Lightship and deadweight

Discussion in 'Stability' started by athvas, Mar 9, 2013.

  1. athvas
    Joined: Feb 2013
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    athvas Senior Member

    Is there any ratio relation between lightship and dead weight for a vessel. If the total displacement (Full load displacement) for a vessel is 'X' Tons then how much % of X will be lightship (normal range not exactly). Is there any thumb rule for calculation purposes. Plz clarify my doubt.
     
  2. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    You have to look at form first... what is the hull designed to do? Carry a lot of weight or go fast or somewhere in between? Many factors there....

    Another part of the answer is the Scantlings... what is the vessel made of? How much equipment does it have that takes away from it's load carrying ability?

    The whole package must be under consideration to get the end result... not the reliance on an abstract ratio.

    Compare the unloaded and loaded conditions of an ULCC and a Battleship... completely different design parameters, scantlings and goals... two wildly different LS vs Loaded ratios.
     
  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    If you understand what it means lightship weight, dead weight and weight at full load, you will understand that there is no percentage relationship between the three concepts. It does not depends on the scantlings or anything. (Mistake, see post #5)
    One of the items comprising the lightship weight is the weight of the structure depending, of course, on the scantlings.
    Deadweight is the sum of the weights that carries a ship, including the cargo, the ship's own fuel, provisions, fresh water for human consumption, ballast water, crew, passengers and their luggage.
    Full load weight = lightship weight + deadweight
     
    Last edited: Mar 9, 2013
  4. lewisboats
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    lewisboats Obsessed Member

    A vessel designed for one scantling and built to another won't have the same design lightship weight. Scantlings can affect lightship weight if they differ from the materials spec'd in the original design. "Calculation" in the opening post implies the design phase of the vessel and therefore scantlings are a factor.
     

  5. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    You absolutely right, lewisboats. The second sentence of the first paragraph of my post is incorrect. As I tell myself below, scantlings determine one of the items forming the lightweight. Sorry for the inaccuracy. I always say that we have to avoid these mistakes that can confuse people.
     
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