Need of an explanation: Tonnage of ships

[mike wightman]

In book 2 first edition it mentions the hull being rated for its mass displacement tonnage.
Isn't mass displacement actually used as a measurement of volume? Therefore right from the start Traveller ships were rated for their displacement, not their mass.

 

[mike wightman]

In book 2 first edition it mentions the hull being rated for its mass displacement tonnage.
Isn't mass displacement actually used as a measurement of volume? Therefore right from the start Traveller ships were rated for their displacement, not their mass.

 

[mike wightman]

In book 2 first edition it mentions the hull being rated for its mass displacement tonnage.
Isn't mass displacement actually used as a measurement of volume? Therefore right from the start Traveller ships were rated for their displacement, not their mass.

 

[Straybow]

Seriously, I think that the volume ton probably does date to the early timeframe...

Since reference to displacement is in the text on hulls in every printing of Bk2 I've read

In book 2 first edition it mentions the hull being rated for its mass displacement tonnage.
Isn't mass displacement actually used as a measurement of volume? Therefore right from the start Traveller ships were rated for their displacement, not their mass.

Yes I think we've all read, "Hulls are identified by their mass displacement, expressed in tons.
…Custom hulls of up to 5000 tons mass displacement may be ordered." While the term tonnage is frequently used, the term displacement (apart from the modifier "mass") does not appear.

"Displacement" is a standard shipwright term. It is a means of expressing mass of a floating ship. It only measures volume for a vessel that is completely submerged, which is not conducive to seaworthiness in most cases. Two ships with the same displacement can have dramatically different volumes (cf battleship, passenger liner). Add load to a surface ship, the displacement changes according to the mass rather than volume filled within or added atop.

"Mass displacement" is not a standard shipwright term. It appears the authors used the jargon without thinking what was to be displaced. Where bouyancy is nonexistent the term is nonsensical. "Displacing" liquid hydrogen doesn't make physical sense because the ship doesn't travel through a medium of liquid hydrogen. It is more a figurative illustration.

The standard of measurement for the hull (excluding what may be contained therein or erected atop it) is length at waterline. For example, a page linked in another thread on cargo tonnage measurements indicated that ships 24 m or longer were governed by the Canadian regulations covered on the webpage.

Recall the controversy several years ago when one Americas Cup entry used a semi-hydrofoil keel to lift the hull partially out of the water, which opponents claimed invalidated the hull on the basis of the stipulated 8 m length at the waterline. The previous controversy over a catamaran hull similarly reduced the water drag by lifting part of the hull out of the water, but the full stipulated length of the side hull was still in the water.

 

[Straybow]

Seriously, I think that the volume ton probably does date to the early timeframe...

Since reference to displacement is in the text on hulls in every printing of Bk2 I've read

In book 2 first edition it mentions the hull being rated for its mass displacement tonnage.
Isn't mass displacement actually used as a measurement of volume? Therefore right from the start Traveller ships were rated for their displacement, not their mass.

Yes I think we've all read, "Hulls are identified by their mass displacement, expressed in tons.
…Custom hulls of up to 5000 tons mass displacement may be ordered." While the term tonnage is frequently used, the term displacement (apart from the modifier "mass") does not appear.

"Displacement" is a standard shipwright term. It is a means of expressing mass of a floating ship. It only measures volume for a vessel that is completely submerged, which is not conducive to seaworthiness in most cases. Two ships with the same displacement can have dramatically different volumes (cf battleship, passenger liner). Add load to a surface ship, the displacement changes according to the mass rather than volume filled within or added atop.

"Mass displacement" is not a standard shipwright term. It appears the authors used the jargon without thinking what was to be displaced. Where bouyancy is nonexistent the term is nonsensical. "Displacing" liquid hydrogen doesn't make physical sense because the ship doesn't travel through a medium of liquid hydrogen. It is more a figurative illustration.

The standard of measurement for the hull (excluding what may be contained therein or erected atop it) is length at waterline. For example, a page linked in another thread on cargo tonnage measurements indicated that ships 24 m or longer were governed by the Canadian regulations covered on the webpage.

Recall the controversy several years ago when one Americas Cup entry used a semi-hydrofoil keel to lift the hull partially out of the water, which opponents claimed invalidated the hull on the basis of the stipulated 8 m length at the waterline. The previous controversy over a catamaran hull similarly reduced the water drag by lifting part of the hull out of the water, but the full stipulated length of the side hull was still in the water.

 

[Straybow]

Seriously, I think that the volume ton probably does date to the early timeframe...

Since reference to displacement is in the text on hulls in every printing of Bk2 I've read

In book 2 first edition it mentions the hull being rated for its mass displacement tonnage.
Isn't mass displacement actually used as a measurement of volume? Therefore right from the start Traveller ships were rated for their displacement, not their mass.

Yes I think we've all read, "Hulls are identified by their mass displacement, expressed in tons.
…Custom hulls of up to 5000 tons mass displacement may be ordered." While the term tonnage is frequently used, the term displacement (apart from the modifier "mass") does not appear.

"Displacement" is a standard shipwright term. It is a means of expressing mass of a floating ship. It only measures volume for a vessel that is completely submerged, which is not conducive to seaworthiness in most cases. Two ships with the same displacement can have dramatically different volumes (cf battleship, passenger liner). Add load to a surface ship, the displacement changes according to the mass rather than volume filled within or added atop.

"Mass displacement" is not a standard shipwright term. It appears the authors used the jargon without thinking what was to be displaced. Where bouyancy is nonexistent the term is nonsensical. "Displacing" liquid hydrogen doesn't make physical sense because the ship doesn't travel through a medium of liquid hydrogen. It is more a figurative illustration.

The standard of measurement for the hull (excluding what may be contained therein or erected atop it) is length at waterline. For example, a page linked in another thread on cargo tonnage measurements indicated that ships 24 m or longer were governed by the Canadian regulations covered on the webpage.

Recall the controversy several years ago when one Americas Cup entry used a semi-hydrofoil keel to lift the hull partially out of the water, which opponents claimed invalidated the hull on the basis of the stipulated 8 m length at the waterline. The previous controversy over a catamaran hull similarly reduced the water drag by lifting part of the hull out of the water, but the full stipulated length of the side hull was still in the water.

 

[mike wightman]

Straybow wrote:
While the term tonnage is frequently used, the term displacement (apart from the modifier "mass") does not appear.

Apart from A. The Bridge: All starships must allocate 20 tons displacement... or how about E. Cargo Hold: The displacement given over..., and several mentions of displacement in the Hardpoints and turrets section

.
Looks to me like the designer had volume in mind

.

"Displacement" is a standard shipwright term. It is a means of expressing mass of a floating ship. It only measures volume for a vessel that is completely submerged

And was adapted to mean completely submerged in liquid hydrogen for Traveller space ships, which are more akin to submarines anyway IMHO

"Mass displacement" is not a standard shipwright term.

Who's building yachts here? I thought this thread was about Traveller space ships?

It appears the authors used the jargon without thinking what was to be displaced.

Then it's a good job someone at GDW noticed the volume of 1000kg of liquid hydrogen would fit the bill.

Where bouyancy is nonexistent the term is nonsensical. "Displacing" liquid hydrogen doesn't make physical sense because the ship doesn't travel through a medium of liquid hydrogen. It is more a figurative illustration.

I agree. Back into Traveller history American jumpships would have been built in cuft while the rest of the world used metres cubed. The adoption of the displacement ton as a unit of ship volume would come later. Why, I have no idea?
Perhaps there's a story behind it .

 

[mike wightman]

Straybow wrote:
While the term tonnage is frequently used, the term displacement (apart from the modifier "mass") does not appear.

Apart from A. The Bridge: All starships must allocate 20 tons displacement... or how about E. Cargo Hold: The displacement given over..., and several mentions of displacement in the Hardpoints and turrets section

.
Looks to me like the designer had volume in mind

.

"Displacement" is a standard shipwright term. It is a means of expressing mass of a floating ship. It only measures volume for a vessel that is completely submerged

And was adapted to mean completely submerged in liquid hydrogen for Traveller space ships, which are more akin to submarines anyway IMHO

"Mass displacement" is not a standard shipwright term.

Who's building yachts here? I thought this thread was about Traveller space ships?

It appears the authors used the jargon without thinking what was to be displaced.

Then it's a good job someone at GDW noticed the volume of 1000kg of liquid hydrogen would fit the bill.

Where bouyancy is nonexistent the term is nonsensical. "Displacing" liquid hydrogen doesn't make physical sense because the ship doesn't travel through a medium of liquid hydrogen. It is more a figurative illustration.

I agree. Back into Traveller history American jumpships would have been built in cuft while the rest of the world used metres cubed. The adoption of the displacement ton as a unit of ship volume would come later. Why, I have no idea?
Perhaps there's a story behind it .

 

[mike wightman]

Straybow wrote:
While the term tonnage is frequently used, the term displacement (apart from the modifier "mass") does not appear.

Apart from A. The Bridge: All starships must allocate 20 tons displacement... or how about E. Cargo Hold: The displacement given over..., and several mentions of displacement in the Hardpoints and turrets section

.
Looks to me like the designer had volume in mind

.

"Displacement" is a standard shipwright term. It is a means of expressing mass of a floating ship. It only measures volume for a vessel that is completely submerged

And was adapted to mean completely submerged in liquid hydrogen for Traveller space ships, which are more akin to submarines anyway IMHO

"Mass displacement" is not a standard shipwright term.

Who's building yachts here? I thought this thread was about Traveller space ships?

It appears the authors used the jargon without thinking what was to be displaced.

Then it's a good job someone at GDW noticed the volume of 1000kg of liquid hydrogen would fit the bill.

Where bouyancy is nonexistent the term is nonsensical. "Displacing" liquid hydrogen doesn't make physical sense because the ship doesn't travel through a medium of liquid hydrogen. It is more a figurative illustration.

I agree. Back into Traveller history American jumpships would have been built in cuft while the rest of the world used metres cubed. The adoption of the displacement ton as a unit of ship volume would come later. Why, I have no idea?
Perhaps there's a story behind it .

 

[TheEngineer]

Does anybody knows something more about the real story behind Travellers displacement unit ?

Was it a basic concept from the very beginning ?
Or was it really just a lucky GDW patch ?

 

[TheEngineer]

Does anybody knows something more about the real story behind Travellers displacement unit ?

Was it a basic concept from the very beginning ?
Or was it really just a lucky GDW patch ?

 

[TheEngineer]

Does anybody knows something more about the real story behind Travellers displacement unit ?

Was it a basic concept from the very beginning ?
Or was it really just a lucky GDW patch ?

 

[Anthony]

Based on looking at very very old traveller supplements, I suspect that they were mapping ships based on a 5' grid with 10' ceilings (traditional D&D style; 5' is roughly 1.5 meters) and had at some point decided it should be two 5' squares per ton. Eventually someone noticed that 500 cf (14 cubic meters) isn't actually very close to a ton for RL designs, and came up with 'tons of liquid hydrogen' as a handwave so they could keep the original 'ton' figure.

Before roughly Striker, the distinction between 'tons displacement' and 'tons mass' was _very_ vague.

 

[Anthony]

Based on looking at very very old traveller supplements, I suspect that they were mapping ships based on a 5' grid with 10' ceilings (traditional D&D style; 5' is roughly 1.5 meters) and had at some point decided it should be two 5' squares per ton. Eventually someone noticed that 500 cf (14 cubic meters) isn't actually very close to a ton for RL designs, and came up with 'tons of liquid hydrogen' as a handwave so they could keep the original 'ton' figure.

Before roughly Striker, the distinction between 'tons displacement' and 'tons mass' was _very_ vague.

 

[Anthony]

Based on looking at very very old traveller supplements, I suspect that they were mapping ships based on a 5' grid with 10' ceilings (traditional D&D style; 5' is roughly 1.5 meters) and had at some point decided it should be two 5' squares per ton. Eventually someone noticed that 500 cf (14 cubic meters) isn't actually very close to a ton for RL designs, and came up with 'tons of liquid hydrogen' as a handwave so they could keep the original 'ton' figure.

Before roughly Striker, the distinction between 'tons displacement' and 'tons mass' was _very_ vague.

 

[Straybow]

Like I said, they originally used the jargon "displacement" without any evidence of a real technical definition. Even with more detailed design procedures there are still huge gaps in functional roles of mass vs volume.

Using the term "displacing [tonnage]" in reference to internal divisions of hull space is even worse. You aren't going to find naval architects (or shipwrights) speaking that way, unless maybe in revising the design and moving one thing to make room for another.

I never saw any official deckplans, but a reverse-engineering explanation might be right on: "We want the ship to be this big on the deckplans, but we've already declared it to be 100 tons."

 

[Straybow]

Like I said, they originally used the jargon "displacement" without any evidence of a real technical definition. Even with more detailed design procedures there are still huge gaps in functional roles of mass vs volume.

Using the term "displacing [tonnage]" in reference to internal divisions of hull space is even worse. You aren't going to find naval architects (or shipwrights) speaking that way, unless maybe in revising the design and moving one thing to make room for another.

I never saw any official deckplans, but a reverse-engineering explanation might be right on: "We want the ship to be this big on the deckplans, but we've already declared it to be 100 tons."

 

[Straybow]

Like I said, they originally used the jargon "displacement" without any evidence of a real technical definition. Even with more detailed design procedures there are still huge gaps in functional roles of mass vs volume.

Using the term "displacing [tonnage]" in reference to internal divisions of hull space is even worse. You aren't going to find naval architects (or shipwrights) speaking that way, unless maybe in revising the design and moving one thing to make room for another.

I never saw any official deckplans, but a reverse-engineering explanation might be right on: "We want the ship to be this big on the deckplans, but we've already declared it to be 100 tons."

 

[mike wightman]

Originally posted by Straybow:
Like I said, they originally used the jargon "displacement" without any evidence of a real technical definition.

They didn't define how the maneuver drive worked until MT, and then they changed it for TNE . Then there are magic inertial compensators and grav plates, magic sensor and weapon systems etc, all of which are not defined until later rulesets (then contradicted in the next ) . At least the displacement ton was defined by 2nd edition CT, where ever it came from.

Even with more detailed design procedures there are still huge gaps in functional roles of mass vs volume.

Only for CT/MT/T20. TNE/T4/GT ship designs all use mass as well as volume to rate final drive performance.

Using the term "displacing [tonnage]" in reference to internal divisions of hull space is even worse. You aren't going to find naval architects (or shipwrights) speaking that way, unless maybe in revising the design and moving one thing to make room for another.

You are in the Traveller Universe

I never saw any official deckplans, but a reverse-engineering explanation might be right on: "We want the ship to be this big on the deckplans, but we've already declared it to be 100 tons."

While I may or may not believe in the "hey, did you notice that 2 deckplan squares are nearly exactly equal to the volume of 1 tonne of liquid hydrogen" coincidence, I know that officially you are allowed 20% leeway on the deckplans and also at least one official deckplan is completely wrong.

Maybe it's a new saying for the TU, "what came first, the dt or the deckplan?"

 

[mike wightman]

Originally posted by Straybow:
Like I said, they originally used the jargon "displacement" without any evidence of a real technical definition.

They didn't define how the maneuver drive worked until MT, and then they changed it for TNE . Then there are magic inertial compensators and grav plates, magic sensor and weapon systems etc, all of which are not defined until later rulesets (then contradicted in the next ) . At least the displacement ton was defined by 2nd edition CT, where ever it came from.

Even with more detailed design procedures there are still huge gaps in functional roles of mass vs volume.

Only for CT/MT/T20. TNE/T4/GT ship designs all use mass as well as volume to rate final drive performance.

Using the term "displacing [tonnage]" in reference to internal divisions of hull space is even worse. You aren't going to find naval architects (or shipwrights) speaking that way, unless maybe in revising the design and moving one thing to make room for another.

You are in the Traveller Universe

I never saw any official deckplans, but a reverse-engineering explanation might be right on: "We want the ship to be this big on the deckplans, but we've already declared it to be 100 tons."

While I may or may not believe in the "hey, did you notice that 2 deckplan squares are nearly exactly equal to the volume of 1 tonne of liquid hydrogen" coincidence, I know that officially you are allowed 20% leeway on the deckplans and also at least one official deckplan is completely wrong.

Maybe it's a new saying for the TU, "what came first, the dt or the deckplan?"