Hydrographic Percentage of a Planet

[punga]

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

 

[aramis]

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.

 

[Axe]

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!

 

[Matt123]

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

 

[Axe]

HI,

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

http://www.travellerrpg.com/CotI/Discuss/showthread.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)

 

[McPerth]

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.

 

[ShawnDriscoll]

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.

 

[egor045]

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 -

 

[Condottiere]

Mars may have water underground.

 

[GypsyComet]

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".

 

[Ulsyus]

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!

T5 is similar: Flux + Atmosphere, Max=A, if Siz<2 then Hyd=0, if Atm <2 or >9 then Hyd DM -4, if Hyd <0 then Hyd=0, if Hyd>A then Hyd=A

 

[McPerth]

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.

See that another side effect of using atmosphere as modifier for hydrographics is tht it makes the fluid ocena worlds quite common. In fact, every world with atmosphere A+ is a fluid ocean world too, as the -4 DM does not overcome the high armposphere digit.

For a world with an A atmosphere, the final DM is -1 (-7 +10 -4), so giving us a mínimum hydrographic of 1. and as atmosphere digit raises, so does the DM.

If it depends on size, even a size 9 world with atmosphere A+ can have hydrographic digit of 0, so not to have fluid oceans.

I'm not saying this is good or bad, just poinitng it. In fact, I'm not sure how likley would such a world to have those fluid oceans. The two we know about (Venus and Titan) are listed (at least in MT:S&A) as having hydrographic percentage of 0, and could not be generated if atmopshere is used, but in both cases they could if size is...

Just for clarity: I'm not dicussing what rules (or errata when appropiate) say, they clearly say atmosphere is the one to determine hydrographics. Just point the consequences and my doubts about its logics.

 

[ShawnDriscoll]

Using Size instead of Atmosphere generates a much larger range of planet types that don't exist when using Atmosphere.

 

[punga]

Hello, all,

This is very much thread necromancy, for which I apologize. Circumstances kept me away from any gaming for the best part of 2018, so I didn't have any chance to check this (or any other gaming venues) out.

Thank you all for the answers. However, the question to me still stands, even with the corrected formulas. Allow me to walk things through an example:

Let's pretend I have a planet size of 1. Since planet size is not 0, that means the atmosphere is not automatically 0. The (adjusted) formula for atmosphere would be 2D-6. If I roll 2,3,4, or 5 on 2D, I get a negative atmosphere number, which doesn't appear on the tables.

flykiller suggested via private message to simply treat all negative numbers as 0, which might be a valid choice (I am not sure how common are planets with no atmosphere at all). Is that what every one else is doing?

 

[McPerth]

Hello, all,

This is very much thread necromancy, for which I apologize. Circumstances kept me away from any gaming for the best part of 2018, so I didn't have any chance to check this (or any other gaming venues) out.

[m;]You don't need to apopogize, as thread necromancy is perfectly accepted if you have something new to say about it.[/m;]

Thank you all for the answers. However, the question to me still stands, even with the corrected formulas. Allow me to walk things through an example:

Let's pretend I have a planet size of 1. Since planet size is not 0, that means the atmosphere is not automatically 0. The (adjusted) formula for atmosphere would be 2D-6. If I roll 2,3,4, or 5 on 2D, I get a negative atmosphere number, which doesn't appear on the tables.

flykiller suggested via private message to simply treat all negative numbers as 0, which might be a valid choice (I am not sure how common are planets with no atmosphere at all). Is that what every one else is doing?

That's how I understand it too, as negative numbeers have no stated meaning (and not only for atmosphere, but also for other UWP digits, as you could also have a negative result for government or Law level).

 

[ShawnDriscoll]

Let's pretend I have a planet size of 1. Since planet size is not 0, that means the atmosphere is not automatically 0. The (adjusted) formula for atmosphere would be 2D-6. If I roll 2,3,4, or 5 on 2D, I get a negative atmosphere number, which doesn't appear on the tables.

It's assumed that OSR-style rules are used with limits that make sense in their contexts used.

 

[Timerover51]

I start with the dice or generating program, and then see what the result is. If I want an ice-capped world, I put in an ice-capped world. I do not rigidly adhere to a random die roll.

If you look at the Jovian satellites, some of them are basically water worlds, just that the water is a bit frozen. They are worlds with a "0" for atmosphere that are completely ice-capped.

 

[punga]

[m;]You don't need to apopogize, as thread necromancy is perfectly accepted if you have something new to say about it.[/m;]



That's how I understand it too, as negative numbeers have no stated meaning (and not only for atmosphere, but also for other UWP digits, as you could also have a negative result for government or Law level).

Thanks, McPerth. I'll follow through with this, then.

 

[GypsyComet]

At least one set of rules does explicitly state that values below zero are to be adjusted to zero. That rule set may not be one of the four iterations of Classic, though.

 

[Enoki]

I could actually see two ways you could interpret this.

The first is to make it zero and that there is no large free standing bodies of water on the planet.

The second is that the negative number represents even the scarcity of water in some other form (ice, ground water, etc.) meaning that the planet has very little water in any form on it.

This second version could make things interesting for a scenario where you need water for survival, fuel, or whatever and there's very little or none to be found in any form on a world. Now you have the players needing to come up with innovative solutions to a problem. For example you can't just drill a well since there's little ground water... There's no ice to be had anywhere... What do you do?