Jump drive discussion (yes, here we go again)

[CosmicGamer]

Jump drives have been one of the things that I've always tried not to think too hard about. Covering my ears and screaming out loud when other people talk about it so I can ignore them and continue waving my hand and saying 'thats just how things work' so that I could play the game and not just sit around saying wtf!

But today I had a thought that popped into my head and unfortunately (for you, because now you are here reading my stupid post!) I thought too long about it before I could shift my brain to something else.

Jump distance for ships not exactly an even multiple of 100 tons
A Jump-C drive can take up to a 600 ton ship Jump-1.
It can take up to a 300 ton ship Jump-2.
It can take up to a 200 ton ship Jump-3.
A 100 ton ship can be taken up to Jump-6.

The max jump for a 110 ton ship with a Jump-C drive would not be Jump-6 (obviously) but also not Jump-5 or even Jump-4, but Jump-3!

Has a good explanation ever been given for this? Do you do things differently? I'm using details from MGT. Do other versions handle it differently?

 

[far-trader]

I don't know that I've seen it, or posted it before, but I vaguely recall using the analogy of a ship at sea. Rather basically and simplistically...

Hull length determines maximum speed of ship in seas. Seas being defined as wave length. And even in calm seas the ship will set up it's own wave length from the bow wake. Go faster and you outrun the wave length and fall into the trough instead of sailing over the waves and slow down. Hull determines maximum speed.

Similar idea in Traveller for Jump Drives and Maneuver Drives...

Each drive factor and hull size determines the performance possible in very distinct breaks. Before you can go faster/farther you have to reach the next plateau. It's more digital in nature than analogue.

Of course that's just for LBB2 and Core Mongoose. High Guard (both CT and MGT) and some other rules will allow you to calculate drive performance to specific hull size, some even allow fractional maneuver drive ratings, but never fractional jump ratings.

 

[Andrew Boulton]

Has a good explanation ever been given for this?

It's broken, or at least it only works for the listed cases.

Use HG/MT/TNE/T4 instead.

 

[robject]

It's simple because quantizing the hull-to-jump ratio below 100t is not an important feature of Traveller.

The referee is free to interpolate, tho.

 

[rancke]

Has a good explanation ever been given for this? Do you do things differently? I'm using details from MGT. Do other versions handle it differently?

Yes. Book 2 rules are not consistent nor compatible with the OTU, even if HG grandfathered them. Just don't use Book 2 rules. Jump fuel is 10% of tonnage per jump number. End of story.


Hans

 

[FreeTrav]

Jump drives have been one of the things that I've always tried not to think too hard about. Covering my ears and screaming out loud when other people talk about it so I can ignore them and continue waving my hand and saying 'thats just how things work' so that I could play the game and not just sit around saying wtf!

But today I had a thought that popped into my head and unfortunately (for you, because now you are here reading my stupid post!) I thought too long about it before I could shift my brain to something else.

Jump distance for ships not exactly an even multiple of 100 tons
A Jump-C drive can take up to a 600 ton ship Jump-1.
It can take up to a 300 ton ship Jump-2.
It can take up to a 200 ton ship Jump-3.
A 100 ton ship can be taken up to Jump-6.

The max jump for a 110 ton ship with a Jump-C drive would not be Jump-6 (obviously) but also not Jump-5 or even Jump-4, but Jump-3!

Has a good explanation ever been given for this? Do you do things differently? I'm using details from MGT. Do other versions handle it differently?

It's a massive simplification that almost certainly developed from the idea that since Jump itself is quantized, anything else associated with it should also be quantized, plus a lot of quick-and-dirty math. It comes down to the difference between PLAYING Traveller, and PLAYING WITH Traveller. Perhaps it was inevitable that Traveller would attract the technical-geekery types, more so than the fantasy-genre games like D&D, and thus show the flaws - but us technical-geekery types, especially those who like their SF chewy at least, and crunchy or hard when we can get it, will tend to find the TECHINCAL misfeatures. And programmer types, or those who are in fields that are conceptually related to the specific area being geeked, are probably the most likely to spot such misfeatures. But again, it's about simplicity of PLAY, rather than accuracy of PLAY-WITH.

That said, if you really want to interpolate, then you want to look at a Jump drive as not so much providing "Jump-X for a hull of Y tons", but as providing "XY Jump-tons" - so, using the example, a Jump Drive-C provides 600 Jump-tons. That leads to the same table that you've given, but it also yields a relatively simple formula for what distance it can take ships whose hull rates don't hit one of those nodes:

For a ship of T tons, a Jump Drive that provides Z jump-tons can take said ship through jump INT(Z/T). (INT is a function that returns the integer portion of its argument (the value in parens). The use of the function is to account for the fact that Jump is quantized.)

So, your Jump Drive-C takes a ship of 150 tons displacement through Jump-4 (Z=600, T=150; 600/150 = 4), but a ship of 151 tons only Jump 3 (Z=600, T=151; 600/151 = 3.9735..., integer portion 3).

Now, some versions of Traveller allowed a ship to 'slop over' its hull rate by as much as 20% without affecting performance or requirements; I think this is actually a bad rule, because knowing that it's permissible offers temptation to actually take advantage of it - design the ship to spec, and then cram extra stuff that you WANT in until you're pressing up against the 20% overage limit. If nothing else, a merchant can cram a fairly large extra chunk of revenue space - staterooms or cargo hold - into the oversized hull, without appreciably impacting costs, and without impacting performance at all (by the rules). If you want to apply that rule, you should also perhaps change the INT in the above formula to a ROUND, and allow a Jump Drive C to provide Jump 4 to anything from 134 tons (calculated jump 4.47... before rounding) to 171 tons (calculated jump 3.5... before rounding).

All of the above assumes, of course, that you're playing on a quantized flat map with quantized jump. It's not unreasonable to de-quantize jump if you decide to play on a non-quantized 3-D map... But that's a whole different argument-cum-flamewar...

 

[FreeTrav]

Yes. Book 2 rules are not consistent nor compatible with the OTU, even if HG grandfathered them. Just don't use Book 2 rules. Jump fuel is 10% of tonnage per jump number. End of story.


Hans

I don't think that CosmicGamer was complaining about the fuel usage so much as the relationship between drive size, hull rate, and effective drive rate, which seemed overly quantized. See my other post in this thread...

 

[Andrew Boulton]

Now, some versions of Traveller allowed a ship to 'slop over' its hull rate by as much as 20% without affecting performance or requirements

That's only when drawing deckplans, not building the ship (and it's only 10%).

 

[Swiftbrook]

Do other versions handle it differently?

MegaTraveller (THE MT) has a formula based on displacement. You choose the jump distance and provide the corresponding number of jump units for your ship displacement.

Jump fuel is 10% of tonnage per jump number. End of story.

Add the appendix .... MT Jump fuel is (jump # +1) x 5%
T20 has two formulas jump # x 10% and an optional jump # * 5%

Note: All the above is from memory. My books are at home.

-Swiftbrook

 

[rancke]

Add the appendix .... MT Jump fuel is (jump # +1) x 5%

T20 has two formulas jump # x 10% and an optional jump # * 5%

I didn't know about T20. As for MT, the answer is simple enough: MT is wrong about jump fuel consumption.

That's my story, and I'm sticking to it.


Hans

 

[sabredog]

I don't know that I've seen it, or posted it before, but I vaguely recall using the analogy of a ship at sea. Rather basically and simplistically...

Hull length determines maximum speed of ship in seas. Seas being defined as wave length. And even in calm seas the ship will set up it's own wave length from the bow wake. Go faster and you outrun the wave length and fall into the trough instead of sailing over the waves and slow down. Hull determines maximum speed.

Similar idea in Traveller for Jump Drives and Maneuver Drives...

Each drive factor and hull size determines the performance possible in very distinct breaks. Before you can go faster/farther you have to reach the next plateau. It's more digital in nature than analogue.

Of course that's just for LBB2 and Core Mongoose. High Guard (both CT and MGT) and some other rules will allow you to calculate drive performance to specific hull size, some even allow fractional maneuver drive ratings, but never fractional jump ratings.

The hull displacement formula is a rule of thumb that factors in something to the effect that the longer a hull is and the narrower it is below the waterline, then with all other things being equal it will move faster through the water than a fatter or shorter craft.

Think tea clipper vs. ship of the line. Of course brute force can add a lot to the equation, as does the fact that a narrow, long craft is often less stable in some situations than a wide one (cruise liners like the Titanic were fast, but in high seas the passengers noticed more than they would in a wider, possibly slower ship...and some of that has to do with the harmonics generated by pounding through the waves instead of skimming along the top)....it's a complicated subject.

But I don't see how it would have applied towards jump drives. The environment is different - no resistance, lateral forces, nothing like a ship at sea.

It has to be more related to power vs. mass and distance.

 

[far-trader]

...it's a complicated subject.

Agreed, I was oversimplifying, and I'm not even fully versed in it.

But I don't see how it would have applied towards jump drives. The environment is different - no resistance, lateral forces, nothing like a ship at sea.

Says who (and where if you do know, please) What I understand is that little is known about jump space. Seems easy enough to imagine it as a medium that could encompass analogues of all that. Or something else entirely.

It has to be more related to power vs. mass and distance.

Yet it's clearly not in Book 2 with it's even breakpoints and "next larger hull" rule and displacement rather than mass*. Of course the metagame reasoning is obvious, but I imagined the original question was seeking an in-game reasoning and that answer is one I've pondered a little.

* is this where I interject my standard "displacement was an error, tons always meant mass and it's so much easier to make and explain the bad canon deckplans if it is" observational rant

 

[Icosahedron]

Tch! Jump Drives on the head of a pin, again.
If you don't like it, houserule it.
Simple.

LBB1, 1st ed, p3:
" [The Referee] must settle disputes concerning the rules (and may use his own imagination in doing so, rather than strictly adhering to the letter of the rules)."

I use (houseruled) HG for everything, it's much more logical thn LBB2.

 

[sabredog]

The LBB2 issues can be settled by assuming the off the shelf components in it are designed more for civilian craft and have more redundancy for safety, and are less finely tuned/lower tolerances for greater ease of maintenance.

So there's room for error and slop.

That's my handwave and I'm sticking to it.

 

[robject]

The LBB2 issues can be settled by assuming the off the shelf components in it are designed more for civilian craft and have more redundancy for safety, and are less finely tuned/lower tolerances for greater ease of maintenance.

So there's room for error and slop.

That's my handwave and I'm sticking to it.

This is more than a handwave, this is the basis of Marc Miller's assumptions about Traveller.

 

[sabredog]

And I'm still sticking to it - it's worked for me for 30+ years and it's Holy Writ from The Marc.

 

[shadowdragon]

I don't know that I've seen it, or posted it before, but I vaguely recall using the analogy of a ship at sea. Rather basically and simplistically...

Hull length determines maximum speed of ship in seas. Seas being defined as wave length. And even in calm seas the ship will set up it's own wave length from the bow wake. Go faster and you outrun the wave length and fall into the trough instead of sailing over the waves and slow down. Hull determines maximum speed.

Similar idea in Traveller for Jump Drives and Maneuver Drives...

Each drive factor and hull size determines the performance possible in very distinct breaks. Before you can go faster/farther you have to reach the next plateau. It's more digital in nature than analogue.

Of course that's just for LBB2 and Core Mongoose. High Guard (both CT and MGT) and some other rules will allow you to calculate drive performance to specific hull size, some even allow fractional maneuver drive ratings, but never fractional jump ratings.

From Wiki:

Hull speed, sometimes referred to as displacement speed, is a rule of thumb used to provide an approximate maximum efficient speed for a hull. It is only ever an approximation and only applies where the hull is a fairly traditional displacement design. It is usually described as a speed corresponding to a speed-length ratio of between 1.34 and 1.51 depending on which of the limited sources one refers to.
In English units, this may be expressed as:

where:
"LWL" is the length of the waterline in feet, and"v" is the speed of the vessel in knots

 

[PathfinderAP]

Has a good explanation ever been given for this?

Its just Traveller jump drive physics,
its a strange idiosyncratic effect, its cause theorized by many, yet still unknown,

Its called the "Snark Boojum - Effect"

Because they were the first people to complete a paper on the subject,
Just like gravity it had been observed by many people well before someone thought of writting up the subject, And Harold Snark and Patsy Boojum were but two of the many scientists who raced to point out the obvious of the yet un-named effect, it was a close race, so much so that Snark and Boojum chose to join forces in a desperate attempt at crossing the line first,

It worked, but at a cost, the result causing a blood feud across scientific community, many lossed their grants, some their tenure,

3 years later both Snark and Boojum had disappeared without trace,
Many believed foul play was involed, Others believe that they may be trapped in some fold of subspace, something they were both involed in studying at the time.....


(Yes, I wuz teh bored, )

 

[captainjack]

From Wiki:

Hull speed, sometimes referred to as displacement speed, is a rule of thumb used to provide an approximate maximum efficient speed for a hull. It is only ever an approximation and only applies where the hull is a fairly traditional displacement design. It is usually described as a speed corresponding to a speed-length ratio of between 1.34 and 1.51 depending on which of the limited sources one refers to.
In English units, this may be expressed as:

where:
"LWL" is the length of the waterline in feet, and"v" is the speed of the vessel in knots

Actually, more than just arule of thumb, LWL also determines the maximum speed for a displacement hull before the power required to accelerate it further goes thu the roof -its a result of how water moves as a wave -the basic idea is that once you are moving as fast as a wave would if it was of your length, going faster requires either climbing the wake, or moving the sea out of the way faster than it can normally move.

That's the speed at which planing hulls hop up onto the surface of the water and move like crazy (thus hydrofoils and etc).

I've always felt it's an interesting model for jump if one assumes that a jump bubble is the same kind of thing - one that determines the maximum speed in that medium before a quantum jump is needed -thus, a jump one drive can create a jump bubble that can move up to but no further than a parsec. Grantd, this needs a 100dton bubble created by a J1 drive to differ from a 100dton bubble created by a J2 drive, but that's fairly easy to model especially since jumpspace is so weird by definition: perhaps it's a logical as a spin charge on the bubble -perhaps as odd as its color.


Lets see:

A jump drive creates a bubble of normal space that can exist in jumpspace - essentially a superparticle. It interacts with jumpspace based on its average density (thus the H2) and gradually erodes away the H2 (thus the need for refined fuel -another Grand unification topic) until it reaches a density limit, at which point it pops into normal space.

Jump difference is a linear function of density, up to the "LWL" value and there is a difference in the bubble containment field that requires a different type of interface with jumpspace. A J2 can preform a J1, but not vice versa.

Essentially, there are a few bubble configurations that allow normal matter to interact with jumpspace, and the drive creates those at the normal/jumpspace interface.....and they are quantized, not continuous. Thus, a J2 bubble is denser (more H2) and has a different "value" at the interface; it erodes differently, and thus produces more phyiscal dispacement (I dunno -time is a constant in a universe where volume and mass are oddly only semi related?) and has a maximum value of how far this displacement from the entry point is -as with a ships non-planing hull.

So: you create a Jump-n type superparticle, fill it with the needed amount of H2 up to your jump limit, and inject it into jumpspace. Minor masses (jump tanks) too near messes up the density of the bubble, and we have trouble. The density determines how far one travels from entry point, and exit is automatic, as enough normal material (H2) boils off at the interface to change the average density below that which can exist in jumpspace.

7 days +/- a bit it pops out -and hopefully you didn't mess up the interface values.

Whoops. Blather attack. I'll stop here.

 

[Whipsnade]

Actually (big snip of excellent stuff)

Cap'n,

That is frighteningly close to my decades-old "theory" on the subject, right down to the use of the term "interface" and it's role in jump.


Regards,
Bill