Overtonnage and Undertonnage - Discussion

[robject]

CONCEPT

Overtonnage and undertonnage does two things:

Given 1. When designing a ship, a grossly overtonned hull must be promoted to the next letter code. Thus a 100 ton hull with 160 tons of stuff in it is forced by rule to be a 200 ton hull. This is entirely for the sake of calculating drive requirements and performance ratings.

Given 2. When operating a ship, a slightly undertonned or overtonned hull gets a small performance change. It's a tactical and operational benefit (or penalty) to Agility.

Hypothesis. Based on Given 2 plus Marc's example of the Daring, this rule applies to the ship as a whole, and not just the hull. This is also supported by the way pod and barge hulls can change the gross performance characteristics of a ship (example: the Gazelle).

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DEFINITIONS

Agility and Stability:

Agility reflects ship movement responsiveness, shown as Power Plant Potential minus Current Used Gs, or Maximum Gs minus Current Used Gs. In the event of Conflict during movement, a ship with greater Agility moves last (which is advantageous). T5 B2 p42 footnote 4.

Stability is a Mod on Turbulence when operating in Atmosphere. T5 B2 p71.

Attached - connected, perhaps temporarily, to the hull, via bracket, streamlined bracket, hull niche, grapple, and connector.
Attached Items - pods (detachable) (includes boats), barges (detachable), subhulls (may be detachable, may be not) and vehicles (attached via a bracket).
Base Hull Tonnage - the ideal volume of a corresponding hull letter code.
Connected - something permanently attached to the main hull.
Hull - the ship sans detachable items.
Overtonnage - the amount by which a hull -or- ship is more than the base hull tonnage. T5 B2 p52.
Ship - the hull and its typical attached items.
Total Tonnage - the Ship's typical operating volume.
Undertonnage - the amount by which a hull -or- ship is less than the base hull tonnage. T5 B2 p52.

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DISCUSSION POINTS

Overtonnage penalties and undertonnage benefits apply to total tonnage.

The only evidence I have is from Marc's design intent for the Daring-class Patrol Frigate:

In combat, the ship ideally sheds its two Fighters and Ship’s Boat to create an undertonnage (348 tons) and Agility +2 (total in Atmosphere +3). T5 B2 p46 penultimate para (not footnoted).

(The ship design on p46 has issues. I think these do not detract from the intent which demonstrates an interpretation that supports Overtonnage being affected by Attached Items).

 

[AnotherDilbert]

My argument: Pods (small craft) are external (not included in the hull), overtonnage is internal (included in the hull). Two different things. External pods affect drive performance, overtonnage affects agility and stability.

So far so good, it gets confusing quite quickly...

As I see it the Daring is a 400 Dt main hull with +20 Dt wings and an additional 50 Dt pods. The Wings are part of the hull and overtonnage (B2 p53 "Streamlining"). Drive performance should be calculated for 450 Dt when carrying craft, or 400 Dt when they are launched.

The write-up in B2 p46-47 is utterly confused: The wings are treated as a component that consumes hull space, not adds hull space as they should. The air/raft housed in the Ship's Boat is deducted from the main hull too. Apart from the small craft the 420 Dt main hull contains about 321 Dt of components, leaving lots of space empty...

The Daring undertonnage is incorrect, I believe. A total of 348 Dt, hence 52 Dt undertonnage is presumably not allowed. That should be a 300 Dt hull:

B2 p52:
In the final design, the Hull may be more or less than the initial design tonnage. Slight undertonnage (49 or fewer tons under design hull tonnage) positively impacts performance by increasing Agility (+1 per 25 tons under). Slight overtonnage (49 or fewer tons over design tonnage) negatively impacts performance by decreasing Agility (- 1 per 25 tons over). Gross overtonnage (50 or more tons) requires rounding the Hull Identifier to the next higher size.

Pods are e.g. drop tanks, and are treated as drop tanks have always been: External to the hull and changes the drive performance.

B2 p70:
PODS AND BARGES
Pods and Barges are detachable ship components. Adding a Pod or Barge to a parent Hull increases the total tonnage for a ship, which potentially decreases the performance of its drives. Detaching a Pod or Barge from a Parent Hull decreases the total tonnage for a ship, potentially increasing its performance.

B2 p117:
Renormalization
When the volume of a ship changes (by dropping drop tanks, changing the number of cargo pods, or adding or removing riders) the performance of the ship may change.
1. Note the jump drive code.
2. Determine the new tonnage.
3. Create new Drive Potential from Drive Potential-1

Opportunities
Some opportunities involving renormalization include:
Drop Tanks. The ship carries a substantial quantity of fuel (jump fuel) in tanks which can be jettisoned. When jettisoned, the ship no longer counts its fuel drop tanks against its tonnage for Jump purposes. For example, a 400-ton Close Escort has Jump Drive-H (potential=4), Maneuver Drive-H (potential= 4), and two 50-ton drop tanks and a 76-ton internal tank. In normal operations, it can do Jump-4 and 4G.
If it jettisons the drop tanks, it becomes a 300-ton ship (Jump potential-5 and 5G).
Cargo Pods. If ship cargo structure is modularized; actual tonnage (for Jump Purposes) calculations may vary.
Riders. The ship carries one or more ships (riders) which can be detached for combat or other missions. Be- cause Riders do not require jump drives and jump fuel tankage, they may be more efficient in combat.

 

[AnotherDilbert]

Trying to put it a bit more simply:

We have a choice: Either put small craft internally consuming hull space (hangar), or put them externally increasing the total tonnage of the ship (grapples).

Grapples are not the same as hangars. Choice is good.

 

[AnotherDilbert]

Here's how I get the Daring:

Note that I had to stuff a 86 Dt cargo hold in there to fill out the ship.

TL-14  GF-DS33                       Ergo 2   Comfort 2    Demand 0        Agility 1
       Gunned Freighter              Total:       -20         221,6        Stability 1
SYSTEM                                    #       DTON         COST   
                                                                      
Hull                                              400                 
Config: Streamlined                                            28     
Structure: Charged Plate       AV=56 ( 560 vs Blast, 560 vs Heat/Beam, 560 vs Pres, 0 vs Rad, 0 vs EMP )   
Coating:                       AV= 0 (  )   
Armour Std                                1                          AV=28 ( 280 vs Blast, 280 vs H/B, 0 vs Rad, 0 vs EMP )   
Armour Std                                1        16                AV=28 ( 280 vs Blast, 280 vs H/B, 0 vs Rad, 0 vs EMP )   
Landing Wheels Wilderness                          12           6     
Wings Incr Perform                                              4     
Folding Fins Incr Agility                                       2     
Lifters Installed                                               2     
                                                                      
Drop Tanks (95% fuel)                     0                                -20  Hull
Total Drive Capacity                    400                                -20  Over/undertonnage: Reduce overtonnage
                                                                      
Jump Field: Jump Bubble                                                    D=351 m, Flash 7
Mod J Drive F  J-3, 660 EP                1        17,5        17,5   
Adv M Drive F  3 G, 720 EP                1         3,7        14,7   
Adv P Plant F  P 3, 720 EP                1         6,3        12,7   
                                                                      
Fuel, Jump   J-3                                  108                 
Fuel, Power  4 weeks                                9,6               
Purifier                                  2         2           2     
Scoops                                    2         2           0,2   
                                                                      
Console, Control C+S=14                  19        38           3,8     
Computer m/4                              1         4          18     
                                                                      
Sensors                                                               
Adv DS Surf Commu-13 +16A+12 PA           1                     7       
Ear AR Surf CommP-14 +13A+7 PA(           1                     3       
Mod AR Ant EMS-14 +17A+7 PA(Ele           1         1           1          ACS S=7
AR Surf Visor-14 +14A-- P(Phot)           1                     2          ACS S=5
Mod DS Surf Neutr-14 +16A-- P(G           1                     5,5        ACS S=10
Gen AR Surf Grav -14 +14A-- P(G           1                     1,5        ACS S=7
Gen G Surf Life -14 +14A-- P(Ma           1                     6,1        ACS S=1
                                                                      
Crew:                                     2                           
Large Stateroom (1) for 1                 1         4           0,2   
Suite (2) for 2                           3        12           0,6   
Double Stateroom (2) for 2                4         8           0,4   
Spacer Niche (1) for 1                   22        22                 
Common Areas                             31        31                 
Life Support:                                                         
Clinic                                    1         2           1     
Life Support, Long term 160%              6        12          12          7200 person-days
                                                                      
Payload, General                                    1                 
Payload, Sophisticated                              1           1     
                                                                      
Standard Air Lock                         4                           
                                                                      
Cargo                                              86,9               
                                                                      
Weapons                                                               
Ult DS T3 Miss-14 +18 H:M                 2         6          22     
Imp G T3 Beam-14 +17 H:3 Def+3            2         8          13     
                                                                      
Screens                                                               
Mod Vd Bo Nucle-14 Def+3                  1         3           3,5   
                                                                      
Carried Craft                                                         
Grapple Ship's Boat 30 Dt                 1         1           9     
Bracket Fighter 10 Dt                     2         2          22

Note the complete lack of freshers, something that might cause some problems...
The Darings hull cost is wrong; Charged adds MCr 1 / 100 Dt hull, not for each armour layer, I believe.


Even if the small craft are included in the hull tonnage, there is a 36 Dt empty hole in there...

 

[Rigel Stardin]

This is what I tried to explain in the Gazelle Study. There is a difference between Hull Size and the ship's actual ton (displacement to use nautical term). You can have a 400 Ton Hull Size and it's fitted out with all the essentials (staterooms, Maneuvering Drive, Jump Drives, etc) and have 50 Tons left over. You can put it into cargo or fuel. For this example, I put it into a 10 Tons Air/raft Hanger/Bay. The Bay when empty can act like an extra cargo bay or when the Air/raft is inside you have an additional 4 Tons (my stats). There is a difference of 6 Tons between the different usage of that room?

The empty room is apart of the original tonnage so, do you count the cargo or just the Air/raft as the extra weight? It's a hard call, even for me.

For me, I keep it simple by just counting Additional Vehicles (in self-contained Hanger/Bays), Cargo, Pod (attachable Cargo Containers), Drop Tanks, External Mounted Vehicles or Equipment and Fuel Tonnage. There are just to many variables when players repurpose a room or bay for something else. Major retrofits are a different story, but if they don't go outside the original room's size and shape then, there should be no change to the Tonnage.

There is also another point here. That missing 50 tons could be all the things your ship need to operate? Landing gear, wiring, plumbing, ventilation, lighting, etc. That's why if a ship I design is over the the limit I was trying to hit , I round down under 50 Tons but if it over 50, then I go to the next Hull Size.

For me Hull Size is a guild and not a hard target, that why I use the Displacement Method in my designs. IMP-525-CE just means, the Close Escort Displacement is 525 Tons (100 Tons Fuel and 25 Ton Gig) but the over all Hull Size is 400 tons. It was the only for my mind to wrap itself around Starship construction and Math will drive you crazy every time if you follow the rules (That goes for any game system vehicle construction rules).

 

[AnotherDilbert]

This is what I tried to explain in the Gazelle Study. There is a difference between Hull Size and the ship's actual ton (displacement to use nautical term). You can have a 400 Ton Hull Size and it's fitted out with all the essentials (staterooms, Maneuvering Drive, Jump Drives, etc) and have 50 Tons left over. You can put it into cargo or fuel. For this example, I put it into a 10 Tons Air/raft Hanger/Bay. The Bay when empty can act like an extra cargo bay or when the Air/raft is inside you have an additional 4 Tons (my stats). There is a difference of 6 Tons between the different usage of that room?

The empty room is apart of the original tonnage so, do you count the cargo or just the Air/raft as the extra weight? It's a hard call, even for me.

Traveller uses "displacement tons" as a volume, not a mass; the volume displaced by a 1 tonne (=1000 kg) hull floating on liquid hydrogen, i.e. about 14 m³. The tonnage of a Traveller ship is a volume, a size. A "100 Dt hull" means a hull with a volume of 1400 m³. Actual mass is disregarded (in CT and T5 at least), presumably for simplicity.

LBB2'81, p13:
The Hull: Hulls are identified by their mass displacement, expressed in tons. As a rough guide, one ton equals 14 cubic meters (the volume of one ton of liquid hydrogen).

So, when a room is repurposed or a craft is launched from an internal hangar the size of the ship does not change, the "tonnage" is the same. Drive performance is unchanged.


The HG'80 Gazelle from S7 and S9 is a 300 Dt (≈4200 m³) ship (including the boat) with additional 100 Dt (≈1400 m³) drop tanks, for a total of 400 Dt (≈5600 m³).

CT S7, p13:
Close Escort (Type CE): The close escort is built using a 300-ton hull with a partially streamlined configuration. It is fitted with jump-5, maneuver-5, and power plant-7 drives, and fuel tankage for 81 tons of fuel. To this basic package is added disposable 100-ton fuel tanks to provide the total fuel necessary for the drives. However, with these tanks installed, the ship tonnage is increased to 400 tons, which reduces the ship's performance to 4-G, jump-4, and power plant-5. The tanks may be dropped to allow the higher performance, but the ship then becomes restricted by its lower fuel supply until the tanks are replaced.

Early CT had, unlike T5, no concept of "internal" or "external" small craft, they were all included in the hull, and drive performance did not change when they were launched. But if we draw an illustration or deck plan we should probably have a 280 Dt (3920 m³) main hull, a 20 Dt (280m³) boat, and 100 Dt (1400 m³) drop tanks, since the boat is described and illustrated as external.


Think of it like a car: If you stuff things into the boot (internal), the size and rough performance is the same, but if you connect a trailer with stuff (external), the size and performance of the total vehicle changes significantly.

 

[Rigel Stardin]

I will say this. If, you put 1 Ton into the boot when it's only made to handle 100 kg the performance will change. This is my point. There is a big differance between (in my example) 4 and 6 tons extra tons. I am just careful about how I count those extra tons. It really comes down to how the ship will be used in the end. A scout may have to run a courier mission and leave behind the air/raft, so I would err of the side of counting the 10 Ton Hanger/Bay as cargo space, thus not having performance issues.

 

[kilemall]

I will say this. If, you put 1 Ton into the boot when it's only made to handle 100 kg the performance will change. This is my point. There is a big differance between (in my example) 4 and 6 tons extra tons. I am just careful about how I count those extra tons. It really comes down to how the ship will be used in the end. A scout may have to run a courier mission and leave behind the air/raft, so I would err of the side of counting the 10 Ton Hanger/Bay as cargo space, thus not having performance issues.

That’s your privilege if it gives you gaming/gearhead pleasure, but most versions are volume only.

 

[AnotherDilbert]

I will say this. If, you put 1 Ton into the boot when it's only made to handle 100 kg the performance will change.

I was assuming "reasonable" use, use well within spec.

You can put 10 tonnes of lead in the back of a Volvo, or 10 000 tonnes of lead in a Free Trader, but I would not expect anything to work, or even move after that...

On the other hand the presence or absence of a 4 tonne air/raft from a 1000 tonne Scout will not make any significant difference. Yes, if we look at the systems that keeps track of mass, e.g. MT, a Scout has a mass of very roughly 1000 tonnes.


But your TU works just as you wish, of course.

 

[Condottiere]

How much does a jump drive or a fusion reactor weigh, per cubic metre?

 

[AnotherDilbert]

How much does a jump drive or a fusion reactor weigh, per cubic metre?

MT says a jump drive system has a mass of 2 tonnes per m³, and a power system between 1-4 tonnes per m³ depending on TL. This is presumably for the entire installation including maintenance access corridors, not just the reactor.

TNE says jump drive 2-3 tonnes per m³ and power plants the same 1-4 tonnes per m³ as MT.

Same ballpark figures for most machinery.

Fuel and accommodations has very little mass, cargo is estimated at a nominal 1 tonnes per m³.

The wildcard is armour. Heavy armour can mass more than the rest of the ship.

Net effect is that civilian ships generally has a mass of a little less than 1 tonnes per m³, hence can float and land on water.
Armoured warships are generally more massive and can't float.

 

[Spinward Flow]

How much does a jump drive or a fusion reactor weigh, per cubic metre?

Fusion Reactors (CT Striker Book 4 p2)

• TL=9-12 ... 4 tons per m³ outputs 2 MW
• TL=13-14 ... 3 tons per m³ outputs 3 MW
• TL=15 ... 2 tons per m³ outputs 6 MW

 

[Condottiere]

1. That still above the supposed one metric tonne per fourteen cubic metres.

2. Bonded super dense does sound ominous.

3. Not to mention thirty five percent nickel iron for buffered planetoids.

 

[whartung]

TNE also assumes a basic ship density (of some value I'm not going to bother looking up right now). Stay in those margins, and just work off the tables and such for performance. Make it heavier, and you get to dig in to the math.

 

[AnotherDilbert]

The limit is basically 1 tonne per m³ = 14 tonnes per displacement ton:

TNE FFS, p69:
Spacecraft require (for the sake of simplicity) 10 tonnes of thrust per displacement ton to achieve an acceleration of 1G. Spacecraft with a final mass of more than 15 times (rounding fractions to the nearest whole number) their hull rate (in displacement tons) should recalculate their acceleration based on the actual thrust-to-mass ratio, dividing thrust (in tonnes) by mass (in tonnes) to determine acceleration in Gs (round fractions down). Most spacecraft, however, will mass less than 15 tonnes per displacement ton.

They also say why they do it this way:

TNE FFS, p69:
Thrust requirements are abstracted by tying thrust energy requirements to hull displacement rather than craft mass. This is an obvious abstraction, but one which is necessary for ease of design. Too many variables affect ship mass throughout the design process, and tying thrust to mass would require you to continually redesign and re-design to get a workable craft. In our opinion, the thrust-to-mass formula is a workable compromise, especially since spacecraft tend to have the same general density. The correction factor for very high mass-to-volume designs takes care of any important distortions.

 

[AnotherDilbert]

1. That still above the supposed one metric tonne per fourteen cubic metres.

That is the mass of fuel, liquid hydrogen. Why would the ship have that very low density?

Metals are often in the region of 5-10 tonnes per m³.

 

[AnotherDilbert]

About 2 tonnes per m³ for machinery isn't chosen at random.

Take this current tank engine and transmission:

EuroPowerPack - Wikipedia

en.wikipedia.org

Both are close to 1 m³ each, and has a mass of 1.8 and 2.4 tonnes respectively. Not much maintenance access overhead built into that though.

 

[Condottiere]

Well, specifically, to the one metric tonne per fourteen cubic metres, isn't that brought up as being the cargo weight cap?

 

[AnotherDilbert]

Well, specifically, to the one metric tonne per fourteen cubic metres, isn't that brought up as being the cargo weight cap?

No, at least in CT Striker and later:

... cargo is estimated at a nominal 1 tonnes per m³.

LBB2'77 probably was mass based, LBB2'81 was volume based with some remaining text from the earlier version. The word "ton" was used in both, but for different things. Not confusing at all...

 

[GypsyComet]

"Reducing Cargo Hold by 17 tons would solve the problem: but most Captains accept the penalties and try instead to carry profitable cargo."

This bugs me a bit. Is it implying that the choice is per trip, or made at purchase by selecting the stretch option?