Cepheus SRD Errata

[Timerover51]

As another thread brought this up, but I am not sure if the poster is looking at the original System Reference Document or the Light Version put out by Stellagama Publishing, I will start a thread covering the System Reference Document.

On page 120, under Displacement Tons, the following statement is made.

A metric ton of hydrogen measures approximately 13.5 cubic meters, which is rounded to 14 cubic meters for ease of calculations. When drawing floor plans or maps of ships, each square measuring 1.5 meters by 1.5 meters, to a height of 3m up from the floor, represents half a ton.

A metric ton of Liquid Hydrogen occupies a volume of 14.11 cubic meters or 498.44 cubic feet, which for ease in calculations is rounded to 14 cubic meters. As the floor plans are based on a 1.5 by 1.5 meter square, and assume a height to the next deck of 3 meters, 2 of the 1.5 meter squares equal 13.5 cubic meters, which for convenience is regarded as equal to a dTon.

I view the 498.44 cubic feet as useful as it is almost exactly 5 gross register tons, or 500 cubic feet, a very common measurement of volume in Real World nautical ships. It makes calculating the amount of cargo that can be loaded in a displacement ton or dTon much easier from the standard stowage factors.

Side Note: As 1.5 meters is equal to a fraction over 59 inches, it does make going from English Measurement Base Data to metric much easier. I simply round to 5 feet or 60 inches.

 

[middenface]

Not errata

 

[Timerover51]

Not errata

Call it a correction then.

 

[SpaceBadger]

Not errata

How is it not? Timerover51 demonstrated that the quoted passage has the numbers wrong, backwards even. It might be corrected as, "One metric ton of Liquid Hydrogen occupies a volume of 14.11 cubic meters, rounded to 14 cubic meters for ease in calculations. This volume is further simplified to 13.5 cubic meters per dTon in ship deckplans, to allow for two 1.5 meter squares per dTon, with 3 meters from each floor of one deck to the floor of the next."

 

[mike wightman]

I agree with timerover51 and SpaceBadger.

This is a DGPism that should have been excised many editions ago, and yet it still pops up in T5 unfortunately.

The 13.5m^3 dt is based off the dimensions of the deckplan mapping squares, whereas since CT times the displacement ton is defined as the volume of one thousand kilograms of liquid hydrogen, which is approximately 14m^3 or 500 cubic feet.

Considering deckplans are allowed a bit of leeway keeping the 14.11m^3 dt actually gives you the wiggle room.

 

[Mithras]

How is it not? Timerover51 demonstrated that the quoted passage has the numbers wrong, backwards even. It might be corrected as, "One metric ton of Liquid Hydrogen occupies a volume of 14.11 cubic meters, rounded to 14 cubic meters for ease in calculations. This volume is further simplified to 13.5 cubic meters per dTon in ship deckplans, to allow for two 1.5 meter squares per dTon, with 3 meters from each floor of one deck to the floor of the next."

But that results in *exactly the same result*. The end result is the same. What you get out at the end is the same. I'm not sure why there is an argument there? Timerover, have you built any vehicles yet, that aren't ships? What did you think of them? Try not to focus on real world designs, no design system so far has achieved creating a perfect 1:1 match for real world designs.

 

[mike wightman]

The argument is over this statement "A metric ton of hydrogen measures approximately 13.5 cubic meters" which is factually incorrect.

 

[middenface]

http://wiki.travellerrpg.com/Deck_Plan

 

[mike wightman]

That just reinforces the definition "A metric ton of hydrogen measures approximately 13.5 cubic meters" as being incorrect, since a metric ton of liquid hydrogen is approximately 14 cubic metres.

Read what it says:
"The creation of starship deck plans is based on the assumption that one ton of mass displacement equals fourteen cubic meters" not approximately 13.5 cubic metres.

 

[Condottiere]

It lies within a ten percent variance.

You could think of deckplans as being a representation of an approximation of the actual layout, with gridlines allowing the less artistically gifted amongst us to sketch out our preferred habitats.

 

[mike wightman]

The deckplans can have 10% variance, I doubt very much Imperial scientists define basic units with plus or minus ten percent variance - which is the issue.

I don't have a problem with defining the deckplan block as almost approximately 14 cubic metres nased on the measured dimensions giving 13.5 since 13.5 rounds to 14.

But if the displacement ton is defined as the volume occupied by one metric ton of liquid hydrogen then it should be written as approximately 14 cubic metres (14.11 rounded to nearest whole number).

 

[Mithras]

How is it different? Space Badger himself said:

How is it not? Timerover51 demonstrated that the quoted passage has the numbers wrong, backwards even. It might be corrected as, "One metric ton of Liquid Hydrogen occupies a volume of 14.11 cubic meters, rounded to 14 cubic meters for ease in calculations. This volume is further simplified to 13.5 cubic meters per dTon in ship deckplans, to allow for two 1.5 meter squares per dTon, with 3 meters from each floor of one deck to the floor of the next."

i.e. 13.5 cubic metres per dTon in ship deckplans.

That's the same end result as the Vehicle Design Guide. To the numbers. TimeRover had the same calculation. To the numbers. It all ends in practical gaming figures as 13.5 cu metres.

 

[mike wightman]

I am not debating the size of a deckplan square. Two of them make 13.5 cubic metres and are almost 14 cubic metres.

But that is not how the displacement ton is defined.

The displacement ton is defined as the volume occupied by one metric ton of liquid hydrogen, which is 14.11 cubic metres or almost 14 cubic metres.

The statement that a metric ton of liquid hydrogen is approximately 13.5 cubic metres is factually incorrect.

 

[lucasdigital]

I am not debating the size of a deckplan square. Two of them make 13.5 cubic metres and are almost 14 cubic metres.

But that is not how the displacement ton is defined.

The displacement ton is defined as the volume occupied by one metric ton of liquid hydrogen, which is 14.11 cubic metres or almost 14 cubic metres.

The statement that a metric ton of liquid hydrogen is approximately 13.5 cubic metres is factually incorrect.

Factually incorrect?

*Approximate:*
close to the actual, but not completely accurate or exact.

13.5 CBM is within 95% of 14.11 CBM. In lab work, 5% could be a massive gulf but in Traveller ship design it is most certainly an acceptable approximation.

 

[Mithras]

I am not debating the size of a deckplan square. But that is not how the displacement ton is defined.

The statement that a metric ton of liquid hydrogen is approximately 13.5 cubic metres is factually incorrect.

But that doesn't affect ant design sequence, or affect play at the table. During some shipboard skirmish when do your players ask how the formula for who the deckplan tonnage was calculated? The results that this thread is pouring over are the same, gameplay and design sequences are blissfully unaffected.

No-one's game, not one's 'fun' designing and building vehicles, is somehow improved from these pages of refutation of a formula that produces the same result as your corrected formula. Maybe your players are different, and do quite like to know the origins of each game forumla while rolling dice.

I kind off feel the whole thread is a debate to no end, as if it is somehow a way to score a few points, despite the outcomes being the same in play.

But then I feel we're all probably above that.

 

[jaymin]

I kind off feel the whole thread is a debate to no end

Pretty much.

But then I feel we're all probably above that.

Yet, I can't help adding...

In my Traveller Universe, the volume of a "ton of hydrogen" is set by the Imperial Weights and Measures Branch, which for historical consistency, is located on Vland. It has a higher gravity than Terra and it so happens that there one ton of hydrogen is exactly 13.5 cubic meters.

 

[mike wightman]

In which case your Vlandian scientists need to go back to school and learn the difference between weight and mass.

Unless the mass is travelling at close to the speed of light it does not change depending on local gravity.

One metric ton is one metric ton regardless of local gravity.

 

[mike wightman]

But that doesn't affect ant design sequence, or affect play at the table. During some shipboard skirmish when do your players ask how the formula for who the deckplan tonnage was calculated? The results that this thread is pouring over are the same, gameplay and design sequences are blissfully unaffected.

I am not debating it effect on play or the scale used to draw up the deckplans. It is the needless inaccuracy of the 13.5 statement.

No-one's game, not one's 'fun' designing and building vehicles, is somehow improved from these pages of refutation of a formula that produces the same result as your corrected formula. Maybe your players are different, and do quite like to know the origins of each game forumla while rolling dice.

Most of my players have enough basic knowledge of science to recognise that the statement is factually incorrect.

I kind off feel the whole thread is a debate to no end, as if it is somehow a way to score a few points, despite the outcomes being the same in play.

But then I feel we're all probably above that.

It's not about points scoring, its about scientific accuracy in a definition that is based on real world known data.

But I shall make this my second to last post on the matter since you are right that the argument is a debate to no end. This is CE after all, so I can edit my version for scientific accuracy.

 

[mike wightman]

And this is positively my last post on the matter unless someone deliberatly drags me back into it.

Factually incorrect?

Yes, factually incorrect, since the factual value of the density of liquid hydrogen is an easy look up.

13.5 CBM is within 95% of 14.11 CBM. In lab work, 5% could be a massive gulf but in Traveller ship design it is most certainly an acceptable approximation.

I don't disagree.

13.5 will round to 14, but the approximate value of a metric ton of liquid hydrogen is 14 cubic metres, not 13.5. It is an acceptable approximation for deckplans but not for defining the volume of one metric ton of liquid hydrogen.

It's a question of do you want to use real science and maths to define your displacement ton or the size of a deckplan square, which varies between editions anyway - check out the scale use in TNE for example.

 

[jaymin]

One metric ton is one metric ton regardless of local gravity.

Correct. But the volume it occupies depends on the pressure and temperature it is stored at. ;-)

I was just trying to point out how silly this discussion is. It's inappropriately Terran-centric to assume Earth pressure and temperature as the norm for determining what volume a certain mass of hydrogen will fill.

(I wanted to say the Imperial Standards office was on Reference, which makes more in-setting sense, but the gravity is too light there to make the hand-wave work.)