[FT] Coilguns

A few months ago, during one of the many "What should we do about the
Kra'vak?" discussions, I posted an idea for a variant Railgun design. Now that
I have finally had a chance to sit down and do some work upon it, here it is
again:

(I will likely be using it for an entirely new race of Aliens, and for a

few human ships, but it could also be employed as another weapon for the

Kra'Vak, supplementing the already existing Railguns.)

COILGUNS:

A Coilgun uses a series of electromagnetic coils to accelerate a piece of iron
or steel down a tube. It is similar, in both function and effect, to a
Railgun, but has no moving parts and is, overall, the more efficient design
(at least according to what *I've* been reading). The Coilgun fires a single
very large projectile at very high speeds (Yes, the "Shotgun" approach makes a
lot more sense. This *looks* cooler, though.), and is capable of doing a
tremendous amount of damage to a target. That's the good news.

The bad news is that hitting one piece of metal--even one the size of a
Carrier--with another piece of metal at the distances and velocities
common to Full Thrust is not easy. It's not impossible, but as a general rule
it is a lot easier to hit a close target than it is to hit a distant one
(although Coilgun ranges are, theoretically, unlimited).

MECHANICS:

The firer must roll higher than the range to the target on 4d6, rerolling all
sixes. If this results in a hit, roll a number of d6 equal to the class of the
weapon (again, rerolling sixes) and total the results to determine damage.
Points equal to the class of the weapon are applied to the target's armor; all
remaining damage (if any) is applied directly to the hull. Screens have no
effect upon Coilguns;
Kra'Vak armor subtracts one point/level from each die rolled.

Example: The HMS "Plot Device" is firing a Class III Coilgun at

the KRS "Convenient Example". The "Convenient Example" is 16 inches away. The
"Plot Device" rolls 4d6, for a total of 19 including rerolls. The target
having been hit, the "Plot Device" then rolls 3d6 for damage, resulting in 18
points of damage (again including rerolls). 3 of these points are applied to
the armor of "Convenient Example", and the remaining 15 are applied to the
hull. The "Convenient Example" then explodes, taking a large piece of the SFX
budget with it.

As already noted, it is not easy to hit a target with a Coilgun. Because of
the amount of processing power this requires, all Human ships

must have a dedicated Firecon linked to each of their Coilguns. If this

dedicated Firecon is lost, the gun can no longer fire. Kra'vak ships can link
up to THREE Coilguns to a single Firecon, but all guns linked in this fashion
must fire at the same target. (Links should be indicated on the SSD by a
dotted line joining the guns to their Firecon.)

Weapon Mass Point Cost Class I Coilgun: 3 10

Class II Coilgun: 6 15 Class III Coilgun: 9 25 Class IV Coilgun: 12 40

Coilguns are limited to a single Fire Arc, and this cannot be improved.

			     *****
I am not sure about the Mass or Point costs yet. Playtesting is, obviously,
required. Should they be able to fire through multiple arcs?

I like making the KV depend on their manueverability myself, but YMMV. The
dedicated Firecons are there strictly as a balancing effect, and to prevent
Capital ships from mounting 30 or 40 Class I Coilguns.

All right, I'm ready...you may fire at will!

In a message dated 99-03-13 09:39:13 EST, you write:

<< A Coilgun uses a series of electromagnetic coils to accelerate a piece of
iron or steel down a tube. It is similar, in both function and effect, to a
Railgun, but has no moving parts and is, overall, the more

efficient design (at least according to what *I've* been reading). The

Coilgun fires a single very large projectile at very high speeds (Yes, the
"Shotgun" approach makes a lot more sense. This *looks* cooler, though.), and
is capable of doing a tremendous amount of damage to a target. That's the good
news. >> You can also use sea water (nice ground based def) or plasma (think
the mass drivers from B5) as the armature. A Coilgun (which is what I bet Jon
had in mind when he wrote the Railgun rules, but Rail Gun or Gauss Cannon
seems to be the popular term).
-Stephen

> << A Coilgun uses a series of electromagnetic coils to accelerate a
The
> Coilgun fires a single very large projectile at very high speeds (Yes,

A) Why not just use a railgun? It's the same thing, ie, an electromagnetically
accelerated object to punch holes in ships. Exactly how it accelerates the
object is just the PSB (or Scientific Babble, at this rate, getting past the
Pseudo point). B) I'd assume the rods have some kind of terminal homing.
Otherwise the
chances of hitting anything as small as a ship--even if it's not
maneuvering--are negligable, unless you assume a ridiculously short
range.

> At 08:17 AM 3/14/99 -0500, you wrote:
The
> Coilgun fires a single very large projectile at very high speeds
Exactly how
> it accelerates the object is just the PSB (or Scientific Babble, at

Because it's an entirely different (and somewhat more spectacular, in my
humble opinion) weapon, and a new name seemed to be warrented in order to
avoid confusion. It was originally designed as a set of variant Railgun rules,
so Coilgun was an appropriate name.

> B) I'd assume the rods have some kind of terminal homing. Otherwise

Short range is a pretty relative term in FT, isn't it? There would have to be
some sort of guidance if you wanted to hit anything at all, just as with the
standard Railguns, but I didn't think that it needed any additional rules or
explication. The important thing, in game terms at least, is to fire it in
approximately the right direction.

The thing about rail guns or coil guns or whatever is not to mount them in
turrets and throw large ferrite rocks. The way to use it best is to put it in
a spinal mount running the length of the ship so acceleration is maximized.
Then, throw a knitting needle size projectile at 30 or 40% the speed of light.
Now you do not need a large bore (if you want to figure the energy conversion,
go ahead  ((e=mc squared+.4). Also at the very high speed targeting is
much simpler and no terminal guidance is neccesary. Use what the technology
promises in the long run for a science fiction game that postulates star
travel.

> DracSpy wrote:

> A Coilgun (which is what I bet Jon had in

Those recent (1998) unclassified weapon research papers I've seen on
EM-launched kinetic projectiles talk exclusively about railguns - no
coilgun discussion at all. 'Course, it *could* all be classified, but
that doesn't seem too likely considering the front-line nature of the
*un*classified stuff <g>

Later,

> John C wrote:

[snip]

> The bad news is that hitting one piece of metal--even one the size of

This gives a higher hit probability for the coilgun than for the
"shotgun-style" KV railguns or Human pulse torps out to range 16, and
at range 19. At range 17-18 and 20-30 the railgun hit ratio is better.

> Weapon Mass Point Cost

> Class II Coilgun: 6 15

Hm. Why are Classes II and III so much less expensive per Mass (and per
damage) than Classes I and IV?

> I am not sure about the Mass or Point costs yet.

Too low IMO - both of them. As written here, the Coilguns out-damage
Pulse Torpedoes (on a per-Mass basis) by at least 45-75% at ranges of
15 or less; the only ranges where the Pulse Torpedoes are actually
better are ranges 23-24 and 27-30.

They also out-damage Class-2 beam batteries out to range 20 and Class-3
beam batteries out to range 22 and then again at range 25-26... and
this is against *unscreened* targets.

I can post a table with the average damage per Class at each range (up
'til 42) tomorrow if you like. I only included 3 re-rolls in the
calculation, but any extras add at best 0.0001% to the hit numbers :-/

Regards,

> John C wrote:

I was hoping that the really limited arcs (and the requirment of dedicated
Firecons) would help offset this. Alternatively, dropping the

range dice to 3 would lower the effective range by a bit. When this was

discussed earlier, most people seemed to feel that the resulting range
would be much too low--my experience with FT involves a lot of combat at

short range, though, so I didn't see this as a problem. For my part,
I'd prefer short range--it would even things out a bit for the humans.

> Weapon Mass Point Cost

My mathematical skills are largely limited to the Dewey Decimal system
at this point; the above point/mass costs just seemed to fit.  I wanted
to keep the Class I small enough that an escort sized ship could manage to
mount one or two, and the progressive steps kinda fell into place.

> I am not sure about the Mass or Point costs yet.

Yeah, that's what I thought. The simple, dirty truth of the matter is this: I
like the mechanic, and I wanted to find some way to use it. And, for some
reason, my vision of the Kra'Vak includes weapons that do a LOT of damage. You
can probably blame the "Aliens Colonial Marines
Technical Manual" for that--it makes Railgun hits sound REALLY nasty, as

well as astronomically unlikely.

> They also out-damage Class-2 beam batteries out to range 20 and Class-3

I'd deeply appreciate that. I know that the average damage for the beam

batteries was posted not too long ago--could someone send me that data
too, so I have a basis for comparison?

Thanks,

> John C wrote:

> >This gives a higher hit probability for the coilgun than for the

I had fortunately mis-read you here. Should be "higher hit prob. out to
range 15" - having to roll >range rather than >= makes a difference.
Not that big a difference, though :-(

> I was hoping that the really limited arcs (and the requirment of

As I understood it, the firearc was 1 normal arc wide, which is the same as
for Pulse Torps. The dedicated FC helps, but only for Human
ships :-(

[snip]

> Yeah, that's what I thought. The simple, dirty truth of the matter

That's all right, as long as they pay the appropriate NPV cost for
it...

Here are the hit probabilities I calculated. "#D" means #D6 rolled to
hit; "+#Re" means I've included # re-rolls. The figures should be
reasonably accurate out to range 36 at least, but the higher ranges
should have slightly higher hit probabilities in the +#Re columns (and
the range is really infinite <g>). We're talking fractions of a% here, though.

Dunno what went wrong in the 3D column; it shouldn't be able to hit at all at
range 18. I was too hurried to check that properly.

Crossing fingers and hoping that the tables won't be *too* garbled in
transmission:

Hit probabilities for various Coilgun variants:
Range   4D+3Re  4D      3D+4Re 3D       Railgun/P-torp
1 1,000 1,000 1,000 1,000 0,833 2 1,000 1,000 1,000 1,000 0,833 3 1,000 1,000
0,995 0,995 0,833 4 0,999 0,999 0,981 0,981 0,833 5 0,996 0,996 0,954 0,954
0,833 6 0,988 0,988 0,907 0,907 0,833 7 0,974 0,973 0,838 0,838 0,667 8 0,947
0,946 0,755 0,741 0,667 9 0,907 0,903 0,664 0,625 0,667 10 0,854 0,841 0,574
0,505 0,667 11 0,790 0,761 0,491 0,380 0,667 12 0,719 0,664 0,421 0,264 0,667
13 0,647 0,556 0,359 0,167 0,500 14 0,577 0,444 0,303 0,097 0,500 15 0,510
0,336 0,254 0,051 0,500 16 0,448 0,239 0,210 0,023 0,500 17 0,390 0,159 0,171
0,009 0,500 18 0,337 0,097 0,140 0,005 0,500 19 0,288 0,054 0,114 0,000 0,333
20 0,245 0,027 0,093 0,000 0,333 21 0,207 0,012 0,076 0,000 0,333 22 0,174
0,004 0,061 0,000 0,333 23 0,147 0,001 0,048 0,000 0,333 24 0,123 0,000 0,037
0,000 0,333 25 0,102 0,000 0,029 0,000 0,167 26 0,084 0,000 0,023 0,000 0,167
27 0,069 0,000 0,018 0,000 0,167 28 0,057 0,000 0,015 0,000 0,167 29 0,046
0,000 0,011 0,000 0,167 30 0,036 0,000 0,009 0,000 0,167 31 0,028 0,000 0,007
0,000 0,000 32 0,021 0,000 0,005 0,000 0,000 33 0,014 0,000 0,004 0,000 0,000
34 0,009 0,000 0,003 0,000 0,000 35 0,006 0,000 0,002 0,000 0,000 36 0,003
0,000 0,001 0,000 0,000 37 0,002 0,000 0,001 0,000 0,000 38 0,001 0,000 0,000
0,000 0,000 39 0,001 0,000 0,000 0,000 0,000 40 0,001 0,000 0,000 0,000 0,000
41 0,001 0,000 0,000 0,000 0,000 42 0,000 0,000 0,000 0,000 0,000

Average damage/Class for the variant you posted - 'course, it is only
4.2 * the hit probability for the 4D+3Re variant above:

        Coilguns 4D6+Re
Range           Avg. Dmg/Class
1 4,200 2 4,200 3 4,200 4 4,197 5 4,184 6 4,151 7 4,090 8 3,976 9 3,808 10
3,585 11 3,317 12 3,020 13 2,718 14 2,422 15 2,141 16 1,880 17 1,639 18 1,414
19 1,210 20 1,029 21 0,869 22 0,732 23 0,616 24 0,515 25 0,428 26 0,354 27
0,291 28 0,238 29 0,193 30 0,153 31 0,117 32 0,086 33 0,060 34 0,039 35 0,024
36 0,014 37 0,009 38 0,006 39 0,004 40 0,004 41 0,004 42 0,004

And finally average damages/Mass for the FB1 weapons (except missiles):

Average damage/Mass for P-torps & SMP:
Range   P-torp(1)       P-torp(3)       Sub-Pack
0 - 6   0,729           0,486           2,400
6 - 12  0,583           0,389           1,600
12 -18  0,438           0,292           0,800
18 -24  0,292           0,194           0,000
24 -30  0,146           0,097           0,000
30 -36  0,000           0,000           0,000

Average damage/Mass for beams vs no screens:
Range   Class-1 Class-2(6) Class-3(1) Class-3(3) Class-3(6)
0 - 12  0,800           0,533       0,600       0,400      0,267
12 -24  0,000           0,267       0,400       0,267      0,178
24 -36  0,000           0,000       0,200       0,133      0,089

Average damage/Mass for beams vs Screen lvl-1:
Range   Class-1 Class-2(6) Class-3(1) Class-3(3) Class-3(6)
0 - 12  0,633   0,422       0,475       0,317      0,211
12 -24  0,000   0,211       0,317       0,211      0,141
24 -36  0,000   0,000       0,158       0,106      0,070

Average weapon/Mass for beams vs Screen lvl-2:
Range   Class-1 Class-2(6) Class-3(1) Class-3(3) Class-3(6)
0 -12   0,467           0,311      0,350        0,233      0,156
12 -24  0,000           0,156      0,233        0,156      0,104
24 -36  0,000           0,000      0,117        0,078      0,052

Later,