# The great conversion of MegaTraveller starships back to High Guard

Because I like you, I did some math (OK, I like math). For a first pass, I assumed a spherical hull which does not address your surface area point. But continuing, I first looked at my Type A models. I converted armor volume to thickness, backed out the TL 14 multiple, and came up with a hard steel thickness of 23.2, or Armor 36, versus the correct value of 40. I then looked at my SDB, and came up with a hard steel thickness of 283.5, or Armor 64, versus the correct value of 67. So...pretty close already! It looks like some small multiple to my volume calculation would get us close to the right value. These results suggest that multiple is somewhere around 1.35 to my hard steel thickness. I'd need more time to figure out why that difference exists.

ETA: Oh cool! I just noticed that the actual weight multiplier for a spherical hull is 0.8x. As both my examples have 1.0x config multipliers, we should adjust thickness by (1/0.8)^(1/3) = 1.08. So now Type A thickness is 25.0 or Armor 37, and SDB thickness is 306.2 or Armor 65. So now we are only off by about 20-30%. Not a bad approximation!
Take another look at ISW - this is all done for you.

Hull weight mod is proportional to hull volume or hull surface area, depending on size. For small ships Weight = ³/₁₀×Hull + 10. For ships larger than 10 000 Dt the weight tapers off, more like proportional to surface area.

The armour mod (~armour thickness) is 5 × 2^((AV-18)/8) [for AV≥14], rounded to three significant numbers.
I.e. armour thickness is proportional to 2^AV, or AV ~ thickness.

Armour (=Hull) weight and price are modified separately by configuration and streamlining:
View attachment 1654

Hull mass is WeightMod(~Hull) × ArmourMod(~AV) × ConfigMod, so proportional to all the things you listed...
Yup, just a shame that the MT authors couldn't spot this.

Yup, just a shame that the MT authors couldn't spot this.
Sorry, I don't understand? That is the MT system.

That they had a way to incorporate armour volume so you were losing interior space on a ship. Armour thickness x hull surface area is a rough approximation for space lost to armour.

Another Dilbert has just made me accept that the 13.5 cubic metre displacement ton and the 14 cubic metre displacement ton are the same.
I have never had much of a problem with this. CT stressed 1 Dt is about 14 m³.
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).

In standard scientific notation "14 m³" means 14±0.5 m³, so anywhere from 13.5 to 14.5 m³. If you only give one significant digit, you are not very precise...

Of course it's a bit annoying to switch between 13.5 and 14 m³, but HEPLAR vs. Thrusters and 10% vs. 5% jump fuel is more annoying.

That they had a way to incorporate armour volume so you were losing interior space on a ship. Armour thickness x hull surface area is a rough approximation for space lost to armour.
OK, yes they ignored that. At a guess they thought it was insignificant?

Just as I was getting ready to post my redesigned SDB, I found that the version in Supp7 Traders and Gunboats is nothing like the one in Supp9, and that the MT version is based upon Supp7, the 400 D-ton version. So two questions: 1) For the long-time players, does anyone know why the design changed between the supplements? 2) Is there a preference? I'm pretty certain I can get more armor with the 400 D-ton version, but is there a reason to want a smaller version? It's fine if no answers are forthcoming--I'll noodle on the 400 D-ton version and likely post them both.

They are both crap,
At least the 400t version has some use in LBB2 combat.

A HG80 SDB needs to be 1999t, with a missile bay, a filled out weapon and screen USP, max agility and armour/screens for TL.

A HG80 monitor should be 19,999t and as above but with the largest meson spinal it can carry.

1) For the long-time players, does anyone know why the design changed between the supplements?
There are many different SDBs, these are just two examples.

The S7 one is TL-10, the S9 is TL-15 and approaching usability with Ag-6 and Comp/9 (still can't scratch a warship with those puny weapons).

A HG80 SDB needs to be 1999t, with a missile bay, a filled out weapon and screen USP, max agility and armour/screens for TL.
Less is more, it needs to be between 1 kDt and 2 kDt, with a bay, if it wants to fight large ships. A say 1000 Dt design is a lot cheaper, hence more numerous, than a 1999 Dt design.

Light ships like these are easily destroyed with PA spinals.

A HG80 monitor should be 19,999t and as above but with the largest meson spinal it can carry.
Again less is more, a 10 kDt design is a lot cheaper, and hence more numerous. More ships with small meson spinals are more cost-effective, and beats larger, more expensive, less numerous large spinal ships. E.g. at TL-15 Meson-N is more effective than Meson-T.

More guns are better, smaller ships gets you more guns and more survivability, when the basics such as max defences are sorted.

Thanks for the SDB info, and as a reward, let's look at some SDBs! These are based upon the 400 D-ton from Supp7 and the 200 D-ton from Supp9, both designed with HG. There are some very interesting tradeoffs in these examples, so I'll be interested in any commentary. Remember to refer back to the OP for the assumptions I'm using in the MT Revised designs.

Let's start with the 400 D-ton (left). I was able to include the original MT RAW design from the Imperial Encyclopedia. My design is only MCr100 more, and I haven't gone all the way through the HG design to see why it's s expensive. Observations:
1) Notice the Fuel differences. MT RAW has much higher fuel, as we all know. But even my redesign has higher fuel than the HG because I have to install much more PP to get Agility 6, which as I noted previously, HG powers the drives for "free" (more on that below).
2) I actually got a bit more armor than HG, so it takes up more space. I highlight that MT RAW has no volume for armor!
3) If my redesign uses HG assumptions wherever possible, why do I have more M-Drive units? Because I'm playing fair. My redesign does away with all volume-based power calculations. MD units have thrust (675 tons per unit), and I have to install a sufficient number based upon the mass of the ship, not volume (using the thrust vehicle rules from Striker/MT). The weight of the armor and PPs adds up.
4) OK, the big MT complaint: only Agility 1 from the RAW design vs. 6 in HG. My redesign gets back to 6, but look at the HUGE PP it requires. Also notice that the HG and MT RAW designs have about the same amount of MWs (using 1 EP = 250 MW). This gets back to that last difference between HG and MT that my redesign does NOT include: HG PPs provide EPs to all non-drive systems (including Agility) and power all the drives for "free" once the PP is large enough. Now from this example, we can see how HG tries to pay for this: its PP volume is much higher. But I prefer the MT paradigm that all power much be explicit. Tradeoffs.
5) The one compromise I had to make was staterooms, but I also installed a bigger computer (Model/9) with more control points (CP) which reduces crew. Staterooms are space hungry, and this a patrol ship--it doesn't need 10 staterooms!
6) Best I can tell, cargo space is all for missiles. The MT RAW design seems punk but holds 135 missiles. The other two can hold thousands.

For the 200 D-ton HG version, the only comment I'll make is that I was not able to design a 200 D-ton version with even Armor 67. I had to go to 300 D-tons, and to get to 79 would require a much bigger ship. A believable tradeoff, and at some point I've got a capital ship designed in MT that I will convert to the redesign where we can test this hypothesis that high volume allows higher Armor without Agility tradeoffs.

Depends on what the planetary government wants, needs, and can afford.

Gunboat, patrol ship, and/or submersible.

4) OK, the big MT complaint: only Agility 1 from the RAW design vs. 6 in HG. My redesign gets back to 6, but look at the HUGE PP it requires. Also notice that the HG and MT RAW designs have about the same amount of MWs (using 1 EP = 250 MW). This gets back to that last difference between HG and MT that my redesign does NOT include: HG PPs provide EPs to all non-drive systems (including Agility) and power all the drives for "free" once the PP is large enough. Now from this example, we can see how HG tries to pay for this: its PP volume is much higher. But I prefer the MT paradigm that all power much be explicit. Tradeoffs.
Still no free power for the drives. If you don't feed power to the M-drive you get no acceleration (= Agility 0 = 0 G acceleration). If you don't feed enough power to the J-drive, you can't jump.

I finished the Heavy Cruiser rebuild, and at first the results were surprising, but then I realized they represented a fundamental conflict between HG and MT that my redesign deliberately did not include. So before I post the rebuild, I need to discuss this conflict.

This exercise has taken the view that MT failed to incorporate many aspects of HG ship design without disclosing the differences, and so we should try to restore the HG assumptions as much as possible. This was rather easy, which suggests that the Digest Group crew might have worked harder to do this. But there is one design difference where I now think HG made the mistake.

HG power plants (PPs) have a very questionable design. They incorporate two incompatible and non-fungible measures of energy. There is "volume percentage" (VPs, proportional to the PP number), which provide energy to all drives, and there are energy points (EPs), which power everything else: weapons, screens, computers, and Agility. Each unit of PP provides both VP and EP. VPs function as a minimum: once a PP is large enough, it powers all the drives (PP number = VPs >= M-number or J-number). Any additional units have no VP value, only EP value.

This is bad design. Energy should be additive and fungible, PPs should use either VPs or EPs, not both. MT and Striker use EPs, specifically MWs, and all power must be allocated to all devices, whose power requirement is known. HG should perhaps have stuck to a strict volume power system (i.e., VPs), which I don't like but can work and is simple. But that would mean that units of PP volume would have to be allocated to all devices additively. So the drives require X% of ship volume. Add weapons? Another Y%. Boost Agility? Another Z%, and so on. Energy should be additive and fungible.

Now let's go back to HG. Let's say (and this is an example, not real units, so don't get too detailed) that each HG PP "unit" provides 1 VP to power the drives and 1 EP to power everything else. These are not fungible in HG. I cannot install 1/2 the normal PP units to just power the drives, though if 1 VP = 1 EP I should be able to do that. Once I have satisfied my VP drive requirement, each additional PP "unit" only gives me 1 EP, not 1 EP + 1 VP = 2 EP. These should be fungible, but are not.

I prefer an EP system. Power should be expressed in real units (MWs) and should behave as physics dictates (e.g., power/weight ratios dictating velocity, as with Agility). But for simplicity, a volume system is possible, so long as it is additive as noted above. HG is not.

So, what does this have to do with my redesign? MT noted that its Agility formula, which explictly referenced mass as it should, would result in massive ships having lower Agility unless sufficient power could be provided. This is what I encountered in my Heavy Cruiser redesign, which I will relate in my next post. I think this is the correct outcome, and HG not reflecting this is a design flaw.

My latest rebuild was the Atlantic Class Heavy Cruiser from Supp9 pg. 32. It is 75000 D-tons, 5G (Agility 5), Jump-4, and Armor 10. I was not able to reproduce all of these parameters. Under my revised rules, Jump-4 and Armor 10 guaranteed that at least 55% of ship's volume was always consumed, a major constraint. In order accommodate all of this ship's specs, I had to increase volume to 200000 D-tons, a 267% increase. And even with this, I could only achieve Agility 2, 3 if no combat systems are used. But I now think this is a reasonable outcome. MT's revised Agility formula correctly converts it to a power/weight ratio calculation, and increasing mass makes increased Agility more difficult. But this ship is already Maneuver-5, much faster than most ships, so I think this result is correct. The more M-drive, J-drive, and Armor we require, the less room is available for the added MWs of power to increase Agility. This is the correct tradeoff, and I am more confident of incorporating this redesign into my game. That HG allowed this design at 75000 D-tons and Agility 5 reflects the questionable PP design I analyzed previously.

HG power plants (PPs) have a very questionable design. They incorporate two incompatible and non-fungible measures of energy. There is "volume percentage" (VPs, proportional to the PP number), which provide energy to all drives, and there are energy points (EPs), which power everything else: weapons, screens, computers, and Agility. Each unit of PP provides both VP and EP. VPs function as a minimum: once a PP is large enough, it powers all the drives (PP number = VPs >= M-number or J-number). Any additional units have no VP value, only EP value.
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.

I wonder if there should be a scale for agility? Mass is still an issue and Traveller (though not dealt with directly), and while it's possible for a 35000 ton battleship to have 30kt capability like a destroyer, it's nowhere near as nimble as it's simply too big and unwieldy when compared to a 3,000 ton destroyer. While the example is naval based in reality, like a 20 dton fighter being able to have armor factor 15 like a 100k dton battleship, that's more a hole in the rules than a good model.

I would also expect a naval architect to design a vessel allowing full maneuver AND to power all weapons (spinals are special cases, though I'd expect a trickle charge capability along with sufficient capacitors to make for a meaningful fire rate without having to divert power from secondary weapon batteries).

I would also expect a naval architect to design a vessel allowing full maneuver AND to power all weapons (spinals are special cases, ...
Yes, of course warships SHOULD, but then there is a refit... At least at lower TLs, there is a trade-off between armour and agility, you can't have both.

I wonder if there should be a scale for agility?
Acceleration is acceleration, twice the thrust gives the same acceleration to twice the mass.

While the example is naval based in reality, like a 20 dton fighter being able to have armor factor 15 like a 100k dton battleship, that's more a hole in the rules than a good model.
Yes, volume armour is a bad idea, but it's simple. The "better" systems in e.g. Striker and FF&S are not universally popular.

Compared to grav tanks, the problem isn't really fighters, but battleships... They should be a lot more sturdy.

TNE and FF&S solves most of your problems, if you can be bothered. The result is of course a lot more complicated design system and a lot more complicated combat system...

Acceleration is acceleration, twice the thrust gives the same acceleration to twice the mass.
Acceleration in a straight line is easy - jinking in a massive battlewagon the same as you do with a dinky tincan should be different. Larger ships are more massive and one would naturally expect them to be slower in maneuvers, to turn, to shift in any direction to avoid incoming fire. Pure acceleration isn't a good example of maneuverability, just speed.

The more M-drive, J-drive, and Armor we require, the less room is available for the added MWs of power to increase Agility.
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.

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

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