Loading case corresponding to Tropical load line mark

Discussion in 'Stability' started by athvas, Aug 4, 2014.

  1. athvas
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    athvas Senior Member

    Hi

    I have a comment from class to include a loading case corresponding to the tropical load line mark in the submitted stability booklet. The max summer draft achieved is 4.28 mtrs (Water density 1.025) .

    Do i need to change the density of water as 1 to run the tropical load line condition ?

    Depth of vessel is 6 mtrs
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    No.

    At what draft is the Tropical LL mark at??...this is your new displacement to be used for the stability booklet. SW for stability checks is always 1.025. It is only 1.000 if FW....i.e. Fresh Water mark.
     
  3. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Why? There's salt water in the tropics.

    You have separate fresh water marks on the typical load line. The 'T' mark is used for 'Tropical Salt Water', while the 'TF' mark is used for 'Tropical Fresh Water'
     
  4. athvas
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    athvas Senior Member

    Load line convention says,
    The minimum freeboard in the Tropical Zone shall be the freeboard obtained by a deduction from the summer freeboard of one forty-eighth of the summer draught measured from the top of the keel to the centre of the ring of the load line mark

    As per above statement, 1/48th of summer draught is 89 mm , so tropical load line draft will be 4280 + 89 = 4369.

    Do i need to show the loading condition for the above draft ?
     
  5. TANSL
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    TANSL Senior Member

    I have to disagree (perhaps badly interpret what has been written). One of the data collected, when making the inclinig test, is the density of water at the time. Why?, because the density of salt water is not always equal to 1,205 kg/dm3. This is not the opposite of what Ad Hoc says but indicates that for making the stability booklet is not always used 1,025 kg/dm.
    "stability checks" is precisely what is done in the booklet.
    As well said NavalSArichoke in tropical sea water is salty but its density is not the same as in the North Pole.
    When a ship sails in the tropics, sinks deeper and therefore, in my opinion, the loading conditions studied in the stability booklet should reflect this.
    New equilibrium waterplane (change the position of the center of buoyancy and therefore change the trim of the boat), taking into account the actual density of sea water, will give you a freeboard which must be greater than regulatory value.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    What on earth has the inclining experiment got to do with the question??..nothing!

    FYI Merchant Shipping Load Line Rules, 2001, schedule 4, rule 26, Freeboards - Interpretation, 1 b) states:

    “salt water” means water having a relative density of 1.025;

    And where does it state inclining experiment in this...again, it doesn't.!

    Why have you introduced a non-sequitur into this thread?
     
  7. TANSL
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    TANSL Senior Member

    Ad Hoc, all I want is to give the OP my mopinión, reasoned, how to do the exercise at hand. And of course, keep him from making major mistakes, if advice is unfortunate.
    No need to answer your questions because, I fear, do not help the OP at all.
     
  8. athvas
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    athvas Senior Member

    I can able to achieve the above draft 4369, without changing the displacement value is only when i change the density of sea water from 1.025 to 1.001

    I believe i need to show the loading condition for the above density 1.001 for the Tropical load line condition .... correct me if iam going wrong
     
  9. TANSL
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    TANSL Senior Member

  10. NavalSArtichoke
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    NavalSArtichoke Senior Member

    For the reasons stated above, IMO, you are going wrong by using a lower density for the water for the Tropical LL.

    The class society wants you to do a loading condition where the vessel is operating at its greatest displacement according to the assigned freeboards. If you arbitrarily use a specific gravity (not density) of 1.001 instead of the customary S.G. of 1.025 for sea water, the vessel will then not be operating at her maximum displacement. To reiterate, the TF mark is used for fresh water, not the T mark.

    See:

    http://en.wikipedia.org/wiki/Ship's_load_line#Load_line

    in the section "Standard Load Line Marks"
     
  11. TANSL
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    TANSL Senior Member

    If so, I have to admit that I was wrong and I was doing exactly what I was trying to avoid: you followed the wrong advice.
    If so: sorry and ask public apology.
     
  12. athvas
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    athvas Senior Member

    The max draft achieved after filling all the cargo tanks, consumables is 4282 mm. So how to increase the draft further and bring it to tropical load line draft of 4369 mm at a Spgr of 1.025 ....Can you tell me the possibilities
     
  13. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Well, what sort of vessel is it?
     
  14. athvas
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    athvas Senior Member

    It's Tanker Vessel .....
     

  15. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Can't you fudge the cargo density slightly? How many tons are we talking about?
     
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