LBB2 M-Drives in LBB5: When does it help?

[infojunky]

But Maneuver/Evade seems to take 1G only, regardless of defensive DM.

Note that ships top out at 2g in Mayday.

A tentative rule addition is to trade thrust for agility, though this is using the simplified computer rules.

 

[AnotherDilbert]

Note that ships top out at 2g in Mayday.

No, I hadn't noticed, thanks.
So, 6 G missiles makes sense.

A tentative rule addition is to trade thrust for agility, though this is using the simplified computer rules.

In LBB2 Evade is generally a fraction of Pilot skill, so that should probably be in teh mix too, somehow?

 

[infojunky]

In LBB2 Evade is generally a fraction of Pilot skill, so that should probably be in teh mix too, somehow?

It's on the list of variations to play.

The list of variations has Pilot skill and points of Thrust as a DM to a piloting roll to provide a defensive DM during that phase. Tentatively it is either a DM-1 per point or per two points the roll is made by.

 

[Grav_Moped]

One last observation on the "what's a real military ship in LBB2?" question: The unrefined fuel rule. If the Types C and T weren't "real" military craft, the rule allowing scout and military drives to use unrefined fuel with no risk would only apply to the Type S, and they wouldn't have needed to mention military craft -- or would have said it didn't apply to them.

Nothing in LBB2'81 has a computer bigger than that dictated by the Mod/n=>Jn rule.

It seems to me (and I may well have missed something along the way) that HG (both editions) became the default system for military ships, and thereby demoted all of the canon LBB2 ships to possessing merely civilian capabilities without this being declared outright. But within the original Classic (LBB1-3, S4) system, the C and T were intended to be front-line combatants or at least plausibly competent in their size classes.

Heck, the 1250Td 4G Kinunir was supposed to be a front-line combatant!

 

[Grav_Moped]

Why would a 200 Dt ship be preferable to a 150 Dt of 300 Dt ship? Why should the system try to force me into a 200 Dt ship?

Because LBB2 is weird like that. I suppose you could build it as a 300Td ship with 100Td of drop tanks, but the Drive Performance Table is going to discourage such nonconformist silliness.

The oversized power plant for Double-Firing the lasers is sort of a halfway measure to bring it closer to what it'd do with a third hardpoint.

 

[infojunky]

Note the merc cruiser has a mod5.

Most of the civilian ships have 1g thrust and generally two or three hardpoints.

Going through the Alien Modules most Cruisers are around 1000 tons and manuver three or four…

Add in the use of unrefined fuel the little things add up.

 

[AnotherDilbert]

One last observation on the "what's a real military ship in LBB2?" question: The unrefined fuel rule. If the Types C and T weren't "real" military craft, the rule allowing scout and military drives to use unrefined fuel with no risk would only apply to the Type S, and they wouldn't have needed to mention military craft -- or would have said it didn't apply to them.

You're moving the goalposts: we discussed warships, not all naval vessels.

A ship does not have to be a dedicated warship to run on unrefined fuel:

LBB2'81, p6:
Military and quasi-military starships often use unrefined fuel because it is more available, and because their drives are specially built to use it.

A coastguard-like ship like the Type T is a "military" ship, but not a warship.

LBB2'81, p20:
_ _ Patrol Cruiser (type T): Using a custom 400-ton hull, the patrol cruiser is a military vessel used for customs inspections, piracy suppression, and normal safety patrols.

This is not the description of a warship. A warship would have the main job of killing other warships and surviving to tell the tale.

This is the description of a warship:

JTAS#4, "Gazelle Class Close Escort Vessels", p18:
Naval tactics in the Imperial Navy call for large ships to be accompanied by well-armed, small fighting craft capable of engaging the enemy at long range, before they approach the principle ships in a task force or convoy. These small ships may be fighter craft carried by the larger ships, or they may be independent close escort vessels.

Heck, the 1250Td 4G Kinunir was supposed to be a front-line combatant!

And it has screens, heavy weapons (particle accelerators), and a maxed out computer with fiber-optic backups...

It's still a lousy warship in either LBB2 or LBB5, but they at least pretended...

If it were capable of Double Fire, I would hazard a guess that it's a decent LBB2 warship?

 

[AnotherDilbert]

Because LBB2 is weird like that. I suppose you could build it as a 300Td ship with 100Td of drop tanks, but the Drive Performance Table is going to discourage such nonconformist silliness.

My point was just that a design system that forces me into narrow choices is not a very good system.

The standard drives and the accompanying performance table is the agent forcing the narrow choices, and the root of LBB2 silliness.

 

[Grav_Moped]

My point was just that a design system that forces me into narrow choices is not a very good system.

The standard drives and the accompanying performance table is the agent forcing the narrow choices, and the root of LBB2 silliness.

It's not the root of the silliness.

It's perfectly reasonable to house-rule that intermediate-sized drives exist (for example, a size "A-and-a-half" drive that would provide a rating of 3 in a 100Td hull) and have specifications that can be calculated using the formulae that underpin the Drive Performance Table (and perhaps multi-point interpolation around the Size W-Z drives to capture their upward performance deviations). The supply chain for spares for intermediate-sized drives might be unreilable, though.

The only glitch is that maneuver drives can't be extrapolated below 200G*tons (Size A) due to the negative constant component of the tonnage formula. Workarounds include setting a minimum maneuver drive size of 1Td while keeping the cost progression as Gs*tons go below 200, or combining the maneuver drive and power plant below 200 rating-tons so their formulas' constant components cancel each other out and scaling becomes linear.

The fundamental flaw in LBB2 is the constant-by-Pn power plant fuel allocation, carried forward from the first edition to maintain backward compatibility with the original seriously-flawed flat kg/G requirement for acceleration.

It was kept because in LBB2 the power plant fuel allocation was the primary constraint on maneuver drive ratings. In LBB5, the constraint shifted to the size of the maneuver drive itself, and -- in second edition particularly -- the size of the power plant, to give Tech Level a significant impact. Different systems, different tradeoffs.

 

[AnotherDilbert]

It's not the root of the silliness.

It's perfectly reasonable to house-rule that intermediate-sized drives exist (for example, a size "A-and-a-half" drive that would provide a rating of 3 in a 100Td hull) and have specifications that can be calculated using the formulae that underpin the Drive Performance Table (and perhaps multi-point interpolation around the Size W-Z drives to capture their upward performance deviations). The supply chain for spares for intermediate-sized drives might be unreilable, though.

You don't think it's a bit ironic to defend a system by saying it needs to be house-ruled to be reasonable?

LBB5 drives, as adopted by most(?) later editions, works perfectly from small craft to megaton behemoths, without need for constant tweaking by house-rules.

The fundamental flaw in LBB2 is the constant-by-Pn power plant fuel allocation, ...

That is only a problem for very small ships, large ships thrive on it... Even at 400 Dt a PP-4 only needs as much fuel as a J-1, hardly a fundamental flaw.

I see it more as a part of the crippling of small ships that is at the core of LBB2, presumably intentionally.

The real limitation of M rating is the cost of the M-drive and the needed power plant. E.g. for a Sub Liner that already has a PP-3, upgrading from M-1 (C) to M-3 (J) would cost 12 Dt (fairly trivial) and MCr 24 which would be keenly felt in the profitability. (In addition to the extra MCr 12 for a custom hull).

To upgrade a 400 Dt J-1 & M-1 ship to M-2 & PP-2 [B->D] would cost 10 Dt (fuel) and MCr 24, increasing the total cost from MCr 66 to MCr 90, taking the ship from potentially profitable to bankruptcy waiting to happen. Unaffordable for a commercial ship...

 

[mike wightman]

Which later editions adopted LBB5 drives? LBB5 based ships only appeared in a handful of CT products, the majority were LBB2 designs.

MegaTraveller tried but broke the design system with their power plants (a fan house rule would be officially adopted to partially fix this, although only if you had access to the MTJ it appears in).

TNE? Totally different drive paradigm to LBB5.
T4?
T5?
I know T20 based ship construction on HG80 as did GT.

 

[Dragoner]

LBB2 Fleets it's turrets, LBB5 it's spinals, and the m-drive means who can out maneuver who. Though I have to say it's been probably ten years since I ran a HG2 combat, and except maybe for nostalgia, I probably will not again. LBB2 I will do again, maybe using the fascimilie rules next time.

 

[AnotherDilbert]

Which later editions adopted LBB5 drives? LBB5 based ships only appeared in a handful of CT products, the majority were LBB2 designs.

I was perhaps a bit sloppy; I meant percentage based drives, rather than lettered drives. I did not mean the percentages were identical to LBB5.

MegaTraveller tried but broke the design system with their power plants (a fan house rule would be officially adopted to partially fix this, although only if you had access to the MTJ it appears in).

Percentage based drives, same as in LBB5, but PP based on actual need. Roughly similar to LBB5 warships. Only problem was PP fuel, not PP itself?

TNE? Totally different drive paradigm to LBB5.

Percentage based drives by default, M-drive percentage of mass as special case. Power similar to MT, by actual demand.

T4?

Similar to TNE, percentage based, power by demand, no lettered drives.

T5?

Lettered drives, but based on formulae. Drive Potential Table as a shortcut to drive potential calculation. Stage effect change drive size, cost, potential, and fuel consumption of drives. In short a simplified lettered drive system that is basically percentage based, turned into a complicated mess by stage effects.

I know T20 based ship construction on HG80 as did GT.

GT: Percentage based (with complications IIRC).
T20: I have no idea.


MgT: Lettered drives for small craft and ACS, percentage for larger ships. Limited stage effect for drives, no problem.


MgT2: Percentage based drives, power by demand.


So mostly percentage based, few with lettered standard drives à la LBB2, none with the weird non-linear effects.

 

[whartung]

TNE? Totally different drive paradigm to LBB5.

Are you talking HEPLaR or Thruster Plates?

Percentage based drives by default, M-drive percentage of mass as special case.

TNE is a Thrust/MW model (for both HEPLaR and Thruster Plates), and in that sense, it's linear. There's no TL benefit for HEPLaR or TP drives, they all produce the same respective ratios. There's no benefit to a bigger (or smaller) drive being more efficient and producing more thrust per ton.

From that point, you need to scale the power plant (which does get better as TL improves) to your thrust requirements, and you should apply the amount of thrust to the mass of the ship to get the G ratings. You can build a ship that's faster empty than loaded, you should consider carried craft, external vehicles, etc.

I don't consider that necessarily "percentage based drives" in contrast to TNE Jump Drive which is, indeed, purely percentage based on ship volume.

I don't honestly know if a 1000 dTon ship is "10 times heavier" than a 100 dTon ship. It might be, but If it's not, then the M drive does not need to be "10 times bigger" for the 1000 dTon ship.

 

[AnotherDilbert]

I don't honestly know if a 1000 dTon ship is "10 times heavier" than a 100 dTon ship. It might be, but If it's not, then the M drive does not need to be "10 times bigger" for the 1000 dTon ship.

For the purposes of dimensioning the M-drive (whether HEPlaR or gravitic) ships are assumed to have a mass of 10 tonnes per Dton, so in effect the M-drive is a percentage of ship's volume.

Only heavily armoured ships need use actual mass to determine acceleration.

TNE FF&S, 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 redesign 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.
...
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.

 

[Spinward Flow]

I don't honestly know if a 1000 dTon ship is "10 times heavier" than a 100 dTon ship.

I would assume not ... because of Square Cube Law.

Instead, I would expect the "density" of the volume to be reduced, because the 1000 dTons will include a lot more "air space" rather than "solid space" relative to the 100 dTon ship.

Easiest comparison would be for a 100 vs 800 dton comparison ... of cubes.

If the exterior hull of the 100 dton ship weighs in at 10,000kg per side (arbitrary number chosen purely to make the math simple), that's 10 tons of weight for a 6 sided ship ... so 60 tons of exterior hull weight.

If the exterior hull of the 800 dton ship is 2x the size in all 3 dimensions, you get 6 sides of 40 tons ... for a weight of 240 tons of exterior hull weight.

So ... 4x (2²) the exterior hull mass (all else being equal), but 8x (2³) the interior volume available to put "stuff" into.

If the interior of the ship is "not as dense as the hull bulkheads" (which will often times be the case) ... as dtons go up the overall "density" of the ship (kg/m³) will tend to go down for an exoskeleton type outer hull structure (crunchy on the outside, chewy on the inside), simply because more of the interior volume is "air space" on larger ships. So with an exoskeleton (rigid hull) structure, the Square Cube Law works in your favor (hence why small ships suffer "penalties" in that their bridges require more than 2% of their displacement, etc., relative to larger hulls).

For endoskeletons though, the Square Cube Law works against you (structurally speaking), because there you've got volume increasing faster than the surface area, putting increased stresses and strain onto the materials of the endoskeleton, hence why endoskeletons have "upper bounding limits" on their practical scale under constant force (gravity) conditions.

 

[mike wightman]

The square cube law should affect the simplistic 1 hardpoint per 100 displacement tons too.

 

[AnotherDilbert]

The square cube law should affect the simplistic 1 hardpoint per 100 displacement tons too.

It does, i.e. TNE does not have "hardpoints", but weapons and many other systems require surface area.

Small ships tend to run out of interior space first, large ships tend to run out of surface area first.

 

[mike wightman]

Yup, I know about TNE and its use of surface area as a design parameter, I referred to the LBB2/5 "simplistic 1 hardpoint per 100 displacement tons" being in need of square cube progression - GT ISW uses surface area as well by the way.

 

[AnotherDilbert]

If LBB2 can't handle straight percentages, I suspect calculating the cube root of the volume, squared, is a bit over the top...