[Spaceships] Homebrew - Alternate Contragrav

[DaltonS]

Gravity Screen System (TL11^) [Hull!]
I decided to go back to first principles (AKA GURPS Vehicles Expansion 2); by analyzing the “Gravity Screen Table” on page 13, a weight reduction of n% requires n/(100-n) kW per square foot of vehicle surface area, with a cost of $100 per kw used. This makes the “Weight Multiplier” equal to 1/(E+1) where “E” is the number of kw/sf used. Using a standard energy point* (and vehicle density) of 100 kW (and cubic feet) per vehicle ton, and the old standard surface area equation Area(sf) = Volume(cf)^(2/3)×6 from GURPS Vehicles, Second Edition, I used a spreadsheet to calculate the table below. Use the “Weight Multiplier” to find the effective weight of the ship. When using a smaller SM system, use three times the “Weight Multiplier” of the larger system to reflect the reduced power of the screen. If multiple systems are used, consider the screens to be layered (ie. use M^n where “M” is the multiplier as a fraction and “n” is the number of systems). Note that this is NOT a force screen variant, and provides no protection against gravitic weapons. The G-Screen Damper described above may still be used against it.

  Size    Cost    Weight  |  Size    Cost    Weight  |  Size    Cost    Weight  
Modifier        Multiplier|Modifier        Multiplier|Modifier        Multiplier   
  SM+4     $1 k   37.50%  | SM+9.5  $600 k    6.64%  |  SM+15  $300 M    0.89%
 SM+4.5    $2 k   32.26%  |  SM+10    $1 M    5.66%  | SM+15.5 $600 M    0.71%
  SM+5     $3 k   29.38%  | SM+10.5   $2 M    4.55%  |  SM+16    $1 B    0.60%
 SM+5.5    $6 k   24.82%  |  SM+11    $3 M    3.99%  | SM+16.5   $2 B    0.47%
  SM+6    $10 k   21.78%  | SM+11.5   $6 M    3.20%  |  SM+17    $3 B    0.41%
 SM+6.5   $20 k   18.10%  |  SM+12   $10 M    2.71%  | SM+17.5   $6 B    0.33%
  SM+7    $30 k   16.18%  | SM+12.5  $20 M    2.16%  |  SM+18   $10 B    0.28%
 SM+7.5   $60 k   13.29%  |  SM+13   $30 M    1.89%  | SM+18.5  $20 B    0.22%
  SM+8   $100 k   11.45%  | SM+13.5  $60 M    1.51%  |  SM+19   $30 B    0.19%
 SM+8.5  $200 k    9.31%  |  SM+14  $100 M    1.28%  | SM+19.5  $60 B    0.15%
  SM+9   $300 k    8.23%  | SM+14.5 $200 M    1.02%  |  SM+20  $100 B    0.13%

* The size of a standard energy point I used came from here.

Originally Posted by Anthony

We can derive it from two sources: power output of weapons, and power output of electric drives.
...
Overall, I'd assume 1 ep is somewhere around 100 kW/ton, which is on a par with a reasonable performance ground car (though said car probably isn't spending only 5% of its mass on its power plant).

Dalton “feeling nostalgic about GURPS 3rd Edition” Spence

[DaltonS]

Design Feature: Gravity Proof Paint (TL^)

This esoteric hull coating blocks any external gravity fields, and may be magical, alchemical or super-science in nature. It has much the same lifting ability as etherwood or skystone (1/3 per hull section) but has no effective mass and requires no power. Any hull section covered will be weightless inside without a form of artificial gravity. This does not cancel the effects of other forms of acceleration or the vessel's inertia. I have no idea what it should cost, except it should follow the standard 1-2-5-10 SM price progression.

Dalton “this may be a dead horse, but it's my dead horse” Spence

[Flyndaran]

Thus making turpentine a terrorist weapon?

[DaltonS]

Originally Posted by Flyndaran

Thus making turpentine a terrorist weapon?

Well, a weapon at any rate. (How would one model paint damage in GURPS Spaceships anyway? ;) )

Dalton “who'd feel stupid saying "Turpentine Gunner! Fire!"” Spence

[Flyndaran]

I would think simple contact of anything capable of scuffing paint would count. It wouldn't have to be vehicle damage by any Gurps or even common language definition.
But defining what percentage is lost over time scuffed, as that would likely matter greatly for anti-gravity purposes, I have no clue.

On a more serious note, I'd imagine anyone above TL 5 or so would try to laminate or cover up the active paint with some kind of ablative material even if it acts as dead weight.

[DaltonS]

Originally Posted by Flyndaran

I would think simple contact of anything capable of scuffing paint would count. It wouldn't have to be vehicle damage by any Gurps or even common language definition.
But defining what percentage is lost over time scuffed, as that would likely matter greatly for anti-gravity purposes, I have no clue.

Sounds like a GM decision to me. Probably quarterly touch-ups at 10% standard cost as part of the standard maintenance cycle to keep full effectiveness (with a 10% reduction for each month touch-ups are missed) with a full strip and re-paint every five years at full cost as part of a regular major overhaul and re-certification effort. Note that this assumes the paint is exposed to the elements (such as they are); paint layers under armor systems (see below) or stealth hull options (SS1. p.30) can be considered maintenance free unless major hull damage has occurred.

Originally Posted by Flyndaran

On a more serious note, I'd imagine anyone above TL 5 or so would try to laminate or cover up the active paint with some kind of ablative material even if it acts as dead weight.

An interesting point. If the GPP layer is "protected" by an armor system, the "weight" of that hull section would be reduced by the mass of the other systems in that section. Thus lift-off thrust would only need to exceed 15% of the ship's mass times local gravity if each hull section has an armor system protecting the paint. As always, net acceleration = (total thrust - lift off thrust)/(ship mass). To find the effective escape velocity from a planet for this ship, multiply the planet's natural escape velocity by the square root of 0.15 (0.3873 approx.). Because this isn't a force field, I'm not sure if the G-Screen Damper mentioned above would work. Maybe a big electro-magnet could hold an iron/steel armored ship in place. This would be a "magnetic tractor beam" system (SS7 p.20).

Dalton “isn't re-painting the ship a crew function?” Spence