Loading case corresponding to Tropical load line mark

athvas · Aug 4, 2014

NavalSArtichoke said: ↑

Can't you fudge the cargo density slightly? How many tons are we talking about?
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Cargo tank status attached in xls sheet.

8.9 cm draft to be increased ( 61 tons)
TPC is 6.86

Plz suggest the changes to be done in cargo tank densities

NavalSArtichoke · Aug 4, 2014

How about carrying a little ballast? Owner carrying some cargo on deck? Owner decides to carry HFO instead of MGO in MGO tanks? There's several different ways you can load this vessel down. You're an NA; be creative.

athvas · Aug 5, 2014

Can we add ballast in this case, Will class allow this ?

NavalSArtichoke · Aug 5, 2014

Why don't you discuss it with the Class society? After all, they are the ones requesting this loading condition.

Ad Hoc · Aug 5, 2014

athvas said: ↑

So how to increase the draft further and bring it to tropical load line draft of 4369 mm at a Spgr of 1.025 ....
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It sounds like your load line mark is in the wrong location!

jehardiman · Aug 5, 2014

athvas said: ↑

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
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I think the concept that you are missing here is that the Load Line is a regulatory item assigned by the geometry of the ship, specifically the permitted minimum freeboard. It is not an actual initial design loading condition, but rather a benchmark against future operations and or operators (cf the SEWOL disaster). It is a totally separate issue from ship stability and deadweight tonnage. In the future, the ship may be loaded in a way unforeseen by anyone right now and what the Class Society is asking for is an analysis that when the ship is loaded down to her "legal" marks, that the ships form is not so unusual so as to make that load line unsafe.

The Load Lines are a quick visual reference to the crew and maritime officials that the ship, for its geometry, is not overloaded. Many ships, because of their cargo, will never be loaded down to their load lines, BUT THEY ARE REQUIRED TO HAVE THEM! Either ask the Class Society how they want you to load her down or just document the changes the density of the cargo and any deck cargo assumed. As has been pointed out the T mark is at normal density and the TF is for fresh water (i.e. Panama Canal transit).

And maybe, as has been alluded to, your hull might not be optimum for this type of cargo. If this is a reconstruction or as built, it is what it is; if it is still in design, you might want to revist B/D ratio and maybe save some steel.

jehardiman · Aug 5, 2014

A quick look at lunch at IMO 1966/1988 Load Line Convention

Regulation 1 - Strength and intact stability of ships
(1). The Administration shall satisfy itself that the general structural strength of the ship is adequate for the draught corresponding to the freeboard assigned.
(2). A ship which is designed, constructed and maintained in compliance with the appropriate requirements of an organization, including a classification society, which is recognized by the Administration or with applicable national standards of the Administration in accordance with the provisions of regulation 2-1, may be considered to provide an acceptable level of strength. The above provisions shall apply to all structures, equipment and fittings covered by this annex for which standards for strength and construction are not expressly provided.
(3). Ships shall comply with an intact stability standard acceptable to the Administration.

Regulation 40 - Minimum freeboards

Summer freeboard
(1). The minimum freeboard in summer shall be the freeboard derived from the tables in regulation 28, as modified by the corrections in regulations 27, as applicable, 29, 30, 31, 32, 37, 38 and, if applicable, 39.
(2). The freeboard in salt water, as calculated in accordance with paragraph (1), but without the correction for deck line, as provided by regulation 32, shall not be less than 50 mm. For ships having in position 1 hatchways with covers which do not comply with the requirements of regulation 16(1) through (5) or regulation 26, the freeboard shall be not less than 150 mm.

Tropical freeboard
(3). 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.
(4). The freeboard in salt water, as calculated in accordance with paragraph (3), but without the correction for deck line, as provided by regulation 32, shall not be less than 50 mm. For ships having in position 1 hatchways with covers which do not comply with the requirements of regulation 16(1) through (5) or regulation 26, the freeboard shall be not less than 150 mm.

Winter freeboard
(5). The minimum freeboard in winter shall be the freeboard obtained by an addition to the summer freeboard of one forty-eighth of summer draught, measured from the top of the keel to the centre of the ring of the load line mark.

Winter North Atlantic freeboard
(6). The minimum freeboard for ships of not more than 100 m in length which enter any part of the North Atlantic defined in regulation 52 (Annex II) during the winter seasonal period shall be the winter freeboard plus 50 mm. For other ships, the winter North Atlantic freeboard shall be the winter freeboard.

Fresh water freeboard
(7). The minimum freeboard in fresh water of unit density shall be obtained by deducting from the minimum freeboard in salt water:

Δ/40T (cm)

where:
Δ is the displacement in salt water in tonnes at the summer load waterline; and
T is the tonnes per centimetre immersion in salt water at the summer load waterline.
(8). Where the displacement at the summer load waterline cannot be certified, the deduction shall be one forty-eight of summer draught, measured from the top of the keel to the centre of the ring of the load line mark.
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Notice that the Class Society has to be satisified (Reg 1) , but once the summer load line is set, everything else is just gometry.

athvas · Aug 6, 2014

thanks for all .... For your suggestions ....

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Loading case corresponding to Tropical load line mark

athvas Senior Member

Attached Files:

cargo tanks.xlsx

NavalSArtichoke Senior Member

athvas Senior Member

NavalSArtichoke Senior Member

Ad Hoc Naval Architect

jehardiman Senior Member

jehardiman Senior Member

athvas Senior Member

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