So I've been doing some math on Nova Cannons for the update. Nova cannon are widely regarded as sub-par or a very hit or miss weapon. Psychologically they are valuable, however in playtest a 'good' player would nearly always beat a NC based fleet.
Nova cannon tend to have a polarization among players, some consider them too powerful (at least in the past) others consider them worthless. With the potential to cripple a ship in one hit, this is an extreme psychological weapon, but good players understand that fearing the NC is the way to lose against it. A majority of players feel that NCs need limitations, primarily for fluff reasons, or they are angered when they face a fleet of half a dozen such weapons.
The weapon has seen a number of changes over the years, as rules writers never really could find an absolute balance with it. Since it is largely psychological, it is the Strategic Conclave's opinion that this produced bias in rules writing. Early in this project, as well as when our members were assisting the 2010 FAQ we tested a number of fleets against all NC lists. Out of 6 games, the non-NC fleet won, and usually by substantial margin. I played an Ork fleet against the NCs and managed a win, in fact the only loser was a Chaos fleet used by a 'timid' player.
The Imperial Navy has a large strategic advantage in torpedoes, and the NC breaks this, the weapon isn't usable at close range where the IN has most of its firepower. So for an additional expense, your fleet's strategy becomes based off an initial luck with NCs, and at close range (where the majority of firefights take place) you've lost a significant amount of effective equivalent firepower (6 torpedo shotgun).There are a few advantages, most notably the vessel does not have to Reload to keep up its firepower.
Problems with official rules: There are a number of problems with official rules, the most predominant is the fact that Nova Cannon are very radically different from normal direct fire weapons. Nova Cannon have no benefit from Lock On orders, and they are very inconsistent. However there is some math that can be applied here.
So assuming that a Nova Cannon has no chance of scattering and hitting another vessel, let us look only at the initial target and damage potential. The Nova Cannon template is 50cm in diameter, with a 12cm diameter central hole, small bases are 30cm in diameter and large are 50 respectively. Basically this means that if a NC placed centrally over a ship's stem scatters in any direction, the central hole will still land somewhere on the base if it only scatters 1-2cm for small bases, and 1-3cm for large bases. Some part of the template will land on the base if it only scatters 3-4cm for small, and 4-5cm for large.
Now we have three different 'bands' where a different number of scatter die are used, ranging from 1D6 to 3D6. Using probability, at each band the percentage of 'misses' that will still do damage are thus;
1D6: 33.3% hole still on part of the small base, 50% hole is still on part of the large. 33% some part of the template is on the base for either.
2D6: 2.8% hole for small, 8.3% for large, 13.9% part for small, 19.4% part for large.
3D6: .5% hole for large, 2.3% part for small, 5.1% part for large.
Now for all intents and purposes I will refer to a hit on the scatter die as a 'direct hit', and a roll where the hole is still over the base as an 'indirect hit', and where the template is somewhere over the base as a 'partial hit'.
Since we can assume that 33.3% of the rolls will come up with a 'hit' on the scatter die, resulting in a direct hit, this leaves 66.6% of the time that a scatter, like those listed above occur. Therefore with official rules these are updated above to;
1D6: 22.2% indirect for small, 22.2% partial for small. 33.3% indirect for large, 22.2% partial for large.
2D6: 1.8% indirect for small, 9.2% partial for small. 5.5% indirect for large, 12.8% partial for large
3D6: .3% indirect for large, .8% part for small, 3.2% part for large.
Now I like to translate this into an absolute damage category, so assuming an average of 3.5 damage for direct and indirect as per current rules, and 1 for partials, and assuming equal opportunities for large and small bases we have: 1.62 damage average across all bands. Or for each individual band:
1D6: 2.36 hits
2D6: 1.39 hits
3D6: 1.19 hits
The previous incarnation of nova cannon only had 2 bands, 1D6 and 2D6, so the 'old' average would be 1.88 hits. This means that the 'new' system is 14% worse than the old. However there is another factor here, the old bands covered different ranges than the new. The old system had 1D6 scatter for 30-60cm of the range, and 2D6 for 60-150cm, the new has 1D6 for 30-45cm 2D6 for 45-60cm, 3D6 for 60-150cm. Taking these all at an equivalent value, this makes the average 1.63 hits for the old and 1.36 for the new, or a more accurate 17% loss. Not much of a difference true, but still notable.
The Trouble with the 'New' bands: The two close bands don't cover a very wide range, in fact they are so small they are almost insignificant, only covering 1/4th of the total range of the weapon.
Previous solutions: In the current version of BFG:R Nova Cannon on LO orders re-roll the scatter die. This proved to be too powerful, as against a small base with 1D6 cm scatter has an 80.1% chance of a direct hit! Although this produces a needed improvement for the NC, it made it a bit too powerful, and in playtest all NC fleets proved to have a substantial advantage.
Proposed Solution: Currently we are still working on it, but we should have a new, final solution by the end of the week. Admiral D' proposed a certain 'gradient' for different types of NC hits. Looking at this the current proposed solution looks like this;
Nova Cannon do 1D6 damage on a 'direct' hit, meaning if the hole is over the target's stem. It does 1D3 if the hole is anywhere over the target's base, and still 1 for partials. This solution, though weakening the efficacy of the Nova Cannon, allows for a logical gradient for damage. Near hits should not do quite the same damage.
Lock on orders still re-roll hits. This allows for the same logic for normal lock on orders, re-rolling the die completely, but also gives the necessary improvement in consistency and damage output for the NCs. Also it follows fluff-lines, which demand that a ship firing a NC not make any turns and concentrate on aiming.
So we have this damage output for each band respectively, for non-LO and LO orders;
1D6: 1.94 hits/2.46hits
2D6: 1.34 hits/2.07hits
3D6: 1.19 hits/1.96hits
So for non LO there is a loss of 9.2% damage. For LO there is a 33% gain. A 24% gain overall. Now notably there is not much difference between the LO damage (only about 25% variance), so for a further endeavor it is our intention to increase the bands to;
This makes our new 'real' value to be 1.41 for non-LO, and 2.11 for LO. So our 'real' value becomes 40% better than official rules, and 23% better than previous rules. Since this overshoots our theoretical value of about 33% improvement we have the final adjustment; limitations of NCs in fleets. This is widely valued for fluff reasons, but the proposed solution is;
Admech fleets may have any number of Nova Cannon (this is due to the premium that they pay for vessels, and the fact that NCs don't really work with carriers, as they have to LO to be more effective.)
Imperial Navy Fleets may not have more Nova Cannon equipped capital ships than non-nova cannon equipped vessels.
So that's the report on Nova Cannons!