Author Topic: Railgun point defence - some clarification required.  (Read 1168 times)

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Offline Lossmar

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Railgun point defence - some clarification required.
« on: March 25, 2016, 04:05:32 PM »
Its been bugging for a loooong time.

I know that railgun fires four "rounds" per shot.
What i dont know is : when those shots target the missile salvo do they all target one missile ? Or do they target up to four missiles ?

Example :

Ship A is armed with one railgun set to final defence. This ship is a target of a four missile salvo. Does this ship have four chances of destroying ONE missile or one chance to destroy each of the four missiles thus annihilating the entire salvo ?

Feel free to move this to mechanics subforum if you feel it belongs there or just lock and point me in the general direction of the answer :P
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Offline firsal

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Re: Railgun point defence - some clarification required.
« Reply #1 on: March 25, 2016, 09:59:59 PM »
Each fire control targets one salvo at a time. Thus, if a reason is linked to a fire control, then the railgun will fire four shots at the salvo which may hit up to four incoming missiles.

So, theoretically, a railgun can take out four incoming missiles in a salvo. I suppose that each of the four shots gets one chance at hitting its mark.
 

Offline baconholic

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Re: Railgun point defence - some clarification required.
« Reply #2 on: March 26, 2016, 12:51:32 AM »
Each railgun can target up to 4 missiles, so if you have a FAC with 3 railguns, it can take out up to 12 missiles.

Railgun is the cheapest and "best"-ish PD weapon in the game, provided you have enough gallicite to strap enough engines to your railgun ships.
 

Online Iranon

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Re: Railgun point defence - some clarification required.
« Reply #3 on: March 26, 2016, 04:38:34 AM »
That's one good use of them. You can get 2 railguns for a turreted Gauss barrel with a little left over.  So when your ship goes 50% faster tan your fire control speed, you're slightly ahead of R3 Gauss turrets, at twice the FC speed you're ahead of R4 Gauss turrets. You'll also have a relative advantage when fighting ships.

I've recently come to appreciate railguns for some slower ships too. Inferior to Gauss by volume, but may be competitive by virtue of being cheap.
 

Offline Lossmar

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Re: Railgun point defence - some clarification required.
« Reply #4 on: March 26, 2016, 04:57:17 AM »
Quote
Each railgun can target up to 4 missiles, so if you have a FAC with 3 railguns, it can take out up to 12 missiles.
Ok thats what i meant to know. Thanks.
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Offline TMaekler

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Re: Railgun point defence - some clarification required.
« Reply #5 on: March 26, 2016, 08:48:25 AM »
So when your ship goes 50% faster tan your fire control speed, you're slightly ahead of R3 Gauss turrets, at twice the FC speed you're ahead of R4 Gauss turrets. You'll also have a relative advantage when fighting ships.

 ??? Not sure I am getting what the advantage is your are talking about. Are you saying that the speed of your ship is added to the speed of the gun, making the shot faster and thereby similar to higher Tech Speeds?
 

Online Iranon

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Re: Railgun point defence - some clarification required.
« Reply #6 on: March 26, 2016, 09:30:13 AM »
First sentence:
a Gauss barrel in an efficient maximum-tracking-speed turret takes up slightly less than 8HS. We could fit 2 10cm railguns and their power plants on that with a bit left over. Bigger fire controls for Gauss and larger crews for Railguns don't change anything major about this.
So on slightly less weight for the railgun implementation we have

(Gauss RoF) shots at 4x tracking speed
versus
8 railgun shots at (actual/base)x tracking speed.

For the same number of expected hits, the railgun ship would have to be 1.5x as fast as the basic fire control speed tech to match R3 Gauss cannons, 2x to match R4 Gauss cannons and so on.

*

Second sentence: So far, I've assumed we are engaging missiles that go faster than even our best fire control speed can handle. If that is not the case, the railgun implementation gets a relative advantage. Against ships slower than ours, either weapon would have the same chance to hit, and in the above example the railgun ship would simply have 8 shots instead of 3, for 2.5x the effective firepower.
 
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Offline byron

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Re: Railgun point defence - some clarification required.
« Reply #7 on: March 28, 2016, 09:33:01 AM »
My concern with this math is that, IIRC, the tracking speed for fixed weapons is based on the ship's actual speed, not its possible top speed.  This is an important distinction.  Unless I want all of my ships to have the same top speed (and 2x tracking speed is quite fast if you've distributed your research relatively evenly), I can't put my railgun escorts in the same TG as my other ships without compromising their effectiveness.  A gauss turret, on the other hand, works regardless of what it's mounted on, or what else is in the TG.  The reduction in operational overhead alone is enough to keep me using gauss turrets at higher tech levels.
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Offline 83athom

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Re: Railgun point defence - some clarification required.
« Reply #8 on: March 28, 2016, 09:44:19 AM »
Also keep in mind that instead of one barrel firing 4 shots an increment (tech = to railgun shot amount for argument), you can have 4 barrels each 0.25 the size that can then fire and possibly shoot down 16 missiles an increment. I know that is unlikely because of the math of the chances (can also be said of the chances of all 8 10cm shells landing), but it still is possible. And because it is in a turret, the tracking isn't speed dependent. Lets do more math, Max size gauss is 6HS, so 0.25 size would be 1.5HS per barrel. That size gauss exists in game and has 25% hit per shot. However, the smalles gauss in game is 0.5HS, 1/3 the size. Lets fit minimum size gauss into turrets and we get 3x the fire rate of the 16 shots (assuming the mass of all the turrets combined equaled with amount of barrels increased) getting a possible 48 missiles hit and destroyed in an increment. But again, the math is against this happening too often, but it will eventually.
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Offline byron

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Re: Railgun point defence - some clarification required.
« Reply #9 on: March 28, 2016, 09:58:07 AM »
Also keep in mind that instead of one barrel firing 4 shots an increment (tech = to railgun shot amount for argument), you can have 4 barrels each 0.25 the size that can then fire and possibly shoot down 16 missiles an increment. I know that is unlikely because of the math of the chances (can also be said of the chances of all 8 10cm shells landing), but it still is possible. And because it is in a turret, the tracking isn't speed dependent. Lets do more math, Max size gauss is 6HS, so 0.25 size would be 1.5HS per barrel. That size gauss exists in game and has 25% hit per shot. However, the smalles gauss in game is 0.5HS, 1/3 the size. Lets fit minimum size gauss into turrets and we get 3x the fire rate of the 16 shots (assuming the mass of all the turrets combined equaled with amount of barrels increased) getting a possible 48 missiles hit and destroyed in an increment. But again, the math is against this happening too often, but it will eventually.
Uhhhh.....
The accuracy of gauss weapons scales directly with size, so there's no gain in terms of average missiles destroyed so long as the to-hit chance of your system with a full-sized cannon is below 100%.  And the gains there are going to be marginal at best.  If you have a crew training of 20% and a FC to-hit of 90% (which means an FC range of 100kkm for point fire), then the effective to-hit will be 108%.  This requires a very big FC system (not worth it) or very high tech and a very well-trained crew to gain 8% over standard-sized cannons.  The only real advantage of reduced-size gauss cannons is the ability to cram them into places where full-sized ones won't fit.
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Offline 83athom

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Re: Railgun point defence - some clarification required.
« Reply #10 on: March 28, 2016, 11:02:49 AM »
Wow, 1HS is very big and not worth it, thank you. (Why are you using 4x range 4x Speed for PD instead of 1x range 4x speed or even 0.5x range 4x speed?)
Reread what I said. "getting a possible 48 missiles hit" "I know that is unlikely because of the math of the chances". Yes I know the average missiles hit will NOT change, however, going from 8 shots to 48 on its own has its own advantages because of the POSSIBLE hits. That is why many modern CIWS use Gatling style weapons for volume of fire over accuracy (Goalkeeper, Phalanx, AK630, etc). However, I will concede that there are CIWS that fire slower (such as Dardo and Millennium) for a larger effect per shot which would equate to railgun point defense.
« Last Edit: March 28, 2016, 11:28:45 AM by 83athom »
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Offline byron

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Re: Railgun point defence - some clarification required.
« Reply #11 on: March 28, 2016, 12:24:51 PM »
Wow, 1HS is very big and not worth it, thank you. (Why are you using 4x range 4x Speed for PD instead of 1x range 4x speed or even 0.5x range 4x speed?)
I'm not.  I was pointing out that the only time when the math works in favor of smaller gauss cannons was when your hit percentage was already over 100, and that that required big fire controls.  Which are stupid.

Quote
Reread what I said. "getting a possible 48 missiles hit" "I know that is unlikely because of the math of the chances". Yes I know the average missiles hit will NOT change, however, going from 8 shots to 48 on its own has its own advantages because of the POSSIBLE hits.
No, for two reasons.  First, because analyzing this based on the maximum possible number of hits is very, very wrong.  It's like analyzing the payoff from the lottery on the basis you'll win.  You will do better in the long run by looking at expected value.
Second, the math doesn't back you up at all.  I decided to do this properly, and used a binomial distribution to compare an 8-shot turret with a 50% hit chance with a 48-shot turret with an 8.333% hit chance.  I will admit that I expected the distribution for the 48-shot case to be much more sharply peaked around 4 hits, and it in fact was not.
I don't feel like re-creating the entire table.  If you wish to do it yourself, the excel binomdist function is pretty easy to use.  So I'll just give the highlights. The 48-shot weapon is much flatter.  For instance, it has a 1.5% chance of no hits, as opposed to a 0.4% chance for the 8-shot case.  42.5% of 48-shots will have 3 or fewer hits, as opposed to 36.3% of 8-shots.  If we raise our target to 4 or fewer shots, then it's 62.9% for the 48-shot and 63.7% for the 8-shot, a dead heat.  On the other hand, 4.3% of 48-shot cases will have 8 or more hits, as opposed to .4% for 8-shots.  (Just to clear up any confusion, the chances of 9 or more hits is 1.6% and 10 or more will only occur 0.6% of the time.  The cumulative chance drops below 0.1% for 12 or more hits.)
Oh, and the chances of 48 missiles getting hit?  1.58E-52. 

Quote
That is why many modern CIWS use Gatling style weapons for volume of fire over accuracy (Goalkeeper, Phalanx, AK630, etc). However, I will concede that there are CIWS that fire slower (such as Dardo and Millennium) for a larger effect per shot which would equate to railgun point defense.
That's not right on several levels.  First, that's not how CIWS works.  They don't just randomly spray bullets in the path of the missile.  They actually use a very sophisticated closed-loop guidance system to bring the bullets and the missile together.  DARDO and Millennium are designed to deal with faster missiles, which need to be killed further out to keep debris from the missile from hitting the ship.  Second, the analogy to railguns is wrong.  Railguns work by throwing up more rounds at lower accuracy when compared to full-sized gauss cannons.  Going to a smaller gauss cannon doesn't change these numbers significantly, and is basically a red herring.  If anything, you could say that Phalanx and its ilk are more like railguns, although the entire analogy is not a very good one.  Aurora weapons are not modern naval ones.

Personally, I'd rather have the 8-shot configuration.  The one thing I most want in a missile defense system is consistency.  Something which always takes out 4 missiles is better than something the same size which gets 10 50% of the time, and 0 50% of the time.  (Assuming that I'm only allowed to mount one, that is.) 
« Last Edit: March 28, 2016, 12:31:15 PM by byron »
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Online Iranon

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Re: Railgun point defence - some clarification required.
« Reply #12 on: March 28, 2016, 02:27:59 PM »
My concern with this math is that, IIRC, the tracking speed for fixed weapons is based on the ship's actual speed, not its possible top speed.  This is an important distinction.  Unless I want all of my ships to have the same top speed (and 2x tracking speed is quite fast if you've distributed your research relatively evenly), I can't put my railgun escorts in the same TG as my other ships without compromising their effectiveness.  A gauss turret, on the other hand, works regardless of what it's mounted on, or what else is in the TG.  The reduction in operational overhead alone is enough to keep me using gauss turrets at higher tech levels.

From my experience, the speed used is the speed of the task group, not the actual speed at which ships move. Same for Thermal signature and ability to evade shots.
When my slow railgun corvettes were followed by fast ships also sporting railguns, the latter had correspondingly better hit chances against missiles.

That said: Speed+Railgun synergy means we sacrifice less for speed, not that we get it as a freebie. Need the speed, to escort fast ships or for strategic/tactical flexibility? Not sure you need it, but figure it's worth a modest sacrifice? Go ahead.
But if your requirements call for a slow efficient escort, build a slow efficient escort. My maths assumed we're just haggling about the weapons, if the Gauss implementation could get by on half the engine power it's no contest.
 

Offline byron

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Re: Railgun point defence - some clarification required.
« Reply #13 on: March 28, 2016, 03:01:35 PM »
From my experience, the speed used is the speed of the task group, not the actual speed at which ships move. Same for Thermal signature and ability to evade shots.
When my slow railgun corvettes were followed by fast ships also sporting railguns, the latter had correspondingly better hit chances against missiles.
That was what I was getting at.  The extra mental overhead is not something I'm fond of.

Quote
That said: Speed+Railgun synergy means we sacrifice less for speed, not that we get it as a freebie. Need the speed, to escort fast ships or for strategic/tactical flexibility? Not sure you need it, but figure it's worth a modest sacrifice? Go ahead.
But if your requirements call for a slow efficient escort, build a slow efficient escort. My maths assumed we're just haggling about the weapons, if the Gauss implementation could get by on half the engine power it's no contest.
An excellent point.  We can't neglect the extra speed necessary to make railguns work when we compare them to gauss weapons, even neglecting the micromanagement overhead.
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