Calculating armor volumes

[robject]

Scott's done this before; now I'm getting a handle on it.

Using a sphere as an example.

* surface area = 4 * PI() * r * r
* armor volume is given
* sphere volume = 4/3 * PI() * r * r * r

So:

outer radius = cube root of ( 3 * hull_volume / ( 4 * PI() ) )

and

volume of space not used by armor (vi) = hull volume - armor volume

and then:

radius of space not used by armor (ri) = cube root of ( 3 * vi / ( 4 * PI() )

and finally:

thickness of armor = outer radius - inner radius


Represented as one big ugly messy equation:

thickness of armor =
cube root of ( 3 * hull_volume / ( 4 * PI() ) )
- cube root of ( 3 * (hull volume - armor volume) / ( 4 * PI() )

 

[Anthony]

In practice, unless dealing with buffered planetoids, Armor/Area is usually good enough. If you want, you can add a hack for loss of internal volume, but for 15% armor it's only 1.06, so it rarely matters much.

 

[Uncle Bob]

The square/cube law blows the hell out of the simple percentages for armor. But to properly account for armor requires scaling factors for both size and configuration (a wedge with 10% armor is much less protected than a sphere with the same 10%).

For the purpose of deckplans it is just outside the mapped area.

 

[Scott Martin]

As Anthony has pointed out, for all reasonable armour thicknesses it approaches surface area x armour thickness.

This conveniently handles Uncle Bob's comment, since the surface area of a wedge is more than the surface area of a sphere, so the same armour volume divided by the surface area will provide different thicknesses

And if you know that your design is "unreasonable" (I have an orbital weapons platform under 100 dTons that is roughly 30% armour) then you can use (outer volume) - (inner volume) to determine the actual armour volume: in this particular case it resulted in more than a 10% reduction in armour volume (and given that the beastie uses reaction thrusters, that's pretty important...)

Scott Martin

 

[BetterThanLife]

However, something to bear in mind, Bulkheads (which include all of your decks) used for internal compartmentalization, are also part of the armor factor and are armor. So you can't simply calculate the surface area of the ship. Armor is more than just the outer skin.

 

[atpollard]

Originally posted by BetterThanLife:
However, something to bear in mind, Bulkheads (which include all of your decks) used for internal compartmentalization, are also part of the armor factor and are armor. So you can't simply calculate the surface area of the ship. Armor is more than just the outer skin.

But at that level of detail, the size of the individual compartments (the spacing between bulkheads) will drastically alter the strength of the ship by making the armor plating stiffer through a reduction in the span. I doubt that that detailed an analysis will ultimately be practical or useful.
I think High Guard tries to somewhat address the issue through the fixed percentage PLUS the variable percentage per point of armor. The Fixed Percentage represents internal bracing/skin to resist G forces since it would yield a non-zero value at armor = 0. (just my opinion)

 

[Anthony]

Originally posted by BetterThanLife:
However, something to bear in mind, Bulkheads (which include all of your decks) used for internal compartmentalization, are also part of the armor factor and are armor. So you can't simply calculate the surface area of the ship. Armor is more than just the outer skin.

Actually, you still can. What you do is make the simplifying assumption that, say, 20% of your armor is used for internal armoring, and the remaining 80% is used on the skin. The skin thickness is then proportional to (armor/surface area), the bulkhead thickness is proportional to (armor/bulkhead area). Bulkhead area is approximately equal to volume * 3 / (average bulkhead separation).

 

[BetterThanLife]

Originally posted by atpollard:
</font><blockquote>quote:</font><hr />Originally posted by BetterThanLife:
However, something to bear in mind, Bulkheads (which include all of your decks) used for internal compartmentalization, are also part of the armor factor and are armor. So you can't simply calculate the surface area of the ship. Armor is more than just the outer skin.

But at that level of detail, the size of the individual compartments (the spacing between bulkheads) will drastically alter the strength of the ship by making the armor plating stiffer through a reduction in the span. I doubt that that detailed an analysis will ultimately be practical or useful.
I think High Guard tries to somewhat address the issue through the fixed percentage PLUS the variable percentage per point of armor. The Fixed Percentage represents internal bracing/skin to resist G forces since it would yield a non-zero value at armor = 0. (just my opinion) </font>[/QUOTE]Or it could be the internal bracing and such to add armor in the first place then simply based on the thickness of the armor after that point.

 

[BetterThanLife]

Originally posted by Anthony:
</font><blockquote>quote:</font><hr />Originally posted by BetterThanLife:
However, something to bear in mind, Bulkheads (which include all of your decks) used for internal compartmentalization, are also part of the armor factor and are armor. So you can't simply calculate the surface area of the ship. Armor is more than just the outer skin.

Actually, you still can. What you do is make the simplifying assumption that, say, 20% of your armor is used for internal armoring, and the remaining 80% is used on the skin. The skin thickness is then proportional to (armor/surface area), the bulkhead thickness is proportional to (armor/bulkhead area). Bulkhead area is approximately equal to volume * 3 / (average bulkhead separation). </font>[/QUOTE]The more heavily armored the ship, the more compartmentalization it is going to have. Depending on the size and overall layout of the ship, you are looking at more than just decks. For example there is the SDB and the Gazelle from Sup-7. Most of the armored ships in canon are laid out in a similar manner. (Valor, Lucifer, are two that I can think of off the top of my head that are extreme in armor.) These have decks laid out along the long axis of the ship, and compartmentalization and bulkheads on those decks. These ships have more compartmentalization as the armor factor goes up.


Rarely, does a ship, such as the AHL, have the decks perpendicular to the long axis of the ship, in the case of the AHL the majority of the bulkheads are the actual decks themselves and the individual decks on the ship actually have rather limited compartmentalization. (The Gunnery and Fuel decks being the major exceptions.) But sicne the AHL is only AR5 and there is really nothing to compare it to that is in a similar vein.

Do ships with more armor use more bulkheads?

I would think so.

 

[Anthony]

Originally posted by BetterThanLife:
The more heavily armored the ship, the more compartmentalization it is going to have.

While not necessarily true, that's what my proposed rule does. A ship with armor-F (16%) will have 8x as much internal structure as a ship with armor-1(2%). That can indicate thicker bulkheads, more bulkheads, or some combination of the two.

 

[robject]

Originally posted by Scott Martin:
As Anthony has pointed out, for all reasonable armour thicknesses it approaches surface area x armour thickness.

This conveniently handles Uncle Bob's comment, since the surface area of a wedge is more than the surface area of a sphere, so the same armour volume divided by the surface area will provide different thicknesses

And if you know that your design is "unreasonable" (I have an orbital weapons platform under 100 dTons that is roughly 30% armour) then you can use (outer volume) - (inner volume) to determine the actual armour volume: in this particular case it resulted in more than a 10% reduction in armour volume (and given that the beastie uses reaction thrusters, that's pretty important...)

Scott Martin

So that's a good point: two formulae might serve, in order to simplify the process for 80% of all ship designs.

Originally posted by atpollard:
I think High Guard tries to somewhat address the issue through the fixed percentage PLUS the variable percentage per point of armor. The Fixed Percentage represents internal bracing/skin to resist G forces since it would yield a non-zero value at armor = 0. (just my opinion)

And that's a very insightful comment as well. Thank you.

 

[TheEngineer]

Guess it was pretty ok to drop the whole armor thickness/volume issue in MT...