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A thoroughly nautical question for salty Jetblasters.

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A thoroughly nautical question for salty Jetblasters.

Old 17th May 2020, 19:07
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A thoroughly nautical question for salty Jetblasters.

Can someone answer me this please? With reference to ships, whenever a telly prog is on and it refers to a ships weight, it is stated in several in several different ways, i.e. displacement, gross tonnage, etc., but what I want to know is, if the ship were to be taken out of the water and placed on some weighing scales, what term is used for whatever the scales show?
Thank you.
N.Z.
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Old 17th May 2020, 19:10
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Heavy

I will get my coat and leave.
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Old 17th May 2020, 19:19
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Before anybody who knows about the subject posts an answer, my guess is displacement.
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Old 17th May 2020, 19:22
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Lightweight tonnage.

Here you go:

Courtesy of Google:

Ship Tonnage

IG
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Old 17th May 2020, 20:05
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Nett displacement without passengers or cargo.

Gross displacement with cargo and/or passengers.
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Old 17th May 2020, 21:07
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Archimedes, innit.....
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Old 17th May 2020, 21:35
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Invariably displacement for warships.

Jack
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Old 18th May 2020, 00:14
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Thanks for the info, guys (and guyesses?)
Spot on Imagegear!
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Old 18th May 2020, 00:24
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The same? Hah, but wait a moment. You measure the weight of the displaced water, but where is it now? If it has spilled over to another container, then the ship will be at a slightly different height than if it was still surrounding it and the world's seas had gone up a bit. If so, the gravitational attraction will differ in the calculation by the difference in r, the Earth's radius.

Why not just weigh the darn thing?

The fact is, I've never understood why they use displacement, despite drinking with two sea captains for years.
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Old 18th May 2020, 05:04
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It is a measure of the number of tuns of wine the ship could carry.

1 tun ≡ 2 butts or pipes
≡ 3 puncheons or tertians
≡ 4 wine hogsheads[6]
≡ 6 tierces
≡ 8 wine barrels
≡ 14 rundlets
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Old 18th May 2020, 08:29
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Gross and net tonnages are volumes and measure the vessels carrying capacity. The wieght of a. Ship is the displacement.
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Old 18th May 2020, 09:15
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Originally Posted by Loose rivets View Post
The same? Hah, but wait a moment. You measure the weight of the displaced water, but where is it now? ....The fact is, I've never understood why they use displacement, despite drinking with two sea captains for years.
As I understand it, displacement is the standard terminology because it a convenient method of measurement. Putting a ship on a set of scales is not easy, and not something that you can do every time you load or unload stores and cargo. However, the volume of the ship is known from the designs, so by measuring the waterline relative to pre-determined marks on the hull, you can easily calculate 'displacement' (and thus weight) just by looking over the side. Technically, the displacement is theoretical; it is possible to float a ship in a much smaller volume of water (e.g. in a dry-dock) than it displaces.
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Old 18th May 2020, 09:36
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Originally Posted by Recc View Post
Technically, the displacement is theoretical; it is possible to float a ship in a much smaller volume of water (e.g. in a dry-dock) than it displaces.
I think we need a diagram :-)
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Old 18th May 2020, 11:15
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Hah, Displacement yes,

Is that in sea or fresh water, treacle or single malt?

I think I need to see a Plimsoll line

IG
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Old 18th May 2020, 11:39
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But what if the dry dock is on a conveyor?
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Old 18th May 2020, 11:56
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Originally Posted by Imagegear View Post
Hah, Displacement yes,

Is that in sea or fresh water, treacle or single malt?

I think I need to see a Plimsoll line

IG
and if in sea water... in the Irish Sea or the Med? (Aren't the Irish called the Mediterraneans of the North? Best country I ever lived/sailed in!!!)
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Old 18th May 2020, 13:22
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In the pool at our hotel there were some lady supertankers who should have had plimsoll lines on their cossies......
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Old 18th May 2020, 13:37
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The "Falkirk Wheel" is rather an elegant use of displacement.
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Old 18th May 2020, 13:56
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Originally Posted by 57mm View Post
In the pool at our hotel there were some lady supertankers who should have had plimsoll lines on their cossies......
Sounds a bit of a kinky hotel. Anybody sport stiletto marks on their backs?
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Old 18th May 2020, 20:43
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Originally Posted by Recc View Post
As I understand it, displacement is the standard terminology because it a convenient method of measurement. Putting a ship on a set of scales is not easy, and not something that you can do every time you load or unload stores and cargo. However, the volume of the ship is known from the designs, so by measuring the waterline relative to pre-determined marks on the hull, you can easily calculate 'displacement' (and thus weight) just by looking over the side. Technically, the displacement is theoretical; it is possible to float a ship in a much smaller volume of water (e.g. in a dry-dock) than it displaces.
In order to float, a ship has to displace a certain volume of water equivalent to the weight of the ship. This is true whether the ship is in a dock or not. The volume of the water in a flooded drydock will be more than if there was a ship in it. Put a ship of say 10,000 tons into that dock then 10,000 tons of water will be 'displaced'. As a drydock is flooded, the amount of water that enters the dock will be less if there is a ship in it than if the ship wasn't there. Archimedes wasn't a numpty!!!
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