Mass of ships - PeachParts Mercedes-Benz Forum

t walgamuth · #1 01-29-2012, 08:38 AM

At lunch the other day the weight of the cruise ship which is hanging on the ledge came up. A friend who was in the Navy in the Viet nam era on the Newport News, a heavy cruiser stated that his ship was heavier than the cruise ship. I thought he was wrong so later looked it up.

It turns out that his cruiser displaced 21,000 some tons and was 770 some feet long, 76 some feet wide at the beam (it fit the panama canal) and drew about 27' of water.

The cruise ship is over 950 feet long, over 118' wide and displaces 120,000+ tons. It also draws 27' of water.

I was shocked at its comparative size.

engatwork · #2 01-29-2012, 09:05 AM

Have you tried to pick up a king size mattress lately Tom? Lot's of mattresses on that ship.

t walgamuth · #3 01-29-2012, 09:12 AM

I bet they are even heavier when wet!

kerry · #4 01-29-2012, 10:35 AM

One of the nightly news programs had drawings of comparative sizes of cruise ships. I think the one that is currently aground is not amongst the largest. They compared them to the Titantic which was tiny by comparison. I think it said the largest cruise ships held 8000 people. Can you imagine trying to evacuate 8000 people from a sinking ship????? My immediate thought was 'How is it possible to have enough lifeboats and liferafts for that many people?" Are that many lifeboats required? Has anyone ever actually tried to do it?

Brian Carlton · #5 01-29-2012, 10:42 AM

You need to be a bit careful when you read anything in the media about the "weight" of a ship.

Although all ships have a "displacement tonnage", the common expression for a ship is "gross tonnage". This parameter has nothing to do with weight and expresses a complex formula for the enclosed volume relative to the main deck.

Of course the gross tonnage will rise with the larger ship. However, there is no consistent proportion.

Also, the cruise ship cannot have 120,000 ton displacement tonnage. A box that has the length, beam, and draft of the vessel has a weight of 86,000 tons. The ship would be considerably less due to the shape of the hull. I suspect that you were reading "gross tonnage". A cruise liner has very high figures for gross tonnage because of the huge volume of enclosed space above the waterline.

engatwork · #6 01-29-2012, 10:48 AM

I suspect the mattresses on a cruise ship could be considered in the gross category.

Brian Carlton · #7 01-29-2012, 10:54 AM

Quote:

Originally Posted by kerry

'How is it possible to have enough lifeboats and liferafts for that many people?" Are that many lifeboats required? Has anyone ever actually tried to do it?

Big lifeboats (maybe 150 passengers per boat).

Enough of them to equal the passenger count (40 would give you 6,000 capacity).

I doubt it. It would take much longer than the available time (a frequent problem with ships..........the water doesn't take a hiatus when the life boats are being loaded)

You put your life in their hands when you go for a cruise..........just like an aircraft. There is no assurance of a good outcome.

t walgamuth · #8 01-29-2012, 11:16 AM

Quote:

Originally Posted by Brian Carlton

You need to be a bit careful when you read anything in the media about the "weight" of a ship.

Although all ships have a "displacement tonnage", the common expression for a ship is "gross tonnage". This parameter has nothing to do with weight and expresses a complex formula for the enclosed volume relative to the main deck.

Of course the gross tonnage will rise with the larger ship. However, there is no consistent proportion.

Also, the cruise ship cannot have 120,000 ton displacement tonnage. A box that has the length, beam, and draft of the vessel has a weight of 86,000 tons. The ship would be considerably less due to the shape of the hull. I suspect that you were reading "gross tonnage". A cruise liner has very high figures for gross tonnage because of the huge volume of enclosed space above the waterline.

Brian, do you mean a box the size of the ship would displace water equal to 86000 tons?

I had thought that displacement weight would be the weight of the water displaced hence the weight of the ship loaded ready to sail.

t walgamuth · #9 01-29-2012, 11:51 AM

At BC's suggestion I dug a little deeper and found a place where it stated that the costa concordia weighed 45,000 tons. It may be the weight without fuel, passangers etc.

A calculation of the weight of the water displaced by the gross dimensions suggests a dicplacement of about half the gross rectangular dimensions.

This would be for either the heavy cruiser or the cruise ship. Unless the hull is more sleek than I imagine on the cruise ship I don't see how it could be the same considering the long tapering bow of the war ship.

Do they pump bilge into the hull to make the ship ride lower when not carrying a big load?

JimFreeh · #10 01-29-2012, 12:01 PM

Another datum point is the extremely shallow draft of the cruise ship relative to a military vessel. Look at the pictures of the ship while it lists, very little below the waterline, compared to the height of the ship.

Jim

t walgamuth · #11 01-29-2012, 01:27 PM

The draft of the Newport news and the Costa are both about 27'.

Brian Carlton · #12 01-29-2012, 01:47 PM

Quote:

Originally Posted by t walgamuth

At BC's suggestion I dug a little deeper and found a place where it stated that the costa concordia weighed 45,000 tons. It may be the weight without fuel, passangers etc.

A calculation of the weight of the water displaced by the gross dimensions suggests a dicplacement of about half the gross rectangular dimensions.

This would be for either the heavy cruiser or the cruise ship. Unless the hull is more sleek than I imagine on the cruise ship I don't see how it could be the same considering the long tapering bow of the war ship.

Do they pump bilge into the hull to make the ship ride lower when not carrying a big load?

The displacement tonnage of 45,000 makes perfect sense for the Costa Concordia. It's about one-half the displacement of a rectangle that is the length x beam x draft.

With regard to ballast, the passenger liners don't require it but some of the tankers do. Way too much ship above the waterline when empty.