Modern ship tonnage

[Jak Nazryth]

I have always been a bit confused about modern tonnage of ships from today's aircraft carriers to the WWII battleships etc...
When the tonnage is given, does that ONLY count the amount of water displaced by the hull below the water line? Or the entire submerged displacement of the entire ship?
I'm trying to give good examples of tonnage between a traveller ship, and a modern ship, like a destroyer, or carnival cruise liner etc... and I can never be sure.

 

[barnest2]

Displacement is the actual total weight of a ship. Therefore, with a full combat load, HMS Daring's displacement is 8,100 tonnes.
Gross tonnage is all enclosed spaces, which is what traveller measures I believe (sort of, it has it's own units of measurement). HMS Daring's gross tonnage is 10,129 tons.

Gross tonnage of HMS Daring as a measurement in cubic metres is: 38,127 cubic metres if I added up right.

Divide by 13.5 to get dTons, and you get: 2,825 dTons :lol:

 

[Ishmael]

maybe this might be some help...
http://freelancetraveller.com/features/shipyard/tonnage.html

 

[navanod]

http://www.freelancetraveller.com/features/shipyard/tonnage.html

Everything you need to know about all kinds of tonnages.

 

[barnest2]

I'm a bit wary of some of those calcs... such as the reverse ones (free trader to Gross Tonnage).
But mostly it seems accurate

 

[PFVA63]

Hi,

Here's a figure that I put together awhile ago, comparing the internal volume of some modern (and relatively modern) warships (in terms of Traveller dtons) to the listed total hydro-static displacement of those ships (or in other words the total weight of water "displaced" by the ship when its in the water - in accordance with Archimedes principle) in metric tonnes.

Here the Black Squares represent Submarine Designs (SS's) and as you can see volume in dtons = 0.0732 * the ship's weight (or hydro-static displacement).

For more common surface ships like Mine Counter Measures (MCM) vessels, Surface Combatants (SC), and some Design Studies (Des) you get in general volume in dtons = about 0.2483 * the ship's weight (or hydro-static displacement).

For large amphibious ships such as Landing Ship - Docks (LSDs) you get a slightly different trend as well as if you look a WWI era battleship type vessels (WWI).

Hence a 1000mt submarine would have a Traveller size of 73.2 dtons. While a 1000mt Light Frigate would have a Traveller size of about 248 dtons.

The general rule of thumb I use then is that if you take a modern surface combatant type vessel and divide its stated displacement (in metric tonnes - mt) by 4 you get a very good guess at how big the ship would be in Traveller terms. Or looking at this the other way around by multiplying a Traveller ship's size by 4 you get an idea of roughly how big that ship would be in modern terms.

Specifically, a 1000 dton Traveller ship would be roughly the same size as a relatively modern 4000mt Frigate and a 2000 fton Traveller ship might be about the same size as a modern 8000 mt Destroyer.

Hope this helps.

Regards

Pat

 

[barnest2]

Hence a 1000mt submarine would have a Traveller size of 73.2 dtons. While a 1000mt Light Frigate would have a Traveller size of about 248 dtons.

Um... no. if you're using hydrostatic displacement, then unless you know how much of the frigate is above water (Which you cant from that measurement), then you cannot figure out the traveller size.

OP, use gross tonnage, rather than this... interestingness.

 

[PFVA63]

Hi,

I think that you are mis-interpreting what is in the plot. The values on the X-axis is the hydrostatic displacement of the modern warships that I have data on, and the values on the Y-axis is the reported total enclosed volume of those vessels converted from cubic meters into Traveller dtons.

Thus the trendlines shown represent the relationship between the hydrostatic displacement of a ship and its total enclosed volume.

Looking at a 1000 mt submarine, it has a weight of 1000 * 1000kg/mt = 1,000,000 kg. According to the trendline it also has an enclosed volume of 73.2 dtons = 988.2 cu meters (here I think that I had assumed that a dton is a block 1.5m wide x 3m long x 3m tall). Therefor, the density of the ship is 1012kg/cu meter which is very close to the density of Salt Water.

On the other hand, here is a thesis from MIT on "Ship synthesis model for naval surface ships". In it the author shows the total enclosed volume of several ships in comparison to their hydrostatic displacement. I have used this data, plus similar information from other sources in putting together my plot. http://dspace.mit.edu/handle/1721.1/32553

Here you ca see from the Data in Tables 3, 4a, and 4c that an FFG7 class frigate has a Superstructure volume of 82,113 cu ft and a hull volume of 434,339 cu ft for a total enclosed volume of 516,452 cu ft (or 14,625 cu meters). Dividing this by a block 1.5x3x3m gives an enclosed volume of 1083 dtons in Traveller Terms. From Table 3 the total hydrostatic displacement of the ship is 3585 Long Tons or 3643 mt. Hence for this ship the relationship between hydrostatic displacement (weight) and enclosed volume (in terms of mt and dtons) is about 3.36 to 1.

For other ships you will come up with slightly different numbers but when I plotted up everything that I had I got a trendline as shown in the plot I supplied previously.

Regards

Pat

 

[barnest2]

Ah I see. My apologies.
I thought you were directly translating hydrostatic displacement, rather than using Gross tonnage. Since you are using gross tonnage, then we are in agreement. I like the chart at that point
Apologies again
Barnes

 

[PFVA63]

Hi,

No problems. I probably wasn't clear in my first post.

Regards

Pat

 

[BP]

Most people actually can't relate to volumes, but only linear measures. So, for size comparisons, I simply use man sized silhouettes and side profiles. Found this works better than trying to relate to real world objects - since none are truly universally understood (many of my players don't know what a 747 is, nor have been in the trucking industry - and don't know what an empty garage looks like ). Never compared them to sea going vessels - as none of my players could relate, even though my original group lived within 2 miles of one of the world's most important oil shipping hubs! (Obviously not the case for a lot of Traveller fans, who served under and/or on the seas..)

Definitely check out: http://www.traveller3d.com/sizechart/index.htm. For a non-Traveller one, but still excellent (and could rescale the former to match - both have 747, IIRC): http://www.merzo.net/

In my earlier CT days, related everything to the Space Shuttle. But, back then all my players had been to Building 9 of JSC (mockups and some training simulators) or had seen the Enterprise atop the modified 747 (SCA)

To avoid confusion caused by the books and term 'ton', for my players I use the definition:
dton - a 'design ton' is a unit of measuring (starship) volumes equal to 13.5 cubic meters, close to that (~14 metric tons) required for a one metric ton mass of liquid hydrogen (see starship fuel). Equal to two standard 1.5 meter deck squares, two squares high - i.e. 1.5 m x 3 m x 3m. Often referred to as 'displacement ton' or just 'ton'.

 

[Jak Nazryth]

This is very helpful.
Thank you very much for the attachments and links.
There was also an image floating around I used to have of a bunch of ships drawn to scale together, including real and imaginary ships from Traveller, A 747, and I think even a couple of ships from Star Wars and Star Trek. It would be great if there was a silhouette "study/comparison" of modern navel vessels on a similar chart.
I can use youz guyz information to better help my players related to "traveller scale" ships.

 

[BP]

Glad to help!

I was thinking of that same image - the http://www.traveller3d.com/sizechart/index.htm one might be an update (same elements - 747 and bunch of traveller ships - note it also has a Nimitz).

Happy Travelling!