With this algorithm, 1 x 3/1/1 weapon will cost the same as 3 x 1/1/1 weapon. The ship with the higher number of weapons will be more survivable and there is no incentive to ever build anything but ROF 1 weapons. Here is a look:

Scenario 1
Given two 10 HS ships, one (Ship A) armed with 5 x 2/1/1 weapons and one (Ship B) armed with 10 x 1/1/1 weapons. They will have the same ORat and ComRat with the [ R*(P+1)*(D+1)/2 ] formula. Both (assuming no armor or shields) will statistically take 20 hits to destroy. Ship A with fewer weapons will have 1 weapon on the damage chart (1 in 6 hits will destroy a weapon) while ship B, with two times as many weapons, will have 2 weapons on the damage chart (2 in 6 hits will destroy a weapon). If both ships take 18 points of damage, ship A loses 3 weapons and ship B should lose 6 weapons. They should still have the same firepower.

Scenario 2
Given two 10 HS ships, one (Ship A) armed with 2 x 2/3/3 weapons and one (Ship B) armed with 4 x 1/3/3 weapons with the defenses as above (i.e. none). Again they will have the same ORat and ComRat with the [ R*(P+1)*(D+1)/2 ] formula. Now however, both only have one weapon on the damage track (1 in 6 chance of a weapon hit). After only twelve hits, Ship A is weaponless while ship B will still have two weapons.

All of this is assuming an even spread of dice rolls (which never seems to happen in the real world). But it seems to me that at best high ROF weapons have parity with ROF 1 weapons and in some situations, are less survivable. They are both equally effective against fighters but you have a better chance of keeping some ROF 1 weapons to shoot back with using this algorithm. This makes ROF 1 weapons superior to high ROF weapons and eliminates the reason to ever build high ROF weapons ever again.

Well, its not really a house rule but in my group we don't use expendable weapons. They are an optional rule anyway so after seeing how they can be easily abused, we just don't use 'em.

Note that the generational armor has 5 levels while the generational ECM and EWS have only 4 levels due to imaginary numbers cropping up in either the SU or DRat calculations for a 5th level.

So Armor ( X ) has the following:

LVL     SU     ORat     DRat     Hit?  Blocks H hits on
1        2%      -          x1.2     No      6+
2        5%      -          x1.5     No      5+
3       10%      -          x2       No      4+
4       20%      -          x3       No      3+
5       50%      -          x6       No      2+

ECM ( X )
LVL     SU     ORat     DRat     Hit?  To-Hit
1        5%      -          x1.5     Yes     -1
2       10%      -          x2       Yes     -2
3       20%      -          x3       Yes     -3
4       50%      -          x6       Yes     -4

EWS ( X )
LVL     SU     ORat     DRat     Hit?  To-Hit
1        5%      -          x1.2     Yes     +1
2       10%      -         x1.5     Yes     +2
3       20%      -          x2       Yes     +3
4       50%      -          x3       Yes     +4

We are playtesting the above two generational equiment pieces in our group. The highest levels of the two take up like 50% of the ship so I cannot see anyone actually using them.

Armor Plating ( X )

As a low-cost, low-tech alternative for increasing the staying power of a starship, several developers have opted for extra layers of reinforced material to protect their designs from harm.

Whenever a ship with armor plating ( X ) takes a hull hit, roll a dice: if the result is  ( 7 – X ) or higher, the hit has no effect on the hull.

SU Cost: + (10 x ( 6 / ( 6 – X ) – 1 )%
ORat: -
Drat: x ( 6 / ( 6 – X ))
Hit?: No

Note: The current Armor Plating is equivalent to Armor Plating (2) which gives:

SU Cost: + (10 x ( 6 / ( 6 – 2 ) – 1 )% or +5%
ORat: -
Drat: x (6 / ( 6 – 2 )) or x1.5
Hit?: No

This is consistent with the current rules.

Of these three options, I prefer the original, option #1. With the other two options it costs the same for 3x 1/1/1 weapons as it does for 1x 3/1/1 weapon. I'll have the same number of shots but it will take more hits to kill me and I'll never build anything but ROF 1 weapons ever again. In my opinion, it isn't broken. With the current algorithm of (ROF+1) x P x D you can get a discount for high ROF but the trade off is, you are easier to kill.

So I was thinking about the concept of customizable spinal mounts and came to the following conclusion. Hasn't Dan already provided most of the mathematical tools to mod the spinal mounts? We already know how to calculate the SU and ORat of weapons based on their Range, To-Hit, ROF, PEN and DMG. Can't we just apply those to the spinal mount calculations to derive say a spinal mount that hits on a 4+ and has a PEN of 2?

The basic spinal mounts assume a range based on the size of the mounting hull. Can't we really change it to any range, as long as we modify the SU and ORat by a similar amount? The same with To-hit, ROF, PEN and DMG.

For example: To get a spinal mount that hits on a 4+ just divide the stock spinal mount SU by 0.67 and multiply it by 0.5 then divide the stock ORat by the old SU and multiply it by the new SU. Voila, a spinal that hits on a 4+

PEN and DMG are even easier because the stock spinal assumes that they are 1 (well, DMG is 1x HS). So to get higher PEN and DMG simply multiply the stock SU by the new PEN and/or DMG and as above divide the stock ORat by the old SU and multiply it by the new SU. Keep in mind that a HS 10 ship with a DMG 2 spinal mount would actually be doing 20 points of damage, at least until it took some internals.

ROF is trickier because all other weapons use ROF+1 in their calculations. So for a spinal mount to have a ROF of say 2, divide the stock SU by 2 and multiply it by ( new ROF+1 ). Again as above, divide the stock ORat by the old SU and multiply it by the new SU.

About Range though, I am not sure what to do. Range is already factored into the stock spinal mount's ORat but not the SU. Anyone have any ideas?

Does anyone see any glaring mathematic or balance issues with any of this?

Well, the thought was to add an electronics warfare platform to the game (similar to special sensors in SFB) that can provide electronic warfare above what the covering ship could generate. If the enemy is pounding your flagship, the scout/jammer/whatever platform could throw up a wall of electronic support. Of course your opponent will then make killing the scout/jammer/whatever unit a priority.
So if a ship mounted ECM the scout/jammer/thingy could still loan it another -1 to be hit.

Bummer, and I was getting my fleets ready.

This still doesn't resolve the basic problem. Three 1/1/3 weapons give you the same chances of damaging another ship as three 3/1/1 but the three 3/1/1 are a hell of a lot better vs. small units  (and a use a lot less SU too). Maybe the DRat needs to somehow take into account the ROF not just total number of weapons.