## 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.
Sincerely

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...

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