Cargo Capacity and volume and mass

[AnotherDilbert]

I see that now from your examples. I am sad that I have been using these rules for years and they're so wonky. But changing rulebook sets is expensive, and I've seen CT and when I looked over the shipbuilding rules, I was wildly confused, so I do not expect to be able to convert.

I haven't seen MgT1 Supp 6, but at a guess it's highly simplified. If so, don't bother mixing it with reality, just go with the flow...

CT and MT are cheap from FarFuture, at $30 for a CD with everything IIRC... Just treat it as a toolbox to take snippets from.

 

[AnotherDilbert]

And as a follow-up, spaceships would need to be 14,000kg per dton to be neutrally bouyant. With 10-60% of the volume filled with 1000kg/dton jump fuel, you'd have to pack the rest very hard to get close to 14,000kg/dton averaged over the ship.

Yes, and therefore civilian ships can generally float, with something like 10 tonnes/Dt. Armoured ships are heavier and generally can't float. That is a rule-of-thumb you can use in any edition of Traveller.

Unarmoured, 2280 tonnes in a 2700 m³ hull ≈ 0.84 tonnes/m³.


Armoured, 172229 tonnes in a 135000 m³ hull ≈ 1.28 tonnes/m³, even with J-4 fuel.

 

[Badenov]

So I have re-mathed my ship designs and estimated masses, a bit. Using the Book 6 relation of mass/m^3 of 1.25:1 for crystaliron to steel since the previously made ship had a crystaliron hull and armor, and the RL density of steel, 7800kg/m^3 (https://www.thoughtco.com/table-of-densities-of-common-substances-603976), I recalculated the mass of a 500-ton ship. I wildly ballparked the equipment spaces (by dton) as 30% of a solid block, the passenger spaces as 20% of a solid block, and the armor as 100% solid material. Fuel is obviously 1 ton/dton. I was not too surprised when it massed almost 3000 tons/m^3. Revising the estimates down a bit to 20% for equipment, because not all gear is high-density gear, and the crew spaces to 10% for the same reason, it was still 2500 tons/m^3. Removing the armor from the modified design brings it to just over 1050kg/m^3, and that's before you load cargo into the empty space. So I suppose I will have to give up the image of a floating spaceport with all the starships gently rolling in the waves. At best, with no cargo and no fuel, they float just above the surface, lower than a submarine (thanks to TasminP the ref for submarine density, the button to add the quote to this post does not seem to work so I have done it manually).

Most modern submarines have a surfaced displacement of around 900kg/m^3; submerged displacement is usually around 1005kg/m^3.

Whether a starship at 1000kg/m^3 would float (and, if so, how much would be above the water surface) would depend on the temperature and salinity of the water.

So, this is all negated by ships having the capability to run their M-drive 24/7 inport to offset as much of their mass as needed to support whatever. Someone else had commented, and I can't recall where, that their traveller universe specifically made M-drives disruptive, like jetwash-level disruptive or more, so as to prohibit that, but I don't know that that's general canon? I can see the debate being 'Super high tech is supposed to solve problems' vs 'Making things too easy to be interesting'.

 

[atpollard]

Some REAL WORLD metrics to use as a yardstick:

Diesel Engine = 1000 kg per cubic meter
Containerized Cargo = 333 kg per cubic meter
Mobile Home = 65 kg per per cubic meter

So I would use:
BRIDGE/STATEROOM/CREW/FUEL space = 1 tonne per dTon
CARGO = 5 tonnes per dTon
ENGINEERING (MD/PP/JD) = 14 tonnes per dTon

ARMOR is too edition dependent for a general rule, but VOLUME OF ARMOR SHELL x DENSITY OF IRON is a ballpark figure ... but I would ignore it for Civilian (unarmored) ships.

 

[Badenov]

Some REAL WORLD metrics to use as a yardstick:

Diesel Engine = 1000 kg per cubic meter
Containerized Cargo = 333 kg per cubic meter
Mobile Home = 65 kg per per cubic meter

So I would use:
BRIDGE/STATEROOM/CREW/FUEL space = 1 tonne per dTon
CARGO = 5 tonnes per dTon
ENGINEERING (MD/PP/JD) = 14 tonnes per dTon

ARMOR is too edition dependent for a general rule, but VOLUME OF ARMOR SHELL x DENSITY OF IRON is a ballpark figure ... but I would ignore it for Civilian (unarmored) ships.

So, my numbers weren't too far off that. My engineering spaces were 1950kg/m^3 vs 1000, which isn't unreasonable given TL7 vs TL12+ and my crew spaces were about 15x your mobile home figure, which is a bit much probably, but didn't account for a huge perentage of the ship, so didn't have a major impact on the final numbers. Cargo's a big swing, because it depends a lot on whether you're carrying consumer goods or processed ore from a mining colony. And ore's a huge swing by itself because aluminum is 2700kg/m^3, but Uranium is 18,700kg/m^3. So I guess the final answer is YMMV.

 

[AnotherDilbert]

So I have re-mathed my ship designs and estimated masses, a bit. Using the Book 6 relation of mass/m^3 of 1.25:1 for crystaliron to steel since the previously made ship had a crystaliron hull and armor, and the RL density of steel, 7800kg/m^3 (https://www.thoughtco.com/table-of-densities-of-common-substances-603976),

No need to guess, this is more or less constant since CT:


But, if you are using MgT1, no masses are defined, just sizes in Dt. If you want a more detailed system MT, TNE, and T4 are available.

Someone else had commented, and I can't recall where, that their traveller universe specifically made M-drives disruptive, like jetwash-level disruptive or more, so as to prohibit that, but I don't know that that's general canon?

IYTU you can do whatever you want, but canon is that M-drives are just (magical) thrust. No fuss, no muss. The heavier ship, the slower it will accelerate with the same drive, the same thrust according to Newton (F=ma).

 

[kilemall]

No need to guess, this is more or less constant since CT:
View attachment 5447

But, if you are using MgT1, no masses are defined, just sizes in Dt. If you want a more detailed system MT, TNE, and T4 are available.


IYTU you can do whatever you want, but canon is that M-drives are just (magical) thrust. No fuss, no muss. The heavier ship, the slower it will accelerate with the same drive, the same thrust according to Newton (F=ma).

Very key to figure in the actual armor tonnage vs volume on that Striker chart.

As toughness increases per better material, the same armor level drops in total weight as less tons are required.

 

[AnotherDilbert]

So I would use:
BRIDGE/STATEROOM/CREW/FUEL space = 1 tonne per dTon
CARGO = 5 tonnes per dTon
ENGINEERING (MD/PP/JD) = 14 tonnes per dTon

Sure, you can do whatever you want but we are not running our ships on diesel.
We do have defined masses for drives, e.g. from MT:
Jump drive: 2 tonnes/m³
M-drive: ~2.6 tonnes/m³
Fusion: 1-4 tonnes/m³ depending on TL.



Fuel and cargo:

 

[Badenov]

No need to guess, this is more or less constant since CT:
View attachment 5447

But, if you are using MgT1, no masses are defined, just sizes in Dt. If you want a more detailed system MT, TNE, and T4 are available.


IYTU you can do whatever you want, but canon is that M-drives are just (magical) thrust. No fuss, no muss. The heavier ship, the slower it will accelerate with the same drive, the same thrust according to Newton (F=ma).

So masses are defined in Supp 6 Military vehicles, and they agree with this table, in that crystaliron is 25% heavier than steel, which is the figure I used for my calculations.

Sure, you can do whatever you want but we are not running our ships on diesel.
We do have defined masses for drives, e.g. from MT:
Jump drive: 2 tonnes/m³
M-drive: ~2.6 tonnes/m³
Fusion: 1-4 tonnes/m³ depending on TL.

More figures I am now learning. I can use these. On to the math, BBL.

 

[TamsinP]

And then the ugly effect of armour being a percentage of hull volume results in the same factor of the same type of armour on ships having vastly different thicknesses at different vessels tonnages. For example, using Cystaliron from MgT2e (1.25% per factor) we get (thicknesses in mm; for a cube-shaped vessel):

Tonnage	Armour Factor
1​	5​	10​	15​
100​	23.4​	119.0​	243.5​	374.0​
1,000​	50.4​	256.5​	524.6​	805.9​
10,000​	108.6​	552.6​	1,130.3​	1,736.2​
100,000​	234.0​	1,190.5​	2,435.1​	3,740.5​
1,000,000​	504.2​	2,564.8​	5,246.2​	8,058.6​

 

[Condottiere]

Today at 12:57 PM
Add bookmark
#5,055
Startrucks: Venture Drive

A. Anyway, megacasting could also apply to manufactured hulls.

B. With armour factor/zero, at the presumed manufacturing technological levels, in microgravity, a mostly complete hundred tonne hull skin should be doable.

C. Cube root of fourteen hundred is 11.1868894208.

D. Times six, times one centimetre thickness, 7.508789694792418 cubic metres.

E. Which I think is 0.5363421210566013 tonnes.

F. Eleven metres should be three decks.

 

[AnotherDilbert]

So masses are defined in Supp 6 Military vehicles, and they agree with this table, in that crystaliron is 25% heavier than steel, which is the figure I used for my calculations.

As Kilemall pointed out, you need less thickness of crystaliron so total mass of armour is less.

More figures I am now learning. I can use these.

I have made a simple ship in MT and MgT1 just for comparison: TL-11, 500 Dt, J-2, M-2:

MgT1:


MT:


You might be able to use it to compare masses of different components.

 

[atpollard]

Sure, you can do whatever you want but we are not running our ships on diesel.
We do have defined masses for drives, e.g. from MT:
Jump drive: 2 tonnes/m³
M-drive: ~2.6 tonnes/m³
Fusion: 1-4 tonnes/m³ depending on TL.

Thank you for your permission.

We also have defined masses from Striker and FF&S (we may have masses in GURPS and T4 and Mongoose Traveller, I never looked). However, Striker and MT and FF&S all provide different values. What they DO have in common is that technology that can be fact checked against reality (like Internal Combustion and Turbines and Rockets) all fail to match empirical reality in one or more basic metric.

So forgive me if I choose to start with the one value that I know is correct (reality) and use that as a yardstick for judging the interpolated fantasy technologies.

Real turbines are LIGHTER than a diesel engine of comparable volume. Real rockets are lighter than turbines of a comparable volume. If MT chooses to assume that further advances will result in flying bricks that crush any pavement they land on, then I feel free to choose to view that particular metric as “unlikely” and look to other Traveller sources for data that better fits with what we KNOW about real mechanical equipment.

 

[AnotherDilbert]

We also have defined masses from Striker and FF&S (we may have masses in GURPS and T4 and Mongoose Traveller, I never looked). However, Striker and MT and FF&S all provide different values.

Slightly different, mostly 2+ tonnes/m³.

System [tonne/m³]	CT Striker	MT	TNE	T4
Fusion TL-12	4	4	4	4
Grav	2	2
Contra-grav			~1	~1
M-drive		2.6	2	2
Jump		2	3	3

Real turbines are LIGHTER than a diesel engine of comparable volume.

Are they?

Tank engine (turbine)

Specifications​

Engine output peaks at 1,500 hp (1,100 kW), with 2,750 lb⋅ft (3,730 N⋅m) of torque at that peak,[2] which occurs at 3,000 rpm.[3] The turbine can provide torque in excess of 667 lb⋅ft (904 N⋅m) at significantly lower RPMs. The engine weighs approximately 2,500 lb (1,100 kg) and occupies a volume of 40 cu ft (1.1 m³), measuring 63 in × 40 in × 28 in (1,600 mm × 1,020 mm × 710 mm).

https://en.wikipedia.org/wiki/Avco-Lycoming_AGT1500#Specifications
Seems to be 1 tonne/m³?


Tank engine (diesel)

Engine specifications​

• Engine: German MTU MT883 Ka-500/501 27.4-litre (27,361 cc) 90° V-block 12-cylinder liquid-cooled diesel engine
• ...
• Engine length: 1,488 mm (58.583 inches)
• Engine width: 972 mm (38.268 inches)
• Engine height: 742 mm (29.213 inches)
• Dry weight (estimated): 1,800 kg (3,968 lbs)

https://en.wikipedia.org/wiki/EuroPowerPack#Engine_specifications
1.8 tonnes in a ~1.1 m³ rectangular space is ~1.7 tonnes/m³.


OK, the turbine is lighter, but none of them are less than 1 tonne/m³.


Electric car motor?
https://www.thedrive.com/news/lucids-new-469-hp-electric-motor-weighs-just-70-pounds
~32 kg in ~0.02 m³ is about 1.5 tonnes/m³.

If MT chooses to assume that further advances will result in flying bricks that crush any pavement they land on, then I feel free to choose to view that particular metric as “unlikely” and look to other Traveller sources for data that better fits with what we KNOW about real mechanical equipment.

If you want lighter vehicles, just say that? Deducing fusion reactors and jump drives from ICE engines is a weak argument at best.

 

[Rupert]

Note that while the engines' block dimensions might suggest quite high densities, the design rules we're looking at include access to the engine, etc., in the volume the engine requires, and that will considerably increase the volume the engine takes up in a vehicle. Mind you, that extra volume will also include stuff that has mass, so just how much it reduces the density is undefined.

 

[atpollard]

"The size of a Reactor Compartment varies depending on the type of nuclear submarine. For Victor-class submarines, the Reactor Compartment is about 10 meters in diameter, 10 meters long, and about 900 tons in weight."

10m dia x 10m long = 785 cu.m.
900 tonnes / 785 cu.m. = 1.15 tonnes per cubic meter (1967 = TL 6)

"For the Ohio class (S8G), the reactor compartment is 42 feet (13 m) in diameter, 55 feet (17 m) long and weighs 2,750 tons (2490 tonnes)."

13m dia x 17m long = 2255.3 cu.m.
2490 tonnes / 2255.3 cu.m. = 1.01 tonnes per cubic meter (1976 = TL 7)

I stand by my opinion that after many TLs of continued improvement, POWER PLANTS will not become DOUBLE the weight per cu.m. but HALF the weight is more likely. The above suggests a 10% reduction per TL [although 2 is a dangerously small sample size].

[PS: Diesel vs Turbine vs Rocket was a TL 5 vs TL 6 vs TL 7 comparison of "MD" density progression and represented something more like this:
TL 5

TL 6

TL 7

... to extrapolate trends forward. Larger - Lighter - more powerful = lower density.]

 

[AnotherDilbert]

"For the Ohio class (S8G), the reactor compartment is 42 feet (13 m) in diameter, 55 feet (17 m) long and weighs 2,750 tons (2490 tonnes)."

13m dia x 17m long = 2255.3 cu.m.
2490 tonnes / 2255.3 cu.m. = 1.01 tonnes per cubic meter (1976 = TL 7)

That is only a part of the "power plant":

Compartment 10 is the reactor chamber, 9 is the main machine room, 2 and 11 aux machinery.
https://en.wikipedia.org/wiki/Ohio-class_submarine

At a guess the reactor chamber only produces hot water, turbines in the machine room turns that into electrical power and rotational energy for propulsion.

[PS: Diesel vs Turbine vs Rocket was a TL 5 vs TL 6 vs TL 7 comparison of "MD" density progression and represented something more like this:
TL 5
[submarine diesel]

TL 6
[aircraft jet engine]

TL 7
[rocket engine]

... to extrapolate trends forward. Larger - Lighter - more powerful = lower density.]

The difference is not TL, but duty cycle. A ship's diesel works for weeks on end, an aircraft engine for hours, and a rocket for minutes (at best).

Ships and heavy vehicles still use diesels, not rockets, just as they did in WWII, for obvious reasons.
WWII rockets used rocket engines, not diesels, for equally obvious reasons.

WWII V2 rocket. Tanks takes most of the rocket for 60 s burn time.
I'm sure modern rockets deliver more power, using less fuel, but why would they have less density?

 

[AnotherDilbert]

Compare a WWII tank engine:
Maybach HL230 [https://en.wikipedia.org/wiki/Maybach_HL230]:
1 × 1.19 × 1.31 m = 1.56 m³ and 1.2 tonnes, for ~0.8 tonnes/m³.
700 hp / 1850 Nm.
~0.3 MW/m³

to a modern tank engine:
MTU MT883 Ka-501 [https://en.wikipedia.org/wiki/EuroPowerPack]
1.49 × 0.97 × 0.74 m = 1.1 m³ and 1.8 tonnes, for ~1.7 tonnes/m³.
1650 hp / 5000 Nm.
~1 MW/m³.

The modern engine is smaller, produces a lot more power, but is certainly not lighter...

 

[atpollard]

Compare a WWII tank engine:
Maybach HL230 [https://en.wikipedia.org/wiki/Maybach_HL230]:
1 × 1.19 × 1.31 m = 1.56 m³ and 1.2 tonnes, for ~0.8 tonnes/m³.
700 hp / 1850 Nm.
~0.3 MW/m³

to a modern tank engine:
MTU MT883 Ka-501 [https://en.wikipedia.org/wiki/EuroPowerPack]
1.49 × 0.97 × 0.74 m = 1.1 m³ and 1.8 tonnes, for ~1.7 tonnes/m³.
1650 hp / 5000 Nm.
~1 MW/m³.

The modern engine is smaller, produces a lot more power, but is certainly not lighter...

I like that ... but I find all VOLUME metrics questionable since they are bounding boxes on one component in a room fill of components plus controls plus access space, plus wires and plumbing. When I tried to use that to create reasonable parametrics (meaning they could predict other real items with fair accuracy) I found it almost impossible to accurately measure volume. For example, what is the volume of the engine compartment in a car? How do you begin to distinguish the volume around the Suspension from the volume around the wheels from the volume around the transmission from the volume around the engine? So the next step is to move to generator engines on skids which at least lend themselves to VOLUME estimates. However Auto Engines are very different from Power Generation engines and the one makes a poor predictor of the other. Notice how the "modern tank engine" is only a little heavier (1.8 tonnes vs 1.2 tonnes) yet it drives a much larger and heavier tank faster than the WW2 engine drove a lighter tank.

Eventually I found weight (kg) per MW (or kW) was a far easier metric to gain accurate data on or calculate. Try comparing those two tank engines and assume that a 1 MW engine will fit in the same Engine Room with space around it. How has TL impacted "tonnes per MW"?

So the STARSHIP needs a certain number of megawatts, yet why should its propulsion system be heavier per MW than more primitive systems. My complaint is not with the space around the machinery, it is with decreasing efficiency at higher TLs. CT ignored mass (which worked fine) but slapping 2 tonnes per cubic meter over an entire engineering room is simply too DENSE for equipment that is not predominantly steel castings with little to no access between them (denser than a Diesel Engine Block). Do you really view ENGINEERING on a ship as a room crammed full of equipment like the space between parts on a modern Main Battle Tank Engine? A room where HULL PLATING must be removed and the MD extracted to reach parts for service and repair? That is what 2 tonnes per cu.m. implies.

 

[TamsinP]

The M1 Abrams tank uses the Avco-Lyoming AGT1500 engine (1.6m x 1.02m x 0.71m = 1.15872m^3) which masses 1100kg, so the density is 949.32 kg/m^3, with a peak output of 1500 bhp/1100 kW.