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Yacht weight measurements

Discussion in 'General Yachting Discussion' started by Ben, Mar 26, 2006.

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  1. Ben, Mar 26, 2006
    #1
    Ben

    Ben Senior Member

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    I was wondering if someone could explain to me the different weight measurement methods used, and how they compare to each other.

    For example, Rising Sun's details are...

    Gross Tonnage : 7841
    Net Tonnage : 2352

    And Octopus's details are...

    Gross Registered Tonnage : 9932 mt
    Net Tonnage : 2979 mt
    Deadweight : 1570 mt


    At this point, my best guess is that GRT is the yachts weight including fluids, tenders/helicopters/submarines, etc. and that Net tonnage is the yachts weight 'dry'. But after seeing Deadweight, I need help.:eek:

    I'll assume that Displacement is simply the weight of the water that has been displaced to make way for the vessel.

    Please help!
  2. cyd, Mar 26, 2006
    #2
    cyd

    cyd New Member

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    Grt

    GRT is based on volume of interior living (non machinery filled) spaces and has nothing to do with the actual weight of the yacht, hope this helps clarify why some GRT.s are very high.
  3. Ben, Mar 26, 2006
    #3
    Ben

    Ben Senior Member

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    Thanks for that cyd.

    I suppose that RS's large engine room would be a drawback in that case.

    When calculating GRT I wonder what they'd class as interior living (non machinery filled) on Octopus. I guess tender storage is not counted, nor would her giant fuel tanks be counted. What about her bridge or ROV control room. I suppose her recording studio would be counted in her GRT.

    El Salamah GRT 12,250!
  4. Ben, Mar 28, 2006
    #4
    Ben

    Ben Senior Member

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    I've found a site that has a pretty good go at explaining the different weight systems. I found it fairly usefull, but it is worded for the shipping industry, not for yachts.

    http://www.answers.com/main/ntquery?method=4&dsid=2222&dekey=Tonnage&curtab=2222_1

    I'll continue looking for more relevant, precise wording.

    For example, what exactly is classed as "non-productive spaces" on a non charter taking megayacht?
  5. Ben, Mar 30, 2006
    #5
    Ben

    Ben Senior Member

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    This link provides the best explination yet of what the different weight types mean when comparing Megayachts.

    It's a couple of pages, but easy reading.

    http://www.oceannavigator.com/article.php?a=1315


    "For a large cruise ship, however, all spaces normally used to house or accommodate passengers would be included in the net tonnage measurement"

    My current understanding is that tender/toy/etc storage isn't included in Net tonnage.
    Cinemas are in, as would be recording studios and all other areas used by passengers.

    So, despite all of the space Octopus devotes to tenders/toys/helicopters/etc, she still has about 25% more interiour space than Rising Sun.
    If my understanding of Net Tonnage is correct.
  6. ESYD, Apr 1, 2006
    #6
    ESYD

    ESYD Member Removed

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    Ben,

    The International Maritime Organization (IMO) held a "Tonnage Conference" in 1969 in London, England, from which was published "Tonnage Measurement of Ships." An earlier IMO document, "Tonnage Measurement--Treatment of Shelter-Deck and Other 'Open' Spaces" was published and adopted in 1964. These are both published as small booklets and are available from Bluewater Books in Ft. Lauderdale, FL. Their website is www.bluewaterweb.com, and the telephone number is 800-942-2583.

    The first booklet costs US$10.95, and the second one is US$6.00, very inexpensive.

    These books give the definitions and formulae for calculating gross tonnage and net tonnage. Collectively, they are referred to as "international tonnage" and are used for measuring vessels trading between countries.

    Gross and net tonnage, as mentioned above, are measures of the volumes of vessels, not the weight. The weight is the vessel's displacement, so called because the weight of the vessel "displaces" a volume of water equal to the vessel's own weight, which is, of course, Archimedes'