Small ship universe

[Timerover51]

Cargo has always been in displacement tonnage, timerover. You start talking mass tonnage with Traveller ships and you're just going to confuse folks. Especially since the mass doesn't matter (between grav lift and acceleration compensation). I'm pretty positive the 1000 Credits per ton cargo fee is per displacement ton, too.

Calling Far-Trader! Oh, Dan! Far-Trader, come in!

Mass does not matter, interesting.

With respect to the difference between displacement tons and mass tons, I am not confusing the two. Real world cargo shipping uses Register tons, a measure of volume of 100 cubic feet, Measurement tons, a measure of volume of 40 cubic feet, Stowage factor, a volume measure of how many cubic feet does a mass ton of a specified cargo occupy, and Deadweight tons, a measure of mass. Another measure is TEU, or Twenty foot Equivalent Units, based on the standard cargo container of 20 feet in length and approximately 8 feet in height and width.

If you have a high volume to weight ratio cargo, say wood, you look at the ship's register ton capacity, if you are moving say, ammunition, you look at the ship's measurement ton capacity, and if you are shipping steel sheet at less than 5 cubic feet to the ton, all you worry about is deadweight ton capacity. For cargo containers, you are charged a flat rate per container, regardless of weight. Typically, there is a do not exceed weight limit on the container, as a twenty foot container fully loaded with sheet steel is going to weight about 275 tons. The last time I checked, there was a limit of 10 tons on containers going from the US West Coast to the Solomon Islands via Brisbane, Australia.

Now, let say that as a PC I hear that Planet B, a low population agricultural planet one parsec away from Planet A, where I presently am, has an urgent need for corrugated steel sheeting for construction of storage buildings. I decide to speculate and buy 1000 tons of corrugated steel sheeting for 200 Credits per ton. A starship displacement ton of 13.5 cubic meters will hold 103+ metric tons of steel sheet, so call it 100 tons. If shipping cost is figured at 1000 Credits per displacement ton, my shipping cost of 10 Credits per ton of steel sheet is immaterial. My 1000 tons of steel sheeting takes up only 10 tons of the Free Trader's 82 available displacement tons of cargo space. That would mean that the deck under the steel is holding 4551 pounds per square foot of deck. For comparison, the design loading for a parking garage is 125 pounds per square foot. Think about how solidly built is your average parking garage. Of course, I guess you could spread it out a bit, but he might have more cargo, and you said that mass does not matter.

Since you say that mass does not matter, how about I load that 200 ton Free Trader with 8200 tons of steel sheeting. If I sell the steel for 260 credits a ton, I make 410,000 Credits, for a 23.8% return on a two week investment. Of course, in the MegaTraveller Referee's Manual, page 62, it is stated that the hull of a 200 Ton Free Trader weighs 70 tons, so I am loading 117+ tons per ton of hull weight, but as you say, mass does not matter. For comparison, the WW2 Liberty ship loaded about 3.3 tons per ton of hull weight. I use the Liberty as an analogue as a lot of them became in effect, Free Traders, following the sell off after WW2.

Two final things.

One, are you still saying that MASS DOES NOT MATTER?

Second, I was under the assumption that the title of the forum in "In My Own Traveller Universe".

 

[Timerover51]

I think an important thing to keep in mind volume wise is that a small ship universe size limit of 5000 dtons really isn't necessarily that small.

I had a plot once (which I currently have misplaced) showing how the internal volume of modern naval vessels compare to their 'hydrostatic' deisplacement (or basically weight).

In general, if I am recalling correctly, the US Navy's amphibious ship LSD 49 USS Harpers Ferry is just a bit over 5000 dtons (70,000 cubic meters) in internal volume, and has a full load 'hydrostatic' displacement (~weight) of about 16,600 tons (37,184,000 lb) and is 610ft (190m) long with a width of 84ft (26m).


[Edit] PS. I also belive that a ship like the US Navy's Burke Class destroyers were near 2000 dtons in internal volume, while the Oliver Hazard Perry class frigates were close to 1000 dtons, and the US Coast Guard's 270ft Medium Endurance Cutters were close to about 460 dtons.

Following that up, the WW2 Liberty ship was listed at 7191 gross tons of 100 cubic feet, so a volume of 719,100 cubic feet. A starship displacement ton of 13.5 cubic meters equals 476 cubic feet, so a Liberty would have the hull volume of a 1510 ton starship. A Liberty could move 10,000 deadweight, i.e. mass, tons of cargo, the ton in this case being the long ton of 2240 pounds.

 

[mike wightman]

One, are you still saying that MASS DOES NOT MATTER?

In the real world of course it does. In the OTU as presented in CT the mass doesn't matter one bit - only the volume matters.

The maneuver drive moves a volume of ship, totally unaffected by the mass of that ship. You could be carrying 14 cubic metres of gold per 'ton' of cargo hold and it does not matter.

The jump drive moves a volume of ship though jump space, again the mass of the ship does not matter.

It's a game - and those are the rules. If you don't like the rules don't play the game. Or modify the rules to more closely reflect how you think thinks will work 3000 years from now in a culture that is 8 TLs above the TL we are living in now. That difference by the way is greater than the difference between the real world (TL7.5) and the stone age.

Second, I was under the assumption that the title of the forum in "In My Own Traveller Universe".

Yup, that's the forum title. But the OP started this thread to discuss the OTU dichotomy of the small ship vs large ship paradigm within the OTU and using the CT and HG rules. So if you want to stay on the topic of the thread stick to the parameters he set out, and use the rules he is asking about.

That's not to say thread drift doesn't happen, it does. And quite often that thread drift is useful.

 

[mike wightman]

Following that up, the WW2 Liberty ship was listed at 7191 gross tons of 100 cubic feet, so a volume of 719,100 cubic feet. A starship displacement ton of 13.5 cubic meters equals 476 cubic feet, so a Liberty would have the hull volume of a 1510 ton starship. A Liberty could move 10,000 deadweight, i.e. mass, tons of cargo, the ton in this case being the long ton of 2240 pounds.

Stop mixing units and definitions, stick to one so the discussion makes sense.

The MT authors got it very wrong to redefine the displacement ton as 13.5 cubic meters.

The most common definition for the displacement ton across Traveller versions is 14 cubic metres per displacement ton.

The GT 500 cubic feet per displacement ton is close enough to this 14 cubic metrre definition to bring it into line with most versions too. MT is the outlier - in lost of ways to other editions.

 

[mike wightman]

I think you may be missing something that is very obvious about Traveller. It is not hard sci fi.

The artificial gravity and acceleration compensators built into ships, not to mention the lack of concern over any waste heat management, mean that by the earliest TLs of starships in Traveller (TL9, 1.5 TLs above today) totally new technology that modern physics and engineering can't even imagine are in use.

 

[rancke]

In the real world of course it does. In the OTU as presented in CT the mass doesn't matter one bit - only the volume matters.

Or rather, given the simplifications inherent in the game rules, mass is usually ignored for game purposes. GT introduced (or did TNE have it first?) mass as a factor by basing maneuver drive performance on mass and calculating a standard 'loaded' weight based on an assumed average mass of a dT of cargo. Thus maneuver drive performance was rated for unloaded and loaded conditions. Such refinements as calculating the actual mass of a load of cargo was left to GMs who cared.

The maneuver drive moves a volume of ship, totally unaffected by the mass of that ship. You could be carrying 14 cubic metres of gold per 'ton' of cargo hold and it does not matter.

Which is shown by the GT rules (and simple common sense) to be a simplification of 'reality'.

The jump drive moves a volume of ship though jump space, again the mass of the ship does not matter.

This is 100% true and the principal reason why mass is ignored in the basic rules.

If you're discussing CT or MT or the other game versions, mass is completely ignored. If you're discussing the OTU -- the setting as opposed to the rules -- it is legitimate enough to consider mass a factor. However, it is a factor that, while obviously being taken into account "in reality", takes a back seat to volume.

Yup, that's the forum title. But the OP started this thread to discuss the OTU dichotomy of the small ship vs large ship paradigm within the OTU and using the CT and HG rules.

And since the OTU is no longer a small ship universe (and hasn't been for three decades), the IMTU forum is the appropriate place for such a thread.


Hans

 

[aramis]

Hans: TNE had a standard mass of 10 tons metric per ton displacement.

Timerover51: The TEU is a combined volume and mass limit. It's limited to a 20' x 8' x 8'8" volume, and 26000 total pounds (13 short tons), for the container plus contents. (1 TEU is roughly 2.77 displacement tons, 13.86 register tons or 13 short tons or 11.82 long tons).

Also note that the real world Registry Ton is roughly a ton-mass of cargo with typical loading practices of the 19th century. And is just about 0.2 Traveller Displacement Tons.

 

[Timerover51]

So, a Maneuver drive simply moves a volume, interesting.

How is it getting around E=mc(squared)? Or in whatever universe GT (which I assume is to be understood as GURPS Traveller), Einstein's equation does not function?

You move mass, you use energy. Now, you are basically saying that in whatever universe this is, mass has no relevance, only volume. So, if mass has no relevance, only volume, then I should be able to throw a baseball made of collapsed matter the same distance as I could a standard baseball, as both occupy the same volume.

I guess that you could say that your maneuver drive, as long as it is not a fusion reaction drive, generates a field that takes your ship out of an Einstein universe into a totally different one where E=Mc(squared) does not apply. If this is the case, why do you need a jump drive? As volume has no mass, you can accelerate to infinite speeds with essentially no expenditure of energy.

Now, if your maneuver drive is a fusion reaction drive, then mass matters in a real big hurry. With that, you are governed by the standard rocket equation:


Delta v = v(exhaust) times ln (m(initial) divided by m(final))

Admittedly, a fusion reaction drive is going to have a very high effective exhaust velocity, but a fusion reaction drive moves mass, not volume. The specific impulse should be over 100,000 based on what Project Nerva was getting simply squirting Liquid Hydrogen through a fission reactor. And you do have a nasty weapon as well for use on unwanted visitors. But you are not going to be able to ignore the mass of your cargo.

I raise the issue of the maneuver drive because when you look though the various books for Traveller, there is this ambivalence as to what a maneuver drive is. Sometimes it sounds like a fusion reaction drive and sometimes is sounds like a Dean reactionless drive.

As for the jump drive jumping a volume, I have no problems with that, as long as the mass is within reason, as that is the way I have my jump drive set up.

But is you want to say that mass has no relevance, then Trade and Speculation just got a whole lot simpler. If I pay only 82,000 Credits to move 410 tons of exotic food from one planet to another, I am more than happy. Food, and a lot of other things, sell by the pound/kilogram.

 

[Timerover51]

Hans: TNE had a standard mass of 10 tons metric per ton displacement.

Hmmm, that is actually pretty close to a measurement ton basis. As a measurement ton is 40 cubic feet, and 13.5 cubic meters is 476 cubic feet, a displacement ton in Traveller is equal to 11.9 measurement tons. That I can most definitely live with. It still is a pretty high ratio of cargo mass to hull weight though.

Timerover51: The TEU is a combined volume and mass limit. It's limited to a 20' x 8' x 8'8" volume, and 26000 total pounds (13 short tons), for the container plus contents. (1 TEU is roughly 2.77 displacement tons, 13.86 register tons or 13 short tons or 11.82 long tons).

Also note that the real world Registry Ton is roughly a ton-mass of cargo with typical loading practices of the 19th century. And is just about 0.2 Traveller Displacement Tons.

Aramis, I understand that the TEU is both volume and mass limit. I was an army supply officer, and did have to learn about such things.

As for the registry ton, it was actually based on the volume taken up by a large wine keg called a "tun" that was shipped from France to England during the Middle Ages. See A. C. Hardy's The Book of the Ship, circa 1949 for the reference.

 

[rancke]

So, a Maneuver drive simply moves a volume, interesting.

How is it getting around E=mc(squared)? Or in whatever universe GT (which I assume is to be understood as GURPS Traveller), Einstein's equation does not function?

You move mass, you use energy. Now, you are basically saying that in whatever universe this is, mass has no relevance, only volume.

No, I'm saying that the relvance is low enough to be ignored for game purposes as far as ships are concerned (Or so the original writers felt). GURPS Traveller had some simple rules to add a limited amount of consideration of mass to the game.

Mass is considered in other parts of the game, such as the encumbrance rules. Though those rules are simplified too and probably would not meet with the approval of a physicist purist.


Hans

 

[PFVA63]

Following that up, the WW2 Liberty ship was listed at 7191 gross tons of 100 cubic feet, so a volume of 719,100 cubic feet. A starship displacement ton of 13.5 cubic meters equals 476 cubic feet, so a Liberty would have the hull volume of a 1510 ton starship. A Liberty could move 10,000 deadweight, i.e. mass, tons of cargo, the ton in this case being the long ton of 2240 pounds.

Hi,

Thanks for that info. I found my plot and I had run some curve fits through the data.

For amphibious ships like the LSD 49, the curve fit is roughly dtons = 0.28 * hydrostatic displacement +650 (though I really only have 2 data points for this).

For modern warships like the DDG and FFG mentioned previously the rough equation is dtons = 0.25 * hydrostatic displacement (or basically divide the ship's listed hydrostatic displacment by 4 to get a rough estimate of its internal volume in dtons)

For submarines the rough equation is dtons = 0.073 * hydrostatic displacement (or basically divide the ship's listed hydrostatic displacment by 13.7 to get a rough estimate of its internal volume in dtons)

For really old battleships (such as maybe pre-dreadnoughts or WWI type ships) the rough equations is dtons = 0.15 * hydrostatic displacement (or basically divide the ship's listed hydrostatic displacment by 6.67 to get a rough estimate of its internal volume in dtons or just about twice the number that you'd get for a submarine, but here this equation was based on a real rough estimate for three ships)

 

[Timerover51]

No, I'm saying that the relvance is low enough to be ignored for game purposes as far as ships are concerned (Or so the original writers felt). GURPS Traveller had some simple rules to add a limited amount of consideration of mass to the game.

Mass is considered in other parts of the game, such as the encumbrance rules. Though those rules are simplified too and probably would not meet with the approval of a physicist purist.


Hans

Oh, encumbrance is actually quite simply. The US Army did a thorough study of that in the 1950s, and then of course, now ignores the findings. The maximum weight you can expect a human to carry and still be an effective fighter is 40 pounds, call it 20 kilos for the metric guys. Once you hit 60 pounds, the person is going to be tired very quickly, have limited agility, and will need a couple of hours rest, minimum, for any additional activity, without continuing to be encumbered. This does assume about a 6 hour route march. If the person is under about 160 pounds, say 70 kilos, start reducing the load for encumbrance real quick, do to half that at 100 pounds, 45 kilos.

 

[Timerover51]

Hi,

Thanks for that info. I found my plot and I had run some curve fits through the data.

For amphibious ships like the LSD 49, the curve fit is roughly dtons = 0.28 * hydrostatic displacement +650 (though I really only have 2 data points for this).

For modern warships like the DDG and FFG mentioned previously the rough equation is dtons = 0.25 * hydrostatic displacement (or basically divide the ship's listed hydrostatic displacment by 4 to get a rough estimate of its internal volume in dtons)

For submarines the rough equation is dtons = 0.073 * hydrostatic displacement (or basically divide the ship's listed hydrostatic displacment by 13.7 to get a rough estimate of its internal volume in dtons)

For really old battleships (such as maybe pre-dreadnoughts or WWI type ships) the rough equations is dtons = 0.15 * hydrostatic displacement (or basically divide the ship's listed hydrostatic displacment by 6.67 to get a rough estimate of its internal volume in dtons or just about twice the number that you'd get for a submarine, but here this equation was based on a real rough estimate for three ships)

You are going to need two, or maybe three, different curves for the ships that you mentioned. The LSD is going to be off because of all of the volume set aside for the floodable dock area, and storage for amphibious craft.

As my friend Norman Friedman spells it out in Modern Warship Design and Development, the ships that you mention are volume limited, as they need space for all of the electronics that they carry, and also for extended quarters for the volunteer crews. They will have a high reserve buoyancy because of that and will have a higher displacement than you would expect compared to earlier ships.

The pre-Dreadnoughts and Dreadnoughts were all weight-limited ships, as they had a lot of dense components. The pre-dreadnoughts were especially short of reserve buoyancy, and could be sunk by a single torpedo hit. Longitudinal engine room and boiler room bulkheads did not heal either. If you take their listed full load displacement, or whatever you can find, and then add about 3,000 cubic meters, that will give you a reasonable idea of their hull volume.

For the Dreadnoughts, you might want to take their loaded displacement and add about 6000 cubits meters to it, and use that for their displacement under Traveller rules. That is based on how much flooding could occur before sinking.

Post World War 1 ships get a bit more complicated.

 

[Carlobrand]

Mass does not matter, interesting.
...

It gets worse. Per CT Book 3:

"When determining the contents of a cargo, the players and referee must be certain to correlate the established price of goods with the cost per ton. For example, the base price of a shotgun is Cr150, while a ton of firearms as trade goods has a base price of Cr30,000. A strict weight extension of the shotgun (3.75 kg per shotgun) would indicate 266 shotguns. Extension should be instead based on price, with weight as a limiting factor. Thus one ton of shotguns would contain 200 guns, at Cr150 each. The extra weight can be considered packing and crates. Similar calculations should be made to keep prices in line on other trade goods."

In other words, a dTon WAS a metric ton. All that extra space was packing material - gobs and gobs and gobs of aerogel-weight packing material. It was enough to make a merchant cry.

One good thing MegaTrav did was abandon that idea, which prompted me to backtrack it into the CT universe and declare for my TU - somewhat arbitrarily - that a dTon amounts to 7.5 metric tons. Why that? Well, a typical shipping container's roughly 4 dTons and carries 30 tons. There are a variety of sizes and potential loads of course, but that works as a shorthand for me. Ergo, a ship could take a maximum of X dTons or X times 7.5 metric tons, whichever was lowest. So, the grain farmer's shipping overhead goes from Cr1000 per metric ton to Cr133, meaning the price of shipped grain goes up 27% instead of 333% - more stuff is worth shipping. Does involve some calculating for the ship-owner and a bit of recalibrating of trade rules, but it worked out. For one thing, the player can dabble in speculative trade without committing so much of his cargo space, thereby assuring a certain base income even if his trades fell through.

 

[Timerover51]

Per your shotgun example, if I can figure out where I put my FM101-10, Staff Officers Logistic Data, I could post the exact number and cube of a ton of 12 Gauge combat shotguns. I was already using the displacement ton for a lot more than a ton of cargo, as otherwise the whole system does not make sense. You do not get a capital loan for a ship, wet or space, without showing that you can consistently make money. Therefore, the idea that your characters are going to get a money-loosing ship via a loan is not going to happen. Ergo, you have to be able to haul more cargo. As for crew, my are all double bunk to free up space for paying passengers. Each cabin can hold up to 4 people. I have been on enough cruise ships to know that 54 cubic meters, 1900 cubic feet is way more that 1 person can claim.

 

[nDervish]

He does see to have confused volume with mass.

Of course, it doesn't help matters any that "ton" is used here as a measure of volume, while it's used as a measure of mass in everyday life, without always making an explicit distinction between "displacement tons" and "metric tons". (This is essentially the same reason why I hate the use of "ounces" as a unit.)

In the non-starship section it mentions fuel being consumed by smallcraft at the rate of 10 kilograms (1/100th of a ton) per 1G per 10 mins.

This, at least, does follow. A dton is defined as the volume of one metric ton of liquid hydrogen fuel, so 1/100th of a dton of fuel would have a mass of 10kg. It does not imply a correspondence between dtons and metric tons when dealing with any material other than fuel.

Which is shown by the GT rules (and simple common sense) to be a simplification of 'reality'.

Not necessarily. It is apparent to me that, in most editions of Traveller, M-drives are reactionless. (Ships carry fuel only for the power plant and J-drive, not M-drive fuel. Power plant fuel is consumed at the same rate regardless of whether the M-drive is in use or not. Therefore, the M-drive does not consume fuel or any other visible reaction mass.) M-drives also appear in the tech chart shortly after gravitics, so I assume that they are, specifically, gravitic in nature. (I think this is even stated in canon, but I could just be imagining that I saw it.)

If M-drives are gravitic and reactionless, then they are likely to function by generating an artificial gravitational field in the vicinity of the ship - they don't use thrust to push the ship through space, rather the ship "falls" through this artificial gravitational field. And, as we all know, gravitational acceleration is independent of mass.

So, provided that my suppositions about how M-drives work are accurate... Mass doesn't matter.

(Yes, I recognize that this explanation of M-drives does great violence to the laws of physics as we know them, but it fits perfectly with my understanding of the game's description of how M-drives behave and we're talking about the game universe, not the real one.)

 

[Fritz_Brown]

How is it getting around E=mc(squared)? Or in whatever universe GT (which I assume is to be understood as GURPS Traveller), Einstein's equation does not function?

Are you sure you're in the right place? You do know there's things like faster-than-light drives and inertialess drives in this game, right? There's a reason it's called science fiction.

Now, you are basically saying that in whatever universe this is, mass has no relevance, only volume. So, if mass has no relevance, only volume, then I should be able to throw a baseball made of collapsed matter the same distance as I could a standard baseball, as both occupy the same volume.

You certainly could - if you were using a Traveller maneuver or jump drive to do so.

You really need to go read the books about how the universe operates. Then you can post about how the tech works in your universe - caveating it with "In MTU,...." Understand that the tech in YTU won't be Traveller tech as written. As it is, given that this thread was about the ship limits using the rules of the game, you're arguing irrelevancies.

I raise the issue of the maneuver drive because when you look though the various books for Traveller, there is this ambivalence as to what a maneuver drive is. Sometimes it sounds like a fusion reaction drive and sometimes is sounds like a Dean reactionless drive.

No, there isn't much ambivalence, really. Probably the only departures from the standard volume-based drive might be in GT. But, GT is considered heretical in a lot of ways. (Obviously a lot of people like it, but it doesn't match the universe envisioned by MM, et al, in a lot of ways. You generally can't invoke very much of it as canon around here.) FF&S give a lot of options for drives - it was written for gearheads. It, however, still has the classic Traveller drive built into it.

 

[Fritz_Brown]

I have been on enough cruise ships to know that 54 cubic meters, 1900 cubic feet is way more that 1 person can claim.

You do recall, don't you - and here I'm assuming you've managed to read the books - the 4 dT per stateroom includes the life support and things like common areas?

Staterooms require four tons at a cost of Cr500,OOO per stateroom. Staterooms actually average about two tons, but the additional tonnage is used to provide corridors and access ways, as well as galley and recreation areas.

 

[rancke]

But, GT is considered heretical in a lot of ways. (Obviously a lot of people like it, but it doesn't match the universe envisioned by MM, et al, in a lot of ways.

'A lot of ways' is putting it much too strongly. It delves into some aspects of the universe envisioned by MM that other versions ignore, but that's not quite the same thing. A lot of the new setting material from GT is accepted by MM and his minions. Probably because the GT writers made a massive effort to build on MM's visions.


Hans

 

[mike wightman]

No, there isn't much ambivalence, really. Probably the only departures from the standard volume-based drive might be in GT. But, GT is considered heretical in a lot of ways. (Obviously a lot of people like it, but it doesn't match the universe envisioned by MM, et al, in a lot of ways. You generally can't invoke very much of it as canon around here.) FF&S give a lot of options for drives - it was written for gearheads. It, however, still has the classic Traveller drive built into it.

On this one timeless actually has a good point.

In original CT it is implied by the maneuver drive fuel use and small craft drive fuel use that the maneuver drive is a reaction drive of some sort.

Now add to that the fact that High Guard first edition flat out states that the maneuver drive is a fusion rocket and can be used as a weapon and you have a very different drive paradigm for early Traveller.

Revised CT dropped the fuel usage rates from the text, and High Guard 2 never mentioned fusion rockets or using drives as weapons. The fuel use rules in Beltstrike may infer the reaction drive model is still in effect.

It was the MT authors who defined the maneuver drive as reaction less, something that the GT authors ran with too.

TNE shifted the paradigm yet again by introducing HEPlaR reaction drives, and finally T4 allowed for both HEPLaR and reactionless thruster models for the maneuver drive.