Tuesday, October 27, 2009

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.

Saturday, October 24, 2009

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.
For those who are interested in learning yacht design, please, read Yacht Design According to Perry. It presents detailed information related to yacht. As an experienced designer, Perry explains the art and science of yacht design with many of its technical challenges in an easy to understand book. by Charles Roring

Monday, October 19, 2009

Simpson’s Second and first Rules for ship’s waterplane area calculation

Naval architects mostly use Simpson's first rule when calculating the waterplane area, the displacement of ship from curves of sectional areas which had been obtained from bonjean curves plotted against ship's draught and many other curves in ship design. In fact there are two other Simpson's rules which can be used for calculating areas of curve forms. They are Simpson's second and third rule. The latter is also called Simpson's 5, 8 minus 1 Rule. In today's post, I am going to explain how to calculate the area under a curve using Simpson's second rule and then compare the result with the calculation based Simpson's first rule.
The half breadth ordinates of a ship which are 20 meters equidistantly spaced are tabulated as follows:
Simpson's second rule calculation for waterplane area of a ship
We should remember that the sum of the area function calculated above is for half breadth only. To obtain the area of the waterplane for both sides of the ship, we have to multiply it with 2. Obviously the waterplane area of the ship will be:
Area WP = 3/8 x CI x Total of Area Function x 2 (for both sides of the ship)
= 3/8 x 20 x 81.9 x 2 = 1228.5 square meters
If the half breadth same ordinates is calculated using Simpson's first rule, then the tabulation will be as follows:
Simpson's second rule calculation for waterplane area of a ship
Area = 1/3 x CI x Total Area Function x 2 (for both sides of the ship)
= 1/3 x 20 x 92.3 x 2 = 1230.666 square meters
The small difference in the two calculations shows that the area obtained from both of the Simpson's rules are only close approximation to the correct area. We should remember that naval architecture is art and science of designing a ship. It is not an exact science but it is a science. As we dive deeper into the science of ship stability, we will use Simpson's rules more often for determining the area, the displacement and other hydrostatic properties of the ship. by Charles Roring

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Saturday, October 17, 2009

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 specific weight of the seawater is heavier than freshwater. When a ship sails from the sea into a river, her draft increases. 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 calculating waterplane area. All naval architects are familiar with Simpson's rule. 
Now, all the design and calculation of ship forms can be executed using such computer software as Delftship, and Maxsurf or Orca 3D (a plugin of Rhinoceros 3D modelling software for naval architecture). But all students of naval architects must perform semi-manual calculation using Microsoft Excel or other spreadsheet software to help them understand the whole philosophy of hydrostatic calculations of a ship.  

Try reading Basic Ship Theory to know more about Simpson's Rules and their application in ship design. by Charles Roring

Friday, October 16, 2009

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 flotation, the transverse metacenter above the keel and etc. It is a tedious calculation if carried out manually. With spreadsheet software such as Microsoft Excel, we can do the job easily. There are also ship design software such as Delftship, Maxsurf that can help naval architects to do those calculations.

  • Basic theories about waterplane area calculation can be found in a number of textbooks such as:
  • Basic Ship theory by K.J. Rawson and E.C. Tupper
  • Statics and Dynamics of the Ships by Semyonov (Mir Publisher)
  • Introduction to Naval Architecture by Eric Tupper

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:
IL = 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:

Wednesday, October 14, 2009

Naval Architecture blog in Many Languages by Google Translate

I have been running this blog since May 2007. At first, I wrote articles about anything that I encountered everyday in my daily life. After some one and a half years, I decided to focus more of my posts on such subjects as naval architecture, resistance and propulsion of ships, and marine propeller. In other words, this blog is now about ship and marine environment.
I just add Google Translate tool which you can see on the top right corner of this blog. Readers of this blog are from many countries around the world and sometimes they don't fully understand the English language which I use in writing the postst of this blog. They can just choose the language in the form and let Google Translate all the translation in seconds. I find this as one of the best tool Google provides to internet users. I hope that after adding the Google Translate tool, readers of this blog can fully enjoy the content of this blog. Thank you Google and thank you all of you for visiting and reading my writings.


Thursday, October 8, 2009

Displacement in Ship Design Calculation

Mr Kumar,
The formula that I used in the article on how to calculate the deadweight and displacement of the ship is for preliminary purpose. It is on page four of the book entitled Ship Design and Performance for Masters and Mates written by Dr. C.B. Barrass. It means that the result is not final. If the material is aluminium which is lighter than steel then the coefficient, in my opinion, can be taken higher than 0.35.After obtaining the displacement, the next step is calculating the principal dimensions i.e., LBP, B, Height and draft, as well as the block, prismatic, midship, waterplane coefficients and etc. The calculation will be continued to construction calculation such as the thickness of plates for hull, decks and etc using rules from NK, ABS or LR.
Watch the following videos of how displacement of a ship or barge is calculated:

Data from the preliminary ship design calculation and construction calculation will be used to draw the ship' lines-plan, general arrangement and other construction  details using such software as Maxsurf, Autoship or Delftship. The software will tell us the weight of the lightship based on the hull components that we have drawn.
We need to use the lightship weight from  the computer  and add it to deadweight (fresh water, oil fuel, stores, cargo and passengers and etc) that we have calculated manually to obtain the ship displacement. The displacement of the ship will be refined again according to the steps of calculation based on the design spiral as explained on page 653 of  the Basic Ship Theory. Accurate assessment of ship weights is very important in determining the displacement of ship and its longitudinal and vertical center of gravity. A change to any one parameter will affect many factors in ship design. As a naval architect we must know that ship design is an art and science subject. It is not an exact science. So, even the final elements have been calculated or decided and drawn on papers, we still cannot 100% sure the exact displacement of the ship unless we put it on a giant scale to know the exact weight of the ship. Thank you for visiting my blog.

Charles Roring

pankaj kumar wrote:

Dear Sir,
I introduce myself as a navaI architect looking after various kind of design activities.I happened to see your note regarding the methodology to determine the displacement of a newly designed vessel.I saw the parametric relations...On that basis I calculated even the Lightship of a 100 passenger aluminium vessel.But My query is that is this formula applied only to steel ships or also to aluminium vessels....e.g. i had total Dwt of 12.25Tonnes..and subsequently,using the formula Cd as 0.35(for passenger cruises),the value of Light wt comes out to be 20.25 Tonnes...But i Want it for aluminium and not for steel..please help me out in this regard..
Looking forward to get your precious coments in this regard...

Warm Regards,
Pankaj Kumar.
Contact No.+919920776657.

Friday, October 2, 2009

Luxurious Trimaran Boat

Luxurious yachting is a special program from Luxe TV aimed at featuring beautiful boats that have exceptional design and modern propulsion equipment. Yacht owners are mostly wealthy people. They need boats that are fast, modern, beautiful and comfortable. Naval architects who design luxurious yachts always put best quality materials for hull construction and interior rooms to create an attractive and comfortable atmosphere inside the boat. Naval architecture is the art and science of ship design. So, a yacht or a boat will be an artwork too.



In the above picture, we can see how the designer of the trimaran designs the boat to look like an airplane. Its futuristic form makes the two balancing hulls at port and starboard sides appear similar to wings of airplane. This yacht or boat, with this kind of hull form, has high speed when operating. In addition, it is also fuel efficient due to lower water resistance properties that the boat has.



The inside of the boat is made of wood that has smooth surface. The naval architect who designed the boat has successfully created an impression that the boat is a home. Yacht or boat owners will feel that he or she is inside a home and not just a cabin of a boat. by Charles Roring. Also read: Trimaran and Tricycle