Cargo Ships - Pods and sizes

[zwerg]

Well, a friend of mine is running a game of Babylon 5 so being a person who likes trade I started looking into that aspect of the game. The first thing I noticed is that most ships and even cargo pods are vastly underrated tonnage wise.
Now then, before I get into some examples I feel I need to define a little bit what tonnage actually means when it comes to cargo and ships. The term Tonne comes from tuns of ale or such being shipped and referes to and amount of volume or weight, whichever hits the limit first. The volume is about 42 cubic feet and the weight is about 2,000 pounds. Now then, air weighs anout 0.075 lbs/cf (STP), steel about 490lbs/cf, aluminum about 165 lbs/cf, wheat 48 lbs/cf, Roasted coffee beans 27lbs/cf, and so on. Therefore a ton of Roasted coffee beans would weigh about 1,134 lbs and take up all of the 42 cubic feet. Wheat would come in between 2000-2,016 lbs and again take up the entire spce. Steel would come in at 2,000-2,10 lbs per ton yet take up maybe 1/10th of the volume. As you can see, more dense materials take up less than the maximum space yet weigh in at a ton, whereas light materials will max out the volume and still weigh less than a ton. Yes, in terms of shipping a ton of feathers does indeed weigh less than a ton of bricks! :wink:

So, on to the next point. Today in shipping there ate TEU or "Twenty-footer Equivalent Units". They refer to the standard twenty foot containers used in shipping. The interior dimensions would be 20 feet long, 8.5 feet wide, and 8 feet high. This is 1,360 cubic feet or 32-34 tons (depending if you use 42cf/ton or 40cf/ton respectively. This means the max weight is about 68,000 pounds.

How this applies to the game is that the standard "Cargo Pod" can only handle 50,000 lbs and thus less than a single TEU's potential capacity! Considering that semi-truck trailers can run higher and longer than a TEU, or a single semi can pull multiple trailers in some areas, this would make a Corporate Standard Freighter incredibly small in morern terms and a Cargo Loader only a bit more than a glorified forklift. Costs are likewise way too high for Cargo Pods to be that dinky (you can purchase a TEU container for about $3,000).

So something is not right here. Then I saw the Maintainance Pods pulling a number of smaller contaners and it hit me ... THOSE are the 25 ton containers and the Cargo Pods are much bigger. As to how big they are, 3 of the Cargo Pods accross can not fit in a docking bay all at once and probable are each about 1/3rd the width of the space between the arms of the upper pilons(?) of Babylon 5. If anyone has that number I can make a fairly good estimate.
:wink:

 

[lastbesthope]

The volume is about 42 cubic feet and the weight is about 2,000 pounds. Now then, air weighs anout 0.075 lbs/cf (STP), steel about 490lbs/cf, aluminum about 165 lbs/cf, wheat 48 lbs/cf, Roasted coffee beans 27lbs/cf, and so on. Therefore a ton of Roasted coffee beans would weigh about 1,134 lbs and take up all of the 42 cubic feet. Wheat would come in between 2000-2,016 lbs and again take up the entire spce. Steel would come in at 2,000-2,10 lbs per ton yet take up maybe 1/10th of the volume.

You have listed 3 different weights for a ton here. You mean to list 3 different volumes I expect. And do you mean metric or imperial tons? I'd guess imperial from your use of lbs, but what is the book using.

Your basic point bears looking into though. When I get the time to dig my books out.

LBH

 

[zwerg]

The volume is about 42 cubic feet and the weight is about 2,000 pounds. Now then, air weighs anout 0.075 lbs/cf (STP), steel about 490lbs/cf, aluminum about 165 lbs/cf, wheat 48 lbs/cf, Roasted coffee beans 27lbs/cf, and so on. Therefore a ton of Roasted coffee beans would weigh about 1,134 lbs and take up all of the 42 cubic feet. Wheat would come in between 2000-2,016 lbs and again take up the entire spce. Steel would come in at 2,000-2,100 lbs per ton yet take up maybe 1/10th of the volume.

You have listed 3 different weights for a ton here. You mean to list 3 different volumes I expect. And do you mean metric or imperial tons? I'd guess imperial from your use of lbs, but what is the book using.

Your basic point bears looking into though. When I get the time to dig my books out.

LBH

Short answer:

There is a BIG difference between a ton as a unit of weight and a ton as a unit or cargo. My numbers seem to be all over the place because of that significant difference (aka, that is my whole point) as well as the fact that there are at least three different values for the weight of a "ton".


Long answer/different definitions:

Short Ton (American) = 2,000 lbs
Metric Tonne ~ 2204.6 lbs
Imperial Ton = 20cwt or 2240 lbs

That being said whether one uses a short ton, ton, or tonne is basically irrelevant as they all come in at about the same thing.

Now then, what I am talking about is a Freight or Shipping Ton. In shipping one must not only conform to a weight but also a volume. The volume may range a bit as well (between 38 and 42 cubic feet) but the numbers I kept seeing in my research were 42cf/ton or 40cf/ton. I am fairly sure the data I found on 42 cf per ton is for an Imperial Ton, therefore a Short Ton could possibly be about 12% less (aka, 38 cf per ton).

In conclusion there are 2 basic definitions of a ton (weight and shipping) and these are both complicated by other factors such as variance in the defined actual weight or volume, but overall doing rough calculations with 2,000-2,100 lbs and 42 cf work about right as they are within the tolerences for a shipping ton.


The real question/problem expressed another way:

Therefore the real question is why would freight haulers in space haul cargos equivalent to about what Columbus's 3 ships could carry when a modern container ship can carry many times more than that?
Actually, the "Corporate Freighter" would haul a bit less than Columbus's ships ... 50,000 pounds per Cargo Pod <= 25 tons per cargo pod. 8 Cargo pods = 200 tons or less, Each of Columbus's ships were under 100 tons but together hit at over 200 tons. Modern container ships are pushing 9,000 TEU of 30-34 tons each or about 270,000+ tons (potentially over 540,000,000 pounds) of cargo per ship. Since the Corporate Freighter in the book can handle 8 Cargo Pods listed at 50,000 pounds capacity each they are 1,350 times smaller in terms of cargo hauling capacity than a modern container ship. I see this accross the board that all of the ships seem to be out of whack in terms of cargo or tonnage by a factor of 10, 10, or even 1000. Heck, a WWII submarine come in at 650-700 tons displacement (German U-Boat ... some American subs may have been larger). All the ground vehicles seem sort of close, but ships are are constantly underated (I would say "consistanty" but by what factor seems to grow as the ships get larger). I am no expert, but I have studied some history and know a person who used to load freight for a living thus why I have an appreciation for what the numbers are/should be and "intuition" for when things seem out of whack.

-Dwarf

 

[zwerg]

Found place that had definitions of tons including as a unit of volume(register ton (both gross (GRT) and net), freight or measurement ton, Panama net ton, and water ton), a unit of mass (metric ton or "tonne" or "ton", long ton, short ton, displacement ton, deadweight ton (dwt), Harbour ton, and assay ton (AT)), plus units of force (long ton, meteric ton, short ton), energy and power. Some of them are equivalent, most are fairly easily convertable between.
Document defined a freight ton (measurement ton) as 40 cubic feet (1.13267 cubic meteres) and a register ton as 100 cubic feet (2.83 cubic meters).
Therefore I find it unserstandable for somebody to be confused. I got the 42 cu ft per ton figure from a bit less reliable source.

Anyway, here are some Carpo Pod data bits based on the width of the pod (column (A)):

Cargo Pods in tonnage					
	Data Area				
(A*B*(C+A/4) = cu ft; cu ft/40 or cu ft/42 = tonnage					
					
A	     B   	     C		Freight Tons per Pod	
25 ft	    37.5 ft	   25 ft		366 tons
27.5 ft	  41.25 ft	27.5 ft		       487 tons
29.5 ft	  44.25 ft	29.5 ft		       602 tons
30 ft	       45 ft	     30 ft		  633 tons
32 ft	       48 ft	     32 ft		  768 tons
37.5 ft	  56.25 ft	37.5 ft		     1,236 tons
50 ft	       75 ft	     50 ft		2,930 tons
474 ft	     711 ft	  474 ft	2,496,010 tons
					
9 m	  13.5 m	   9 m		       587 tons
10 m	    15 m	  10 m		      805 tons
15 m	  22.5 m	 15 m		   2,715 tons
20 m	    30 m	  20 m		    6,437 tons
25 m	  37.5 m	  25 m		  12,571 tons
50 m	    75 m	   50 m		 100,571 tons
100 m	   150 m	100 m	      804,565 tons
144.7 m	217.05 m   144.7 m	  2,507,679 tons

You may note that the volume in tons is exponential. This is indeed correct.

Now then if a corporate freighter can carry 6 pods and its overall length is 128 feet then I would go with 32 feet per pod (column A) as 3*32 =96 leaving 32 feet for engines and bridge. This would also put the width of each individual pod at 1/4th the total length of the ship.

--the Dwarf[/code]

 

[lastbesthope]

What shape are these cargo pods? I couldn't work it out from the volume formula.

LBH

 

[zwerg]

What shape are these cargo pods? I couldn't work it out from the volume formula.

LBH

Shape is not always as relevant as people think. Basically their shape is roughly diamond., but only from the side. This allows for a conceptual rotation/shifting of prts of the pods into basically a brick while retaining the ability to faierly accurately estimate cargo capacity. I will try and represent this graphicly:
..... ____
..../..........\
../..............\
/_________\ could be estimated by
________
|\.............|
|..\...........|
|__\_____| because the angles on both sides are the same. A cargo pod is basicly a skew hex therefore the top abgles could be mentally brought to the botom, split apart, rotated, and the resultant area is a brick. If A is the width of the pod, B the length, and C the height at the greatest point, and, for example, if A=C and B = A+A/2 then the volme of the pod would be less than A*B*C. How much less would depend on how mach area the vertical flat sides take up, but the minimum value would be A*B*C/2 as the angles on top and bottom are the same and thus the area has to be at least hlf the length times height. Simple algebra gives the final result. I hope the cheap graphic worked/helped (ignore all the dots and just look at the lines).

..... ____
..../..........\
../..............\
/..................\
\................../.
..\.............../..
....\.........../...
......\......../....
........\__/

That is the approximate shape of the pod, but that would put it standing on its nose. In this orientaion "C" would be the distance across and B up and down. A would be the third dimension. As you may have guessed even by this small image that the two ends are not the same and therefore my formula basicly using just over C/2 to estimate the volume is underrating it slightly as a slice near the longer end is being lost but hey, that is why it is called an "approximation".

-Dwarf

 

[lastbesthope]

Thanks zwerg, I see what you're getting at now.

LBH

 

[zwerg]

Some friends of mine and I have been watching Season 5 and in a scene in the episode "The Ragged Edge" a Drazi ship flies extremely close to a Coprorate Freighter, so close that one can see both ships plus a partial shadow from the Drazi vessel. Suddenly a revelation hit me ... in the past I have assumed that both docking bays (th main one and the one between the two big arms are a) the same size, b) 65 m across, and c) that the width of a Cargo Pod is about 1/3-2/3 the width of the docking bay. Well, this episode calls that into question and makes me seriously wonder if a Cargo Pod is more like 125m-160m wide! Comments?

-Dwarf

p.s. At that scale a corporate freighter would be hauling more than modern container ships and could carry a fighter inside of them.

 

[lastbesthope]

I always thought that the zero-G cargo entrance on the front of the stationary part was much bigger than the docking bay at the core.

LBH

 

[zwerg]

I always thought that the zero-G cargo entrance on the front of the stationary part was much bigger than the docking bay at the core.

LBH

I suspected, but I found "hard" estimates of the core but not the other.
The core is defined by one website as "Xm because it is N pixels wide" and the estimate set at 65m IIRC.

If anyone can find any alternate view or data on this I would appreciate it.

In other news, a few more episodes into Season 5 I saw an 8-pod corporate freighter pass fairly close in front of B5 in a long distance view and the freighter appeared to be about as long as the station is wide. This would seem to confirm that the pods are indeed very close to my latest estimate.

Like I said, give me good data and I can do some wonderful estimates.

-Dwarf

 

[qstor]

If you work this out it would probably be a good start for a trade article for the Mongoose in house magazine.

Or has there one been done already?

Mike