Stealth detection roll's distance

[gesus]

I am confused about distance of a sense roll vs sneaking opponent.
Let's make some abstract examples.
1.
Fighter 1 (F1) is sneaking to fighter 2 (F2) from his back. F2 cannot see F1 because of arc of vision. But he can hear and he's on guard. So it have to be a quick contest of Stealth vs hearing. Let's assume there are no modifiers to hearing except distance.
At which distance this hearing roll have to be made?
Does it have to be only one roll?

2.
F2 is patrolling so he can possibly turn towards F1. Does a vision roll needed? And a hearing roll too? At what distance?

3.
F2 is completely unaware and is not on guard. No sense rolls at all in this case?

[Mailanka]

My friends and I started working out a "Tactical Stealth" system. Here's what we came up with.

1. If you're doing it "on a map" I'd probably make it one hearing check per turn, but "hearing distance" is tricky. The book lists it as -1 per doubling, so it can get pretty high in penalties for the listener pretty quickly. Remember that running is at -5, but it will mean you get to him faster, which means you might kill him better. I'm curious what the numbers would be of 5 turns of sneaking up on someone vs a 1 turn run at -5 to stealth.

If you're not doing it with a map, I'd just roll once.

2. Stealth never beats vision unless you're hiding. It covers the sort of "ducking behind something." Think of it like "sticky cover." If you're near something where you could hide, the stealth roll covers how well your character IS hiding, or how quickly he can duck behind cover if someone sees him. If that fails, or you can't hide, roll vision vs camoflage. Rolls to see something "in plain sight" are at +10.

So if you're standing in the middle of a road, even with camo, the other guy has +10 to see you. If you're lurking near some bushes, he doesn't have the +10 to see you and you get a stealth check and if that fails, you get a camo check.

3. I think you do, you just can't substitute observation for perception? Good question.

[vicky_molokh]

The system is incomplete (i.e. so far requires some judgement), but here are the bits that seem solid to me:

Stealth can generally be used to resist Vision rolls by hiding. "A successful roll lets you conceal yourself anywhere except in a totally bare room." Thus, it gets the RAW -5 if there are few places to hide, up to +3 for good cover.
Note that since Vision normally rolls at +10 against a human-sized target, your chances will start looking equal at about 100 yards of distance. Plus/minus modifiers, of course.

As for hearing, I asked this question, but don't remember it enjoying an official answer.
However, GURPS High-Tech, page 158, lists "Leaves rustling, stalking person
40 dB(A), 0.25 yards" in the table of distances at which a sound is heard on an Unmodified Hearing Roll. For each doubling of range, you get -1 to Hearing.

[gesus]

Originally Posted by Mailanka

My friends and I started working out a "Tactical Stealth" system. Here's what we came up with.

1. If you're doing it "on a map" I'd probably make it one hearing check per turn, but "hearing distance" is tricky. The book lists it as -1 per doubling, so it can get pretty high in penalties for the listener pretty quickly.

So between 16 and 8 yards F2 still has -6 to hearing but will make 8 rolls. And 4 more rolls between 8 and 4 yard as -5 to hearing.
Seems a bit hard to get to melee range. But also realistic I suppose.
Thanks for the answer.

[vicky_molokh]

Also note that the skill description of Stealth offers a single roll to get within 30, and another to get within 15 yards of an animal. So you shouldn't make too many rolls: the more you roll, the higher the chance of failure.

I suppose it's reasonable to record the dice result and then apply modifier to it.

[fifiste]

Someone had a really decent stealth vs perception skill system worked out, with an example of sneaking up to a sentry. In this forum.
I'm not sure I think it was Bruno. I try to find it I think I bookmarked the post for my use, when I should GM something stealth
related.

OK found it i think its Captain Joy's post.

Spoiler:  

Originally Posted by Captain Joy

This is how I handle Stealth. I'd be delighted to get feedback from the forum community. While this is a house rule, my intention is not to go against the RAW, simply add detail. So, if anything here is actually against the rules, do let me know.

HOUSE RULE: Stealth
This house rule adds a quantifiable component to how close you can sneak up on someone.

Stealth

DX/Average
Defaults: DX-5, or IQ-5

Stealth vs Perception
The GM will use the result of the Quick Contest between Stealth and Perception and apply the results to the Size and Speed/Range Table [B550] to determine at what distance the stealthy person is seen and/or heard. Since the Stealthy person will know how good their roll is, they will have an informed opinion when they tell the GM how close and how quickly they intend to approach their quarry. If they chose a distance that is not too close, then they will not be detected; if they choose a distance that is too close, then they will be detected the moment they step into the range determined by the Size and Speed/ Range Table [B550]. On a tie, the quarry has noticed something (heard a twig snap, caught movement out of the corner of their eye, etc.) and can react, but will not know the source of the disturbance.

After the Stealthy person makes a roll, they must move one or more hexes towards their intended target. Assuming they were not discovered, they can then request another Quick Contest (at no penalty for a repeated attempt). Thus, a Stealthy person can break up their approach into more than one Quick Contest if that is to their liking.

Modifiers
In some cases, it's not obvious if a modifier should be applied to the Stealth roll or the Perception roll. Whatever is decided, be sure not to double dip.

• a penalty equal to your encumbrance level
• -5 to fool those with Discriminatory Smell, usually animals (unless you are downwind of them)
• darkness penalties will affect vision rolls

Environmental Modifiers

• a +10 if they're in an enclosed structure, e.g. they're on the other side of a closed door
• +5 if they can't possibly see you, e.g. their back is to you
• +3 for many hiding places, e.g. stalking game in a forest where tree trunks will hide you
• -3 for an area void of ambient noise, e.g. inside a empty building, no a/c, no fluorescent lights,
  isolated from outside street noise
• -5 an area without "natural" hiding places, e.g. stalking someone down the hotel hallway
• -10 a bare area with no shadows, e.g. a clearing in the woods or an empty room

Movement Modifiers

• a penalty equal to your move-1 (i.e. no penalty if you're moving 1 yard/sec)
• +3 if you're move is 0, but you are still active, e.g. staying put but took a Ready maneuver
• +5 if you're move is 0, and you are effectively motionless and silent, e.g. staying put but took an Aim
  maneuver
• +10 if you're move is 0, you're completely hidden and not observing your foe, i.e. you're just plain
  hiding

Examples
Sentry Removal
Corporal Lee Linda wants to sneak all they way up to a guard who is guarding the door to an enemy safe-house. It is night; the guard and door are dimly illuminated but the rest of the surrounding area isn't. The guard is 5 yards from the corner of the building. Lee's Stealth is 13; the sentry's Perception is 11. Lee informs the GM he wants to use Stealth to sneak up to the guard, so situational modifiers are assessed. Since Lee will approach from the side of the building, where the guard can not possibly see him, he'll be at a +5 until he rounds the corner. Once he rounds the corner, he'll be in a bare area, a -10 penalty; but it's dark, so the GM decides a net penalty of -5 is appropriate.

Lee sets out, rolling an 11, a success by 2. Assuming the sentry made his Perception roll exactly and ignoring situational modifiers, Lee would be detected when he got 1 yard from the guard: -2 on the Size and Speed/Range Table [B550]. Applying the -5 penalty after rounding the corner results in a failure by 3. +3 on the Size and Speed/Range Table [B550] means Lee would be detected 7 yards away. Lee thinks he can do better, so he informs the GM he'll move up to the corner of the building. Lee doesn't know this, but the guard also rolled an 11. Since Lee is at a +5 until he rounds the corner, he easily makes it to the corner of the building without being heard.

Having gotten to corner, Lee now rolls to proceed even closer. He'll be at -5 after he rounds the corner. Lee rolls a 9, succeeding by 4, adjusted to failing by 1: 3 yards on the Size and Speed/Range Table [B550]. Lee knows this in not close enough to attack with his Garrote, but he is committed to moving at least one yard closer. Lee informs the GM he'll move only one yard closer this turn. (He's hoping that if he's not detected this turn, he'll be able to All Out Attack him next turn with the element of surprise.) The sentry rolls an 8, succeeding by 3; so Lee actually lost the Quick Contest by 4, resulting in detection at 10 yards. The GM informs Lee that as soon as he rounds the corner, the guard looks over and sees him. (The element of surprise diminished, Lee will be forced to choose between attempting to take him out quietly in hand-to-hand combat, or readying his M4.)

Bow Hunting
Shung Jiao and Shung Li are out bow hunting. Jiao would like to get as close as possible before taking his shot. Li is tracking the wild boar and they are both moving stealthily as the trail seems fresh. They are in the woods and the boar is not downwind of them, so the GM gives them a +3 bonus situational modifier. Shung Jiao's Stealth is 10, Li's is 12; Shung Jiao rolls a 9, Le rolls an 11; they both make their rolls by 1, by 4 with the modifier. They would like to get within 15 yards of the boar. (Shung Jiao's bow skill is 12. Acc 1 with 3 seconds of aiming can increase this to 15. The range penalty at 15 yards is -5.) If they lose the Quick Contest by 4 or less, they're okay. (5 is not okay because then they'd be detected at 15 yards.) They decide this roll is good enough that they've probably not even lost the Quick Contest and commit to approach to 5 yards. Unknown to them, the boar with Perception 12 rolled a 10, succeeding by 2. They won their Quick Contest by 2. The GM informs then they're 5 yards away from a wild boar that is ignoring them. Shung Jiao can now set up his shot. If Shung Jiao decides he wants to move even closer (maybe Shung Jiao decides he wants to staff hunt instead) they will both have to engage in another Quick Contest. Of course, Li will be at +10 since he will choose not to approach with Shung Jiao.

[kirbwarrior]

Hmm, I had always thought you rolled Stealth vs Observation (Per-5) when sneaking up on someone. Observation seems to imply that, but Stealth says vs Perception. That even lined up with what I had thought (someone trained in Stealth can easily sneak up on someone who doesn't know how to observe).

[the_matrix_walker]

Originally Posted by kirbwarrior

Hmm, I had always thought you rolled Stealth vs Observation (Per-5) when sneaking up on someone. Observation seems to imply that, but Stealth says vs Perception. That even lined up with what I had thought (someone trained in Stealth can easily sneak up on someone who doesn't know how to observe).

I don't think you have to use Observation at default, I believe the intent is to use the better of Per or Observation.

[the_matrix_walker]

Yeah, I fond a Kromm post to support that...

Originally Posted by Kromm

Skills like Camouflage and Stealth normally go up against straight Per (or Vision or Hearing, where applicable). If your Observation happens to be at Per+1 or better, you may use it instead. That isn't the main use of Observation, though, but a nice side-benefit having the skill. Observation's principal use is covertly gathering intelligence in the manner of a spy, a detective on stakeout, a military scout, or a gangster casing a mark: defenses, security, staffing levels, alertness levels, shift changes, objectives of strategic interest, etc.

As for when it's a Quick Contest, the easiest way to think of it is like this:

• When Stealth could actually achieve total surprise, roll a straight success roll. Success grants total surprise.
• When Stealth could at most grant the sneaky party partial surprise, roll a Quick Contest. Victory grants partial surprise.

This decision is necessarily subjective . . . the GM may or may not accept "I'm on alert!" as good enough to shift the first case to the second, and might even wish to tie the choice of mechanics used to a plot point, not rules action.

[GodBeastX]

Stealth works on hearing too, I think you guys missed that part of the skill. It is NOT just vision.

Modifiers: A penalty equal to your
encumbrance level. -5 to hide in an
area without “natural” hiding places,
or +3 or more if there are many hiding
places. -5 to move silently if you are
moving faster than Move 1. -5 to fool
those with Discriminatory Smell (e.g.,
dogs).

So clearly stealth is to resist being seen AND heard as well as smelled, notice you still roll stealth to get past a dog who might smell you.

Things you might want to look at:

- Silence Advantage which helps with stealth. Noisy is it's opposite as a disadvantage.

- Light Step Skill adds to your stealth roll when moving.

- Observation is countered by stealth visually.

etc etc