Layer Properties of Delftship

Last night while exploring Delftship.net website, I came across a new sailboat design called the "Loyalist". It was designed by Richard J. Saunders. I immediately downloaded and opened it in Delftship free edition to explore it more in 3D virtual environment. Honestly, I am amazed by the details Mr. Saunders created especially on the hull frames and the deck house. Mr. Saunders has shown to us all the possibilities the Delftship software can offer to naval architects and boat designers. Before seeing this design, I thought that Delftship could only be used to design simple hull lines (lines plan) of a ship or a boat. Now, I fully realize that it is a powerful naval architecture software that ship designers should have. If you haven't used Deftship before, I suggest that you visit www.deftship.net and download the free edition of this great ship design tool. As the price of the professional edition is not expensive, I think buying it is a great investment.

Back to the discussion about this "Loyalist" wooden sailboat. In order to visualize the inside parts of the boat, we need to hide the hull (skin). Hiding or displaying certain parts of the ship design is very easy in Delftship. It can be done by activating or deactivating a number of layers that make up the sailing boat design. To do that, with the Delfship program is active on your computer screen, Click Edit and Choose Layer, then click Dialog.... You will see such layers as rudder, keel, floors, hull, hull frames, deck, deck frames, and etc in the layer properties window. Checking and unchecking any of the layers will directly display and undisplay certain parts of the ship that we are exploring at the moment.

As a new learner of Delftship, exploring the designs submitted or uploaded into the Delfship website by ship designers is a great way to know more tools and capabilities of this great ship design software. I am now convinced that Delftship is a right choice for all naval architects who want to design and analyze boats and ships.Charles Roring

Ship Design

I have written several articles related to ship design calculation. If you are interested in reading them, please, check the label Ship and Boat Design of this blog. During the design process, naval architects will be required to determine such parameters as main dimensions, hull form, displacement, freeboard, depth, capacities, trim and stability, economic considerations, longitudinal and transverse strength, structural scantlings, resistance and powering, machinery, endurance, wood and outfit, lightweight and deadweight, and the material costs.

After calculating the above parameters, the next step will be the design or drawing of the ship. The first drawings will be the linesplan and the general arrangement. The detailed construction drawing will be made based on the rules and guidande provided by such classification societies as NK, ABS, LR, DNV, and etc.

Propeller and Ship Propulsion

I have written a number of articles related to resistance and propulsion of ship especially in relation to the design of marine screw propellers. You can see them at labels Marine Propeler and Resistance of Ship that you can see on the left column of this blog. Please, click the following links to read each of them. In the design of marine screw propeller, the first thing that naval architects must perform is carrying out resistance calculation. After obtaining the effective power and speed curve the next step is doing the forward calculation to obtain delivered power, shaft power and finally the brake power. The calculation will then be continued backward using the real break power (in kilowatt or horse power) obtained from the engine's brochure to obtain the shaft power and delivered horse power by considering the losses in gear box, shaft bearings, stern tube and bossing. When these have been done, the next step is executing the propeller design calculation.

Adding Knuckle Line or Hard Chine to a Boat’s Hull in Delftship

Delftship is a ship design software which enables naval architects to create, or modify the hull of a boat or a ship effortlessly. In my previous article, I discussed about the drawing modes which delfship has and how to draw deck for yacht design in Delftship.

When designing high speed boat, a naval architect will design the form of the hull that is not fully displacement one. In high speed displacement form boat will face problems related to stability. So, to solve the problems, naval architects will use plane hull or semi displacement hull which has V form. In other words, the hull will not round but will have knuckle lines.

To create such hull with chines, with the Delfship program on your computer screen opens, first click the longitudinal line of a half bread hull in perspective view while you are pressing Ctrl key. Look at the above picture.

After that when the line has got yellow color, click Edit in the menu bar and select Edge. Then click the Crease option. Now, the yellow line of the hull line which we want to knuckle will be stronger.

To visualize the hard chine which we have just created for the boat's hull, in perspective view, press Ctrl - G. The computer screen will present a 3D view of the designed boat like the following.

If we want to see the underwater form of the boat, we just turn it by moving the scroll bar at the right and at the bottom of the computer screen. The boat's or ship's hull with hard chine should look like the one below:

If you do not have the program, just go to delftship.net and register your name in the website. They will give you access to the content of the Delftship website including the download link for getting the free edition of Delftship. Delftship is similar to Maxsurf, Rhino Marine, and Autoship. It can be used to create 3D forms of ship models including the hulls, superstructure, masts, rudder and other appendages. It can also calculate the hydrostatic properties and resistance of the boat or ship. by Charles Roring

Delftship Drawing Modes for Naval Architects

Delftship is light yet powerful ship design software for naval architects capable of developing hull form or ship's lines plan and calculating hydrostatic properties. In my previous post, I discussed about how to design the main deck of a yacht using extrude function of the software.

Now I am going to discuss various drawing modes which the Delftship has to visualize the ship drawings in three dimensional views. On page 14 of Delftship user manual book we can read that the computer ship design software provides five drawing modes which ship designers can use to see the fairness and the 3 dimensional forms of their design.

After designing the hull form of the yacht, I want to visualize it on computer screen in 3D views. The first view is Wireframe. This is the view which naval architects can use to see the boat or ship through its points, lines and edges. The designed ship is presented only with lines. Press Ctrl-W and you will see the yacht that looks like the following drawing

To further explore the Delftship design capability, we can visualize our yacht in Shade drawing mode. The surfaces of our yacht will be represented in solid color, lines and curves. The submerge surfaces of the boat will have different color. Press Ctrl-F to see the boat in Shade Mode.

Naval architects can check whether the surfaces of their design are developable or not. This can be done by pressing Ctrl-D. The boat will look like the following

The above view is needed by the shipbuilder to see whether the hull which naval architects develop can be manufactured or not. Most of the ships' hulls have curve forms in two directions. These are also called compound curves. Naval architects need to design the hull form of the boat in a way that the surface will look green to enable plate development.

The next drawing view to visualize the yacht is the Gaussian curvature. Press the Ctrl-G, then the drawing of the boat will look like the one below:

The Gaussian curvature is used to check the fairness of the hull. Please read page 14 of the Delftship user manual to understand more about this view. The last drawing mode is Zebra shading. To activate it, press Ctrl -E.

Computer ship design software such as Maxsurf, Delftship, Rhinoceros and Autoship are powerful in helping naval architects in visualizing their designs in 3D forms to ship owners. These software have greatly shorten the drawing or design time period naval architects usually spend when executing it manually. by Charles Roring.

Yacht design with Delftship

The following video from Youtube shows how a racing yacht moves at sea. It uses sails as prime mover. To have a faster speed, the yacht must have smaller block coefficient with streamlined hull that minimizes water resistance.

The design of ship and boat is now easier due to the availability of such computer aided ship design software as Delftship, Maxsurf, Autoship and etc. In today's post, I am going to explain how to design the main deck of a yacht using Delftship. If you haven't got the software, just go to Delftship.net and download it. You need to register yourself first before being able to get the free version of the Delftship.

The boat that I am about to design is the default hullform given by Delftship when I first launch Delftship's new file. The principle dimension is Length: 12 meters; Beam: 3.7 meters and the draft: 0.5 meters. After launching the new file, we will get the yacht design plans as shown on the following screenshot:

Choose the Perspective view so that we can visualize our steps of hull design in 3D form.

With the perspective view of the Delftship screen as the main window, while holding Ctrl key, please, click the edge of the boat. After that, highlight the Edit button. The pull-down menu will show up. Then select the Edge and click the Crease button. This will prevent the curving along the edge of the deck and the side hull.

After clicking the Crease, while the yellow line along the deck edge is still active, click the Edge again at the pull-down menu of the Edit and then select the Extrude option. You will be asked to enter some value.

Because we need to extrude the deck line to the centre line of the boat, we fill -1.75 meters as the half value of the yacht's breadth in the Transverse direction form.

As a result, we will get the following hull form in Plan View Window of the Delftship.

Now, we need to move the yellow edge of the deck line until it really in one axis as the center line. To do this, with Plan View of the Delftship Window is activated, click the Control points of the deck line while holding the CTRL key.

As you will see on the computer screen, the Delfship will show X Y Z coordinates. Fill in 0.00 in the Y form to move the points of the yellow deck line to the centerline of the yacht. When you have done it, press Enter, finally you will get the hull form of the yacht as shown below.

If you still haven't seen the 3D view of the boat, select Window which is located next to Help option menu. Then choose the Perspective view. After that Click the Show both sides from the pull-down menu of the Display. The remove the red lines and the control net, just click it. Now, your yacht design should look like the one above. by Charles Roring

Ship’s Displacement Calculation using Simpson’s Rule

Before we begin to calculate displacement of a ship, please watch the following video to understand the basic theory of how Simpson's rule is applied in calculating areas of curves.





Displacement of a ship is the volume of sea or fresh water displaced by the ship when floating. The volume of the displaced water is the same as the volume of the immersed hull of the ship. To calculate the volume of the immersed hull, first, we must calculate the several equidistantly spaced waterplane areas from the keel to the designed load waterline. Please, read my previous post on Boat's Waterplane Area Calculation Using Simpson's Rule which I uploaded on this Naval Architecture blog yesterday.

The method for calculating the displacement volume is the same as the one used in waterplane area calculation. All naval architects are familiar with the Simpson's rule. To make my explanation more understandable, I will give a sample of calculation as follows:

A ship is floating at sea at her 4 meters draft. Common interval or CI is 1 meter ( the waterplanes are equidistantly spaced from draft 0 to draft 4 meters). She has waterplane areas and drafts presented as on the following table:


Calculate the ship's displacement in metric ton.
Using Simpson's first rule, the ship's hull volume of immersed in the sea water (mass density = 1.025 ton per cubic meters) is calculated in tabular form as follows:

Ship's volume displacement = 1/3 x C I x total of volume function
= 1/3 x 1 x 7,206 = 2401,999 cubic meters

Because she is floating in sea water her weight = 2401.999 x 1.025 = 2462.049 metric tons

Now, all the design and calculation of ship form can be executed using such computer software as Delftship, and Maxsurf. But how all the ship hydrostatic properties are calculated manually are important to be presented in this blog to help students in naval architects and those who are interested in this field understand the whole philosophy of ship design.  by Charles Roring

Waterplane Area Calculation with Simpson’s Rule

Naval architects will always have to deal with ship form calculations. These include the calculations of areas of waterplane, transverse sections to obtain the curve of sectional areas, the calculation of hydrostatic properties of the ship such as the displacement, the center of buoyancy, the center of floatation, the transverse metacenter above the keel and etc. In this post, I am going to explain how in Naval Architecture studies we use Simpson's rules to calculate the waterplane area and the position of its centroid of area and finally, the second moments of area for a boat.

For example, we get the ordinates (in meters) of the waterplane of a boat which is defined by a series of half breadth ordinates at 2 meters separation, as follows:

For illustration, I have drawn or sketched the waterplane using pencil on a piece of paper.

To carry out the ship or boat form calculation, I use Microsoft Excel. I entered the half bread ordinates of the boat in a table and perform the calculation as depicted on the table below:

As explained by E. C. Tupper on page 55 of Introduction to Naval Architecture, The column F(A) represents SM x y; F(M) = SM x lever x y; F(I)long = SM x lever x lever x y and F(I) trans = SM x y ³. From the summations in the table:

The area of the waterplane (for both sides of the boat) = 2/3 x 2 x 67.2 = 89.599 square meters.

The centroid of the area is 2 x 21/67.2 = 0.625 m forward of amidships.

The longitudinal second moment of area about amidships = 2/3 x 2 x 2 x 2 x 284.4 = 1516.799 m⁴

The minimum longitudinal second moment will be about the centroid of area and given by:

I_L = 1516.8 - 89.599 (0.625)² = 1481.647 m⁴

The ship form calculations can be carried out not only by Simpson's rules but also by Trapezoidal, Tchebycheff's rules. With the use of computer spreadsheet program like Microsoft Excel and Lotus 123, the calculation can be done and modified in real-time easily. by Charles Roring

Watch the video of ship displacement calculation on the following posts:

• Ship Displacement Calculation
• Ships Displacement Calculation using Simpson's Rule 

Trimaran and Tricycle

In the design of high speed marine vehicle, we know that there are ship types such as Catamaran, Trimaran, or Jet Foil. Fast ship needs twin boat and trimaran to stabilize the ship when moving fast on sea surface. Trimaran especially is further improvement or development of traditional outrigger boat used by Pacific islanders when catching fish around the coastal region near their villages.

On land there is also a term called tricycle or triseda. This is a popular vehicle in Indonesia which is used by kiosk or shop owners to deliver goods to their customers. My father just bought a new one. On the picture above, one of our workers was riding it. I see from the design, it looks like a small truck but with only three tires. If at sea a trimaran-hull increases the stability of the boat at high speed, I am doubtful if tricycle or triseda has similar properties in terms of stability. Four wheels will be more stable on the road than three wheels vehicle. From the fuel consumption point of view, the tricycle is lighter and the trimaran has finer body. So they are more efficient during operation.

Sea Travel and the Maritime Industry in Indonesia

Indonesian people have traveled from one island to another for years. Sea travel is not seen as tourists journey but business one. As the largest archipelago in the world, Indonesia has more than 17,000 islands big and small. Before the introduction of modern passenger ships from Germany by Pelni lines, the islands between Asia and Australia continents had been served mostly by small steel cargo vessels, ro-pax ferries, and thousands of traditional wooden boats.

Sea travel and maritime industry are two inter-related sectors that support the mobility of travelers and goods in Indonesia. Airplanes from tens of airline companies in Indonesia cannot replace the vital role of passenger - cargo ships that have existed in this country for years. So, although the number of flights continues to rise in many cities and towns in Indonesia, it is not enough to fulfill the needs of means of transportation to move goods and people. Ships and boats still play significant role in Indonesian islands.

The growth of population in Indonesia is around two percent every year with the current population has reached more than 220 million people. This figure puts this country as the fifth most populous nation in the world. Such a large number of people scatter around thousands of islands from Sabang to Merauke. Besides having a lot of population, Indonesia too has high economic growth.

Indonesia's high economic growth, in the middle of world financial crisis, needs the provisions of various types of ships to support it. Indonesia needs hundreds of small passenger ships to serve the mobility of the Indonesian people and cargo ships to transport goods. Big cities in Java and Sumatra needs raw materials from Kalimantan, Papua and Sulawesi islands whereas small towns in the remote islands need cargo ships to deliver manufactured products to support the economic development. by Charles Roring

Efficient propulsion system in ships and boats

There are many factors that influence the fuel consumption of ships or boats. Naval architects know that the interaction between the propeller, the hull and the main engine greatly influences the fuel consumption of ships whether they are big or small. So, in order to obtain ships that have optimum propulsion efficiency, naval architects must design the ships with the propulsion system that are fully integrated.

This is not an easy thing to do because every propulsion unit is contradicting one to another. For example an efficient hull form must have lower block coefficient with streamlined shape that in the contrary reduce the carrying capacity of the ships or boats that are being designed. In addition, the use of diesel engine is seen as a highly efficient main engine that is now used in many ships but we must not forget that diesel engines have vibrations and exhaust gases that will not be comfortable for crews and passengers.

Besides the hull form and the main engine, the propeller plays very important role in the design of the propulsion system of a ship. Marine propeller is usually located under water at the stern of a ship or boat. If the propeller is well designed and manufactured by experts in ship's propulsion, the fuel and financial savings will be greatly significant throughout the operational years of the ships or boats. by Charles Roring. Also read: How to estimate ship's length for a new design

Delineating ship lines-plan and drawing human figures

All naval architects have lives other than designing ships or calculating resistance, propulsion and stability of marine vehicles. For me, my pastime activities include drawing human figures, jogging and photography. After reading complicated hydrostatic properties of ships in some naval architecture textbooks during the day, at night I prefer to make sketches of beautiful girl, birds, scenery, and color it using Derwent watercolour pencils that I bought several years ago in Gramedia bookstore of Surabaya city.

Drawing lines plan of a ship is different from drawing the body of a beautiful girl.  Drawing human figure does not need a lot of technical calculation only more practices that are needed. Ship's lines plan can only be delineated after principal dimensions have been determined from preliminary design calculation. In the past, naval architects had to draw and fair ship lines manually. The body-plan of ships or boats has to be streamlined to minimize the resistance while moving on the water. Now, computer software such as Delftship and Maxsurf is specially made to help ship designer for doing such kind of job with better accuracy.

As I have previously said in the first paragraph of this post, I am very fond of drawing human bodies especially girls. Naturally girls' figure is streamline but to draw them we don't need any complicated calculations. It is the skill level of the artist's hand that determines the quality of the drawing. Usually, before painting or coloring, I make the sketch of the girl using Staedler 2B pencil. I will draw the macro drawing first, i.e. drawing the major parts of the body such as head, arms, body, and legs. After correcting the proportions of the body, I will continue the drawing by adding details to eyes, nose, lips, fingers, and clothing ornaments. The sketch of the drawing has to be perfect before the coloring is done.

Because I use Derwent watercolour pencils to colour the girl, I have to do it little by little. After applying first layer of colour, I have to let it dry for one day and continue the coloring again. So, the finished painting takes one week to accomplish. I can do that in one day but I will get drawing results that looks rough. by Charles Roring Read: Boat building and Living tradition of the Mentawai Tribe ; Sailing Across the North Pole with Boat to the New World and How to estimate ship's length for a new design

Sailing Across the North Pole with Boat to the New World

by Charles Roring

On this article, I am not going to talk about ship but a little about a legendary boat. There was a legend in Ireland which says that the Irish monks were the first European to land on the New World. Around one thousand years ago, an Irish boat sailed across the north-pole waters to find a new land. They used a boat whose hull was not made of wood but animal skin. I read the story about this expedition on an article of National Geographic Magazine. I forgot the year of its publication. I wonder how a small boat crossed the Atlantic. It was too dangerous to sail from Ireland to the New World with a boat that was not seaworthy. All naval architects would agree with this.

There were some Irishmen who re-built similar boat and used it to cross the icy ocean and landed on Canadian territory. They proved that the Irish monks could have been the first Europeans to find the New World. I saw that the cover picture about the story was very interesting and I drew it on a small paper. The boat had sails decorated with red-cross. I used Derwent watercolor pencils to make the drawing. It took three days to finish the drawing of the boat.

How to estimate ship’s length for a new design

by Charles Roring

After performing the calculation for estimating the ship's displacement, deadweight, as well as the lightweight of a new design, the next step a naval architect will usually calculate is the length. There are many books about ship design that deal with the estimation of ship's length. I recommend Merchant Ship Design by Munro-Smith, Ship Design and Construction published by SNAME, or two other books that I will mention below.

If the new ship is going to operate on international shipping, it might pass through Panama Canal which only allows the maximum length to be 289.56 m. Length of the ship can be estimated using Sneekluth's formula. Please, see page 2 of Ship Design for Efficiency and Economy, written by H. Sneekluth and V. Bertram.

Sneekluth Formula

LPP = Length Between Perpendiculars (meters)

Δ = ship's displacement (ton)

V = speed (knots)

Fn = Froude number

The length of the new ship can also be calculated using cube root format which is presented on page 5 of Ship Design and Performance for Masters and Mates as follows:

Cube root format

L = LBP

p= density of sea water = 1.025 metric tons/ m³

C_B = block coefficient

C_D = deadweight coefficient

Although I only present two formulas here, actually, there are still other formulas for estimating the length of a new ship. If you are now designing a new ship, I suggest that you design its lines plan using delftship. Also read: How to calculate displacement of newly designed ship and Ship rudder

How to calculate displacement of newly designed ship

by Charles Roring

Naval architects when designing a ship often face many difficulties in determining the displacement due to the lack of data for the weights of hull components, propulsion machinery, wood and outfit, equipment and etc.

Displacement of a ship is the volume of water that it displaces when floating at sea or river. The volume is calculated in cubic meter. If it is multiplied with the sea water density (1.025 metric ton/cubic meter) then we can get the displacement which equals to the ship weight.

On page 4 of Ship Design and Performance for Masters and Mates, Dr. C.B. Barrass gave a simple formula for calculating the displacement of ships. The formula is called deadweight coefficient.

C_D = dwt/W

The following table is the typical deadweight coeffiecient for various types of merchant ships

The deadweight coefficient varies from one ship to another depending on its type and is calculated up to SLWL or Summer Load Water Line. It is the condition where a ship is fully loaded.

Worked Example:

For a new design, the deadweight of the ship is determined to be 12,000 metric tons. Information from previously built similar ships suggests C_D to be 0.6. Estimate or calculate the fully loaded displacement (W) and the lightweight of the new ship:

W = dwt/C_D

W = 12,000/ 0.6 = 20,000 metric tons.

Lwt = displacement - deadweight

= W - dwt

= 20,000 - 12,000 = 8,000 metric tons This is for only for preliminary design calculation.

If we see on the table above, the ship is container ship.

Also read: Ship rudder

Ship rudder

Every cruise ship and cargo vessel needs at least one rudder. This is usually installed behind a propeller which is located at the stern of the ship or boat. Although we cannot see it, the functions of rudder are vital for the maneuverability of the ship. A rudder, according to page 87 of Ship Design and Performance for masters and mates, is needed
1. To keep the ship on a straight line, from Port 'A' to Port 'B.' In other words, to have good course keeping properties.

2. To turn the ship in a small turning circle diameter. In other words, to have good turning characteristics, say in confined waters.

The dimensions of a rudder are determined by the coefficient K according to the type of ship, the length between perpendiculars, and the loaded draft of the ship.

The following formula is used by naval architects to calculate the rudder area of ship. A_R = K x LBP x d (m²)

If a ship is a fast one, generally, its K value is lower. So, the rudder of high speed marine vehicles is smaller than conventional speed marine vehicles with the same displacement. Below is the coefficient K for several merchant ships. The above formula can also be used for ships with twin screw propellers.

We have to remember that rudder is not the only equipment that is available for ship's maneuvering. Most cruise ships and cargo vessels have bow thrusters to help them turning to the right or to the left.

Usually the height of a rudder is 1.75 its length. Please, see the following illustration as a guidance for naval architects when designing ship's rudder.

It is important to note that the rudder size should not be too large. If it is larger than appropriate, it will be an additional resistance for the ship itself as well as decreasing the course keeping properties of the ship.Rudder is turned by hydraulic mechanism that has been installed above it inside the stern part of the ship's hull. by Charles Roring Also read: Are cruise ships safe for the marine environment?

Ship Design Books

by Charles Roring

The study of naval architecture is related to the theory of ship that is aimed at designing, building and repairing of ships and other floating structures. There are many books that discuss about ship designs. Some of them that I used to read are Ship Design and Construction, Ship Design and Performance for Masters and Mates, and Ship Design for Efficiency and Economy.

I downloaded the Ship Design and Construction book from rapidlibrary.com yesterday. It is a very thick book written by a group of authorities in the field of naval architecture. Unfortunately, the quality of this e-book is so bad. So I recommend that those who want to study or read the book buy or order it directly from the Society of Naval Architect and Marine Engineers (SNAME). Amazon online bookstore also sells the book, some are used books that are offered in cheaper price.

The book of Ship Design and Construction discusses various aspects that are related to ship design such as mission analysis and basic design, general arrangement, load line assignment, tonnage measurement, analysis and design of principal hull structure, hull materials and welding, hull outfit and fittings, cargo handing, ship maneuvering, navigation and motion control and many other subjects.

If you don't have the background in naval architecture, I suggest that before reading this book, you have to read basic ship theory volume I and II or the Principles of Naval Architecture. These books provide you with strong theoretical foundation before dealing with more complicated aspects of ship design.

Naval Architecture is different from Land Architecture. Ships are moving structures. So, there are other aspects such as stability of ships and resistance and propulsion that need to be studied. Also read: Are cruise ships safe for the marine environment? and Is traveling with cruise ship still an attractive adventure? ; 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