Spaceships 7 and Cannon/Catapult Damage

[cvannrederode]

We're working on a Spelljammer inspired campaign at the moment, and looking at using GURPS Spaceships (and SS 7 in particular) for ship design.

My current question regards the damage done by Low TL cannons and catapults. Unless I'm missing something very obvious somewhere in SS 7, there is no difference in damage done by TL 6 and under guns, and catapults, versus their high TL counterparts. So we have a TL 5 slow firing 12 cm Gun (equivalent to a 24 lbr?) doing 6dx30 dDamage, and a 5 cm TL 4 catapult doing 6dx12 dDamage.

The closest matches I can find in Low Tech is 6d x 5 (non decade) for a 24 lb cannon, and 6d for a 5 lb Ballista.

I know that the damages listed in SS is based on a Kinetic warhead with a 1 mps base impact. But a 5280 fps muzzle velocity is a stretch for TL 7 guns, let alone TL 5 or less, or for mechanical artillery.

Is there any rules for adjusting damage of these weapons? Espeically more in line with the dDR 10 and that seems to be the upper limit for SM +8 or +9 ships using wood and iron armor.

[David Johnston2]

Originally Posted by cvannrederode

We're working on a Spelljammer inspired campaign at the moment, and looking at using GURPS Spaceships (and SS 7 in particular) for ship design.

My current question regards the damage done by Low TL cannons and catapults. Unless I'm missing something very obvious somewhere in SS 7, there is no difference in damage done by TL 6 and under guns, and catapults, versus their high TL counterparts. .

No, if you aren't TL 7 you don't usually use TL weapon stats. If you want to put TL 4 cannon or TL 3 siege weapons on a spelljammer you'll have to dummy up your own stats.

[ericthered]

don't they have good low tech stats in a pyramid somewhere? it doesn't seem to be either of the spaceship pyramids though...

[weby]

Basically for the low velocity weapons you should reduce the minimum speed appropriately. But no, it is not said anywhere in the rules.

The 1 mps is fairly suitable for UT level guns as minimum, though ships traveling away from each other would be lower...

[Varyon]

Honestly, your best bet is to designate some of your cargo capacity as "this is actually for weapons and ammunition," then use the devices from Low Tech. So, when you make your flying ship of the line, rather than giving it some Batteries of various sizes, instead work out its assortment of Low Tech cannon and make certain it has enough additional cargo space to hold them. Let's say you've got a second rate ship of the line with 25 cannon of seven, 30 culverins, 20 demiculverins, 10 minions, and 3 swivel-guns. Including their mounts, each cannon of seven weighs in at 16,300 lb, each culverin at 11,000 lb, each demiculverin at 6,500 lb, each minion at 2,250 lb, and each swivel-gun at 205 lb. The ammunition (powder and shot) for these weigh in at 60 lb, 28 lb, 16.5 lb, 7.5 lb, and 2.5 lb each, respectively. You need 890615 lb of cargo capacity to hold all of those weapons, which is 445.3075 tons. That's 9 systems on an SM+8 ship, or 3 on an SM+9 one. In either case, you'll have almost 5 tons left over for ammunition.

[David Johnston2]

Really though with a spelljammer, there's not much point because inflicting structural damage won't actually make it less flightworthy. Your emphasis should be on eliminating the crew.

[Ulzgoroth]

If you're using Spaceships combat rules at anything other than the 10 minute/Close scale you can just use the Base Relative Velocity without worrying about the weapon's contribution...

[Phantasm]

Originally Posted by ericthered

don't they have good low tech stats in a pyramid somewhere? it doesn't seem to be either of the spaceship pyramids though...

Low-Tech itself has good cannon stats. Probably best to just say "Has X number of $cannon per side" on the spelljammers.

[cvannrederode]

So it seems to me that there's something going on in SS, or else the cannon damage is very broken.

A 12 cm cannon from SS does 6dx30 dDamage, multiplied by speed in mps. So 6dx300(2) p++ (non-decade) at 1 mps (or 5280 fps, ~ 1600 m/s)

The D-81TM TL Russian tank cannon is in High Tech. It's 125 mm, or 12.5 cm. And it's damage, with APFSDS, is 6dx30(2) p++. It's muzzle velocity, according to wiki, is 1700 to 1800 m/s, or better than one mps.

What is being used to justify the order of magnitude increase?

[FenrisLoki]

It almost seems to me like the conversion to decade scale damage was accidentally done backwards. Multiplying by 10 instead of dividing.

Am I right in seeing this is fixed in the Errata?
Quote:
P. 68. In the Conventional Warhead Damage Table, the dDamage column progression should be:

3d
3d+2
4d
5d
6d
7d
9d
11d
6d×2
3d×5
6d×3
3d×7
and a "0" chopped off the end of all of the other numbers.

Just below the Conventional Warhead Damage Table, "6d × 140 × 10 = 6d × 1,400 damage" should be "6d × 14 × 10 = 6d × 140 damage".

So this would make the table
2cm 3d
2.5cm 3d+2
3cm 4d
3.5cm 5d
4cm 6d
5cm 7d
6cm 9d
7cm 11d
8cm 6d×2
10cm 3d×5
12cm 6d×3
14cm 3d×7
16cm 6dx4
20cm 6dx5
24cm 6dx6
28cm 6dx7
32cm 6dx8
40cm 6dx10
48cm 6dx12
56cm 6dx14
64cm 6dx16
80cm 6dx20
96cm 6dx24
112cm 6dx28