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T20 - Traveller for the D20 System Open discussion on the D20 version of Traveller!

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Old July 20th, 2003, 05:11 PM
far-trader far-trader is offline
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Hmm so many places to fit this, here seems best I guess.

As mentioned recently in "The Fleet" section I came up against a couple issues with T20 vehicle and craft Structural Integrity. What I'd like is a home-brew rule that doesn't unbalance the game while allowing a little more detail without too much work.

Right now SI is based solely on the vessel's size which is not a bad starting point, much like the level 0 armor factor included in the basic chassis/hull.

First, one problem I have with the current SI tables may be a minor nit to pick but possibly an errata issue too.

1) p253 the "Vehicle Structural Integrity" table needs to have a "Base SI" column entry of "0.1" for the "Fine" "Size" row to work with the formula.

2) p261 the "Hull Structural Integrity" table needs the entries in the SI column to be changed from "per additional X ton" to "per X ton" to maintain the proper progression.

Second, and the grittier fun, pumping up the SI.

"Ramming speed Mr. Stryker!"
"But sir, we're in a Yugo!?"

1) It seems to me that Armor should bump up the SI but that would be a bigger wrinkle (changing published designs) so I'm willing to accept that it is just added onto whatever structure is there to begin with.

2) Vessels with higher accelerations should have more SI to withstand said acceleration but again this too is not factored so I'll also accept that the stated SI is rather the free SI left after the minimum for the drives is accounted for, perhaps as part of the drives themselves.

3) Which brings us to adding SI, best treated like adding Armor and not done on every ship. In fact using the Armor Factoring system may be the easiest. I propose the following system. Let me know if it seems reasonable and if I've explained it clearly.

Structural Integrity Upgrades

The base Structural Integrity (SI) of a vessel, be it a vehicle, small craft, spaceship or starship, is included in the original chassis or hull construction. In some cases though a builder may desire a more robust frame for certain applications.

To add SI units first determine the vessel's Armor Factoring (p259) or Base Armor Volume (p235). Using this number and the appropriate Armor section (p268 or p236) select the desired SI upgrade factor just as you would for adding Armor factors with the same double for the first factor and TL limit. This will give you the cost and volume required for the SI upgrade.

eg1-pt1) A TL5 helicopter (see p300) with a basic SI of 55 (see errata) in its civilian form is built to military spec to better survive combat with a greater SI, in this case adding the maximum allowed for TL5. The helicopter's Base Armor Volume (used to calculate the SI upgrade) is 50vl. 5 levels of upgrade (based on TL) will be 6 (2+1+1+1+1) times 4 (TL 4-9) times 50vl = 1200vl. The cost will be cr3,000 + (cr9 times 1200) = cr13,800 before discounts.

Next go to the appropriate SI table (p261 or p253) and look across from the vessel's size to the find the Additional SI column and multiply the added factor by the SI upgrade factor above to find the bonus to the vessel's basic SI.

eg1-pt2) We now know that the TL5 mil spec helicopter will have an SI upgrade factor of 5. Looking on the table (p253) the 5000vl helicopter has an Additional SI factor of 2.5. So 5 times 2.5 = 12.5 SI (round fractions down) = 12 SI added to the basic 55 SI for a robust 67 SI total for the military version of the helicopter, comparable to other vehicles twice its size.
Dan "far-trader" Burns

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Old July 21st, 2003, 09:05 AM
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Mornin (PDT) far trader,

Interesting suggestions and comments about SI. One comment was that Armor should add to SI. IIRC the purpose of armor is to minimize damage to the hull and underlying structure. In reality adding armor increases the stress placed on the hull structure at a minor increase to SI.
Tom Rux
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Old July 21st, 2003, 03:22 PM
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Game mechanically, I think that adding armor to SI is inappropriate, since it already reduces the amount of damage coming in. I think it would probably be unbalancing to let armor take dice away from attacks and then also add more to the total damage that must be penetrated by incoming attacks.

In essence, it would be like letting a character's CON modifier add to his AC as well as his Stamina, or allowing DEX to impact a character's Stamina as well as AC. That just doesn't make sense that Armor should pull double duty like that.

But that's my concern, from a game mechanics viewpoint. Otherwise, the idea has merit, and purchasing additional SI would be an interesting option.

Looking forward to how this develops,
Jason "Flynn" Kemp
Editor of Stellar Reaches, a free fanzine for Traveller T20 and Classic Traveller
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Old January 16th, 2017, 10:46 AM
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Default Robots

Can someone explain how to add si to a robot, 100vl the t20 table makes no sense to me and the example builds don't show the si addition.
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Old January 22nd, 2020, 05:44 PM
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bookwyrm bookwyrm is offline
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Default Improved SI Is Awesome!

in the example shown with the helicopter. the final SI is wrong.

the extra SI for a 5000 volume vehicle is +2.5 per 1300 volume over 2000 rounded down. 5000 - 2000 = 3000. that would make it 2.5 x 2 = 5. factor of 5 x 5 = 25. 55 + 25 = 80 SI for a tech-5 military helicopter.

to answer Zelt (yes I know, necro, but I like the idea of tougher robots also), the lowest TL for a robot is 11. I am guessing that you want a sturdier build for a robot PC or a more rugged NPC robot.

volume 100 robot has a base SI of 13 and base SI volume of 1 (from armor table).

11 levels of upgrade is 2 +10 = 12. 12 x 2 (for tech level) = 24. 24 x 1vl = 24 volume. cost is 24 x 9 = 216. 216 + 3000 = Cr3,216. this is added to the cost of the robot before it is doubled for Humanesque or x8 for Humaniform chassis configurations.

the upgrade factor for the robot is 11. 1.5 SI per 22 over 30 (rounded down) gives us 11 x 3 =33. 33 + 13 (original base SI of the robot) = 46.

the downside for having this much SI is that there is 76 volume left for everything else. robot brain, any appendages, drive train, power plant, fuel, sensors, and anything else.

since robots are considered vehicles in T20, they take 5 dice less DMG from any life forms before applying any armor reductions. so unless you are in combat zones a lot with a lot of AP or HE ordinance flying around, or are doing robot vs. robot or other dangerous types of campaigns, you probably don't need that much SI on your robot.
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Old January 22nd, 2020, 06:07 PM
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Default great IS update

the final SI for the helicopter should be 80. the 2.5 for extra SI should be 5, so it would be 5 x 5 = 25. 25 + 55 = 80.

the numbers come from 5000vl - 2000 = 3000. +2.5vl per 1300 over 2000 rounded down gives 2.something, or 2. 2.5 x 2 = 5.

for a tech 11 robot (lowest tech for robot PC) 100vl.

vl24 maximum SI for tech 11. cost Cr3,216. 63 SI for the robot.

14 from base 10 and 1.5 per 22 over 30 gives 4.5, or 4 rounded down.

factor 11 SI multiplied x 4.5 (1.5 x3) = 49.5, or 49 SI rounded down.

49 + 14 =63.

it's a lot of SI, but the robot only has 76 volume left for everything else.
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Old February 15th, 2020, 04:14 PM
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Default an aplogy

not sure how to edit my earlier posts, so I am posting again.

I apologize for mentioning that far-trader calculated the extra SI incorrectly.

I have been working up some starships recently using his formula based on AR, and realized that my interpretation was wrong.

a 100 dton ship gets AR 1 the same way a 200 dton ship does, except the 200 dton ship requires more volume of AR to protect the ship for the same AR rating. and of course, more AR can be gotten by taking up more volume (and spending money) up to the tech level of the shipyard the ship is/was built at.

the extra SI, or reinforcement, is the same. the 200 dton ship requires more volume for reinforcement than the 100 dton ship does to get the same +15 SI reinforcement. using more volume of the ship, up to the tech level of the shipyard that built the ship, will increase the reinforcement rating of the ship.

lastly, after doing a lot of thinking on the subject, military ships would probably use AR first, and if there is enough/any room left over, maybe reinforce for extra SI. for commercial ships, especially traders that need space for cargo and/or passengers, AR takes up too much space and therefore isn't very efficient. but one or two ratings of reinforcement can be huge. a 200 dton trader with an SI of 115 and tech C, can get an extra 15 SI at the expense of 8 dtons, +30 for 12. but this would only make sense in a campaign with lots of space combat, like with pirates, smuggling, competition. of course, a tech F ship only needs 4 dton for the +15, 6 dton for +30.
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