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Old January 1st, 2018, 09:54 AM
punga punga is offline
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Default Hydrographic Percentage of a Planet

Hello, all! I've slowly been dipping my feet into other versions of Traveller after playing GT some time ago. While working on a subsector, I hit the following snag:

The rules for world creation in CT (and MT) specify that to determine the hydrographic percentage of a planet, one rolls 2D6-7 + size; if the planet's size is 0 (or 1, in MT), the hydrographic percentage is automatically 0. If the planet's atmosphere is 0,1,A,B, or C, one add a DM of -4 (so the roll is really 2D6-11). This means that there's non-trivial chance of rolling a negative number, which of course is rather odd to me. Am I missing something in the rules? Perhaps I'm misreading the dice notation?

Thanks in advance.g
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Old January 1st, 2018, 02:41 PM
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Quote:
Originally Posted by punga View Post
Am I missing something in the rules? Perhaps I'm misreading the dice notation?

Thanks in advance.g
Only that hydrographics has a minimum of 0.
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Old January 1st, 2018, 04:24 PM
Axe Axe is offline
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Howdy,

The correct Hydrographic Percentage formula is:

2D-7+atmosphere


Several releases of CT use the same incorrect World Generation Checklist, which lists the formula as:
2D-7+size

In Book 3, the correct formula is on page 7 (World Creation section).
In The Traveller Book, the correct formula is on page 82 (World Creation section).
In Starter Traveller, the correct formula is in the Rules Booklet, page 44. The incorrect formula is listed in the Charts and Tables Booklet, page 15.


Welcome to CT!

Cheers!

Last edited by Axe; January 1st, 2018 at 04:43 PM..
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Old January 1st, 2018, 05:02 PM
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Hey Aramis,

I just went to grab the link for Don's Consolidated CT errata, but the website is no longer up. I also checked the FFE website, but the link there points to Don.

Cheers
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Old January 1st, 2018, 05:09 PM
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HI,

Just download it from the link in the first post of Don's CT Errata Compendium thread:

http://www.travellerrpg.com/CotI/Dis...ad.php?t=20051


He kept that first link up to date. There were more corrections brought up after v1.2. Look at the later pages of the CT Errata Compendium thread (about page 47ish, and on).

(The last sentence was for newer readers. I see your comments in there, Matt123)

Last edited by Axe; January 1st, 2018 at 05:23 PM..
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Old January 1st, 2018, 05:43 PM
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Quote:
Originally Posted by Axe View Post
Howdy,

The correct Hydrographic Percentage formula is:

2D-7+atmosphere


Several releases of CT use the same incorrect World Generation Checklist, which lists the formula as:
2D-7+size
While you're right, see that this makes ice-capped worlds quite rare, as the -4 for having atmosphere 0, 1 or A+ to hydrographics digit is added to the -7 if atmosphere is 0 or -6 if 1, for a -10 or -11 final DM to hydrographics, quite rare.

So, if atmosphere is used (as in the books and errata), on atmosphere 0 worlds only boxes give an hydrographic of 1, while on atmosphere 1 worlds, only 11 or 12 roll in hydrogrphics give a result of 1 or 2...

OTOH, if size is used instead of atmosphere, ice capped are more posible, and can have hydrographics over 2.
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Old January 1st, 2018, 06:56 PM
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Interesting. I'll have to see what my app is using (size or atmosphere) and see what ice-capped worlds are doing on my generation chart, using both functions.

ADDED:
It's a world of difference using size instead of atmosphere. Different kinds of planets come up for sure that wouldn't exist otherwise.

Last edited by ShawnDriscoll; January 1st, 2018 at 08:30 PM..
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Old January 1st, 2018, 07:20 PM
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Quote:
Originally Posted by McPerth View Post
While you're right, see that this makes ice-capped worlds quite rare, as the -4 for having atmosphere 0, 1 or A+ to hydrographics digit is added to the -7 if atmosphere is 0 or -6 if 1, for a -10 or -11 final DM to hydrographics, quite rare.

So, if atmosphere is used (as in the books and errata), on atmosphere 0 worlds only boxes give an hydrographic of 1, while on atmosphere 1 worlds, only 11 or 12 roll in hydrogrphics give a result of 1 or 2...

OTOH, if size is used instead of atmosphere, ice capped are more posible, and can have hydrographics over 2.
Mars has (if my calculations are correct) about 1.2% hydrographic percentage (ice cap diameters are 1100 km and 400 km, Mars' diameter is 3400 km). 10% sounds pretty good in that respect. I picked Mars as an example because it's the only rocky world apart from Earth that has ice caps.

As you've shown, CT worldgen won't give you an actual icy world like Europa or Enceladus. I think you'd need to use something like GT's First In rules for that. I have somewhere a set of scripts that will generate a star system using the approach laid out at https://wiki.rpg.net/index.php/RTT_Worldgen. IIRC, you get fewer classically habitable systems that way -
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Old January 1st, 2018, 11:33 PM
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Mars may have water underground.
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Old January 2nd, 2018, 02:14 AM
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Mars may have water underground.
Determining that may be of vital interest, too. For our purposes here, however, Traveller defines Hydrographics as surface water, or "water".
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