling with cruise ship or yacht, I said that yacht is more flexible for those who like to experience sea voyages that are not in accordance with regular shipping route. Whether you travel with large ship or boat, the speed of these floating structures is much slower than airplanes. So, traveling with ship won't be attractive for those who want to attend an urgent business meeting in Tokyo while he lives in New York. The best thing to do is of course going there by airplane.

People will choose ships because of several reasons. One of them is the enjoyment which they can get when they are on board of a luxurious cruise ships. Passengers of airplanes cannot move around whereas passengers of cruise ships can spend the long voyage time by dancing, singing, sunbathing, gambling, or just standing along the port and starboard sides of the passenger ships to enjoy the mysterious beauty of the blue ocean.

In developing countries such as Indonesia and the Philipines that consist of thousands of islands, traveling with ships is still the most affordable mode of transportation. Ships are vital transport vehicles for people particularly when they want to go to other islands.

Some experts might say that with the improvement in economic condition, people will prefer to travel by planes even in island countries such as Indonesia and the Philipines. Yes, they can be true, but the habit of living in unity with sea water has been the habit of millions of people in both countries for centuries. Remember Indonesia and the Philipines, and to some extent the Carribean are maritime countries. So, I see that there are many wealthy Indonesian who still travel by passenger ships although they can afford for the first class tickets of airplanes. Why they are reluctant to go by airplanes? Because the sea has been part of their daily live. And this has been going on for generations.

Even though there are now a lot of airline companies operating in Indonesia, millions of people still travel with passenger ships. The recent frequent plane crash shown on TV news is also one of the reasons. I don't say that PELNI, as the largest passenger ship line in Indonesia, is now in safe position. With growing competition with other shipping companies and the rapid growth of airlines especially for long distance trips, passenger ship line such as PELNI must improve her professionalism to better serve her customers. Ships have to be maintained in spotless condition so that passengers will feel comfortable and the crews must show respect and provide better service to their passengers. I believe that the market of passenger ships in Indonesia is still large and growing.

So, my answer for the above question is definitely yes. You will find it more adventurous if you bring with you digital camera or handy cam which you can use to take some beautiful pictures or videos of your sea voyage and enjoy them later after you arrive in your next destination. Also read: The interior of passenger ship and cruise ship and Cruise ship and passenger ship

The Speed of Ship and Propeller Pitch

by Charles Roring

The speed of a ship is closely related to the resistance and propulsion characteristics of the ship. One of them is the propeller pitch. In my previous article, I explained in detail about the propeller pitch ratio. The pitch ratio of a ship's propeller is usually determined from Bp-delta diagram after the delivered horse power or DHP, the rpm of the main engine at the designed vessel's speed and the speed of advance, as well as the diameter of the propeller have been obtained during the propulsion calculation.

So, increasing the pitch of a propeller will not automatically increase the speed of the designed ship. Pitch ratio is not an independent propulsion parameter. There are other propulsion factors that influence the propeller pitch which have to be taken into account during the design process of a ship.

In cruise ships or passenger ships that require high maneuverability, the number of propellers can be more than one. Also there can be consideration to install bow thrusters to help the ships maneuvering in ports and resticted waters.

The speed of ship in fixed pitch propeller is always controlled by the controlling the rpm or the speed of the main engine. In modern ships, the control of ship's speed can also be done with the application of controllable pitch propeller. So, the speed of the ship can be varied through the adjustment of pitch and the speed or RPM of the main engine. In addition, ships such as cruise, and passenger ones that are installed with CP-Propeller can move backward. Such maneuvering capability is highly needed when the ships are arriving or leaving a port. For more discussion about propeller pitch and its relation to the propulsion characteristic of ships, I suggest that you read my other articles: Pitch diameter ratio of a propeller and engine performance of a ship and Propeller Mean Pitch Calculation

Watertight bulkheads in cruise ships and theory insubmersibility

by Charles Roring

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Cruise ships have many accommodation rooms for passengers. Yet, they don't function as watertight bulkheads which are important in protecting the ships from sinking. How Titanic sank, during her maiden voyage, raised questions to many people whether modern passenger ships may face such tragic accident at sea. All ships may face accidents at sea and it is the responsibility of naval architects to design ships that are stable and cannot easily sink if their hulls are broken due to collision with iceberg, other ships or explosions.

Naval architects when designing ships know that they have to divide the ship into a number of smaller compartments as a preventive action to protect the ships from easily drowning in case if they experience fatal flooding during their voyages. As a standard, there will always be forepeak (collision bulkhead) and after peak tanks, and double bottom tanks in large ships. To give more protection to the ships, naval architects will add some watertight bulkheads, according to the rules stipulated by classification societies and the calculation of flooding table which was introduced for the first time by Admiral Makarov and A.N. Krylov, two scientists from Russia.

The shameful defeat of the Russian Navy from the Imperial Japanese Navy during the naval battle of Tsushima on 27-28 May 1905 encouraged Russian Naval Scientists to thoroughly review the designs of their warships especially the battle ships. During the naval battle, the Russians lost two thirds of their entire fleet. The defeat inspired A.N. Krylov and other Russian scientists to introduce the concept of insubmersibility which in most western naval architecture textbooks are known as watertight subdivision.

When I was still studying Naval Architecture in Pattimura University in Ambon of Maluku islands, I was introduced with this concept. Insubmersibility, according to the book entitled Statics and Dynamics of the Ships written by Semyonov and translated into the English language by Maria Konyaeva, is the ability of a ship to remain afloat when one or more of her compartments brake and are flooded with sea water. A.N Krylov formulated that when a compartment is flooded with water, one or some compartments have to be filled with water to restore her stability. In addition, he introduced the concept of dividing ships, especially naval vessels, with smaller compartments to protect them from sinking. The development of the insubmersibility study of naval vessels led to the introduction of 100 percent insubmersibility concept. This is a very innovative idea which was formulated by A.N. Krylov and other Russian scientists. In this concept, a war ship will remain a float, and still have her fighting capability although her whole compartments are broken during a naval battle. The theory of reserve buoyancy is thoroughly discussed in the book to support the concept of 100 percent insubmersibility of a naval vessel. I find that insubmersibility is a brilliant idea from Russian naval scientists which naval architects from around the world should study. The subject is well presented in the Statics and Dynamics of the Ships. If you are interested in studying this subject, I suggest that you read the book. It is now offered on the internet. Also read: The interior of passenger ship and cruise ship and Cruise ship and passenger ship

Traveling with Cruise Ship or Private Yacht?

Cruise ship and private yacht, although different in size, are constructed for the same purpose. They are ship and boat that will carry their passengers to enjoy the beautiful scenery of the ocean and islands around the world.

Cruise ships, because they are mostly bigger in size, cannot travel like tramp. They are cruise lines. Cruise lines or shipping companies such as Holland America, Carnival and Silja have ships that travel along definite routes in pre-planned schedules. So, if you buy a ticket to Carribean islands, you cannot, in the middle of the sea, ask the captain to change the voyage route to the Pacific islands. Cruise ships are large and luxurious floating hotels with many facilities enjoyed by thousands of people on board. There are restaurants, gambling floors or casinos, movies, massage and spa treatment center and of course dance hall. Today, almost all modern cruise ships provide massage and spa treatment to their customers. They can enjoy deep tissue or relaxation massage while the vessels are in the middle of the sea heading to an island in Caribbean countries or to the tropical Bali island in the Republic of Indonesia. A lot of passengers say that they really like the relaxation massage and spa treatment particularly when the their ship was sailing through a bad weather. 

Different from cruise ship, private yacht is build to cater for wealthy customers. Some even buy their own yachts. Due to its size, although it is luxurious, yacht does not have the facilities that a cruise ship has. For larger yacht, there are some cabins to accommodate guests on board.
Most cruise ships are mono or displacement hulls whereas for yachts they can be displacement or catamaran hulls. Yacht owners who prefer to travel across the sea in higher speed will prefer to order or have their yachts built in catamaran style.
Yacht is more flexible in terms of its voyage. It can go anywhere according to the order of the owner or the customers who rent it. The travel range of cruise ship is longer than yacht due to its fuel tank capacity. In addition, if you plan to cross Atlantic or Pacific oceans, then I suggest that you take cruise ship. It is more stable and safe (read my other article on this issue Stability of Cruise Ship). But if you plan to have more private time with your loved ones traveling around the beautiful islands of the Carribean and the Hawaiian, then the better choice will be to rent a private yacht. So, the choice is yours. Happy traveling. by Charles Roring Also read: The interior of passenger ship and cruise ship and Cruise ship and passenger ship;

The interior of passenger ship and cruise ship

In my previous article about the Cruise Ship and Passenger Ship, I mentioned that both ships are built for transporting people but their purpose of service is different. For passenger ships, the faster they reach their destinations the better their services will be. For cruise ships, the more the passengers spend their time aboard the ships the better should be the service of the ships. When passengers spend more time inside the cruise ship, the companies that own the ships will get more profit. These differences in purpose of service determine the interior of the ships. Please, read Oasis of the Seas Interior if you want to know more about how a Cruise Ship looks like.

In passenger ships, cabins for accommodating passengers are grouped into several classes of passengers. They are Class 1, Class 2, Class 3, Class 4 and Class Economy. The facilities in Class 1 will definitely be different from facilities provided for economy class passengers. Class 1 passengers have their own private bed rooms equipped with a television set, and wash rooms whereas the economy class passengers sleep in large halls similar to school dormitories or military barracks where some 50 to 100 passengers sleep in one large compartment.

For cruise ships, naval architects prefer to design the cabins with smaller range of classes. A cruise ship may only have VIP and First Class. Every cabin is designed to accommodate two passengers. It means that the ships are designed for couples who like to enjoy their ocean travel in their own private rooms that sometimes overlooking the blue ocean. Rooms and facilities in cruise ships are usually more spacious. Some ships even have casino or gambling floors and golf floors.

For short distance travels across a straight or gulf, naval architects prefer to design small ships that are fast. The choice for this requirement will be catamaran or swath ships that have higher speed with water jet or highly skew propellers as their propulsion systems. The use of highly skew propellers greatly reduces the vibration which is the main issue in passenger ship design.

the interior of Iris catamaran passenger ferry with capacity of 240 passengers. It looks similar to the interior of an airplane. There are not any bedrooms for fast ferry because the duration of sailing is between 1 and 2.5 hours. A TV set is usually installed to entertain the passengers. I haven't seen any catamaran whose passenger cabin interior has tv set in every seat as what we now see in modern first class airplanes manufactured by Boeing and Airbus.

Besides designing lavish and comfortable interior for ship cabins, the material choice for passenger and cruise ships are chosen from the ones that are strong, light weight and most importantly fire resistant. Port and starboard side cabins of cruise ships may have walls that are fully made of glasses to enable the passengers to enjoy the beautiful scenery of the islands or the blue ocean as the ships go by.

Although the facilities and cabins of passenger and cruise ships are different, the life-saving equipments for these ships are the same. When accidents happen, each crew and passenger will have his own life jacket. The capacity of life boats and life rafts are usually double the number of passengers aboard to ensure that all passengers can survive at sea. by Charles Roring

Cruise ship and passenger ship

Cruise and passenger ships are ships that transport people from one port to another. Although these ships look similar, they have different purposes. Cruise ships usually emphasize their services on cruising experience for passengers aboard with various facilities such as restaurants, movies, sun-deck, swimming pool, sport centers, message and spa rooms. Cruise ships, to some extent are the same as hotels. In other words, cruise ships are floating hotels for sea or ocean travelers. Therefore, many cruise ships sell round-trip tickets and have voyages that are longer than passenger ships.

Between 1800s and early 1900s, passenger ships are transport oriented ocean liners that bring passengers and goods from European ports to American ports. Millions of migrants moved from Europe to America using passenger ships. One of them is the unfortunate RMS Titanic. During that time, the faster the voyage the better the service of the ships and the higher would be the profits they could get due to the reduced operational cost for every trip.

Indonesia's state owned shipping line, PELNI, operate dozens of German made passenger ships to serve the ever growing Indonesian passengers. Indonesia has more than 17,000 island which makes it as the largest archipelago in the world.

With the advent of large passenger airplanes in 1960s, travelers switched from ships to airplanes. For transatlantic service, the passenger ships ceased their operation in 1986 whereas in many other parts of the world such as in Mediteranean Sea, the Indonesian islands, the Philipine islands, and the Pacific islands, passenger ships still play very significant role in transporting people and goods. Indonesian government, through its state owned passenger liner - PELNI, has even bought more passenger ships from Germany to meet the increasing number of people moving from one island to another. For smaller islands where the number of population is small, PELNI operates smaller passenger ships which are constructed by local shipbuilders such as PT PAL. It is the largest state-owned shipbuilding company operating from Indonesian Naval Base in Surabaya city.

Passengers and porters in Manokwari of Papua were waiting for the just arrived Indonesia's PELNI's passenger ship, MV Nggapulu. The ship can carry 3,000 passengers. The ship was built in Germany.

As the largest archipelago in the world with tens of thousands of big and small islandss, Indonesia will constantly need a lot of ships and boats to support the mobility of its people and economic activities of the country. It is not surprising to see that every new year more passenger ships are needed in this country to serve the increasing number of population. The potential market for passenger ships and RORO or ferries in Indonesia is huge compared to cruise ships due to the purchasing power parity of the people. The same situation may also be seen in the Philipines where people need more passenger ships than cruise ships. Yet both countries have potential market for cruise ships operation especially for middle to upper class citizens.

While the market for cruise ship in Asia is still small, the market for North America and Europe is still growing but with high competition. Cruise ships operators such as Holland America lines, Royal Carribean International, and Carnival Cruise Lines are launching new ships to meet the increasing number of tourists who prefer to spend their precious time on various recreational activities both on board of these luxurious floating hotels or on exotic resorts in private islands of the Carribean sea.

With the improving economic growth in Indonesia, Malaysia, Thailand, Singapore, Vietnam, and the Philipines and other ASEAN countries, the potential market for cruise ships in this region will attract cruise line operators to invest billions of US dollars and Euros in building new cruise ships. It is now a matter of time for us to see hundreds of luxurious passenger liners and cruise ships operating along the seas of South East Asia. To realize this economic and business potentials, Governments of ASEAN countries need to be approached by investors to open their market for the development of ocean tourism and traveling industry through a number of deregulation in tourism sectors of the region. by Charles Roring Also read: Stability of Cruise Ship and The effect of turbulence on propeller and safety of cruise ship

Stability of Cruise Ship

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In initial stability assessment, naval architects will always have to make sure that the cruise ship they are designing has positive GM. It is the distance between the center of gravity of the ship and the metacenter, an imaginary point which is created when a line from center of buoyancy is vertically drawn and intersect with the vertical axis of the ship that passes through or divides the ship into two equal halves. Watch the following video where naval architects conduct model test to assess or to find out how stable the  Oasis of the Sea , a new cruise ship will be when it has been constructed into full scale. Cruise or passenger ships are sophisticated floating structures that are constructed to transport people from one place to another. Today's modern passenger ships are equipped with advanced navigational equipments that will help the ships' crews handle the ship safely.

In addition, cruise ships or passenger ships now have more decks which make them taller. An example of such ship is Carnival Destiny. This beautiful ship is built by Fincantieri Cantieri Navali in Italy and classified to Lloyd's Register, one of the best and the most experienced classification societies in the world. Besides having 16 decks, the luxurious cruise ship has a swimming pool at the top or sun deck. From the stability perspective, the mass of water in the swimming pool raises the center of gravity of the ship.

In addition, the taller the superstructures, the higher will be the center of gravity. Ships that have higher vertical center of gravity (VCG) will have smaller righting lever, GZ. Such condition is dangerous for traveling around the ocean. To have lower VCG or higher metacentric height (GM), ship designer will balance the passenger ship with ballast tanks that are filled with sea water.

In addition, ship designer will use lighter materials such as composite materials, aluminum, plastics and wood, for higher decks so that increase of height of CG will not jeopardize the ship's righting lever (GZ). Ship with larger GZ will be more stable compared to ship with smaller GZ. The ship will be unstable if the metacentric height is zero or negative.

Source: K.J. Rawson and E.C. Tupper, Basic Ship Theory 1, page 105

Cruise ship with positive GM will be more stable when sailing at sea. The position of VCG (Vertical Center of Buoyancy) depends on the loading condition. Sometimes when there are too many passengers on the uppur decks, ballast tanks which are at the bottom of the ship will be filled with sea water to balance the ship and to lower the position of VCG and balance the LCG.With this arrangement, the ship will be stable and safe to travel across the ocean around the world.

Also read:  

• The effect of turbulence on propeller and safety of cruise ship and
• Ship Displacement and Capacity Limitation

The effect of turbulence on propeller and safety of cruise ship

by Charles Roring

Naval architects or ship designers when designing a marine vehicle will always have to design the propulsion system according to the designed speed stipulated or required by ship owner. The most common form of propelling device in ships or boats is propeller.

When designing the propeller, one of the propulsion factors which they have to determine is the blade area ratio which is the ratio of the blades' area compared to a disc area with the same radius as the propeller blades. The developed area ratio (DAR) of a propeller is determined from cavitation chart, commonly Burril chart, obtained from experiments of a number of propeller series conducted by various cavitation tunnels around the world. Cavitation occurs when the flow of fluid, or sea water, is not steady. In other words, when there is turbulence, cavitation will occur in ship's propeller.

Now the question is will it be harmful to passenger? My answer is No. If there is turbulence in the propeller of airplane, my answer will be different. Turbulence which causes the cavitation of propellers in ships is not dangerous for passenger ships but will be very dangerous to airplanes. The safety of passengers in cruise ships will not be jeopardized if there is turbulence or cavitation in the propellers.

The effect of cavitation is the loss of lifting force on propeller blades. If this term is confusing then the simple explanation for the occurrence of turbulence and cavitation is the loss of thrust that is required both in ships and airplanes. The loss of thrust is the same as the loss of speed. Ships will remain afloat whereas for airplanes, they will fall. This is the most common cause of plane crash. In bad weather, the flow of the fluid is not steady. It is not good both for ships and airplanes.

Cavitation causes erosion on blade surface of the propellers. It also increases the rpm of propeller which in turn, will cause vibration, and overheating in the main engine. The most common solution which naval architects do to minimize the cavitation of the propeller is increasing the blade area ratio. Also read: Ship Displacement and Capacity Limitation and Traveling with ship; Propeller Rake and Blade Thickness Diameter Ratio

The Management Principles of the Toyota Way

All of us know what Toyota is. It is a giant automaker from Japan. This company was a small company in the rural areas of Nagoya during 1950s. Now with around 240,000 employees, Toyota Motor serves millions of car owners around the world.

Gemba is a Japanese term for "the actual place," while "kaizen" is the Japanese terminology for continuous improvement. So the phrase "gemba kaizen" means continuous improvements at the actual place. The main theme of Toyota Way management principles is the elimination of wastes along the production line of Toyota automaker to create the highest added value of the products to satisfy customers.

According The Toyota Way, a book which was written by Jeffrey Liker, Toyota has developed and standardized its management principles since 1950s when the Japanese were trying to recover from the ruins of Word War II.

After reading the book, I can conclude that the fourteen management principles can be applied to any business. Everybody who has not read the book might think that the Kaizen is only effective for automakers or manufacturing companies. But the principles such as grow leaders who thoroughly understand the work, live the philosophy and teach it to others are applicable to all companies.

When Toyota was still a small company it had to face many challenges during its operation, from the lack of capital to the competition with other world class automakers. It is amazing to see that Toyota now is a world leader in car industry producing the best quality cars for all market segments. Toyota tremendous achievements are reached through the application of Toyota Production System (TPS). Toyota emerges as the best automaker in the world that manufactures the most fuel efficient cars. The Toyota Way inspires many companies to streamline their operations. 
Also read: Car Manufacturers Develop Air Bag for Pedestrian

Implementing Kaizen and Hansei in Retail Business

I am reading a book entitled The Toyota Way these days. This book is written by Jeffrey K. Liker, Ph.D. The book is about how to understand fourteen management principles which has been used by Toyota, the best automaker in the world, and how to implement them in our own business.

Toyota Hilux G Series the preferred transport car in Arfak mountains

Toyota Prius

Actually, I used to read some short articles about Gemba Kaizen management system but it was a long time ago.
Kaizen is a Japanese word for incremental or continuous improvement whereas Hansei means reflection. In the US, the concept of Kaizen is similar to the principles of Lean Management. When I run my bookstore, I feel that I need to make many improvements in the business. But I think that this small retail shop is totally different from the giant manufacturing industry - Toyota.

We all know that Toyota produces the best selling cars in the world but thinking or applying their management system to my small bookshop might be an incompatible approach.
In fact, after reading the book, I am surprised that Kaizen and Hansei can also be applied to any kinds of business including small, medium and large companies. There are always rooms for improvements. For instance, when I stand in the middle of my bookstore watching the display of the books, how the shelves are arranged and how the books are sold, I know that there are still many things that I need to do to improve my service to customers.
One of the most important things the Toyota Way teaches to its readers is the elimination of wastes in all segments of the production or servicing processes. These wastes include unnecessary movement of workers, defects in products, overstock, unnecessary transport, that do not directly contribute to adding values to the products or services we are about to deliver to our customers or consumers.

How these wastes are eliminated. The answer is through the implementation of hansei and kaizen. Hansei means that we have to identify the wastes first. To be able to identify the wastes, we have to monitor the manufacturing process, or the servicing process at the place where it happens. After identifying the wastes, the next step is implementing Kaizen. Improvements after being implemented have to be maintained. This means that we will not create or let the wastes to happen again.
In retail business, we sometimes order things that are really not requested by our customers. To minimize the occurrence of excess inventory, we need to provide order forms or wish list where customers can place their orders. Retail manager must use this list to order merchandise from manufacturer. If we can apply this process into our retail process then we can minimize or prevent the occurrence of excess inventory and at the same time increase profit to a maximum value.
I have applied this method for more than year now and the result is amazing. I am able to triple the monthly profit of the bookstore by just providing order form of wish list near the cashier table. Collecting wish list from customers can be a tedious job but it will streamline the whole performance of the business. Customers cannot find the books that they are looking for, they can write the titles; authors, and if possible the publishers of the books. We then order the books from our partner discount bookstore. When they have arrived in our bookstore, we will call or send sms to our customers. We only need one to three days to sell all the books which have just arrived in our inventory. Improvements must be done at the place of the process (gemba).
Buy some books about Kaizen from the following Amazon.com online store if you are interested in learning more about it.



I have seen that Hansei and Kaizen really work when I apply them in my bookstore. I recommend this book to all of you, business owners around the world to read the book and adopt the management principles of the Toyota Way and the Toyota Production System, of course with some adjustments, into our business. by Charles Roring in Manokwari of West Papua of Indonesia

Car Manufacturers Develop Air Bag for Pedestrian

Recently, NHK, a Japanese national TV station screened a news which says that Japanese car manufacturers are now developing technologies that can protect pedestrians from suffering fatal injuries or deaths during a street accident. Such technologies include speed and pedestrian sensors, as well as air bag, for pedestrian. The sophisticated and expensive equipment will be installed at cars' bonnet or hood. If a pedestrian stands in front of a fast moving car, the pedestrian sensor will instruct the computer to activate the car's brake to prevent it from hitting the pedestrian.

Toyota, a leading car manufacturer is developing this technology. One of its shareholders has requested this accident prevention technology to be developed and installed in cars after his daughter was hit by a car several years ago.

According to a researcher in the car industry, installing such equipment will be considered very expensive for car buyers. The additional price of such pedestrian sensor and air bag is 6,000 US dollars per car. Many car buyers do not see such technology or equipment as a must for their cars.

Japanese car manufacturers are trying to lower the cost so that the technology will commercially be viable for all cars. Until now only owners of luxurious that can afford for such pedestrian protection technology to be installed in their cars. by Charles Roring

Ship Displacement and Capacity Limitation

by Charles Roring in Manokwari of West Papua of Indonesia

Ship is the product of human engineering. It is intended to transport goods and people from one island to another. Ships support the progress of human life. People trade goods to every corner of the world with ships. In the same way, people also go around the world with ships. The invention of airplanes does not replace ships as the major transporter of goods and to some extend people.

The competition in business forced ship designers or naval architects to build ships that are efficient. Therefore, they tend to design and construct ships that are bigger both in displacement and passenger capacity. Ships that carry more goods and people are effectively more efficient than small ships.

But the construction or the design of ships should not only be seen from efficiency and dead weight tonnage. There are still other factors which ship-designer and shipbuilder have to think before a final design is approved for construction. Two of them are ship's safety and environmental assessment impact. For instance, if the newly designed ship is an oil tanker with a dead weight of 500,000 ton then it will not be wise to build it due to its potential environmental impact. This giant oil tanker might face an accident at sea. Oil spill from such tanker can be difficult to overcome due to the massive amount of oil which has to be contained and collected from sea surface. If 500,000 ton of crude oil covers the surface of the sea, it will block sunlight, and choke a lot of marine animals.

Such consideration also applies to passenger ships. Cruise ships that are designed with passenger capacity of more than five thousand people might not be wise to be constructed. It might be an efficient transporter but it will be dangerous if the ship face similar accidents to Titanic. Passenger safety should also be taken into account when designers want to decide the carrying capacity of a bus, a train, and most importantly a passenger airplane. Airplane that carries more than 500 people will be potentially dangerous for the passengers if it crashes. There will always be a possibility of accident at sea, land and air to all man made structures no matter how perfect or how advanced they have been designed and constructed. Also read: Traveling with ship; and Propeller Rake and Blade Thickness Diameter Ratio

Traveling with ship

by Charles Roring in Manokwari of West Papua Indonesia

Traveling with ships or boats has been a good choice for people living near the sea for hundreds of years. Ships help people traveling from one island to another.

When passenger airplanes were introduced some one hundred years ago, the number of people traveling by ships began to decrease. In recent years, the increasing number of airplane crash makes people worried about their safety. We can see that many airline companies release reports which say that they are facing bankruptcy. The real reason for the decreasing number of passengers, which they say, is the economic downturn. However, honestly we cannot ignore the psychological effects the news about plane crash brings to TV audiences. Although most of the accidents are caused by bad weather, some people who have watched such bad news are now considering of traveling by other mode of transportations.

In recent years, travelers are now considering ships as safe mode of transportation compared to airplanes. Traveling with passenger ships can be a boring voyage especially if the journey takes more than one day.

Therefore, ship designers or naval architects must design passenger ships as comfortable and enjoyable as possible. Modern passenger ships now are identical with luxurious hotels. They have such facilities as swimming pools, sun-deck, restaurants, movies, library, fitness centers, internet café, gambling hall, shops and even conference rooms. These facilities are provided to help the passengers feel relax so that they will be able to enjoy the trip rather than feel bored or anxious when looking at the dark color of the deep sea.

Besides, providing various facilities similar to luxurious hotels, passenger ships have to be designed with the highest safety standard stipulated by classification societies such as LR, GL, NK, ABS, and DNV, to prevent accidents. Modern navigational equipment as well as inflatable rafts and boats are installed in passenger ships to protect the passengers in case if an accident happens.

Today's modern technology helps naval architects and shipyard owners to design and build ships that are fully safe for sea transportation. It is important to note that the number of ship accidents is quite low compared to plane crash in recent years.

We will see that with improved speed, and better safety measures, passenger ship will be a good alternative for traveling in short distances which only takes one or two days to reach a destination. Also read: Propeller Rake and Blade Thickness Diameter Ratio; Controllable Pitch Propellers; Material and Strength of Marine Screw Propeller

Propeller Rake and Blade Thickness Diameter Ratio

by Charles Roring in Manokwari of West Papua Indonesia

Rake in propeller is made to increase to amount of water mass which can be sucked and propelled to drive the ship. Most of the rake is aimed at inclining the blades of the propeller backward relative to the generator line of the propeller. Usually the rake is between 0⁰ and 15⁰.

The larger the rake the higher will be the tensile stress of the blades. As a result, the blade thickness diameter ratio of a propeller with 15 degrees of rake is higher than the propeller without a rake whose overall parameters are the same. As I have said before, the higher the rake, the higher will be the working stress.

A propeller designer must carefully perform strength calculation for ship's propeller whose blades have high rake degree. The stress calculation is carried out using Taylor strength criteria for various blade thickness diameters until the allowable working stress is achieved. As a guidance, the formulas for calculating the blade thickness diameter ratio for a given rake can be read at my other article entitled: Material and Strength of Marine Screw Propeller. If you want to learn more about this subject, I suggest that you read page 301 of The Design of Marine Screw Propellers written by T.P.O. Brien. Here is a sample of propeller strength calculation whose rake is 10 degrees:

Propeller design data: DHP = 13210.56 hp; Blade number = 4; RPM= 97; diameter= 6.8 meters or 22.309 ft; chord diameter ratio at radius 0.2 = 0.230; the material density w = 480 lb/ft³; t₂/D = 3.52; rake = 10 degrees; S₂ = 1310, S₃= 0.22; S₄ = 0.746; S₅ = 0.31.

It is suggested that propeller designer avoid applying to high rake degree in his or her newly designed propeller to keep the blade thickness diameter ratio lower and to simplify the manufacturing process.

The Taylor Strength Criteria for Propeller whose material is Ni-Al-Bronze

After the strength criteria calculation has been executed, the figures in the above table can be represented in a graph such as the one shown below:

Also read:

• Pitch diameter ratio of a propeller and engine performance of a ship;
• Ship displacement calculation

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