Deep Load Line and Light Load Line

Discussion in 'Boat Design' started by marufuddin0, Jun 23, 2021.

  1. marufuddin0
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    marufuddin0 Naval Architect

    Hi, could you please explain to me what is the definition of Deep Load Line and Light Load Line? Is the boot top area the surface that goes underwater due to the change of density of the waterway? I need to know it for applying marine paint.

  2. Ad Hoc
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    Ad Hoc Naval Architect

    It all depends upon what the vessel has been asigned as its notation in the stability book.

    Light is just that - a light load...but what the designer defines as a,"light Load" is anyone's guess. It is however, often related to what the statutory rules define as - light load. Thus you need to know which rules it is to comply with.

    The deep load load is usually the maximum draft that will pass the stability rules that the vessel is compliant with at a given displacement.

    The boot just a paint line... nothing else. You define that one.
    Last edited: Jun 24, 2021
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  3. gonzo
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    gonzo Senior Member

    Is the "light load" where the vessel complies with the minimum stability?
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  4. TANSL
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    TANSL Senior Member

    What does "minimum stability" mean? I don't think it means anything. A ship will never weigh less than its light ship weight (except perhaps at the time of launch and a few days after) and will never weigh more (it should not) than at maximum design load condition. Stability, regardless of the parameter that is taken to measure it, is usually greater in the condition of light ship weight. But it all depends on how you measure stability, be it the maximum or the minimum.
    If we study the limit KG curve, it is usually a decreasing ordinate curve (KG value) as the abscissa (displacement) increases. If we take the KG value as a measure of stability, stability decreases with displacement.
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  5. kapnD
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    kapnD Senior Member

    Large vessels can control their waterline through the use of cargo distribution and water ballast.
    This is an issue under investigation with the car carrier that was wrecked in Georgia last year.
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  6. jehardiman
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    jehardiman Senior Member

    Marufuddin0; all the comments above are correct in their context. How you define "light ship" and "full load" depends on what type of ship and whomever's rules you are using. But, generally, for most "boats" (i.e. fishing, yachts,etc.) you only need to consider two conditions for the water density you are in to set the boot topping. The lower edge of the boot topping is usually in the "burned out" condition...this means all fuel, water, stores, cargo, etc have been expended, but crew, sumps, etc. are complete. It represents the last day of a zero fish/zero cargo voyage. The condition that usually sets the top of the boot topping is the "full load for sea"....this means that all normal fuel, water, stores, cargo, crew and effects are on board. It represents the first day of leaving for a maximum duration/maximum cargo voyage.
    But really, the boot topping is just to present a neat appearance and hid the scum line.
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