First, let me tell you that I love this game, and that this forum is a fantastic place to find new ideas.
Second, I have to say that the spaceship part of Rogue Trader was kind of light. We don't have a lot of ships to play with, just a few generic weapons, and not a lot of rules to play with. And IMO some balance problem. I have 2 main balancing problems: shooting distance and raider ship.
First the shooting distance.
The regular weapon reach is 6 VU, and everything except slow cruiser and merchant outrun this. Raider speed is 10 VU, light cruiser 7.
The meaning of this is that every weapon except laser battery (VU 9) is short range. That's also mean that fast ships, up to and including Light cruiser will be out of range in one turn, two if it start fleeing at point blank (of course you can follow the coward, if you are fast).
Now look at Battlefleet Gothic rules (best source of ships, like eldar, chaos, tau etc.. or just more imperial ships). Raiders speed is 30cm, frigate 25cm, cruiser 20cm and merchant 15cm. And basic weapon reach is 30cm.
That means that your average weapon reach should be something like 9 or 10 VU, not 6. And long range laser battery should have a range of 15 VU. This is STILL very short range when compare to speed, but a little bit more playable. It now takes 2 or 3 turns to flee out of range.
R(a)iders on the storm
My second concern is the almost equal power of destruction of every ship.
I mean, ok, cruiser have 2 broadside batteries and a prow, compare to 1 dorsal and 1 prow for a raider. That means that cruisers have one more shoot (at possibly STR 6), slightly better armour and more than double hit points. And that’s it.
Now the infamous Havoc-class raider: you can fit this beast with a plasma battery and a lance battery. With your speed and manoeuvrability, short range is not a problem, and you can always shoot from the front. You still have space for a reinforced Hull and armour.
You can fight a cruiser and easily win, manoeuvring in his back and shooting him with your capital-class weapons. You have almost the same armour, and only half the hit points. And you are just an escort ship.
Let’s again have a look at Battlefleet Gothic:
Hit points :
BG: Lunar-class cruiser have 8 hit points, Destroyer (Navy raider) have 1 hit point. Only ONE. 8 time less that a cruiser.
RT: Lunar-class 70 Hull integrity, Havok 30 Hull. Uh...
Speed:
BG :Lunar-class speed 20cm, Destroyer speed 30cm. That’s 50% more.
RT : Lunar-class speed 5 VU, Destroyer speed 10 VU. That’s 100% more.
Weapons.:
Raider :STR 2 for dorsal battery, STR 1 for lance.
Cruiser : STR 6 broadside battery, STR 2 lance (port and starboard), STR 6 torpedo in front.
Conclusion :
For me, raiders are overpowered in Rogue Trader : 2 time the speed of a cruiser, only half the hit points, and access to the same class of weapon.
Also, the range of the weapon, compare to speed of the ships, hugely help fast ships like raiders, making them impossible to defeat. Except at very close range, they are out of range (and I mean maximum range) in one turn. And they can shoot at full force from the front arc, making speed and manoeuvrability more important.
Well, they cost half the ship points. But 25 profit factor IS a big deal.
Solution:
Well, this is what I use. it is not perfect, because BG and RT don't work the same way. BG is a board game, where the life and death of one destroyer or cruiser is not a very big deal. In RT, this is your ship, your life, and it IS a pretty big deal, so the focus is not the same.
Raider should have 10 Hull Integrity and 10 armour (read the description: it is glass cannon).
They should be limited to thunderstike macrocannon and starbreaker lance.
With this big nerf, I let speed and manoeuvrability the same. They are still better than the destroyers in Battlefleet Gothic, and you can still upgrade them.
Frigate should be somewhere between 20 and 25 Hull integrity with the same armour.
Light cruiser are perfect.
Cruiser goes up to 80 hull integrity.
For weapon range, I use:
Thunderstrike : 7VU
Mars pattern : 10 VU
Sunsear (laser) : 15 VU
Ryza (plasma) : 8 VU
Starbreaker lance : 8 VU
Titanforge lance : 10 VU
After a lot of testing, I fell this is better and more on par with Battlefleet Gothic, but without the limitations of the board game.
Raiders are still very dangerous, and 3 of them will destroy a single cruiser almost every time (so a cruiser should use some escort ships). One to one, they are not really a match for a frigate (and they should not be).
They will no more charge a merchant ship head-on, but using hugely superior speed and manoeuvrability, they will do whatever they want from an isolated merchant.
With 10 armour 10 Hull integrity, a raider can take a good salvo of another raider and still be kicking : first hit goes in the void shield, second hit make an average 6 points of damage, right in the armour, and the last hit (if any) will make another average 6 points. So it is an average 6 hull damage on a full salvo. Big hit, but not a killing blow.
A good salvo from a broadside battery (or two broadside batteries if it's a cruiser shooting) will in all probability one-shot a raider. Well, I guess this is why they fight in squadron, and try to out-manoeuvre capital ships.
Also, a raider can't take a lance hit that well. Almost every lance bigger that Starbreaker lance will cut a raider in two with a solid hit. Well, what did you expect? Lance are made for capital ship destruction. Shoot an imperial guard with a meltagun and see what happens...
A raider fighting a raider will have a very big advantage if he can shoot with his lance, front arc ONLY. That's like dogfight from WW2, with one trying to go in the 6 of the other.
It is something else than big badass Havok with plasma and lance batteries shooting everything into oblivion. It is a glass gun. It can still cause a LOT of critical hits to a cruiser with the lance, if it can avoid to be destroyed when closing in, and goes in his 6.
So, yes, it will take an ambush, and a lonely cruiser. Or you will have to work as a squadron, and shoot the escorts ships first. yes, it is VERY difficult to destroy a cruiser, and almost impossible to destroy a light cruiser, and you are at a big disadvantage in front of a frigate. And that's just the way I like it.