Author Topic: A ships Draft ????  (Read 3866 times)

Offline henrycourt

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A ships Draft ????
« on: January 11, 2008, 08:21:44 PM »
Please forgive my ignorance in this matter but is there, and I'm sure there is, a mariner of some substance out there that can, in plain english, give the definition of the ships draft ??? Exactly how is it measured ??? You hear broadcasts that state that the maximum draft is xx mtrs. What does this mean ?? I saw earlier today  that because the draft of Ras Laffan was , I think, 8.6 mtrs she was empty and going to take bunkers,what would have been her draft when full ?? Please can someone put all this in a form that I can properly understand !!! Once again please forgive my ignorance. Regards, j.w.

Offline miraflores

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Re: A ships Draft ????
« Reply #1 on: January 11, 2008, 08:43:14 PM »
the draft is the difference from the keel of the ship to the waterline.

In this case approx. 10 m

In this case approx. 3.80 m

Hope, you understood what I mean.


Offline Arnes

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Re: A ships Draft ????
« Reply #2 on: January 11, 2008, 10:04:24 PM »
As Miraflores correct stated; it is the distance from keel of a vessel to the waterline. Or said in another way; how deep a vessel is under the waterline.
Wery important, as many ports has draught-restrictions. When loading in one port, we always have to obtain information of max.depth in discharging-port.
In the 70's and 80's many supertankers had to lighten the vessels to get a less draught, so that they could go alongside in many continental ports. Part of cargo was then transferred to "smaller" tankers of lets say 70000 tdw. in places like Lyme Bay. Then the supertankers had got a less draught, so that they could continue their voyage to final discharging port.
One must also be aware that a vessel is quite deeper in fresh-water than in sea (salt)-water, so when loading a vessel for max.draught in discharging-port, one must get information from agent about water-density in discharging-port.
Another thing affecting draught, is the hog/sag, which mean that if the vessel is completely flat on the sea, there may be difference between forward/aft-readings and the readings on the middle. Example: If we load all cargo in the middle of a vessel, she will be deeper on the middle than on the ends. This we call sag. If we load all cargo in the ends and leave middle empty, she will be deeper in the ends, and this we call hog. But this is never done, as a vessel then will break in two normally. Cargo has to be even stowed. Some years ago a large tanker broke in two in Rotterdam due to wrong discharging.
This was supposed to be a simple explanation, but I'm afraid it turned out to be a long lecture.
regards from Arnes

Offline Luko P.

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Re: A ships Draft ????
« Reply #3 on: January 11, 2008, 11:36:24 PM »
Please note that traditionally the draft readings may be used (and in some cases are the only way) to calculate the weight of cargo (and/or other 'added' weights) on board. The weight of ship, crew, fuel, consumables etc. is allways known to ship's crew, so when draft is read carefully at all forward, aft and amidship draftmarks - then by use of ship's tables and curves (or computer program) it is possible to calculate the weight of cargo on board.


Luko P.

Offline portagent

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Re: A ships Draft ????
« Reply #4 on: January 12, 2008, 09:50:23 AM »
... read more detailed info  here.
dead slow ahead !  :-)
best regards, Klaus

Offline Kier Shackleton Gigeroff

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Re: A ships Draft ????
« Reply #5 on: January 12, 2008, 03:47:35 PM »
Also should be mentioned is the freeboard, which is the distance from the waterline to the top of the hull. Example: the Draft of a vessel = 9.9 m, and its freeboard = 6.4 m, which means the total depth of the vessel equals 16.3 m.



Offline Ron

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Re: A ships Draft ????
« Reply #6 on: January 12, 2008, 09:53:12 PM »
There is also Air Draft, the distance from masthead to waterline. An important measurement for vessels navigating under bridges.


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