This is a cut and paste from a formula by Shamen Riel Krall posted at portmaw when it was operational:
(Maybe something is of interest)
Hi everybody,
I found the smotherman formula, but some things annoyed me. The first one is that any weapon (weapon batery, lance etc) was the same price firing only one arc or three...
The second was the standard deviation* of this formula, and errors that can occurs (around 30 points on a cruiser for devastation, styx and gothic...).
So I tried to put my mathematical abilities on it, and, with an excell sheet, I worked on an amelioration of the well-known smothemran formula.
I made it for light cruisers, cruisers and heavy cruisers/battlecruisers of the imperial and chaos fleets (rules book and armada), and so I can't say anything for battleships and grand cruisers, excepts that it worked for the despoiler class and the emperor** class when I wanted to verify it (I had less than one point of error).
The formula that I will propose you has a maximal error of 8 points, is sometimes less effective than the smotherman formula (on 19 ships, the smotherman formula is better on 6 ships, 12 for my variation, and one ship is equall for the two).
Firstly the arcs modifiers:
For weapons batteries:
30 cm times 1+0,1 by fire arc after the first.
45 cm times 1+0,25 by fire arc after the first.
60 cm times 1+0,4 by fire arc after the first.
For lances:
30 cm times 1+0,25 by fire arc after the first.
45 cm times 1+0,35 by fire arc after the first.
60 cm times 1+0,45 by fire arc after the first.
Costs:
For weapons batteries:
30 cm 1,875 pts per point of firepower. (22,5/12)
45 cm 3,0729 pts per points of firepower. (36,875/12)
60 cm 3,58 pts per point of firepower. (43/12)
For lances batteries:
30 cm 5,625 pts per point of strength (22,5/4)
45 cm 9,21875 pts per point of strength (36,875/4)
60 cm 10,3021 pts per point of strength (123,625/12)
For launch bays:
without assalt boats 12,375 pts per point of strength.
with assault boats 12, 875 pts per point of strength.
(I tried to fit with the fact tha t an emperor or an oberon will pay 5 pts to switch the kind)
Special: The 5th and the 6th launch bays counts as two, it works with it, maybe it's besause of the fact that with only one reload special order we have more effect...
For torpedoes:
2,8125 pts per point of strength. (22,5/8)
For Nova-canon:
384,38 pts. (275/8)
(I tried to fit with the extra cost of +20 pts when a lunar or a tyrant switches its 6 strength torpedoes by a Nova-canon for +20 pts. But the mars and the dominator would have liked to have it cheaper.)
Hull:
Hit points: 2,5 points each.
Shields: 10 pts each.
Turrets: 10 pts each.
5 armor: 10 pts.
6+ prow: 38 pts.
Virage: 5 pts for 45°, 10 pts for 90° (I think this one should be light cruisers only).
Speed: 1 pt per 5 cm.
+1D6 cm AAF: 18 pts.
+1 on boarding actions: 18,75 pts.
(It was made to represent the endeavour, endurance and defiant classes, on the other hand, to fit with my method, I was forced to estimate it at 20 pts in the smotherman formula, to minimize the quadratic average error and avoid that this error had a big impact on the result. CHAOS CRUISERS DON'T PAY FOR IT, it represents the corridor of these three ships, not a fleet special rule)
As you can see I also tried to fit with options, as the +1 turret for +10 pts of tre overlord, th +20 pts for switching stength 6 torpedoes by a Nova-canon etc... (And the Despoiler with its torpedoes option will not fit, making me think that maybe having torpedoes AND launch bays was payable, as the fact of having "too many" launch bays).
And, in order to be very impressive, the "standard deviation" with the smotherman formula is around 12,79 pts, for my version only 3,89 pts, I only have 4 ships with an error worst than 5 pts, against 10 for the smotherman formula (and I repeat that it was only on 19 ships) and no ship worst than a 10 points error with my variation.
I Think I've not forgotten anything, so if you wnat to comment it I'll be glad.
Thank's for reading me.
* Trully it's not exactly the standard deviation, but the quadratic average error, but with an error on average equal to 0 it become a good estimator of it. If you don't know, the standard deviation gives an idea of how the repartition is made. A little standard deviation means that all the ships have an error really comparable to the average error, meanning that there is a constant error easily repaired; but a high standard deviation means generally that there is a lot of variation on this error. For example, with marks between 0 and 20, the highest standard deviation will be 10, meaning that half the marks are 0 and the other half 20; the lowest, 0, means that all the marks are equall.
The quadratic average error has two intersts, as I said it can easily become a good estimator of the standard deviation, but it also include the average error, meaning that I just had to minimize it.
** In this two cases the formula I propose you was better; I'm just disturbed by the fact that the emperor don't have to pay for his +1Ld. The same way the chaos ships don't pay for their +1 bonus against boarding actions...
(end of quote)