# Heavy Lift Ships



## lucasm1

I was looking at a program about the heavy lift ship "Hawk" and was wondering how much space is needed between the sea floor and the bottom of the ship when it is submerged to receive a large cargo. I know it submerges approx 34 ft.

Thanks


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## david freeman

lucasm1 said:


> I was looking at a program about the heavy lift ship "Hawk" and was wondering how much space is needed between the sea floor and the bottom of the ship when it is submerged to receive a large cargo. I know it submerges approx 34 ft.
> 
> Thanks


interesting? while the HL vessels sails in to receive load, is she in ballast, or down to her marks, and then de-ballast's : re-ballast for stability, during the expected sea voyage, and I would image while on station unloading heavy load, (Not a Heavy lift cargo vessel, working in commercial docks- but a designed hL crane-then I would expect computer controlled simultaneous ballasting lifting, luffing, and stability, being a continuous simultaneous operation.
The draft alteration of 34ft is a red herring, unless under way, and then the vessel is subject to 'squat', or at least maybe.
The depth of water minimum under the keel, may be as little as 20feet or even less? A naval arch would provide or may provide the answer.
Maybe you are looking at the problem? if there is one, with the wrong assumptions of operations.


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## A.D.FROST

When discharging some times nothing, because they are designed to unload aground.


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## Supergoods

A very interesting post, but not one that is easy to answer.
It is very unusual to sit on the bottom when loading or off loading as ship will be trimmed to ensure that when the deck submerges or emerges it does so in an incremental manner. This is to avoid rapid changes in the water plane area which can result in minimal or slightly negative stability.
I have manuals for several on and off loads I have participated in, usually about a ***ulative 12" thick of paper. I will dig out my old files when I get the chance and should be able to give a bottom clearance.
Ian


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## lucasm1

Thank you for answering my question. I didn't think the keel could set on the sea floor, stability issues. I figured there had to be some distance, just wondered the minimum distance


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## Supergoods

This is the water depth required calculation for an actual loadout, names not shown.
It shows an under keel clearance of 1 meter, however in the event the clearance was much more than this.
The operation took place in the Gulf of Mexico and due to the water depth required was done offshore.

"After approval of the deck preparations by the attending Marine Warranty Surveyor, the Transport Vessel will ballast down to a draft of approximately 24.46 meter, providing 10.86 meter of water above the cribbing. 
A water depth of 25.46 meter will be required, see table below:
Minimum Required Water Depth
Drilling Rig (Cargo) 10.36 meter
Clearance 0.50 meter
Cribbing 0.30 meter
Depth of vessel 13.30 meter
Total 24.46 meter
Minimum clearance under keel 1.00 meter
Minimum required water depth 25.46 meter"

Ian


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## lucasm1

Thanks again you have answered my question


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## O.M.Bugge

A.D.FROST said:


> When discharging some times nothing, because they are designed to unload aground.
> View attachment 147410


HL Ships are Not normally designed to sit on bottom while loading/discharging, but in the early days of dry transport of rigs on barges that was how it was done (1975>) 

There are still a few barges that does it this way, but they are not often used for rig transport. If they are the barges has aft columns and stay afloat, like the ships.

I did one grounded loading in Singapore back in 2011, but that was of an Accommodation Barge which was to remain on the transport barge during operation. (Barge to be grounded to protect the bottom of the Accommodation barge from direct bottom contact)

On the original question: Minimum required UKC is usually 1.0 m. and UKC for the cargo over cribbing is usually 0.5 m., but some time there are compromises for whatever reason.
It is not normally advised to have too deep water when submerging, just in case. The MS 3 sinking at the Congo River mouth will explain why: http://www.shipspotting.com/gallery/photo.php?lid=323040


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