Thursday, May 27, 2010

Cargo Wooden Boat

People in shipping industry are familiar with such term as cargo ships and container ships. In today's post, I want to introduce another term cargo boat or cargo wooden boat, to be exact. "What is it?" you might ask. Well, it is a kind of vessel made of wood and used to transport cargoes and some people. If you visit small coastal towns and villages in the Indonesia islands, you will find such boats.
 Cargo wooden boats play very important role in inter-islands shipping industry. You will not find containers and cranes in seaport where these boats stay. All the loading and unloading of cargoes are conducted using man power. Porters carry the cargoes on their shoulders and throw them into the hatch at the main deck of the boat. Most often, passengers and cargoes are placed on the same deck inside the superstructure. Well, although these boats cannot be called passenger ship, they most often carry more than twelve passengers. So, if we enter one of the wooden boats, we will see cargoes among people and people among cargoes.
I had a chance of visiting Anggrem seaport of Manokwari city in Papua island of the Republic of Indonesia two days ago. I climbed and jumped on the main deck of a cargo boat and took some photographs of the outside view of the deck, the interior of the passenger deck and the cargo hold and the engine room. I was surprised to find out that the engine room was dark and I had to use flashlight to get the inside view of the engine room and the engines.
Although this boat can be considered traditional, they are powered by diesel engines and manned by experienced crews who didn't study in maritime academy but got their nautical knowledge passed down through generations by great seafarers of Indonesia. You won't find radar inside the wheel house. They use compass, maps and stars (if the weather is bright) to determine their position relative to the islands which they are heading. I don't how long these boats can continue serve the remote islands of Indonesia but I believe that they have been part of the daily life of most of the Indonesia people especially those who live along coastal towns and villages that cannot be accessed by cargo shipping or passenger shipping that emphasis their operation on the economic of scale and not on the delivery of goods to small number of people living in remote islands. Here such wooden boats are the princess of the sea. by Charles Roring

Thursday, May 13, 2010

Pitch Ratio of Ship Propeller

In propeller design, pitch ratio is one of the most important parameters that naval architect must determine. Pitch is the distance (measured in meters) a propeller travels along the direction of a moving ship in one propeller revolution. Pitch ratio is propeller pitch divided by diameter. The determination of pitch is usually carried out through the reading of Bp delta diagrams which were created through extensive open water test over a number of propellers. 
A naval architect or marine engineer cannot choose pitch ratio as high as he or she likes. It is a parameter that affects all of the propulsion parameters of ship propulsion. In other words when a pitch is altered it will change all the propulsion performance of a ship. If the pitch of the blades is too high, it will overload the main engine that drives the propeller. If it is too small, the main engine will work under-load. Both conditions are not good for the performance of ship propulsion. Thus the determination of the right pitch ratio is important to ensure that the ship will move fast at sea surface with efficient consumption of fuel oil and without overloading the main engine.
Modern ship propellers (both fixed pitch and controllable pitch propellers) have pitches that are variable. From radius r/R 0.2 to 1, the pitches are not the same. Usually the pitch of a ship or boat propeller that was designed based on B-series standard propeller or also known Troost series propeller will have pitch ratios based on the following table or diagram
We can see that from radius r/R = 0.6 to 1, the pitch diameter ratios are full, i.e. 1 or 100% where as pitch ratios from radius 0.5 to 0.6 are different. After we get the Pitch/Diameter ratio (only one value) from the Bp delta diagram of B-series standard propeller, we have to develop it into variable pitches according to the above table. When we have entered the values of these pitch diameter ratio, we can continue the calculation of the propeller design by conducting Propeller Mean Pitch Calculation. by Charles Roring

Propeller Blade Area Ratio

Propeller Blade Area Ratio are usually explained in three terms Projected Area Ratio; Developed Area Ratio (DAR) and Expanded Area Ratio. In the design of marine screw propeller, the DAR has to be determined usually from the cavitation calculation. To get the value of the DAR, there are some propeller design calculations that a naval architect or marine engineer must perform.
  1. The calculation of Bp or power coefficient
  2. The determination of delta value (usually read from Bp delta diagram of B- series propellers at the optimum propeller efficiency)
  3. The calculation of delta value which is obtained from the product of propeller's RPM (N) and diameter (D) divided by speed of advance Va 
  4. The reading of optimum efficiency from the Bp delta diagram based on delta value obtained at point 3 above.
  5. The determination of propeller pitch ratio
  6. The calculation of Ku or thrust loading coefficient
  7. The calculation of Y7 or conversion factor of speed resultant
  8. The determination of Kv or thrust loading coefficient whose value is obtained from Ku divided by Y7
  9. The calculation of static pressure (po-e) measured at propeller axis 
  10. The calculation of cavitation number sigma A
  11. The calculation of cavitation number sigma R at the fraction radius x = 0.7
  12. The reading of Developed Area Ratios from the diagram of blade areas. 
 Diagram of thrust loading coefficients and developed area ratios according to Burril and NSMB (TPO Brien - 1962)
The values of DAR are proposed by Burril (read Cavitation of Marine Propeller) and NSMB (the Netherlands Ship Model Basin). Usually propeller designer choose the value from Burril that is larger than that shown in the diagram by NSMB. Because the difference between Expanded Area Ratio (EAR) and DAR is small, propeller designers usually ignore the value of EAR. EAR can be obtained through calculation using simpson's rule after the ordinates of DAR have been developed into the expanded blade in the drawing of propeller using Holst method.
If you have never performed a propeller design calculation, you will be confused about this explanation. As a propeller designer, I can only suggest that you read page 194 of a book entitled the Design of Marine Screw Propellers written by T.P.O. Brien.
This is an old book but it contains a very good explanation about important steps a naval architect has to perform to design a ship or boat propeller with optimum performance. Another book, Marine Propellers and Propulsion by John Charlton is also good but lack of samples of manual calculation. So, Mr. Brien's book is better in explaining the the design philosophy behind a good ship or boat propeller. by Charles Roring
Also read: How to Design Ship Propeller

Wednesday, May 5, 2010

Wooden Boats in Indonesian islands

Wooden boats have been transporting goods and people from one island to another in Indonesia  for years. As the largest archipelago in the world, sea transportation plays a very important role in the economic livelihood of the people. Wooden boats have been used by villagers in Indonesian islands to bring agricultural produce to coastal towns and big cities and to buy manufactured goods that they need. In the past decades, Phinisi sailing boats were used by seafarers in South Celebes. They sailed with their traditional wooden boats throughout the world. They have even claimed that the Phinisi have traveled as far as Europe and North America.
Today, cargo wooden boats that are powered by marine diesel engines and four blade propellers serve the people in coastal villages and towns in Indonesia. In the photograph of this post, you can see three wooden boats berthing at a jetty in the Dorey bay of Manokwari. Their sizes and design are not too different. These boats transport goods and people and have become important economic backbone for the development of villages in the isolated region of West Papua. The wooden boats play two function. They are used as ferries, and at the same time cargo boats. Although small holds are provided, goods are also stored together with the passengers at the same decks or compartments. Sometimes we will see domesticated animals (such as pigs, and goats) are loaded at the same decks with the passengers. Well, that's how these boats are used in developing maritime nations such as Indonesia, and perhaps the Philipines.
When I visited these boats, and checked the inside interior, I found that they are lack of life saving appliances. SOLAS and Load lines regulations have not been strictly enforced in Indonesia especially among the seafarers who operate such boats. 
It is not surprising to see that sea accident frequently occurs due to overload of goods and passengers on these kind of boats. Although Indonesia has a classification society, Biro Klasifikasi Indonesia (KI), most of the constructions of these boats are carried out in the villages where the offices of KI do not exist. The boats are designed and constructed without the supervision of naval architects whose expertise include the checking of the position of center of gravity (VCG and LCG) and the calculation of initial stability, and the application of freeboard or loadlines regulation, as well as other construction rules related to wooden boat construction. As a result, many of the traditional wooden boats both the sailing ones and the motorized ones are still not equipped with KI certifications.

Monday, May 3, 2010

Erosive Effect of Cavitation on Propeller

Cavitation of marine propeller creates negative effect on the blades of a propeller. Besides reducing the thrust power, it also erodes or wears the surface of the blades. Not all of the propellers in cavitation condition experience this erosive effect.
Experts in marine propellers and ship propulsion explain that cavitation erosion is caused by the traveling of bubbles around the surface of blade aerofoil. When these bubbles collapse, they generate pressures that are harmful to the surface of the blades and at the same time these bubble turn into smaller bullets usually called microjets whose speed is very very high. When the microjets hit or travel along the surface of the propeller blades in very high pressure, they cause erosion on the blade surface. Continuous microjets impacts (or also called (bombardment) of the bubbles on the surface of the blades of the propellers is the cause of fatique failure of the blade surface that triggers the beginning of propeller erosion.
To prevent erosion of the propeller, naval architects and marine engineers perform cavitation testing of propeller which they have designed before they are manufactured. When the tested propeller model shows the phenomenon of cavitation, usually they will reanalysis the propeller to find the solution. Propeller designer might increase the blade area ratio of the propeller and adjust the pitch ratio. Another alternative is changing the RPM which will eventually effect the selection of main engine of the ship whose rpm greatly influences the RPM of the propeller. If the RPM of the engine is too high, a reduction gear can be installed. But naval architects will prefer to find another engine whose RPM is lower without reducing the specified power which has been determined previously from resistance calculation or ship resistance model test.
In recent years, the need for high speed marine vehicle is increasing. This is answered by ship designers by the introduction of catamaran. This type of twin hull ship still uses marine diesel engine as its driving power. To fully support the high speed, propeller designers work hand in hand with marine engineers and naval architects to design an integrated propulsion unit that has high propulsion efficiency with low risk of cavitation on  the propellers. by Charles Roring

Ships in Manokwari harbor

The number of goods or containers that are unloaded in ship harbor of Manokwari is increasing nowadays. This is due to the change of the city's status into the capital of the newly formed West Papua province.
Container ships and cargo ships frequently visit Manokwari to deliver goods that are needed to support the development of the city and its rural areas. Most of the cargoes that these ships bring are construction materials. And small amount of agricultural produce that they load to be exported to Java or Makassar from this city are plantation commodity such as cocoa beans.
Every week PELNI passenger ships arrive in Manokwari ship harbor to bring hundreds of migrants from outside Papua and take hundreds from the city to other coastal towns of Papua island or to other islands in the Indonesian archipelago.
 Besides seagoing steel ships, smaller wooden boats that are operated by the Butonese provide service both to the Papuan people and the government. These boats have different berthing pier. The government has provided a small wooden jetty for these boats in Anggrem area.These boats are greatly important in carrying government logistics to remote coastal villages in the Cendrawasih bay (Geelvinkbaai).
Although more cargoes and containers have been delivered to Manokwari city, the cargo handling equipment used to unload them are still from the derrick booms or crane that the ships have.  Although Manokwari harbor has been enlarge to increase its capacity for berthing ships with larger displacement, it still hasn't got container cranes that can speed up the process of loading and unloading of cargoes at the moment. by Charles Roring

Saturday, May 1, 2010

Cargo Ships and the Dorey bay of Manokwari

Cargo ships and the scenery of Dorey bay are the photographs that I want to discuss with you here. This morning I walked to the ship harbor (haven) of Manokwari city. As the capital of (newly formed) West Papua province, this city is growing rapidly. Ships (general cargo, container ships and passenger ships) load and unload goods, containers and people every week.
 The jetty of Manokwari haven has been enlarged several times to provide more space for ships and containers. This harbor is located near the Governor's office and the building of house of representative of West Papua province.
While I was walking in the pier, I saw four sea going steel ships there but there were no activities of loading and unloading of containers. It was very quite with several people fishing near the ships at the end of the pier.
I am amazed by the view of the Arfak mountain. Using my Sony cyber-shot, a handy digital camera, I take some pictures of the morning scenery in the ship harbor of Manokwari. One ship crew seems to pay attention to what I was doing. When he saw that I was taking photographs of the surrounding view, especially the sea and the mountain, he left me.
To brighten the picture, I set the control dial of the camera to ISO mode.
Unfortunately, I did not see any PELNI passenger ships around. I hope that in my next visit to this ship harbor of Manokwari, I will be able to shoot some photos of PELNI passenger ships that transport passengers to and from this city. Right across the ship harbor, there is a PELNI office. There people can buy tickets if they want to sail to other towns in Papua or outside this island by PELNI's passenger ships.  by Charles Roring

Wooden Boats in the Dorey bay of Manokwari

Wooden boats, similar to modern seagoing steel ships, are used to transport goods and people from one port to another. In the Dorey bay of Manokwari city, I saw some traditional wooden boats in a small jetty in Anggrem area during my walking tour yesterday afternoon. The hull and superstructure of one of the boats are painted with white and yellow coatings. On the average, the boats are powered by 200 horse power marine diesel engine and conventional three or four blades propellers. I was able to climb its top deck and took some photos of other boats around the area. There was a steel ship belonged to the local government. I know that it has been used as ferry connecting small coastal villages in the northern region of Papua island. Although the boats were constructed using traditional tools, they are quite safe and stable to sail across the sea.
When we are talking about traditional wooden boats design and building in Papua, we cannot categorized them as cargo ships and passenger ships. The decks where cargoes are stored are also used to carry passengers. I am doubtful if the crews or operators of these boats provide life-jackets to all the passengers and crews on board.
I went there with a friend of mine. On the other side, I saw the former shipyard built by a Dutch shipbuilding company.  Formerly known as Manokwari Scheepswerf Konijnenburg. Now it is called Fasharkan (Fasilitas Pemeliharaan dan Perbaikan or the Facility for the Maintenance and Repair). I am sad to tell you that it not working anymore. The expensive slipway and the shipbuilding facilities left by the Dutch  are  not developed or operated by the Indonesian government anymore. 
We talked with the some of crews of the boats. I asked them how much does it cost to go from Manokwari to Wasior. They said the ticket is Rp. 100,000 or around 11.3 US dollars. I requested this information because I want to get the exact ticket price for Wasior. a small town which now becomes the capital of Wondama Bay Regency. This regency has a large sea area which has been preserved by the government as the National Marine Park of Cendrawasih bay, one of the best coral reefs and scuba diving sites in the world.
From Wasior, tourists or scuba divers can hire another boat or small outrigger boats to continue their trip to Auri islands where they can do snorkeling and scuba diving there.
Most of the big islands of Indonesian archipelago have their own techniques in building traditional wooden boats. In Maluku, a small village that is famous for building boats is Asilulu. In North Sulawesi, villagers of Tanawangko are expert in building big boats that can carry up to one hundred passengers and several tons of cargoes.