## Saturday, May 30, 2009

### Cost Estimation of House Construction

Suppose that you are going to have your new house built by a home construction company, and you have just received from an architect or a house designer a number of drawings of your new house. These drawings are floor plan, general arrangement of the house with front and side views, detail drawings of foundation, windows and doors, ceiling and roof.

The next step is consulting the cost of construction with the architect or a home builder. If you appoint an architect to do the design, the cost estimation and the construction of the new house, you don't have to find a home construction company by yourself. All you have to do is pay the cost and receive the keys of your newly built house.

If you want to minimize the cost, after receiving the design drawings of your house, you will consult them with a home builder. He will make the cost estimation for the construction of your house. In general the cost estimation is devided into two main subjects. The cost of materials and the cost of building the house.

You might probably be confused with all these terms. To help you understand them, I will give you the scope and sequence of calculating the house construction. The followings are types of works which have to be performed for building a conventional house.

1. Preparation works

2. Foundation and concrete works

3. Wall works

4. Floor and ceramic works

5. Roof works

6. Roof of the garage works

7. Ceiling works

8. Windows and door works

9. Sanitair works

10. Clean water and dirty water works

11. Electrical installation works

12. Painting works

13. Cleaning works

There are many points which a cost estimator needs to calculate for each number or type of works. For instance, for preparatory works, the works which a home builder has to perform are the clearing of land, the measurement and installation of marking or profile boards, the excavation for foundation works, earth removing.

After calculating the volumes of each of the works of the above list, they have to be multiplied with the unit cost of material to obtain the cost of material. Then the amount of cost for each type of work have to be summed to obtain the total sum of the cost of the material of the new house.

Similarly, the volume of works for each type of works of the above list have to be multiplied with the man-hour factors to obtain the labor cost for the construction of the house.

The price of house material is different from one place or country to another. This also applies to the labor cost.

If you are serious about building your own house the cheaper way, I suggest that you read some books related to this subject. One of the titles which I recommend is
Fundamental Building Technology
written by Andrew Charlett. Also read: How to add column and beam to a house using Archicad and Wooden house of Minahasa an earthquake resistant construction

by Charles Roring in Manokwari of West Papua Indonesia

## Tuesday, May 26, 2009

### Marine Diesel Engine the most preferred propelling machinery

Marine diesel engine is now the most used prime mover of modern ships. In the past, steam reciprocating engine was widely used with coal as the fuel. Steam reciprocating engine actually is a flexible engine in terms of the type of fuel it uses. When there is no coal around, ship crews could cut trees as fuel. This happened in the past, when a ship sailed to remote islands, ship crews would use wood as fuel if they ran out of coal.

Now most shipbuilders and ship designer choose marine diesel engine as the prime mover of ships that they build or design. Diesel engine is smaller, and compact compared to steam reciprocating engine. In addition, marine diesel engine does not need large room for storing coal. Fuel oil is stored in tanks usually at the double bottom of a ship and a smaller daily tank above the engine.

The improvements in engine design has made the operation of marine diesel engine both in small and large ships fully automatic. Unlike the steam engine which needs constant manning from ship crews to feed coal into the combustion room that heats up the boiler, the marine diesel engine is controlled by ship crews only by several touching buttons or moving levers.

In the future, marine diesel engine will continue to be used with expectation that the engine will be more efficient, and emit less CO2 gas and with lower vibration. by Charles Roring in Manokwari of West Papua - Indonesia. Also read: Design constraints of propeller diameter and Propeller and ship's hull

## Tuesday, May 19, 2009

### Traveling around the farmland of Minahasa

My travel story today is about going around the farmland of Minahasa. After arriving at Sam Ratulangie international airport and staying for one day in one of the hotels in Manado city, the next day, you will want to begin your tour around Minahasa highland. What place will you visit first? I will suggest that you go to Tomohon. It is not far from Manado, the capital of the Province of North Sulawesi.
Tomohon municipality is a small town located around 45 minutes drive from Manado. It is also called as Kota Pelajar or Town of Students. There are a lot of schools in this town. Here, tourists can enjoy the fresh cool air of the town and visit the traditional gardens the local farmers are working on. They grow vegetables such as cabbage, carrot, onion, cauliflower, and read beans. Many farmers also grow flowers. After taking pictures and talking with the farmers, you might become hungry. There are many restaurants along the Jalan Raya Tomohon serving local, Chinese and Western cuisines. Or you might want to go to all you can eat restaurants in Kasuang. It is not far from Tomohon. If you take bendi, you need around fifteen to twenty minutes to reach Kasuang. The price of food per one package of lunch is around 25,000 rupiahs. While you eat, local singers will sing songs. Sometimes they ask you to sing with together. For the drinks, there is a palm sap called saguer. When drunk cool, you will not only need one glass but at least three glasses.
 Farmland in the slope of Mount Mahawu
After having lunch in Kasuang, you will have many options of places to visit. You can continue your trip to Tondano or travel to Sonder. In Tondano, you will be welcomed with vast area of paddy field scattered along the bank of Tondano lake. If you go to Sonder, you will be able to visit fish ponds along the river heading to Tincep village. Sonder is famous for its Terapung restaurant. The local farmers there grow clove, the raw material for Indonesian kretek cigarette. The clove blooms every one or two years depending on the occurrence of long dry season. Different from Tondano which is mostly of flat plain, Sonder lies on hilly region. There is a small inn in Sonder which you can stay for one or two nights before continuing your travel to other villages of Minahasa.
My recommendation to you will be Kawangkoan. It is located further south of Minahasa. Farmers here grow peanuts, corn and coffee. At the entrance gate of the village, you will be welcomed with a large statue of peanut.
If you continue your trip to Langowan, you will see farmers plowing their farmland with cow or buffalo. Many Langowanese migrate to the US. So, don't be surprised if you see American flag decorating many big houses there. Well, I think I should stop my story right now. I will continue it next time.

## Monday, May 18, 2009

### My travel story about Minahasa

by Charles Roring in Manokwari of West Papua - Indonesia

Minahasa is one of the most potential tourist destinations in Indonesia. It is one of the regencies in the province of North Sulawesi - Indonesia. People from around the world like to travel to this region to enjoy the beautiful scenery of the mountainous region as well as the pristine coral reef of Bunaken national park. There are many travel deals offered by travel agencies in Europe, North America and some countries in Asia.

You can fly to Manado the capital province of North Sulawesi from major cities in Indonesia. There is a direct flight from Singapore too. Contact your airline company to check whether they have flight heading to Manado city.

During high season, hotels and inns in Minahasa offer special package to tour groups who book or order rooms several weeks in advance. The hotel fare per room can range from 10 US/night to 100 US/night. In addition, for scuba divers who are interested in traveling around the waters of North Sulawesi, diving operators provide diving boats and full accommodation in affordable price.

Minahasan cuisine is full of spice. Tourists can try all you can eat package along the restaurants in Kasuang or Tinoor. While enjoying the delicious food, travelers can see the beautiful view of Manado city or the panoramic view of Minahasan highland.

When traveling to Bukit Kasih (love hill) in Kanonang, tourists can ride bendi, a traditional horse driven cart which is able to bring you through the farmlands of Minahasa. My recommendation for you is that after enjoying the beautiful coral of Bunaken, you should carry on your trip to towns in the highland of Minahasa to meet the people and experience the unique their culture.

There is one thing that I have to remind you through this writing. If you are offered to drink Cap Tikus, an alcoholic drink, don't drink too much or you will not be able to control yourself. Cap tikus contains high percentage of alcohol. Tourists like to drink it at their hotel rooms to prevent having problems with the locals in case if they get drunk.

Minahasan are friendly people. They always welcome people from foreign countries with smiles.

I personally like to visit the waterfalls of Tincep and enjoy food in Sonder village. These places are so romantic and rich of natural environment. Here, the air is fresh. People like Tincep because it is the center of flower market. Although you don't go there to buy flowers, you can still visit that village to take pictures of the beautiful flowers there.

Traveling during this dry season is good because you will not have to cancel many of your trips in the interior region just because of the rain. The word interior here does not mean that the area is underdeveloped. Interior in this term means that the area is a further from the sea. Actually, there are still a lot of things which I should write here about the beauty of Minahasa region but it will not be enough to cover them all in one piece of article. It is better for you to travel by yourself to this region to experience it. Also read: Travelling with Passenger Ships; Travelling with Passenger Ships; Traveling around the traditional market of Manokwari

### Traveling across the tropical region

If you plan to travel across the tropical region this year, this is the best time for you. Why travelers should go now? Many travel agencies now offer various travel deals to South East Asia and the Pacific islands where the economical development is growing rapidly. Hotels, air and sea fares are affordable to any tourists who are interested to come.
Tropical region is located along the equator. It stretches from the islands of Indonesia, the beautiful coral reef of the Pacific islands, the exotic tropical rainforest of Amazon in Brazil, to Congo - a rich country in Africa. Tropical region is now entering dry season offering full sun shine, and richness of biodiversity.
Travelers from Europe and the USA will be interested in enjoying the beautiful nature of rainforest in Papua and Brazil as well as the pristine the underwater coral reef of the Palau islands.
If you have decided that you want to travel this season, you'll need to make some preparations. What you should bring when you want to travel around the coastal region. After you have arrived at your hotel, you might want to take sun-bathing. During the dry season, the temperature is very high. Tourists or travelers are recommended to apply lotion to protect their skin from burning. This is important because it can prevent you from suffering from skin cancer. The lotion is also needed to protect your skin from insects' bites that mostly thrive along the beach.

If you plan to dive around the coral reef, be sure that you bring diving equipment. Check it from any damages or defects before diving. Don't forget to fill out forms provided by the diving operator in case of any accidents happened to you so that they will be able to contact your relatives or close friends.

Traveling without recording the happy moment will be one the most stupid decision you've ever made. So, don't miss the precious moment when you are visiting certain places. Most tourists bring digital camera or video recorder. But don't forget to also bring rechargeable batteries and their charging equipment. Sometimes, when you take a vacation in remote region you will not find shops that sell them.

Suppose that you like hiking and traveling through the forest of Papua to enjoy bird watching and orchid observation will be your choice this season. If that's your travel plan then don't forget to bring portable tent for camping. In addition, you will need some medicine such as mosquito repellent lotion and anti-malaria pills.

Tourists or travelers who want to explore the tropical rainforest of West Papua and Amazon in Brazil must be accompanied with local guides with them. Also it is recommended that tourists or travelers do not bring flammable material such as kerosene, or matches with them into the forest. This is good to avoid forest fires. Bring canned food or biscuits so you don't have to cook in the forest. If your stay inside the forest is long and you'll have to cook, then you have to water the wood ember to completely extinguish it.

These are some of my suggestions to you if you plan to travel to tropical region this season. If you have finished traveling, don't forget to write me and tell some of your travel stories. by Charles Roring in Manokwari of West Papua - Indonesia Also read: Travelling with Passenger Ships;

### Traveling with passenger ships to remote islands in Indonesia

by Charles Roring in Manokwari of West Papua - Indonesia

Travelling from one to another island in Indonesia is mostly done by passenger ships. There are around 18,000 islands in Indonesia. Therefore, ships play very important role as a means of sea transportation carrying millions of passengers and cargoes every year. In addition, besides having high demand in passenger and cargo ships, with high number of population, Indonesian also need a lot of fishing boats.

For short distances small passenger ferries operated by both state and private owned companies offer affordable transportation service. For travelling in long distance, the government has provided many passenger ships which are operated by PELNI, a state owned shipping company.

Most of these passenger ships are constructed in Germany. Each can carry between 2,500 to 3,000 passengers. The interior of the ships has been designed to look more like a floating hotel than just a mere transport vehicle.

Foreign travelers who are interested in visiting exotic islands such as the Moluccan islands, after arriving in Ambon city - the capital of the province, can continue their trip by taking some fast boats. These high speed marine vehicles can travel with a speed of up to 30 knots. Depending on the type of the boats that you take, the time they need to arrive in such islands as Haruku, Seram and Saparua can range between 1 to 3 hours.

With high demand in ships, Indonesian ministry of education has opened the study program of naval architecture and marine engineering in four state owned universities. They are Pattimura University, Hasanuddin University, Surabaya Institute of Technology, and Diponegoro University. In addition, some private universities also have such study programs.

For the convenience, and safety of sea travel, people who work in the passenger ships must be the competent ones who have got certificates from maritime colleges. Also read: Travelling with Passenger Ships; Pilatus Porter, a suitable aircraft for travelling across mountainous region

## Wednesday, May 13, 2009

### Design constraints of propeller diameter

by Charles Roring in Manokwari of West Papua - Indonesia

When designing a controllable pitch or fixed pitch propeller, a naval architect or propeller designer must face many design constraints which have to be compromised. One of them is the diameter of the propeller. After obtaining the lines plan and general arrangement from the ship designer, a propeller designer will check the stern detail drawing of the ship, to find out such data as stern draft measured at the after perpendicular of the ship or boat, and rudder dimension.

Ideally, the diameter of the propeller should be as large as possible to obtain a higher propulsive efficiency, but it will not be possible to do that. Too large propeller diameter will result in air drawing to the propeller thus abruptly reducing the propeller efficiency itself. In addition, there has to be an adequate clearance between the hull and the propeller tip to ensure that the propeller can be installed and dismantled during ship construction, and can operate properly without creating vibration.

The propeller whether it is controllable pitch or fixed pitch has to be fully immersed under water to give maximum propulsive efficiency during operation. Large ships such as bulk carriers or tankers often have to sail in ballast condition. To avoid air drawing, the diameter of the propeller will be smaller compared to other merchant ship type such as cargo or container ship.

The determination of propeller diameter is also based on the RPM of the main engine. The lower the RPM of the main engine, especially marine diesel engine, the larger can be the propeller diameter. As a general guidance, the propeller diameter and design draught ratio d/D of ships are as follows:

For bulk carrier and tanker: d/D < approximately 0.65

For container ships: d/D < approximately 0.74

Another factor which naval architect or propeller designer consider when determining the diameter of propeller is its strength. Too large diameter will create to large compressive and tensile stresses to the propeller. If the stresses are very large and close to or more than the maximum allowable stresses stipulated by classification societies, the propeller will brake during operation. Generally, for this reason, the diameter of propeller is limited to 10 meters. Also read: Propeller and ship's hull; Controllable Pitch and Fixed Pitch Propeller; Propeller design methods

## Tuesday, May 12, 2009

### Propeller and ship’s hull

Ship propeller and boat propeller is still considered as the most economical propelling devices for ships and boats. Other propelling devices such as paddle wheel, magnetohydrodynamic propulsion system have efficiencies that are lower than screw propeller.
Propeller designer and naval architect must understand how propeller, ship's hull, rudder and main engine interact from one to another.
Ship's Hull - The hull form of a ship influences the flow of water from the forward end of the ship to the stern where the propeller is mostly installed. The finer the hull form the faster will be the ship's speed in water. The fullness of ship's hull form is reflected by its block coefficient or CB. Ships with higher block coefficient (0.70 to 0.98) will tend to be slow in the water. Even if the block coefficient is small (0.50-0.70), the speed of ship moving in the water can be slower due to the fouling of hull surface. Hull fouling is mostly caused by barnacles, and tube worms. If the fouling is worse, it can increase the frictional resistance of ship up to 40%.
Another way which naval architects do to reduce the resistance of ship thus increasing the speed or improving the propulsive efficiency is by adding bulbous bow to the ship. By doing this, the naval architect and propeller designer can reduce the wave making resistance of the designed ship.
Ship, hull and rudder are integral propulsion system of ships. But they will not work without a main engine inside the hull. Today, marine diesel engine is used as the prime mover of ships. The use of steam and gas turbines are only used in small number of ships due to the complexity of the design although they relatively have low vibration.
Marine diesel engine for large vessels is especially designed to have low RPM. Theoretically, the lower the RPM of a propeller, the better will be its efficiency. Modern propellers are designed and manufactured to have high skew to minimize the vibration and maximize the efficiency.
In the last few decades, the development of multi-hull ships has led to the building of catamaran, trimaran and SWATH (small water plane area twin hull) ships. These new hull types are mostly used on passenger ship, ferries, fast patrol boats and ships or boats that need high speed. by Charles Roring in Manokwari of West Papua - Indonesia. Also read: Propeller design methods; Propeller Strength Calculation; Cavitation of Marine Propeller

### Controllable Pitch and Fixed Pitch Propeller

I remembered time in 1999 when I was designing a propeller for a large 45,000 DWT Open Hatch Bulk Carrier. At the time, I had to choose between CP Propeller and FP Propeller as the propelling device for the ship. I was not sure whether the ship will need high maneuverability during her service especially at narrow straight, ports and bays.

Naval architect and propeller designer often have to compromise all the design constrains to obtain the optimum dimensions of the ship and the propeller so that the required speed can be met and the fuel efficiency can be reached.

After reading a large number of books and publication on resistance, propulsion and steering of ships, I finally knew that CPP or Controllable Pitch Propeller has boss diameter which was larger than the conventional fixed one.

In addition, the CP-propeller was mostly used for ships such as passenger ships that need high maneuverability. In theory, if the propeller has larger boss diameter, its efficiency will be lower.

Now, we come to the discussion of propeller efficiency. There are many factors that affect the overall performance of a propeller operating under the sea water behind a ship. To obtain higher efficiency in CP-Propeller, experts in hydrodynamics and cavitation tunnels around the world develop what is now known as highly skewed propeller. This kind of propeller has more skew on its blades. Computer calculation and model test results have shown that the CP-Propeller with highly skewed blades have better efficiency and less vibration.

Just because the CP-Propeller can now be equipped with highly skew blades does not mean that the problem related to overall propulsion efficiency is solved. There are still many conflicting factors which naval architect, marine engineers and of course propeller designer must consider.

For operational point of view, CP-Propeller has more complicated mechanism than the traditional FP-Propeller. It means that if the propeller face mechanical failures during its service in the middle of the sea, it will not be easy to repair it, especially if they happen inside the boss.

Based on this consideration, I chose the fixed pitch propeller as the propelling device for the OHBC ship.

The standard model which I used was the Troost B-4 Series from Wageningen, the Netherlands. I didn't use highly skew blades because of the lack of data of such blades at my hand. Highly skewed propeller is quite a new blade type which was invented just several decades ago.

Years after my first propeller design work, I finally found that the highly skewed propeller was designed using special computer program that applies the surface panel method developed from lifting line theory. I wish I could understand this innovative theory.

As propeller designer, I need around two weeks to do the resistance calculation, propulsion calculation and propeller design calculation and additional one or two days for drawing the propeller of a ship. Now, with the availability of computer software, a propeller designer can do his or her job just within one or two days.

But for larger ships, naval architects, marine engineers, and propeller designers must perform model tests in towing tank and cavitation tunnel before finally delivering the final design of the ship and the propeller to the shipyard. The power of a newly designed ship has to be accurately predicted before the construction to ensure that the ship will have the required speed during her service at sea. In addition, the ship also needs to have high propulsion efficiency to ensure that fuel oil consumption will be as low as possible. I believe that fixed pitch propeller will still be used in the world of shipbuilding but the controllable pitch propeller is increasingly being used in many ships today due to the improvements in blade design, material and the availability of computer technology. by Charles Roring in Manokwari of West Papua Indonesia

## Monday, May 11, 2009

### Propeller design methods

There are two methods available for the design of marine screw propeller (both ship propeller and boat propeller) at this time. They are hydrodynamics and aerodynamics theories; and the test results of systematic propeller models carried out by towing tanks and cavitation tunnels.

The hydrodynamics and aerodynamics theories - The propulsion phenomenon of ship's or boat's propeller is still difficult to be explained. The existing theories are divided into two main theories, i.e.:
• Theory of momentum - this is based on the assumption that the propeller acts as the accelerator of water that passes through it. The resulting reaction creates thrust force which propels a ship.
• Propeller blade element theory - this is based on the assumption that each propeller blade consists of a large number of concentric strips relative to the boss of the propeller. Every strip acts as a small aerofoil which has resultant velocity as the result of the combination of axial and rotational speeds. These speeds react against the aerofoil and generate elementary lifting forces and drag forces on the blade surface. If they are integrated throughout the whole area of propeller blade, they will provide thrust force that propels the ship, and also torque to the propeller.
In practice, most naval architects and propeller designers use the second design method, i.e. the test results of systematic propeller models. To enable ship and propeller designers do their jobs, a number of research institutions have made propeller model standards whose characteristics are presented in a journal under the title "A New Usable Propeller Series," on page 174, vol. 26 No. 3, July 1989 of Marine Technology tabulated by S.B. Denny et al.
The propeller models which I usually use are Troost/ Wageningen B-Series. Before using the models, a naval architect or a propeller designer must understand the theories of resistance and propulsion of ships. This subject is extensively explained in such books as Resistance and Propulsion of Ships - Sv. Aa Harvald, Resistance; Propulsion and Steering of Ships - Prof. W.P.A. van Lammeren, Troost L, Koning J.G.; The Design of Marine Screw Propellers - T.P.O'Brien.
When designing the propellers of ships, I usually use or read the latter two books as my main references in deciding the parameters of ship resistance and propulsion. The books may not be available on the market. If you are serious about learning this subject, I suggest that you read similar books published by Elsevier publisher. By Charles Roring in Manokwari of West Papua - Indonesia. Also read: Propeller Strength Calculation and Cavitation of Marine Propeller

## Sunday, May 10, 2009

### Propeller Strength Calculation

by Charles Roring in Manokwari of West Papua - Indonesia

Propeller strength calculation is one of the many factors which a naval architect or propeller designer must perform when designing the propeller of a ship. A propeller must have an adequate thickness to enable it to rotate and propel the ship without failure.

Ideally, the blades of a propeller should be as thin as possible to have higher efficiency. But it will make the propeller easily to vibrate and brake during its operation. If the propeller is too thick, the efficiency of this propelling device will be low and the cost of manufacturing the propeller will be higher.

Therefore, a propeller designer must compromise all these contradicting factors to obtain the most optimum blade thickness.

Usually propeller designers use Taylor method for calculating the strength of a propeller. This method is simple and effective. The use of Taylor method is suitable for propeller blades with normal forms and whose blade area ratio or B.A.R is not too large. The use of Taylor method on B.A.R. which is more than 0.80 will result in blade stress that is 10 to 15 percent too low.

The calculation of propeller strength is needed to assess the value of design stress so that a safe blade thickness could be determined. Generally, the calculation of propeller strength with Taylor method is carried out at the blade radius of 0.2 R. Taylor provides a number of formulas which propeller designers and naval architects can use to calculate the compressive and tensile stresses of the blade. Some design parameters which we must know prior to performing the calculation are the number of blades, the RPM of the main engine, the diameter of the propeller, the chord diameter of the expanded blade at radius of 0.2R, and the material density of the propeller.

The thickness of the propeller is largely determined by its material. Marine propeller can be made from cast steel, special propeller bronze, Ni-Al-bronze, cast iron, gun metal and etc.

The explanation and example of propeller strength calculation can be read on page 288 of The Design of Marine Screw Propellers which was written by T.P. O'Brien.

To help propeller designers, Taylor has provided a chart which is called Taylor Propeller Strength Criteria. To use the chart we have to calculate the compressive and tensile stresses of the propeller. The chart and the strength calculation have to be used with propeller strength requirements stipulated by classification societies such as LR, GL, DNV, NKK, and BKI. These classification societies provide a table with a list of propeller materials and their minimum ultimate stress in km/mm2, and minimum elongation in percent.

After performing the strength calculation, a propeller designer can continue his work by drawing the propeller which is usually done using Holst method. Such method is well and extensively explained on page 171 of a book entitled, Resistance, Propulsion, and Steering of Ships A Manual for Designing Hull Forms, Propellers and Rudders. The book was written by Prof. W.P.A. van Lammeren, Troost L., and Koning J.G. Also read: Cavitation of Marine Propeller; Resistance and Propulsion Calculation in Ship Design

## Saturday, May 9, 2009

### Cavitation of Marine Propeller

Every naval architect or propeller designer knows what a propeller cavitation is. Cavitation happens when the pressure in the fluid flowing around the propeller blades drops and causes some fluid to change into water vapor. When cavitation of marine propeller happens, it changes the homogeneity of the fluid flow. This causes the racing of propeller shaft but the speed of the ship drops. Cavitation on propeller also causes the erosion of material particularly on the surface of the propeller blade. Read my other article Erosive Effect of Cavitation on Propeller to know more about it.
The phenomenon of propeller cavitation was first noticed by Thornycroft and Barnaby on their destroyer, Daring. When the ship was being tested, they expected it to reach a speed of more than 27 knots. In reality, it could only reach 24 knots. Finally, Thornycroft and Barnaby solved this problem by increasing the surface area of the blade up to 45%. They concluded that the loss of the propelling force in high speed propeller had been caused by the high loading of propeller blade. According to them, the phenomenon happened when the thrust/inch2 of the projected surface of the propeller was more than 11.25 lbf (77.55 kN/m2). After modifying the propeller, finally, Daring's speed could reach more than 29 knots.
Source: Marine Propellers and Propulsion, by John Carlton, pp. 214
High loading of propeller will create high negative pressure at the back of the propeller which forms cavities that will be filled by air and water vapor. It was then R.E. Froude who suggested Thornycroft and Barnaby that the phenomenon be called "cavitation."
When designing the propeller of a ship, I have to check whether the propeller, at the service speed of the ship, will experience cavitation or not. The tool that I usually use to check the cavitation is the Method of Burril.

This method is also my basis for determining the developed area ratio or AD/A0 of the ship's propeller. Before determining the ratio I have to calculate, according to Burril method, some such cavitation parameters as, thrust coefficient, the conversion factor of resultant speed at radius blade fraction of 0.7, static pressures at shaft axis, and static and dynamic pressures at the shaft axis of the propeller.
After determining the propeller blade area ratio, I then can continue the process of designing the ship's propeller by performing the strength calculation of the propeller's blade.
In theory and in practice, the thinner the propeller the better will be its efficiency. But, the chance of it to experience cavitation will be higher. In addition, the thin blade may fail or brake due to high stress during operation. But if the blade is too thick, it will be uneconomical and inefficient. Therefore, I have to perform the blade strength calculation, using Taylor method, to determine the most optimum thickness of the blade. I will discuss this matter in detail in my next posting. by Charles Roring in Manokwari of West Papua - Indonesia

## Friday, May 8, 2009

### Resistance and Propulsion Calculation in Ship Design

Naval architect when designing a ship has to perform resistance and propulsion calculation. This is done using statistical methods which are available from various standardized data released by a number of ship model basins around the world. While I was still a university student in the Department of Naval Architecture of Pattimura university of Ambon city, the resistance calculation was based on such methods as Holtrop Mennen, Taylor, Guldhammer and Yamagata. There are various power prediction methods available but naval architects have to determine or choose one of them based on the similarities in hull forms of the designed ship and the model data.  Power obtained from this calculation is called effective power. This is the power that is required to tow a ship or boat at certain speed. To determine the brake horse power of a marine engine, this effective power has to be added with a number of losses at the stern, shaft bearings and reduction gears. When all of these losses have been added, the brake power obtained from the calculation can be used to find a marine engine that is suitable for the designed ship. Most often the rated power of the marine engine that we need is not exactly the same as the brake power that we have calculated. To solve this problem, we just need to round the rate up to match it with the available engine on the market.
Please, watch the following Youtube video of how a resistance test is carried out using model in a towing tank.

For large ships, the power prediction method may not be enough. So, to better predict the resistance and propulsion characteristics of the designed ship, model test has to be carried out.
After performing the resistance calculation, the next step is adding the losses from the effective horse power obtained to predict the delivered horse power, the shaft horsepower and the brake horse power of the main engine of the designed ship. This is also known as forward calculation. The bhp obtained in this calculation might slightly be different from the available engine on the market as I have explained above. Therefore, after selecting the main engine, usually based on the brochure data from the marine diesel engine manufacturer, the propulsion calculation will be continued at afterward direction to the propelling device or the marine propeller.
Here, the brake horse power of the real engine will be reduced with the frictional losses along the shaft bearings and hull forms to obtain what is called effective horse power curve of the resistance calculation and the reduction of losses from the real main engine. When naval architects delineate these curves, they will be able to check the resistance and power of the designed ship.
I want to remind you here, that if you are designing a propeller, the rated power of the main propulsion machinery that is used for "afterward" calculation must not be the 100% MCR (Maximum Continuous Rating). The rate that naval architects or propeller designers must choose is the normal continuous rating which is around 80% to 85% of the MCR.  The easiest way to find it is by reading the engine's performance graph which is the work of the engine at the most efficient fuel consumption. This is chosen to prevent the engine from broken down. Naval architects must based the propeller design, on the engine brochure supplied by the manufacturer, on the most efficient rating of the curve on power - speed and specific fuel oil consumption of the marine diesel engine.
After determining the main engine and the propulsive efficiency of the designed ship, the next calculation is determining the QPC or Quasi Propulsive Coefficient which can be obtained by using Emerson formula. The design of the propeller can then be done if speed of advance of the ship VA and the value of Bp has been obtained.
I used Bp delta diagrams of Troost B4 series when designing the propeller of an Open Hatch Bulk Carrier in 2000. The ship was being constructed by PT PAL shipyard at that time.
The propeller designer must also perform cavitation calculation usually using Burril Cavitation Chart, and propeller blade strength calculation usually using D.W. Taylor method to ensure that the propeller is save and reliable in performing its duties during the operation of the ship.
The last step in the design of propeller is drawing. Generally, the drawing method used is Holst dated in 1924 as explained by Prof. W.P.A. van Lammeren in his book Resistance, Propulsion and Steering of Ships.
Resistance and propulsion calculation of a ship is now easier to be performed due to the availability of various software on the market. But it is advisable for naval architects and propeller designers to understand the whole process of manual design procedures which is the concept or philosophy of ship design that has supported the art and science of naval architecture for hundreds of years. by Charles Roring in Manokwari of West Papua

### Rolling Period of A Ship

When I was still studying in Naval Architecture department of Pattimura University, I was told that the rolling period of a ship should be between 7 and 8 seconds. This is to ensure that passengers and crews will not suffer from sea sick if the rolling period is less than seven. It means the centre of gravity of the ship is too low creating a big righting moment that is responsible for restoring the ship into its upright position. If the rolling period is higher than 8 seconds than it will be considered not safe for the stability of the ship herself.

Sometimes if the cargo is not evenly distributed, the crews have to balance the ship by filling the ballast tanks with sea water. The ballast tanks are usually placed in the double bottom of the ship. The ballast condition improves the vertical and longitudinal center of gravity thus making the ship more stable during her voyage in the middle of the sea.

Back to the discussion of the rolling period. I remembered that there was other explanation from a book entitled Buoyancy, Stability and Steering of Ship written by Dutch Naval Architect Drs. A.R. Bakker, If I am not wrong, which said that the rolling period of a ship can be expressed in a non dimensional period number which is between seven and fourteen. I wish that I could get that book again. I have forgotten how to calculate the non-dimensional rolling period of Kemp stated in that book but I believe some naval architects still read the book as a reference material especially in the Netherlands. by Charles Roring in Manokwari of West Papua - Indonesia

## Wednesday, May 6, 2009

### Prime Mover of Passenger Ship

When designing a passenger ship, naval architects have to come to a decision whether to choose steam turbine or diesel engine as the ship's prime mover. In the past, most of the passenger ships used steam turbine as their prime mover. The choice of this kind of marine engine was based on a consideration that steam engine has relatively very low vibration. Therefore, steam engine was more suitable for passenger ships. However, steam turbine installation needs more spaces for boiler, condenser, turbines, reduction gears and piping installation.

Improvements in the design of marine diesel engines have led to the application of diesel engine to passenger ships. Marine diesel engines are specially designed to have low RPM to adapt to the diameter of the propeller. This design constraints led to the development of low speed diesel engines for big ships. The lower the speed of the main engine, the better will be the efficiency and the larger will be the diameter of the ship's propellers. In smaller ships where low speed diesel engines are not available, reduction gears are needed to lower the RPM to match it to the RPM of the propeller at its optimum efficiency.

The vibration of marine diesel engine, as the prime mover of a ship, has to be kept lower to make the ship comfortable to all the passengers and crews. If the vibration of a vessel is high, passenger will not be able to sleep well or to enjoy the cruise. Marine engineers and Naval Architects have to work hand in hand to analyze the vibration of a ship before applying damping devices such as rubber and bearings to propeller shaft and engine bed foundation. Now the use of marine diesel engines in passenger ships is a common thing. by Charles Roring in Manokwari of West Papua Indonesia

## Tuesday, May 5, 2009

### Naval Architecture books and ship design software

I just received a phone call from an old friend of mine, Yunus Kermite. He is a naval architect who works for Department of Marine and Fishery. He is responsible for assessing the gross tonnage and net tonnage of fishing boats. We talked a lot this afternoon mentioning the good old memories of our past time in department of naval architecture the University of Pattimura.

Then, I said that I was about to send him a CD containing textbooks in pdf formats such as basic ship theory, marine screw propeller and the free version of ship design software, delftship.

The number of titles is around 50. Most of them are related to ship design and ship theory. I personally still understand this subject but I don't work in shipyard. With free ship design software in my hand, I think, I will write a book or website about how to design ship hulls, and other subjects on resistance and propulsion of ships or the stability calculation of ship.

Indonesia is the largest archipelago in the world consisting of more than 17,000 islands. Ships and boats are needed to connect the islands for transporting people and goods. Therefore, the Indonesian government should invest a lot of money in developing its maritime industry. It is sad to see that many universities that have department of naval architecture and marine engineering do not get enough financial support from the government.

I hope that the opening of Departement Kelautan dan Perikanan will support the educational institutions that have such study programs as Naval Architecture and Marine Engineering.

## Sunday, May 3, 2009

### Taking pictures of people and giving the print outs to them

I like going around my neighborhood walking. I usually bring with me my Sony Cyber-shot digital camera. It is a compact device which I like to carry around while traveling. Whether I visit an old friend of mine or flying to other island, I like to take pictures and the surrounding scenery.

What will I do with those pictures? I use them most for my blogs. I write travel stories in insert these photos in the posts. The latest ones are the photos of local Papuan people who live some 100 meters behind my house. They were preparing a tent for Saturday night party. These local West Papua look happy when I shot them with this digital camera. I told them to pick up the print out the next day. Then I continued walking into the tropical jungle. You can read the story of what I did in the jungle at my previous post

## Saturday, May 2, 2009

### Surveying the spring water in Table Mountain for Local Community

My travel story today is about a short journey to the jungle several hundred meters behind my house. I just returned from Table Mountain of Manokwari. I went there with Oom Cornelis to survey the spring water there. The purpose of this "expedition" is to construct a reservoir which will supply the local community of Kompleks Missi with clean water.

Clean water has been a serious matter for local people here although there are many spring-waters at the foot of the Table Mountain. It took fifteen minutes walking from my house to the spring water. I took some pictures a long the way to the spring water. It is located in a cave. The entrance of the cave is very small. One has to squat to enter the cave.

It was very dark inside the cave and I did not bring any flashlight. Fortunately, my mobile phone has the flash light, enough to guide me and Oom Cornelis to enter the cave.

There is a piping installation inside the cave from the spring water to the house of Catholic sisters of Manokwari. The distance between the spring water to the place where the local community live is 700 meters.

After surveying the spring water and taking some pictures, I have to compose a proposal which I have to send to the office of social agency for requesting the construction fund. It will take around one week to make the proposal. The office is a local government's body which handles things that are related to social welfare of the people. I hope that the local government will give positive response to the request of this local people. by Charles Roring in Manokwari of West Papua Indonesia

## Friday, May 1, 2009

This afternoon, an architect came to my bookstore asking if I sell AutoCAD 2009 books. I said I have some AutoCAD books. While he was reading the titles of the books on the computer bookshelf, he came across with Archicad. Then he came to my desk. He asked, "Do you know the difference between AutoCAD and Archicad? Which one is better?"
Well, it is difficult for me to answer his question. AutoCAD and ArchiCAD are two different things. They may look similar but they are different. Which one is better? Better for what? For designing complex building, I might say that ArchiCAD is faster in meeting the needs of architects. For designing machinery and their elements, individual work piece such as a bolt or a car frame or a table, I will say that AutoCAD is more flexible. Yes, you can design such things with Archicad but you need more steps and extensive knowledge of GDL programming language.
The better way to compare Archicad with its right counterpart is by comparing it with AutoCAD Architecture or Revit Architecture. These are the softwares which provide features that are similar to Archicad. Revit has even been released in three forms, i.e. Revit Architecture, Revit MEP, and Revit Structure.
I am not an expert of Revit Architecture or Archicad so I dare not compare them. For me, both of them are good for designing homes and buildings. I have used Archicad for some three or four months and I feel that I am comfortable with it. I just need to practice more to find many features the software has. When I have mastered Archicad, I will write more tutorials about it in this blog.
Archicad and revit for house design
Recommended book for home building technology

### The Ceiling and Windows of a Wooden House

When designing a ceiling whether manually or automatically using such software as Revit Architecture or Archicad of Graphisoft, an architect must think both the function and aesthetic appearance of the ceiling. Ceiling is an integrated part of every house.

It can be made of wood, metal sheets or composite and other fiber material. On the ceiling, we have lamps, fan, loudspeaker and fire fighting equipment. The following pictures are ceiling of a wooden house. The surface of the ceiling is not flat. It is made of many smaller wooden boards that are artistically arranged.

To balance the dark color of the wood, the surrounding side of the ceiling and the walls are painted with leaving the contrast look of the house. The exterior of the house is also similar to the interior one. The ceiling and the windows are made of wood. The owner of the house does not apply brighter painting to them. Instead, he painted the wall white to balance the dark brown color of the wood.

To protect the house from theft, steel frames are installed at the window openings separating the interior and exterior of the house without blocking the sunlight from entering the interior. This house was designed and constructed by the owner alone in Manokwari of West Papua following the typical design of the Minahasan wooden house in North Sulawesi.

The use of wood as the main material of a house will not threat the tropical rainforest as long as the practice is done in sustainable way. It means that after cutting the trees, people have to replant them with new trees. Tropical rainforest is important not only for the animals living inside it but also for human beings who need clean air and water as well as coral reef that lies deeper under the sea. by Charles Roring in Manokwari of West Papua - Indonesia Also read: