better engine efficiency vs power & fuel considerations

[Steve Walmsley]

It is however not always an option. Especially for many smaller military designs ( fighters, FAC, offensive destroyers/scouts or beam warships ) that need so high speed that a low powered engine would leave them with zero mission tonnage.

Also adding more tonnage means more space devoted to armour plus a higher failure rate because that is related directly to size. Once you add more engineering you add more crew so crew quarters expand.

[Ninetails]

Congratulations, you have found the some numerical evidence for efficient engines being good for commercial ships.  I would however not go screaming about imballance, simply because the effect does not grow into the sky.  What do I mean? This has to do with optimization, matematical optimization.  Simply put, for certain requirements, like cary T mission tonnage to atleast range R. . .  in the most efficient way after some target function, then there is an optimal value of engine power/fuel ballance to strike.

Let us first look at commercial shipping first.  The effect of a cargo like freighter with negitible fuel usage (meaning we are already using low power multiplyers), is something allong the lines of: cargo*speed/cost.  Now we can split this up a bit into main section and engine section parts.  The speed can be split up into: engPowMult* engineSize /(engineSize +CargoSize).  While cost can be put into something like: cargoCost + engCostMult*engineSize*engPowMult^X.  Sadly I have not checked what this X is, but for military grade ships it is 1 and for commercial ships it appears to be above 1.  This gives us the following target function to optimize:
f(engPowMult,engineSize) = cargo*engPowMult* engineSize /((engineSize +CargoSize)*(cargoCost + engCostMult*engineSize*engPowMult^X))

To optimize this, we first calculate the gradient:
df /d engPowMult = cargo * engineSize /((engineSize +CargoSize)*(cargoCost + engCostMult*engineSize*engPowMult^X)) -X * engCostMult*engineSize*engPowMult^(X-1)*cargo*engPowMult* engineSize /((engineSize +CargoSize)*(cargoCost + engCostMult*engineSize*engPowMult^X)^2)
df /d engineSize = cargo*engPowMult * ( 1 /((1 +CargoSize/engineSize)^2 * CargoSize/engineSize^2 *(cargoCost + engCostMult*engineSize*engPowMult^X))
 - engPowMult^X * engCostMult*engineSize /((engineSize +CargoSize)*(cargoCost + engCostMult*engineSize*engPowMult^X)^2) )

The next step is then to set this gradient equal to the zero vector and solve the corrisponding equation system.  We first reduce each equation quite a bit (no, I will not post the intermediate steps, there are too many)
for df /d engineSize = 0:
 cargoCost/(((1 +CargoSize/engineSize) * CargoSize/engineSize^2 -engineSize)*engCostMult) =  engPowMult^X

for df /d engPowMult = 0:
cargoCost = (X-1) * engCostMult*engineSize*engPowMult^X

We can then substitute the left hand side of the first equation into the second to solve for engineSize:
cargoCost = (X-1) * engCostMult*engineSize* cargoCost/(((1 +CargoSize/engineSize) * CargoSize/engineSize^2 -engineSize)*engCostMult)
0  = X * engineSize^4 - engineSize* CargoSize^2 + CargoSize
This is "just" a forth degree equation, so it will have several solutions which are locally extremal.  From this point on, it can get a little bit ugly and depend on the actual value of X, so I will leave it at this for now.  I might also have made some error somewhere allong the way, since it was all done by hand.

Anyway, the point is that there is an optimal setup for commercial shipping.  For military ships there are optimizations too, but they are more complicated and there are many other possibly things to optimize on them.
You should also remember, that there are many things on military ships which scales (roughly) with size, such as armor, engineering, jump drives, cloaking, termal signature/speed and so on.  Since these play in, putting on some extra engines might require you to put more of other stuff on, eating up most of the benifit.  This is part of the reason why I usually design this part of military ships based on percentage of total tonnage.

[Jorgen_CAB]

There obviously are some optimisation you can make, especially with commercial ships, but at the end of the day the most important thing is what constraints you have on your designs. What are your needs...

As Haji I play mostly in multiple nation games with no AI, only aliens are AI driven... sometimes not even that. In such campaigns it is rare that you can optimise designs because of other constraints such as fuel, minerals, workers, shipyards, money, time.. etc...

If just commercial designs at least had some maintenance cost, at least in money I would also have a reason (other than seriously outdated fuel guzzling ships) to upgrade or replace them.

For military ships there are soooo... many constraints, so building an optimised ship is nearly impossible. Fuel is often a very high constraint, especially with your main combat ships that tends to be both larger and fuel hungry, even if they consume less fuel per mass than a smaller ship it is a problem. In multi National game you can't often afford to keep all your ships stationary and just wait for combat. They need to patrol and make a presence to show strength of force when political pressure demands it. They need to go on fleet training operations etc...

[Jorgen_CAB]

Some more comments on commercial ships... I rarely use anything but size 50 engines for those, see no reason not to unless it is a really small ship and I put a size 25 on them. Research and construction of commercial engines are so cheap anyway.

For military ships it is another issue entirely, most military ships is also much smaller than commercial ships since you are constrained by your shipyards. You need at least two if not three engines on military ships to reduce the overhead cost of maintenance, crew and risk in combat.

In general I have three or four different engine designs apart from small craft engines, so the usually are something like size 1,10-15, 20-25, 35-50... something  like that depending on my naval yard sizes and doctrines. I also tend to reduce the power efficiency on bigger engines and increasing them on smaller engines. Which means in general that larger ships become cheaper but slower and smaller ships more expensive but faster, but that is part of my overall combat doctrines. Larger ships require more maintenance facilities and can be stationed at fewer places so they need more generous maintenance times and deployment times, smaller ships pack more punch but are more expensive per tonnage and drink more fuel but don't need to move around as much, unless they are scouts or recon ships which are designed differently.

[Jorgen_CAB]

i'll explain my problem with an example. in the ship designer i design a ship that has 25,500 tons without engine. i picked an empty ship with one terraforming module, and 1 fuel storage (50,000 litres). but it doesn't matter how the ship looks like (instead of the terraforming module you can use total 500 HS of war tonnage if you prefer). total ship size does not matter for this either, but for ships below 5,000 tons it can be even more efficient to use one larger (higher HS) engine to also take advantage of the fuel modifier (see my other thread concerning engine efficiency for that).

then i have to decide on the engine. my technology is solid-core anti-matter drives and fuel consumption 0.25 litres per power hour. the relative results will be the same if you have different technologies. i consider 2 different engine designs, both HS 50 (the relative results are the same if you use smaller engines):
#1 engine power x0.25 (power 500) - cost 625 to research and 62.5 to build - using 2 of them
#2 engine power x0.35 (power 700) - cost 1225 to research and 122.5 to build

note: you can use ANY technologies for test designs, i just happen to have these right now - the relative result is the same

two engines #1 cost about the same to build as one engine #2. now lets compare the ships speed and range (which tells us how much fuel it uses) using either 2 engines #1 or one engine #2:
#1: speed 1,633 kms, range 75b km, total ship size 30,600 tons
#2: speed 1,245 kms, range 35b km, total ship size 28,100 tons

surprise! #1 is cheaper to research and costs the same to build. but the ship is faster and needs less than half the fuel (more than double range). shouldn't the more powerful engine make the ship faster? (or at least, give any advantage)

well if we want a faster ship, lets try doubling the engine number, now we're either using 4 engines #1 or 2 engines #2:
#1: 2,805 kms, range 65b km, total ship size 35,650 tons
#2: 2,287 kms, range 32b km, total ship size 30,600 tons

still the same... double the number of engines again to 8 for #1 and 4 for #2:
#1: 4,366 kms, range 50b km, total ship size 45,800 tons
#2: 3,921 kms, range 27b km, total ship size 35,650 tons

that's pretty fast already and still the only advantages of the faster engine is a lower total ship size and less termal signature(2,800 compared to 4,000). the difference in ship size hardly matters compared to the obvious advantages.

lets double the number of engines again to 16 for #1 and 8 for #2:
#1: 6,060 kms, range 35b km, total ship size 66,000 tons
#2: 6,106 kms, range 22b km, total ship size 45,800 tons

finally!! by now the #1 ship is over 60% just engines, but it is no more faster than #2. though it still needs 30% less fuel, and the research cost was half as much.

the result is pretty much the same for any ship size and power multiplier. a higher power multiplier makes the ship only faster, if engines are at least 50 % of the whole ship.

to sum it up: i would like to see more reason for using more powerful engines. a simple solution would be to make all engines of same size have the same build costs, independent from the power multiplier.  this way, engine stacking at least makes your ships more expensive.

there is another problem: comparing examples 1 and 2 doubling the amount of engines, i only need 10% more fuel to travel the same distance with 75% higher speed. if we compare examples 1 and 4, the speed is about 4 (5) times higher and the fuel needed increased by about 100% (50%) for engine #1 (#2). now that's an efficient power vs fuel usage ratio! there's hardly a reason to build slow ships if we can make them twice as fast by only needing 10 % more fuel.

the problem comes from aurora putting very different weight on speed vs fuel considerations. while in the case of using multiple engines you get higher speed for very little fuel, it's extremely expensive in the case of using more powerful engines.

i suggest to reduce the impact of the engine power multiplier on fuel usage. currently, every 100% increase in power increases the fuel per EPH by 566%. that means you need 11 times as much fuel to travel the same distance in half the time. i suggest to increase the fuel per EPH only by 200% for each 100% increase in power. that still means, to travel the same distance in half the time you need 4 times as much fuel. or you can save 75% fuel by using engines of half the power.

this would make engine stacking much less efficient and give higher power engines more use. it would also need some testing to find out if my suggested values are good and how it influences total fuel needed. i am willing to help if possible.

i also suggest remove the fuel consumption tech line, or make it much more expensive (in the way that you get the lower multipliers much later). better engines already help you save fuel because they increase ship size less for the same engine power. and you also have the advantage of getting fuel more easily at higher tech levels. keeping a big fleet supplied with fuel should be a real challenge!

finally, fuel weight should be increased. i guess the weight for the fuel is included in the HS of fuel tanks (that's exactly 1kg per litre). currently, it's not much of a problem to give all ships the range that you want them to have. even with my suggestions above, fuel tanks just don't need enough hull size to really matter. trippling or quadrupling the HS of fuel storage components would make range considerations more important. it seems reasonable that such powerful fuel as used in trans-newtonian engines have higher density than our modern fuels. this suggestion is independent from the rest.

Commercial ships are in my opinion uninteresting because there you pretty much always want the biggest most fuel efficient engine you can fit into them and you have no maintenance facilities to worry about and expanding those yards are pretty cheap, as is researching them. That and commercial production costs usually concise of a fairly small part of your empire budget anyway.

Let's compare two military ships of equal size... we can NOT allow to compare ships of different size because if you expand your yard space then ALL new designs can use it so all designs MUST use the same constraints.

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Furious Type A class Cruiser    10,000 tons     297 Crew     1452.6 BP      TCS 200  TH 720  EM 0
3600 km/s     Armour 4-41     Shields 0-0     Sensors 1/1/0/0     Damage Control Rating 6     PPV 53.97
Maint Life 2.49 Years     MSP 499    AFR 145%    IFR 2%    1YR 111    5YR 1672    Max Repair 180 MSP
Intended Deployment Time: 9 months    Flight Crew Berths 10    
Hangar Deck Capacity 500 tons     Magazine 90    

360 EP (HS30) Ion Stardrive (2)    Power 360    Fuel Use 49%    Signature 360    Exp 10%
Fuel Capacity 300,000 Litres    Range 11.0 billion km   (35 days at full power)

Twin Barrelled Pulse Laser Turret (7x2)    Range 48,000km     TS: 12000 km/s     Power 6-4     RM 3    ROF 10        3 3 3 2 0 0 0 0 0 0
PDFC Fire-control (7)    Max Range: 48,000 km   TS: 12000 km/s     79 58 38 17 0 0 0 0 0 0
Gas-Cooled Fast Reactor Technology PB-1 (7)     Total Power Output 28.35    Armour 0    Exp 5%

Active Search Sensor MR1-R1 (1)     GPS 16     Range 1.3m km    MCR 139k km    Resolution 1

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Furious Type B class Cruiser    10,000 tons     289 Crew     1360.04 BP      TCS 200  TH 653  EM 0
3265 km/s     Armour 4-41     Shields 0-0     Sensors 1/1/0/0     Damage Control Rating 5     PPV 53.97
Maint Life 2.35 Years     MSP 425    AFR 160%    IFR 2.2%    1YR 105    5YR 1574    Max Repair 138.72 MSP
Intended Deployment Time: 9 months    Flight Crew Berths 1    
Hangar Deck Capacity 500 tons     Magazine 90    

326.4 EP (HS32) Ion Stardrive (2)    Power 326.4    Fuel Use 31.71%    Signature 326.4    Exp 8%
Fuel Capacity 190,000 Litres    Range 10.8 billion km   (38 days at full power)

Twin Barrelled Pulse Laser Turret (7x2)    Range 48,000km     TS: 12000 km/s     Power 6-4     RM 3    ROF 10        3 3 3 2 0 0 0 0 0 0
PDFC Fire-control (7)    Max Range: 48,000 km   TS: 12000 km/s     79 58 38 17 0 0 0 0 0 0
Gas-Cooled Fast Reactor Technology PB-1 (7)     Total Power Output 28.35    Armour 0    Exp 5%

Active Search Sensor MR1-R1 (1)     GPS 16     Range 1.3m km    MCR 139k km    Resolution 1None of these designs are optimised and could perhaps be changed to tweak some numbers here and there, but I believe they roughly show the differences in real numbers.

So, here we have two ships with roughly equal in mission payload, range and maintenance. Where they differ is in cost, fuel efficiency and speed.

Model A has an advantage of +10% speed for a drawback of -6.5% cost and -37% fuel efficiency.

I presume, that in any way we scale the ships up or down in size the difference will be roughly the same. The difference in cost can vary, though depending on, how much resources go into the mission tonnage of the ship. But it will likely be somewhere around 5-10%.

My question is... how much is it worth to pay for more speed and how important is it?!?

I usually like cost efficiency over speed on the grounds of refit cost/time, less investment into retooling of shipyards, cost of expanding/maintaining the fuel industry. I believe this will pay for more ships and mission tonnage in the end.. but... sometimes the speed of your ships can mean more than an infinity number of mission tonnage, so, the questions stands... what should the price be on a ships speed?

[alex_brunius]

earlier this thread you talked about 25 %

Because it was for a different ship with different weaponry, requirements and mission...  

Have you already forgotten that we are the ones saying that each ship has it's own optimal solution, and you are the one claiming that somewhere 45-50% and low engine power is always best regardless of situation?

Or here even above 50% ( which is why my first example had 60% engines ).

unless you're somehow size restricted (fighters, missiles) - the optimum ship design always consists of 50-66 % engine. it's boring.

For me the optimal can be anywhere between 20% and 50% depending on what the ship needs to do!

unless you want to discuss if the optimum engine space is not 50 % but 45 %, but that would require you to agree with my basic assumption in first place.

I already agreed with you that 45-50% can be an optimum engine space ratio for certain civilian designs or designs where fuel efficiency is more important then all other factors. But for military ship that is not really the case unless they are optimized for carrying munitions with minimal fueluse ( and need to be military simply to fit magazines ).

[Jorgen_CAB]

For me the optimal can be anywhere between 20% and 50% depending on what the ship needs to do!

This is very true. Any ship design that you don't intend to move around as much can easily benefit from an expensive engine with a high multiplier since it either give high speed or additional mission tonnage for roughly the same cost. The main drawback obviously is your fuel cost. You obviously can't take up too much space on your ships for fuel either, so it has to be a balance for your ability to protect a supply train.

I would also say that as technology develops you probably would increase the power and reduce the size of the engine to maximize the mission part of your ships.

As an empire develops you could probably keep the engine power very high in smaller ships such as frigates and destroyers, ships that you station close to the front, ships that act as the first line of defense such as corvettes and FAC are just extreme variants of those.

Ships that you usually station several system or even sectors away from the outer systems who tend to be large and fuel hungry would need more space for fuel and bigger engines for better fuel efficiency. These ships serves a different purpose and usually have to travel quite the distance to get to any hotspots. Depending on your game these ships might also perform some form of paroling of troubled areas from time to time, if they do you don't want them to burn half your fuel reserves in a couple of months in the field.

That is why there are no easy answer to this question on the importance on speed versus cost, fuel or flexibility.

[Jorgen_CAB]

Ok, I know I said that commersial ships was uninteresting but I did some investigating into different engine to weight ratio on freighters.

I use Ion technology engines and two settings, x0.5 and x0.3 power settings... The freighters carry one standard cargo module, that is 25000 ton cargo capacity and all engines are 50HS engines, no point using smaller engines than that on larger commercial ships. All the ships use a 250.000 litre tank module and one cargo handling module. In reality you might optimise the design more these are just for a good reference point.

On the .5 power setting I get the following values

FI=Fuel Index, which mean how efficient it burns fuel (for cargo mass carried) in comparison with the other ships, higher is better.
CI=How efficient the ship carry cargo in relation to its build cost and speed, higher is better.

A: 10xEngines, 2900km/s, 1050BP, 56FI, 69CI, 51.100t
B: 5xEngines, 1940km/s, 617BP, 75FI, 78CI, 38.700t
C: 2xEngines, 967km/s, 358BP, 94FI, 68CI, 31.000t

For the .3 power setting I get...

A: 12xEngines, 1911km/s, 612BP, 180FI, 78CI, 56.500t
B: 4xEngines, 997km/s, 3287BP, 280FI, 75CI, 36.100t
C: 2xEngines, 580km/s, 255BP, 340FI, 57CI, 31.000t

My finding is that for Ion tech engines you should have about 2000km/s speed on your freighter for long range delivery to maximize cargo carrying efficiency but slower 1000km/s on shorter trips. The reason is that we do not include load/offload time in these calculations and in shorter trips such as delivery within the same system loading and offloading will take a considerable time of a ships time spent rather than travel. Also, slower ships will save a considerable amount of fuel, so building ships slower will only lower the cargo efficiency in a minor way sometimes not at all but will save you fuel, you just have to build more of them.
There are generally not a problem building many freighters since they build so quickly anyway, especially of you divert a small percentage of industry to construct their engines in advance if time is important to you.

Although, the cargo efficiency between these two engine types pretty much remains the same, using another engine just reduce your fuel usage, more or less.

You can't apply this on, say cryo ships, because cryo modules are MUCH more expensive than cargo modules. They require a completely different strategic approach to designing an efficient ship.

[Jorgen_CAB]

Freighters also scale up pretty nice in size... here is the x0.5 C version scaled up five times...

10xEngines, 979km/s, 1428BP, 95FI, 86CI, 153.000t

[letsdance (OP)]

Any ship design that you don't intend to move around as much can easily benefit from an expensive engine with a high multiplier since it either give high speed or additional mission tonnage for roughly the same cost.

*sigh* i thought we had covered that already... higher power engines you do NOT give you additional mission tonnage for the same cost. they make your ships more expensive. the only benefit of higher power engines is a small reduction in total ship size. you posted these results yourself in the other thread! (see also my next post below where i'm quoting your designs)

My finding is that for Ion tech engines you should have about 2000km/s speed on your freighter for long range delivery to maximize cargo carrying efficiency but slower 1000km/s on shorter trips.

the difference in CI from 2000km/s to 1000 kms/s is less than 5 % for 50 % more fuel needed. i see no reason to use 2000 km/s engines for freighters while you have ion drive technology. but no matter what speed you prefer, you'll always be better off using lower power engines...

power x0.5:
B: 5xEngines, 1940km/s, 617BP, 75FI, 78CI, 38.700t
C: 2xEngines, 967km/s, 358BP, 94FI, 68CI, 31.000t

power x0.3:
A: 12xEngines 0.3, 1911km/s, 612BP, 180FI, 78CI, 56.500t
B: 4xEngines 0.3, 997km/s, 3287BP, 280FI, 75CI, 36.100t

this shows very well the balancing problem from higher to lower power engines. there is no point in using a x0.5 power engine when you can achieve a better result using the x0.3 engines.

that's why in this thread i suggest to change the balance among engines with different power levels in a way that makes all of them useful!

[letsdance (OP)]

you are the one claiming that somewhere 45-50% and low engine power is always best regardless of situation?

not always, but usually. if i said 50-66 % before, i revoke that. clarification: overhead (armor, crew, engineering spaces) is included in the size %. a side benefit of this method is more total armor and HTK.

if you have less than 40 % engines (from 40-45 it should be possible but the margin might be too small) you can usually improve your design (cheaper, less fuel needed and/or faster) by dedicationg more tonnage to lower power engines in return for a small increase in total ship size. so far you and Jorgen_CAB posted designs that fullfilled this requirement and in both cases it worked. so far i did not see an example that didn't work.

from the other thread:

Iowa (A) class Cruiser    10,000 tons     267 Crew     1454 BP      TCS 200  TH 720  EM 0
3600 km/s     Armour 5-41     Shields 0-0     Sensors 1/1/0/0     Damage Control Rating 5     PPV 53.46
Maint Life 2.52 Years     MSP 500    AFR 145%    IFR 2%    1YR 110    5YR 1646    Max Repair 120 MSP
Intended Deployment Time: 9 months    Flight Crew Berths 26    
Hangar Deck Capacity 1000 tons     Magazine 150    

240 EP (HS20) Ion Drive (3)    Power 240    Fuel Use 48%    Signature 240    Exp 10%
Fuel Capacity 400,000 Litres    Range 15.0 billion km   (48 days at full power)

Iowa (B3) class Cruiser    10,850 tons     274 Crew     1433.13 BP      TCS 217  TH 796  EM 0
3668 km/s     Armour 5-43     Shields 0-0     Sensors 1/1/0/0     Damage Control Rating 6     PPV 53.46
Maint Life 2.53 Years     MSP 495    AFR 156%    IFR 2.2%    1YR 108    5YR 1613    Max Repair 112.71 MSP
Intended Deployment Time: 9 months    Flight Crew Berths 26    
Hangar Deck Capacity 1000 tons     Magazine 150  

265.2 EP (HS26) Ion Drive (3)    Power 265.2    Fuel Use 29.57%    Signature 265.2    Exp 8%
Fuel Capacity 270,000 Litres    Range 15.1 billion km   (47 days at full power)

[Jorgen_CAB]

*sigh* i thought we had covered that already... higher power engines you do NOT give you additional mission tonnage for the same cost. they make your ships more expensive. the only benefit of higher

High powered engines do not scale in cost as low powered engines does. So if you increase the power mod from 1 to say 1.25 but still use the same total power output you get less engines tonnage for the same cost, so now you can add more mission tonnage to compensate or just get a slightly smaller ship with higher speed if you prefer that. That is what I meant with that comment. Yes, a warship with a 0.85 power setting will be a few % cheaper and use less fuel but will also be slower given the same tonnage ships.

Your biggest problem is that you keep increase the size of the ship and still want to compare them, but then you MUST be able to redesign all other ships to be able to meet that tonnage as well. So, you can only compare ships with the SAME tonnage. My examples were good examples to show that the ship would become bloated and not legal for comparison...

I agree that lower powered engines on commercial ships is always wanted if fuel and build economy is all that matters to you. But in a real setting speed can actually also be important even in a freighter, but perhaps only on a few. Sometimes it is more important to get some place first than it is to do it efficiently.

I don't see how the current system is flawed because more research heavy technology is clearly better then easier technology. I refer to the power settings of commercial engines now, on military ships it's not the same as we have proved to you over and over.

Don't argue that you can just increase the size of the ship to get something "better", that is not true... all designs MUST (again) be compared with the same tonnage. If you have Naval Yards/maintenance facilities for 10.000t you can't build ships that are bigger than that. Doing something else will need a change on overall doctrine change. The same go for smaller ships. If you have five 6000t Naval Yards all with 12 slipways and most of your outer colonies have 6000t maintenance facilities to accommodate smaller destroyer squadrons. You can't just expand them with a few hundred tons on a whim, and even if you did you now can produce ANY kind if design using that tonnage, so now you can pack more high powered engines in there to make the ship even faster if you like.
The two ships you just showed that I did is a good example of two designs that are in practice impossible to compare if you are relegated to 10.000t naval yards.

Please present two 10.000t ships where a low powered engine with an *.85 powered engine is as fast as a *1 engine design (say 25% total tonnage engine) and the same mission tonnage with a mission range of around 10-20b km and using starting technology from a 500m people start. I think that is a good strategy for comparison where most people will have full understanding of the numbers involved.

[Haji]

*sigh* i thought we had covered that already... higher power engines you do NOT give you additional mission tonnage for the same cost. they make your ships more expensive. the only benefit of higher power engines is a small reduction in total ship size.

It really depends on what you mean "small reduction". Rather than using some made up test designs, I have tried to replicate the results on ships I actually used in my previous campaign, which were generally larger than those shown here (20 000T  - 70 000T) and any attempt to use less powerful engines usually resulted in a massive increase in size even if the costs remained lower.

But that actually doesn't matter. For all instances and purposes the entire discussion is meaningless, because our two sides are discussing things from entirely different perspective. You're just concerned with the cost vs speed ratio, completely disregarding any role-playing. Me and other people don't care about those numbers - we only care how it fits within the framework of our stories. If we were to compere this discussion to apples, you would argue that apples are healthy while we would argue that they're tasty. We're talking about two completely different things from completely different points of view.

That does not mean we're right of course - but I think we have the ultimate arbiter on our side, namely the creator of Aurora. Why? Because Steve always role-plays his campaigns, which means that the ability to put a ship into production now (which means size restrictions) rather than after the next round of shipyard expansion is very important. Go ahead and read his NATO vs. Soviets campaign to see how putting a ship into service now, even if the ship will be scrapped in six months due to being useless, can have an enormous impact for strategic balance between powers. (The link to the campaign is: http://aurora2.pentarch.org/index.php/board,112.0.html)

Long story short you're right that you can decrease the cost of a ship by putting a lower powered engine with the only drawback being larger size (although I'm not sure this holds true for larger vessels), but the thing is no one cares because in our role playing games everything works fine. If you want us to agree with you than you have to show us that the cost per mission tonnage (total ship cost/total tonnage of the armament) decreases if we use lower powered engines within the ship of the same size. Otherwise you're basically talking to a wall, and in this particular case I have no problem being considered a brick.

[Jorgen_CAB]

Long story short you're right that you can decrease the cost of a ship by putting a lower powered engine with the only drawback being larger size (although I'm not sure this holds true for larger vessels), but the thing is no one cares because in our role playing games everything works fine. If you want us to agree with you than you have to show us that the cost per mission tonnage (total ship cost/total tonnage of the armament) decreases if we use lower powered engines within the ship of the same size. Otherwise you're basically talking to a wall, and in this particular case I have no problem being considered a brick.

Yes, this is what I have been trying to say but perhaps in not as good words...


However... I might still agree with letsdance that I would in many instances favour better economy for some reduced tactical flexibility... here is a good example.

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Resolution Type-A class Missile Destroyer    10,000 tons     275 Crew     1357 BP      TCS 200  TH 600  EM 0
3000 km/s     Armour 3-41     Shields 0-0     Sensors 8/16/0/0     Damage Control Rating 5     PPV 48
Maint Life 2.58 Years     MSP 424    AFR 160%    IFR 2.2%    1YR 90    5YR 1345    Max Repair 150 MSP
Intended Deployment Time: 9 months    Flight Crew Berths 8    
Hangar Deck Capacity 250 tons     Magazine 736    

300 EP (HS25) Ion Drive (2)    Power 300    Fuel Use 52.5%    Signature 300    Exp 10%
Fuel Capacity 400,000 Litres    Range 13.7 billion km   (52 days at full power)

Size 4 Missile Launcher (12)    Missile Size 4    Rate of Fire 40
Missile Fire Control FC69-R100 (2)     Range 69.1m km    Resolution 100
Size 4 Anti-ship Missile (206)  Speed: 24,000 km/s   End: 43.3m    Range: 62.3m km   WH: 6    Size: 4    TH: 104/62/31

Active Search Sensor MR64-R100 (1)     GPS 8000     Range 64.0m km    Resolution 100
Thermal Sensor TH1-8 (1)     Sensitivity 8     Detect Sig Strength 1000:  8m km
EM Detection Sensor EM2-16 (1)     Sensitivity 16     Detect Sig Strength 1000:  16m km

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Resolution Type-B class Missile Destroyer    10,000 tons     270 Crew     1233.58 BP      TCS 200  TH 595  EM 0
2975 km/s     Armour 3-41     Shields 0-0     Sensors 8/16/0/0     Damage Control Rating 5     PPV 48
Maint Life 2.57 Years     MSP 405    AFR 152%    IFR 2.1%    1YR 86    5YR 1292    Max Repair 119.04 MSP
Intended Deployment Time: 9 months    Flight Crew Berths 8    
Hangar Deck Capacity 250 tons     Magazine 592    

297.6 EP (HS31) Ion Drive (2)    Power 297.6    Fuel Use 27.65%    Signature 297.6    Exp 8%
Fuel Capacity 210,000 Litres    Range 13.7 billion km   (53 days at full power)

Size 4 Missile Launcher (12)    Missile Size 4    Rate of Fire 40
Missile Fire Control FC69-R100 (2)     Range 69.1m km    Resolution 100
Size 4 Anti-ship Missile (206)  Speed: 24,000 km/s   End: 43.3m    Range: 62.3m km   WH: 6    Size: 4    TH: 104/62/31

Active Search Sensor MR64-R100 (1)     GPS 8000     Range 64.0m km    Resolution 100
Thermal Sensor TH1-8 (1)     Sensitivity 8     Detect Sig Strength 1000:  8m km
EM Detection Sensor EM2-16 (1)     Sensitivity 16     Detect Sig Strength 1000:  16m km
Type-A
* Take 2.2 (2.0) years to build (-)
* Burn almost twice the amount of fuel (-)
* Can shoot 15(12) salvoes of missiles (+)

Type-B
* Take 2.0 (2.2) years to build (+)
* Burn almost half the amount of fuel (+)
* Can shoot 12(15) salvoes of missiles (-)

In essence the cost is 90BP per missile salvo on Type-A and 102BP on type-B. 26000 litre of mission fuel per missile salvo on Type-A and 17500 litre on Type-B. If that help anyone...

If you then would like to lower the BP per missile salvo fired (or volume of each salvo) you can increase the power of the engines and fit smaller engines and gain mission tonnage but seriously increase mission fuel usage per missile fired in combat.

I would probably go for Type-B since I value economy over fire-power in this instance. But in order to get the same fire-power I need more resources and time. As time go by and your engines get more and more fuel efficient it will get less and less incentive to use extra fuel efficient engines since you are going to use much less space on your ship for fuel. At this early stage you are still using relatively large mass for fuel and even at relatively short ship mission ranges fuel efficient engines are economically very strong.

If you take the same ships with just two levels more of fuel economy you will just start loosing too much mission space for such engines to be interesting, unless you are prepared to compromise your speed as well. Personally I choose slight speed reduction on larger ships to get more mission tonnage and cheaper ships that are also faster/cheaper to retrofit.

[letsdance (OP)]

@Haji: if you just care about roleplaying, there is no sense in discussing game mechanics. but then you shouldn't care either way. seeing how much thought Steve puts into mechanics, i do think it matters to him.

@Jorgen_CAB since design B is 10 % cheaper, we assume we have 10 % more of it. that means i can fire 10 % more missiles for the first 12 volleys. then i'll run out, while you still have 3 volleys with your design A. but your whole advantage of more volleys is gone, because you already lost at least 10 % more ships than i did, reducing your total number of missiles - if you lose just 10 % of your missile load you're at the same total number of missiles that i had. the higher damage per time is a big advantage that you did not consider at all.

if you don't want to calculate 10 % more ships, you'd have to take into account the timing advantage. i destroy your planet while you still have 0.2 years left to build your fleet... that's not calculable of course, but the above example with higher ship number is.