Thanks - the daft thing is I'm trying to point out the rule is odd and should probably have been spotted for errata
Scrap all references to lasers and sandcasters having USPs for 10 weapons and instead change it to 12.
Makes more sense to me that way.
The sandcaster table gives even more scope for tomfoolery
USPs for 8 weapons, 10 weapons, 20 weapons.
Multiples of 3 make a lot more sense.
Mike is right. He is applying the exact, written rule without interpretation. His position is even somewhat supported by the example on HG p29:
"For example, a ship has eighty triple beam laser turrets. The ship may have 80
batteries of one turret (attack factor 3), 40 batteries of two turrets (attack factor of
4), 16 batteries of five turrets (attack factor of 6), or 8 batteries of ten turrets
(attack factor of 8).
Other configurations are possible, but these selections constitute
the optimal battery configurations on the turret weapon table."
And it is not explicitly written anywhere that I can find (if it is, please give me the pointer) that batteries must be whole turret increments. It is heavily implied, but not strictly stated (which is the basis for the whole tempest).
Ok, so we do what you ask, and now have the weapons table in multiples of three for each break point.
There are canon examples of ships that mount dual beam laser turrets. Are they now invalid if they aren't in batteries of 6 (or 12 or ...)?
The issue is that while trip turrets are often the OPTIMAL configuration, they are not the only configuration. Just like how you want to arrange your 30 beam laser. 3 batteries of 10 lasers is not optimal. Closer optimization would be two batteries of 15 (factor 6) and fully optimized would be one battery of 30 (factor 8). Of course all factors go up by one if we are talking TL 13+.
Note that this is based on optimization for a likely hit and penetration. This is not an optimization for the maximum number of shots. If we optimize for maximum number of shots, regardless of penetration ability we have 30 factor 1 shots. Clearly, your request for 3 factor 5 shots is not optimal for number of shots either.
So, you must ask yourself, under what conditions is my requirement for 3 factor 5 shots optimal for 10 trip turrets of 3 beam laser each? If it is a role-play requirement (so and so noble, being a noble and thus arbitrary, wants it that way, or some such) you are taking it out of the HG ship combat conditions and batteries don't matter except where you want them to.
If there is a design element unrelated to some role-play (npc or otherwise) that makes your configuration optimal, then please tell us what that design element is.
Warship designers try to optimize their design configurations. In real life, these design optimizations are subject to political (and hence role-play) realities that make for some, ahhh, "interesting" compromises (and probable cost overruns, c.f. the development of the Bradley Fighting Vehicle).
If you are designing outside any political reality, then why are you not trying to optimize?