The great conversion of MegaTraveller starships back to High Guard

[AnotherDilbert]

Larger ships are more massive ...

And have more thrust. A 100 000 Dt ship would have a 100 times the mass of a 1000 Dt ship (less with with proportional armour), and 100 times the thrust.

... and one would naturally expect them to be slower in maneuvers, to turn, to shift in any direction to avoid incoming fire.

We are not dodging bullets, more like dodging depth-charges. The enemy doesn't know exactly where we are, but has to predict where we will be seconds later.

Zig-zagging isn't a solution, don't be where the enemy believes we might be is a solution, and that requires straight line acceleration.

Pure acceleration isn't a good example of maneuverability, just speed.

You are thinking of moment of inertia, resistance to turning, that would punish large ships more than small and elongated ships more than spherical. That is way out of the chosen simplifications for even FF&S, much less CT.

Even so, it's much less of a problem with thrust vectoring, as we don't have to turn the ship to accelerate sideways. Thrust vectoring isn't discussed much in CT, but is defined in MT.

We can't have full thrust vectoring as:

LBB2'77, p1:
The typical travel times list indicates the time required to travel a specified distance (assuming 1 G constant acceleration, turn- around at midpoint, and 1 G constant deceleration).

But we can have some, as defined in MT.


Aircraft and ships turn by hydrodynamical forces on fins and hull, spacecraft have no such luxury they have to turn by thrust from the drives, aka agility.

 

[Sigtrygg]

Spacecraft use very small and weak maneuvering thrusters to turn around their centre of mass, and then can switch on the main engines.
Inertial compensation copes with the g forces involved apparently.

 

[Sigtrygg]

HG makes the same trade-off balance, but with a steeper TL curve. It's only at very high TL you can get nearly everything at the same time, but even then you can't get an armoured Agility-6 J-4 warship.

You can , but you only get enough internal fuel for jump 1... which is enough to break off by jumping having used drop tanks to enter the system.

Try making a armoured, high agility spinal warship at TL-12...

Again use drop tanks for jump performance, at TL12 it is still requires trade offs though.

 

[AnotherDilbert]

You can , but you only get enough internal fuel for jump 1... which is enough to break off by jumping having used drop tanks to enter the system.

Again use drop tanks for jump performance, at TL12 it is still requires trade offs though.

Sure, but after the first skirmish you don't have J-4 warships, you have J-1 warships.

Drop tanks are great, but not for frontline warships. Drop tanks works for TCS Tournaments (e.g. Eurisko), but not for TCS Campaign or any other interstellar wargame.

 

[Sigtrygg]

The jump 1 allows you to break off by jumping, only necessary if you are losing.

 

[AnotherDilbert]

The jump 1 allows you to break off by jumping, only necessary if you are losing.

And when you lost the drop tanks, then what do you do?

When you jump into an adjacent empty hex, with no fuel left, then what do you do?


An extra J-1 is an interesting idea for battle riders, to break off by jumping and rendezvous with the tender. It might seems attractive, but is too expensive in practice. You can just rendezvouz with the tender in the reserve and let the tender jump.

 

[Sigtrygg]

You are part of a fleet. The fleet includes tenders and refueling ships, drop tank manufacturing ships, the lot.

During peacetime you can potter around at jump 2 or 3 with tanks in place.

During wartime you drop tanks every jump, replacing them with tanks from IN bases or provided by your own manufacturing tankers. or you hitch a ride with a battle tender.

When jumping into a contested system you do not take the drop tanks with you, but you do have a pre-arranged bug out hex identified where you will meet up with your fleet support tankers etc.

Stop thinking in terms of the warship and nothing else, the Imperium can provide a massive support structure for each warship. IN bases, fuel and drop tank depots, manufacturing/refinery tankers.

One of the reasons the Rebellion era was so viscous, the support structure was known to all.

 

[phavoc]

And have more thrust. A 100 000 Dt ship would have a 100 times the mass of a 1000 Dt ship (less with with proportional armour), and 100 times the thrust.



We are not dodging bullets, more like dodging depth-charges. The enemy doesn't know exactly where we are, but has to predict where we will be seconds later.

Zig-zagging isn't a solution, don't be where the enemy believes we might be is a solution, and that requires straight line acceleration.



You are thinking of moment of inertia, resistance to turning, that would punish large ships more than small and elongated ships more than spherical. That is way out of the chosen simplifications for even FF&S, much less CT.

Even so, it's much less of a problem with thrust vectoring, as we don't have to turn the ship to accelerate sideways. Thrust vectoring isn't discussed much in CT, but is defined in MT.

We can't have full thrust vectoring as:

But we can have some, as defined in MT.


Aircraft and ships turn by hydrodynamical forces on fins and hull, spacecraft have no such luxury they have to turn by thrust from the drives, aka agility.

In a 3d environment the zig-zag concept is the same as 2d for discussion purposes. It's both simplified and more complex. In a terrestrial 2d environment you have drag from water that has to be overcome, but you also can use it to your advantage. In space you have to expend X amount of thrust to go in any one direction, then spend the same amount to counter it (in water your drag will do it for you).

Mass though is still Mass, and smaller ships typically have better thrust to Mass ratio that allows more maneuverability. Traveller (MT SOM has a section on an alternative explanation) has the thrusters at the rear to push the ship using newtonian movement. Moving side to side the entire Mass requires the same level of thrust as it does to push it forward - if you want the same power to mass ratio. MT postulates a sort of universal field/thrust in 360 degrees, and also says it's normal to use 400% thrust to land and takeoff - which violates most engineering principles for engine designs. I have always considered the explanation fraught with inconsistencies and don't feel it gets the explanation of how it might work correct. As it's DGP, I don't want to go down the canon/ de-cannoned argument. I love the DGP stuff, but this explanation has always seemed inconsistent to me.

So a ship doing dodging in space will do it in 3 dimensions. But it still operates under normal physical laws, so radical pitch and law actions would be done using maneuvering thrusters and not main engines. That puts a definite upper limit on what it's capable of doing (just as ships with rudders are limited to X amount of steering charges vs ships with thruster pods).

I've never seen any design in the game with the thruster pod (gimbaled engines). The Firefly class transport from Firefly is closer to this ideal than a standard traveller ship. About 50% of a Firefly ships thrust is from its main engine, and the other half from its engine pods. Traveller ships have 100% thrust from main engines at the rear, so that sort of maneuvering should be impossible.

 

[AnotherDilbert]

Mass though is still Mass, and smaller ships typically have better thrust to Mass ratio that allows more maneuverability. Traveller (MT SOM has a section on an alternative explanation) has the thrusters at the rear to push the ship using newtonian movement.

Yes, mass is mass, but smaller ship does not have better thrust-to-mass ratio, at 6 G they both have the exact same ratio, that is what the acceleration is.

F = ma => a = F/m

MT postulates a sort of universal field/thrust in 360 degrees, and also says it's normal to use 400% thrust to land and takeoff - which violates most engineering principles for engine designs. I have always considered the explanation fraught with inconsistencies and don't feel it gets the explanation of how it might work correct.

SSOM says it's safe enough for a few minutes, as I have no idea how gravitic thrusters work I can't say if that is reasonable or not.

 

[AnotherDilbert]

You are part of a fleet. The fleet includes tenders and refueling ships, drop tank manufacturing ships, the lot.

I don't subscribe to the infinite resources school of thought.

Of course the fleet has some supply ships, but mobile shipyards and tankers that can refuel a batron tend to cost more than a batron. With limited resources I would prefer another batron...

With MgT2 we can actually build mobile shipyards and they are horrendously expensive.

I'll stick with ye olde canon and manufacture drop tanks at actual shipyards, making them unattractive to warships.


Of course, battle rider tenders can use drop tanks, but they should never be shot at...

 

[Sigtrygg]

Mass though is still Mass, and smaller ships typically have better thrust to Mass ratio that allows more maneuverability.

No, smallcraft have 6g thrust to mass ration, the same as capital ships.

Traveller (MT SOM has a section on an alternative explanation) has the thrusters at the rear to push the ship using newtonian movement. Moving side to side the entire Mass requires the same level of thrust as it does to push it forward - if you want the same power to mass ratio.

You turn the ship about its centre of mass using fairly weak thrusters and then fire up the main engines. This is Traveller, we have acceleration compensation. You mention this in this bit.

So a ship doing dodging in space will do it in 3 dimensions. But it still operates under normal physical laws, so radical pitch and law actions would be done using maneuvering thrusters and not main engines. That puts a definite upper limit on what it's capable of doing (just as ships with rudders are limited to X amount of steering charges vs ships with thruster pods).

This is where smallcraft may have an advantage, they can spin around faster, but it doesn't really matter at the timescale of ship combat.

 

[Sigtrygg]

I don't subscribe to the infinite resources school of thought.

No, not infinite.
But similar to armed forces throughout history - a very small fighting force with a huge logistic support.

Of course the fleet has some supply ships, but mobile shipyards and tankers that can refuel a batron tend to cost more than a batron. With limited resources I would prefer another batron...

So why does the US build support and supply ships instead of another CVN?
The tanker squadrons in FFW etc can refuel entire fleets every turn.

With MgT2 we can actually build mobile shipyards and they are horrendously expensive.

It doesn't need a shipyard to manufacture drop tanks.

I'll stick with ye olde canon and manufacture drop tanks at actual shipyards, making them unattractive to warships.

Demountable tanks can be built at type B starports - they don't have shipyards. I don't recall if a statement is made that drop tanks must be built at shipyards.

Of course, battle rider tenders can use drop tanks, but they should never be shot at...

 

[AnotherDilbert]

No, not infinite.
But similar to armed forces throughout history - a very small fighting force with a huge logistic support.

Sure: Naval bases, depots, supply ships, hospital ships, etc, etc... but no mobile shipyards.

So why does the US build support and supply ships instead of another CVN?

Why do the USN seem to prefer a few CVs over a mobile shipyard? As far as I know there are no ocean-going shipyards?

The tanker squadrons in FFW etc can refuel entire fleets every turn.

Yes, there are some strategic tanker resources, but not for every batron or fleet.

It doesn't need a shipyard to manufacture drop tanks.

At a guess, they do, same as demountable tanks:

CT TCS, p14:
Demountable tanks may be fabricated at any class A or B starport, at a cost of Cr1,000 per ton, in 10 weeks.

Drop tanks may be built onto a ship when ... In both cases the tanks themselves must also be purchased at Cr1000 per ton. Building time is 10 weeks; installation time is only a few minutes.

Demountable tanks can be built at type B starports - they don't have shipyards. I don't recall if a statement is made that drop tanks must be built at shipyards.

Class B starports have shipyards, they just can't handle jump drives.

CT HG'80, p20:
Starships (with jump drives) may be constructed at the shipyard of any class A starport; non-starships (without jump drives) may be constructed at the shipyard of any class A or class B starport.

I made an attempt to design a mobile shipyard here:
https://forum.mongoosepublishing.com/threads/how-many-crew-for-smelters.118812/post-899945

At 2.6 MDt, 1.5 TCr, and 68000 crew it's a bit impractical...

 

[phavoc]

Yes, mass is mass, but smaller ship does not have better thrust-to-mass ratio, at 6 G they both have the exact same ratio, that is what the acceleration is.

F = ma => a = F/m



SSOM says it's safe enough for a few minutes, as I have no idea how gravitic thrusters work I can't say if that is reasonable or not.

Mass is still mass. Acceleration curves are going to be different - always have been in reality for two vehicles that can reach the same speed. And acceleration and top speed are not related to maneuverability. Ships only use their main engines to move forward, not to rotate or spin. Engineering wise that isn't how things work.

SOM ignores how engineering works. Running any engine at 100% all the time is possible, but hard on it. Quadrupling it's output means every part of it has to handle 400% output PLUS a safety margin. Again, not how engineering works regardless of how they wrote it. It's a terrible explanation that fails common sense for no good reason. That's poor world-building.

But I can see we'll disagree here, so I'll leave it at that.

 

[phavoc]

No, smallcraft have 6g thrust to mass ration, the same as capital ships.

You turn the ship about its centre of mass using fairly weak thrusters and then fire up the main engines. This is Traveller, we have acceleration compensation. You mention this in this bit.

This is where smallcraft may have an advantage, they can spin around faster, but it doesn't really matter at the timescale of ship combat.

Actually that's not correct. The amount of thrust output vs. mass is never defined for any ship, just what the drive is capable of. At best we can take the displacement of a ship (which isn't its' mass) and divide that by the displacement of the power plant, which gives a displacement to top speed number, but not an actual thrust to mass.

Naval vessels (closest actual example we have to spaceships) are built around shaft horse power driving propellers - and typically the higher that number the faster the vessel. This analogy breaks down due to hull design/wave flow, propeller design and other naval characteristics. However the overall displacement (mass in water at least) of a ship can be roughly compared to the amount of weight it's power plant and engineering spaces are. A 30,000 ton armored battleship has a different ratio compared to a 3,000 ton unarmored destroyer. While some is attributed to the hull itself, the majority of it is due to the amount of additional weight the armor has. I can provide actual examples if you like (just gotta go get the books) if you are curious.

Traveller ships ignore mass in the game, though the game still uses standard physics to explain acceleration/deceleration in normal space. Thrusters, no matter what, still have to expend energy to move a ship. The amount of energy you apply from the forward third to move it is still the same amount of energy required from the main engine at the rear. In zero G the mass of a ship remains the same regardless of where you apply the thrust from. By their definition though, a thruster is NOT an equivalent to a main engine, thus it is not capable of the same amount of energy expenditures as the main engine. The space shuttle is probably the best equivalent we have in reality to a Traveller ship. It's main engines are used for lift-off, it's orbital maneuver system (OMS) is used for orbit changes, de-orbit actions and would be the a starships equivalent to it's main engine. And the reaction control system (RCS) is what is used to spin, maneuver and brake it's forward velocity. The energy output of the RCS (or thrusters) is much less than the OMS because they are meant to maneuver and not move the ship.

Traveller ships doing a 3D zig-zag would need to actually shift the entire mass of the ship in any direction along it's axis. Otherwise it wouldn't really be dodging, it would be more of a corkscrew path.

There's a lot of hand-wave and assumptions built into the game, which is fine since it's a game and not meant to be a simulation. And much of this doesn't matter as much of the mechanics of movement are thrown out. As Miller has pointed out in multiple interviews, the Traveller space combat has a lot of things tossed out of the model for gaming play ease. The idea of ships having newtonian movement yet being able to be intercepted easily is the first mismatch. Miller states in his JTAS article on jump space that ships CAN retain their direction and built-up acceleration going into and coming out of jump space, which would render any intercept not only impractical but a near impossibility. Vector movement seems like a fix, but doing all the accounting for it gets to be a pain quickly. So we have thrust and range bands to simplify it for a game that's not meant to be a space combat game (like saye Renegade Legion or even Star Fleet battles).

 

[Spirit of 1977]

There is no separate VP, only EP. A PP-1 feeds enough power for a Drive-1 is a simple shorthand to be compatible with LBB2. EP is just a more granular measure, to be able to count how many lasers you can power.

Yes there is, I have provided you with ample math on this, and you refuse to provide similar math.

>>A PP-1 feeds enough power for a Drive-1 is a simple shorthand to be compatible with LBB2

This is precisely the power fungibility problem I laid out that you refuse to acknowledge. Compatibility with LBB2 should have been dropped. That Drive-1 power should require EP like the other EP that can power other systems. Tell me what is the EP equivalent of the power going to Drive-1.

Unless you start providing some math, I'm no longer going to engage with you on this. I realize you know a lot about this system, but you are wrong about this issue.

 

[AnotherDilbert]

>>A PP-1 feeds enough power for a Drive-1 is a simple shorthand to be compatible with LBB2
This is precisely the power fungibility problem I laid out that you refuse to acknowledge.

I have been trying to tell to for awhile that you are flat out wrong, there is no extra power or problem.

A PP-1 can't power a drive and also provide some extra EP to weapons. In other words: There is no VP, just EP.

A PP-1 can power a MD-1, a JD-1, OR some weapons, not at the same time.

Of course power is fungible, that does not mean that there is extra magical power. The PP doesn't care where the power is consumed. The MD doesn't care where the power came from.
A PP-1 produces 0.01M EP power (HG'80, p27).
A MD-1 consumes 0.01M EP power to produce 1 G acceleration (HG'80, p28).
If the power is used for something else there is no acceleration.

Yes there is, I have provided you with ample math on this, and you refuse to provide similar math.

I did, you ignored it, e.g.:

Yes, that would be bad design, but of course it isn't so in HG.

There is no separate VP, only EP. A PP-1 feeds enough power for a Drive-1 is a simple shorthand to be compatible with LBB2. EP is just a more granular measure, to be able to count how many lasers you can power.

A PP-1 cannot power a M-drive-1, a J-drive-1, and a bunch of weapons at the same time, you have to choose.
That choice is called Agility:
1. All power to the M-drive = Emergency Agility = max acceleration.
2. Power to the weapons first = Agility = limited acceleration
3. All power to the J-drive = no Agility, no weapons = no acceleration.

Example: A Scout with a laser. The PP-2 produces 2 EP, the M-drive consumes 1 EP for each G of acceleration, the laser consumes 1 EP.
1. Send 2 EP to the M-drive => 2 G acceleration, no laser fire. [Emergency Agility]
2. Send 1 EP to the laser, and 1 EP to the M-drive => 1 G acceleration [Agility]
3. Send 2 EP to the J-drive, no acceleration, no laser fire [break off by jump]

There is no free magical power.

But I can repeat it if you like:

Example: A Scout with a laser. The PP-2 produces 2 EP, the M-drive consumes 1 EP for each G of acceleration, the laser consumes 1 EP.
1. Send 2 EP to the M-drive => 2 G acceleration, no laser fire. [Emergency Agility]
2. Send 1 EP to the laser, and 1 EP to the M-drive => 1 G acceleration [Agility]
3. Send 2 EP to the J-drive, no acceleration, no laser fire [break off by jump]

Please show me specifically what you think is wrong in the simple example above?

 

[Sigtrygg]

Actually that's not correct. The amount of thrust output vs. mass is never defined for any ship, just what the drive is capable of. At best we can take the displacement of a ship (which isn't its' mass) and divide that by the displacement of the power plant, which gives a displacement to top speed number, but not an actual thrust to mass.

The acceleration rating of the ship is defined, it doesn't matter what the mass is or the volume or thrust or anything, all we have is that a drive produces 1-6g.

You were the one who brought up mass.

F=(ma), rearrange to a=(F/m)

Here's the thing we are only given the acceleration because it is a magic reactionless gravitic based drive (with every illustration showing an exhaust plume)

10t fighter 6g
100,000t BB 6g - both have exctly the same 6g acceleration.

Naval vessels (closest actual example we have to spaceships) are built around shaft horse power driving propellers - and typically the higher that number the faster the vessel. This analogy breaks down due to hull design/wave flow, propeller design and other naval characteristics. However the overall displacement (mass in water at least) of a ship can be roughly compared to the amount of weight it's power plant and engineering spaces are.

The analogy is incorrect from the very first sentence. Naval ships are not even close to Newtonian maneuvering in space.

A 30,000 ton armored battleship has a different ratio compared to a 3,000 ton unarmored destroyer. While some is attributed to the hull itself, the majority of it is due to the amount of additional weight the armor has. I can provide actual examples if you like (just gotta go get the books) if you are curious.

Not as a 6g spacecraft.
A 6000t 6g destroyer has the same acceleration as a 30,000t armoured cruiser.

Traveller ships doing a 3D zig-zag would need to actually shift the entire mass of the ship in any direction along it's axis. Otherwise it wouldn't really be dodging, it would be more of a corkscrew path.

Which requires spinning the ship with thrusters and then firing the main engine.

 

[phavoc]

The acceleration rating of the ship is defined, it doesn't matter what the mass is or the volume or thrust or anything, all we have is that a drive produces 1-6g.

You were the one who brought up mass.

F=(ma), rearrange to a=(F/m)

Here's the thing we are only given the acceleration because it is a magic reactionless gravitic based drive (with every illustration showing an exhaust plume)

10t fighter 6g
100,000t BB 6g - both have exctly the same 6g acceleration.

The analogy is incorrect from the very first sentence. Naval ships are not even close to Newtonian maneuvering in space.

Not as a 6g spacecraft.
A 6000t 6g destroyer has the same acceleration as a 30,000t armoured cruiser.

Which requires spinning the ship with thrusters and then firing the main engine.

Actually the game brings up mass, and then ignores it. It says it follows some physics rules, but not others (more on that below)

Most versions of Traveller do posit the magical reactionless drives - and there are notable exceptions. MGT has now introduced a new magic limitation to a magic drive - these magical gravitic drives do not operate outside of a star's heliosphere. CT uses mass of ships and the idea that it's possible to "overload" them - hence the idea that you could have repulsor stations on the ground to help lift ships up when their drive rating was just 1G. They could also help them land on planets with gravity slightly in excess of 1G and the ship only has a 1G drive. Free traders are supposed to be ubiquitous in the game, so with only a 1G capability they could not take off from a greater than 1G world on their drive alone. There are many logical inconsistences across the editions for this entire question. Which is why I was excited to get SOM, but then disappointed in their explanation that was full of even more logical holes. Having anti-grav that offsets local grav (say 2X your drive rating) would explain away all of this without any mental gymnastics of trying to justify the holes.

Using MGT v2 rules - A 100,000 Dton 6g battleship requires 6,000 Dtons for it's maneuver drive. A 10dton 6G fighter requires 2 Dtons (HG and Core Rulebook - in the High Guard book the fighters engines are now also 1% of displacement). The 100,000 Dton ship requires 1%, the 10 Dton ship requires 20% (or 1%, depending on which book you are looking at). Acceleration is same, displacement tonnage for the smaller ship is 20x the larger ship, and (going out on a limb here) their mass are going to be quite different for the same acceleration. I will continue to point out the obvious, displacement is not an equivalent to mass. The battleship is going to mass a wee bit more than the fighter, so their thrust to mass ratio's are also going to be different. Especially considering that a battleship will have a much greater armor factor than a fighter. So it's a mess even within the same MGTv2 rewrites for some of the rules.

I don't think the analogy is wrong (comparing vacuum to water). Vacuum has no drag (which was noted), but as I factually pointed out, one can use this to your advantage when necessary. In a vacuum if you accelerate to 6G for one turn and turn your engines off you will continue at that speed until you expend 6G for one turn to decelerate (no drag). If you accelerate to 10kts for 6min in water and turn your engines off, you will decelerate (via drag, or waves or currents) at a variable rate. You do not need to expend any energy to slow down.

While you can indeed spin your ship on thrusters, you now have introduced another vector to your movement. It's not the same as shifting the entire ship in laterally while maintaining your same core heading. Under your example if you are travelling in one direction at 1G (for 10 turns) and want to do a 180 degree turn to change course you CAN turn and fire your main engines, however you are still travelling along your original course axis at 1G (10 turns) velocity while now building a new course. Your center of mass also remains the same if you using bow thrusters to turn and use your M-drive to change course. If I'm an enemy I'll always target your center of mass since you are spinning on your axis rather than shifting the entire hull in a direction (again, thrusters v drive logic).

 

[Sigtrygg]

Actually the game brings up mass, and then ignores it. It says it follows some physics rules, but not others (more on that below)

I have tried very hard to avoid starting replies with words like "actually, nope, wrong" as I have come to the conclusion people immediately think I am being snarky even when that is not my intent. I still make mistakes but am trying to come across a little less confrontational

CT uses mass of ships and the idea that it's possible to "overload" them - hence the idea that you could have repulsor stations on the ground to help lift ships up when their drive rating was just 1G. They could also help them land on planets with gravity slightly in excess of 1G and the ship only has a 1G drive. Free traders are supposed to be ubiquitous in the game, so with only a 1G capability they could not take off from a greater than 1G world on their drive alone. There are many logical inconsistences across the editions for this entire question. Which is why I was excited to get SOM, but then disappointed in their explanation that was full of even more logical holes. Having anti-grav that offsets local grav (say 2X your drive rating) would explain away all of this without any mental gymnastics of trying to justify the holes.

Do you mean MegaTraveller here? I am not a fan of the handwavium DGP wrote to "explain" thruster plates.

Using MGT v2 rules - A 100,000 Dton 6g battleship requires 6,000 Dtons for it's maneuver drive. A 10dton 6G fighter requires 2 Dtons (HG and Core Rulebook - in the High Guard book the fighters engines are now also 1% of displacement). The 100,000 Dton ship requires 1%, the 10 Dton ship requires 20% (or 1%, depending on which book you are looking at). Acceleration is same, displacement tonnage for the smaller ship is 20x the larger ship, and (going out on a limb here) their mass are going to be quite different for the same acceleration. I will continue to point out the obvious, displacement is not an equivalent to mass. The battleship is going to mass a wee bit more than the fighter, so their thrust to mass ratio's are also going to be different.

No, this is your error. If they have the same acceleration then they have identical "thrust to weight" - The BB drive produces a larger "force" than the fighter drive.

Especially considering that a battleship will have a much greater armor factor than a fighter. So it's a mess even within the same MGTv2 rewrites for some of the rules.

If the BB and the fighter have 6g acceleration then everything in the right of the equation has to equate to the same answer.

6g =F(BB)/m(BB) = F(fgt)/m(fgt)=BB(handwavium)=fgt(handwavium)

I don't think the analogy is wrong (comparing vacuum to water). Vacuum has no drag (which was noted), but as I factually pointed out, one can use this to your advantage when necessary. In a vacuum if you accelerate to 6G for one turn and turn your engines off you will continue at that speed until you expend 6G for one turn to decelerate (no drag). If you accelerate to 10kts for 6min in water and turn your engines off, you will decelerate (via drag, or waves or currents) at a variable rate. You do not need to expend any energy to slow down.

So completely different. Also in space you can spin about your centre of gravity, something an ocean ship can not do.

While you can indeed spin your ship on thrusters, you now have introduced another vector to your movement. It's not the same as shifting the entire ship in laterally while maintaining your same core heading.

I'm not surre you have a picture of how the thrusters work. They have to be in pairs (x,-x), (y,-y}, (z,-z)

If I want to spin about the x axis I fire the x and -x thrusters, this produces circular motion about the and has no effect on forward momentum.

Under your example if you are travelling in one direction at 1G (for 10 turns) and want to do a 180 degree turn to change course you CAN turn and fire your main engines, however you are still travelling along your original course axis at 1G (10 turns) velocity while now building a new course. Your center of mass also remains the same if you using bow thrusters to turn and use your M-drive to change course. If I'm an enemy I'll always target your center of mass since you are spinning on your axis rather than shifting the entire hull in a direction (again, thrusters v drive logic).

Once I have altered my pitch, roll and/or yaw I fire the main engine, this alters the forward momentum vector, by doing this randomly for a few minutes at a time then the future position becomes more difficult to predict.