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Cargo and its Effect on Performance
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CRMcNeill
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PostPosted: Wed Dec 24, 2014 6:17 pm    Post subject: Cargo and its Effect on Performance Reply with quote

As near as I can tell, a ship's cargo capacity under the RAW seems to be an arbitrary hard ceiling, in that a ship is allowed a maximum mass of cargo which it cannot exceed. However, in the real world, things are more gradual, in that the more cargo you load on a given vehicle, the greater the vehicle's performance degrades. IMO, it should be possible to overload a ship, turning it into a wallowing pig hauling a massive load of cargo. IIRC, the 1E of GG6 Tramp Freighters even had rules under which a ship captain could trade Speed for Cargo Capacity.

So, what would be a good rule to take this into account?
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Whill
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PostPosted: Wed Dec 24, 2014 7:27 pm    Post subject: re: Cargo and its Effect on Performance Reply with quote

Quote:
Our focus determines our reality.

We all have our individual tolerances for how realistic we want the various aspects of the cinematic reality of our games to be. Some of us may be happy with the RAW for a lot of things because we don't want to nickle and dime everything. I have added a little crunch to my game here and there but cargo load effecting performance is not something I've thought about.

My personal experience of operating a vehicle carrying a somewhat notably heavier cargo load is limited to driving U-Haul trucks when moving. Of course this a ground vehicle in standard gravity. I imagine that flying a vessel through zero gravity with a massive cargo would in some ways be more difficult because of the full effect of inertia not being diminished by the friction of surface gravity, but I don't think I could provide any kind of realistic mechanic to govern that.

I guess for simplicity's sake, I can only suggest that making a chart with effects that come as a ship's load gets to some benchmark percentages of the ship's full capacity.
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atgxtg
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PostPosted: Wed Dec 24, 2014 9:27 pm    Post subject: Reply with quote

I was working on something along these lines:

First off the SPACE rating of ships appears to be tied to their acceleration (in Gs). There is a rough correlation of about 1 SPACE per 400Gs acceleration. For example a TIE fighter, with an acceleration of 4100G, has a SPACE rating of 10.

Secondly acceleration, in real word terms, especially in space, is based off of the Thrust-to-Mass ratio. For example, a TIE fighter with an acceleration of 4100Gs has a thrust to mass ratio of 4100. Now anything that would chance the mass of the ship would change the acceleration and SPACE rating in the same way.

Thirdly, a not to bad rule of thumb is to assume that a cargo vessel's hold can contain 20-25% of the total mass of the vessel. If we assume 25% as a rule for the RPG, then a YT-1300 that could haul 100 tons would have a total mass of 400 tons.

Now, if we put it all together, then you could determine the effect of cargo on any ship by the formula:

SPACE = OLD SPEED x OLD MASS/NEW MASS


For example, if you loaded up 200 tons of cargo on a YT-1300, then:

SPACE = 4 x 400/500

or SPACE 3


The formula could be reduced to reduced to an easy to use reference table.


Also, the same would hold true for MANEUVERABILITY.





At least that was the approach I was going with.
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garhkal
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PostPosted: Thu Dec 25, 2014 2:52 am    Post subject: Reply with quote

But would their losses be worse or less in space than in atmosphere?
What of ground or repulsorlift vehicles, such as speeder bikes or airspeeders?
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Bobmalooga
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PostPosted: Thu Dec 25, 2014 6:53 am    Post subject: Reply with quote

In atmosphere -2 move and a die off of maneuverability if exceeded and that goes up depending on how bad they exceed the limit...
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atgxtg
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PostPosted: Thu Dec 25, 2014 9:04 am    Post subject: Reply with quote

garhkal wrote:
But would their losses be worse or less in space than in atmosphere?
What of ground or repulsorlift vehicles, such as speeder bikes or airspeeders?




The losses would actually be less in an atmosphere. In an atmosphere, the limited effect on top speed (as opposed to just acceleration), is drag due to the aforementioned atmosphere. The faster a vehicle is moving the greater the drag. This drag force increases so much that you need four times the thrust to go twice as fast.

What happens is that as the vehicle goes faster and faster a greater percentage of it's thrust is needed just to maintain it's current speed, until eventually, all of the thrust is needed just to maintain the current speed- which turns out to be the top speed.

Now,flying vehicles get a bit more complicated, as a vehicle climbs the atmosphere gets thinner, which reduces drag and thus frees up more thrust for speed, letting it travel faster. But...the thinner atmosphere often reduces engine performance (as it gets harder for the engine to "breathe"). Also, vehicles that use wings (airplanes, helicopters, ornithophers) would also get less lift due to the thinner atmosphere and would half to work harder to counteract the vehicle's weight, which would mean less power (and thus less thrust) available for speed.


Respulsorlift vehicles are relatively easy to figure out as far as math goes. To fly a vehicle has to exert enough force to counteract the force of gravity. Now the force of gravity is usually referred to as an object's weight. So for most purposes we could consider this a constant (it isn't) and just factor it off the top.

For example, an XJ-6 airspeeder has a mass of 1600kg. The XJ-6 will have to lift itself, plus carry a driver and possible a passenger and/or some gear in the passenger seet on slung onto the back. A good designer would want to give a safely margin for mass, so that the XJ-6 can still get off the ground if the driver has a big dinner on Life Day, or a fat friend in the passenger seat. So the XJ-6 might be designed to lift 2000kg - which should be more that enough to lift itself and any occupants. Now it would take something like 20kW of power to do that if you had a 100% efficient repulsorilift engine. If they have a 50% efficient engine about twice that. Our mordern engines have something like a 30% efficiency rating.

Now overloading the weight could overload the resulsorlift engine. For injstance, stapping in a ton of gold into the passenger seat of the XJ-6 will overload the vehicle and throw of it's center of gravity, forcing it to tilt to one side -assuming it cvan get off the ground at all.


Just what the effect would be would depend on how badly the vehicle is overloaded. In most cases it would probably just throw off maneuverability a bit. In extreme cases the vehicle wouldn't be able to get off the ground.



I could simplify all that into a formula or table. The tricky bit would be in estimating the total mass and "safety margin" for various vehicles. Big cargo ships are relatively easy.Vehicles such as X-Wings, or speeder bikes are harder, since the cargo listed is only a small fraction of the total mass. Kinda like estimating the weight of a car based on the size of the trunk- or glove compartment.
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atgxtg
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PostPosted: Thu Dec 25, 2014 9:07 am    Post subject: Reply with quote

Oh, another way to simplify this would be to just reduce the number of moves a ship or vehicle could taken when overloaded. For example, if that overloaded YT-1300 could only make 33 moves instead of 4, you'd get the same effect to game play.
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garhkal
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PostPosted: Thu Dec 25, 2014 3:51 pm    Post subject: Reply with quote

Sort of like saying unencumbered ships can go all out, those laden at full capacity can only go double speed. 50% over max can only go cruise speed, and those at double capacity can only go cautious!
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CRMcNeill
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PostPosted: Thu Dec 25, 2014 3:56 pm    Post subject: Reply with quote

Or perhaps:

<50% cargo = No Restrictions
50% - 100% = Full Speed Maximum
100%-150% = Cruise Speed Maximum
151%-200% = Cautious Speed Maximum
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Kytross
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PostPosted: Thu Dec 25, 2014 6:53 pm    Post subject: Reply with quote

How about for every 10% weight you go over the maximum it knocks off 1 pip of maneuverability and 1 move point?
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atgxtg
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PostPosted: Thu Dec 25, 2014 8:08 pm    Post subject: Reply with quote

garhkal wrote:
Sort of like saying unencumbered ships can go all out, those laden at full capacity can only go double speed. 50% over max can only go cruise speed, and those at double capacity can only go cautious!


Well, in space it's tied directly to the change in total mass as a percentage of the total. Since the majority of a ship's mass isn't cargo, it would actually take a lot of cargo to really slow down the acceleration.

A ship that masses 400 tons fully loaded, and can move 16 full out, isn't going to lose 75% of that just by taking on an extra 100 tons of cargo. It would need to load up about 1300 tons of cargo for that dramatic a drop.

The big restrictions on cargo would probably be more in terms of space required and wear and tear on the ship.


For example if a ship had a hold of 100 cubic meters, it can't fit more than that aboard in cargo inj the hold, The excess would spill over into the other areas of the ship and/or have to be carried externally somehow. And that's not taking into account things like packaging materials and containers.

If you were to cram 100 cubic meters of gold into the hold, you'd get 1920 tons of cargo in the hold, but you wouldn;t actually be able to go into the hold. Worse still the gold would collapse under it's own weight (so a good reason to lower the gravity in the hold), and shift around as the ship moves - probably banging into doors and such. And the ship would need to be strong enough structurally to handle all that weight in one location. And it would probably fly a bit heavy on the end where the cargo is.

All of which could be compensated for with advanced technology such as antigrav, but at a cost of energy and more wear and tear on the ship.
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atgxtg
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PostPosted: Thu Dec 25, 2014 8:16 pm    Post subject: Reply with quote

The problem with just tying it to the cargo tonnage is that most small vehicles have a very small cargo area. For instance, an X-Wing can carry something like 100 kg of cargo, Taking on an extra 100kg is not going to really affect the X-Wings performance very much.

The limit, in this case is more a matter of where to put it than of mass.


Likewise, a YT-1300 probably masses several times what it can carry in cargo. Doubling the cargo carried would probably only result in a modest increase ,say 20% to the total mass. And, a corresponding reduction in performance.



I think what we need are two different progressions. One for freighters, and another one for starfighters, speeders, and other vehicles that have fairly small cargo space.
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garhkal
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PostPosted: Fri Dec 26, 2014 4:37 pm    Post subject: Reply with quote

But is it more on the space cargo takes up, or the 'tonnage' it weighs?
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atgxtg
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PostPosted: Sun Dec 28, 2014 9:10 am    Post subject: Reply with quote

garhkal wrote:
But is it more on the space cargo takes up, or the 'tonnage' it weighs?


Probably the mass ("tonnage") but the mass relative to the mass of the ship. At least for freighters.

I got something that I have been working on, off and on, that dealt with all this. A vehicle design system. I tapped into the old stats from the X-Wing PC games and came up with a correlation between things like KTU, the official acceleration scores in Gs, and the RPG stats. I even got it to match up- somewhat- with D6 Space (the freighter in D6 Space is a Ghtroc).

Where the project got bogged down was when I came to the forum and tried to get some sort of consensus on the masses of the Star Wars ships.

BTW, does a 80 ton X-Wing sound alright? .
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cynanbloodbane
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PostPosted: Fri Jan 09, 2015 12:51 pm    Post subject: Reply with quote

atgxtg wrote:
garhkal wrote:
But is it more on the space cargo takes up, or the 'tonnage' it weighs?


Probably the mass ("tonnage") but the mass relative to the mass of the ship. At least for freighters.

I got something that I have been working on, off and on, that dealt with all this. A vehicle design system. I tapped into the old stats from the X-Wing PC games and came up with a correlation between things like KTU, the official acceleration scores in Gs, and the RPG stats. I even got it to match up- somewhat- with D6 Space (the freighter in D6 Space is a Ghtroc).

Where the project got bogged down was when I came to the forum and tried to get some sort of consensus on the masses of the Star Wars ships.

BTW, does a 80 ton X-Wing sound alright? .


Well, a fully loaded F-16 weighs in at 21,772 kg or 21.722 metric tons. (This is the maximum takeoff weight.)
A fully loaded X-wing would probably be double that just for the heavier structural build, so I would go with 42 tons. However that would be just if the players disassembled an X-wing to pack into the hold for transport. A docking bay would take up quite a bit more tonnage as you need room to move and turn in.
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