Hexcrawling Rules

I'll be sure to update this post periodically, but these are my rules for hexcrawling.

Basics

The character's effective Move after encumbrance is how many 5-mile hexes he can move in a day. A group moves at the speed of its slowest member. Once a day, everyone in the group makes a Hiking, Running or Skiing roll, depending on which way of moving that he is using. A success lets the character move another 20%; a critical success lets the character move another 40%. A critical failure drops the character's move by 20%.


The premise for the 5-mile hex is, other than that the Judges' Guild used them, that a normal man, without burden, can walk 25 miles in a day. That means about 10 hours of travel, per GURPS High Tech p. 55, 8 hours of sleep, and 6 hours of setting up camp and other things. A 6-mile hex will work if you accept that a normal man can walk 30 miles in a 12-hour day. Four-mile hexes are just too small.

Weather

The rules for weather in GURPS Basic Set: Campaigns aren't workable for this. On a hot day, you fail a HT roll and you lose FP, so you have to stop and get your FP back. That's lots of rolling for no gain.

Cold

Per p. B430, when the effective temperature drops below the bottom of a character's comfort zone (for humans, this is 35° F), his movement for the day drops by 10%. For every 10° below 35° F effective temperature, that is another 10% drop in movement.

If a character has an encounter at any point, he then makes the HT roll as described on p. B430 to see if he is down any FP at that point. The usual modifiers apply.

Heat

Per p. B434, when a character gets to the top 10° of his comfort zone (which, for humans and the like is 80° F), instead of losing FP, the character moves 10% slower for the day. For each extra 10° of temperature, the character moves an extra 10% slower. This is to assume that when a character starts to overheat, he ducks into the shade, and that's where the time is lost.
If a character has an encounter at any point, he then makes the HT roll as described on p. B434 to see if he is down any FP at that point. The usual modifiers apply.

Rain and Snow

When on the ground, rain and snow modify the terrain as p. B351: rain and light snow halve speed, snow deeper than ankle-deep quarters it. Roads don't matter; none of them are any good. Rain goes away after the day; snow stays until the temperature has been over 35° for 10 days with no snow. When falling, rain and snow halve movement for a time equal to the number of half-hour cells (I'm using the d30 Sandbox Companion) for non-severe storms, and stop it for severe storms. Or, in short, it's -2.5% per half-hour cell of non-severe storms and -5% per half-hour of severe storms. You can round to the nearest 10%, so a half-hour of light rain is no big deal.

Pressure

Low atmospheric pressure happens at 6,000 ft. (And please, Steve Jackson Games, stop using the prime and double prime symbols, and write out "ft." and "in." It is much easier to read. Ask Nigel Tufnel.) Unlike cold and heat, the rules on p. B429 work well, since they handle effects for a whole day.

Weather Sense

Once a day, one character makes a Weather Sense roll. A success means he knows what the weather will be for the day, and can negate 10% of penalties for each of heat/cold and rain/snow. A critical success means he can negate 20% of those penalties, while a critical failure slows down all travel by 20% (if there's a rain storm, the group walks right into it, or if it's a sunny day, it keeps trying to prepare for rain).

Camping

If camping in the cold, make an HT or HT-based Survival (Arctic) roll if camping in less than 35° weather. The daily Weather Sense roll gives a +2 to the group's rolls if made. On a failure, a character wakes up with FP loss equal to points by which he missed the roll. Use usual modifiers in Basic under Cold. He must rest longer to get back this loss, resulting in -10% to Move for each FP lost unless he is willing to always be down the FP at any encounter. Winter bedding like a sleeping fur is considered the +5 clothing; a tent gives another +5.

Same story for camping in heat, except the Survival specialty is Desert. Yes, a tent gives a bonus.

If there is rain or snow during the night, a tent protects against light rain or snow. If not in a tent, the storm length counts as missed sleep. Tents might blow over in a storm: they stay up on 15 or less on 3d in a light storm (10-20 mph), 12 or less in a non-severe multicell storm (20-40 mph), 9 or less in a severe storm (40-60 mph), 6 or less in a supercell storm. They always blow over in a tornado. If in cold weather, the character now makes his HT rolls as wet.

Encounters

When traveling through civilized areas, an encounter happens on 6 or less on 3d. Two rolls happen: one for the day, one for the night. For savage areas, I use a variant of Roger SG Sorolla's One-Page Wilderness System, with a roll of 12 on the d20 becoming a totally random encounter.

Encounter distance is 4d×10 yards (stolen from the Cook Expert Set). Add the biggest SM on each side to the roll before multiplying.

Surprise is a Perception check, modified by relative SM. If one side succeeds and the other fails, the winning side can move to 1d×10 yards before the other notices. See more details.

Evasion uses the rules for chases on p. 31 of GURPS Action 2: Exploits. Use party size as a modifier from Speed/Range as a bonus for the pursuer and a penalty for the quarry (e.g., a group of four men get a +1 against a lone elf, who gets a +2; when a lone dragon comes and chases all five of them, it gets a -2 penalty, as does the group of 5). Make only one roll a side, likely the best one.

Ugh, I lost some stuff, so here's the order, again adapted from the Expert set:

1. The GM rolls weather.
2. The GM or a player (depending on taste) rolls Weather Sense. Since we're talking about travel speed, I can't see too big a deal in a player rolling this, but it seems weird to me.
3. The group makes Hiking (or Riding or Skiing) rolls.
4. The GM calculates travel speed. This takes into account the weather, the Weather Sense roll, the Hiking/Riding/Skiing roll, and how well rested the group is.
5. The GM makes two encounter checks: one for the first half of the day, one for the second.
6. When going into a hex, there are two rolls the GM makes. The first is a Navigation (Land) roll. If this is failed, then the characters go into one of the nearby hexes, and the GM makes a Per-based Navigation (Land) roll to see if the navigator notices he screwed up. The other is an encounter check.
7. If there's an encounter, resolve it. If really crappy weather happens, resolve it.
8. Once the travel day is done, the party makes camp, and makes its Survival rolls to see if they lose HP (2d-4 HP loss on a failure)
9. After this, it makes its Foraging rolls.
10. There are two encounter checks, one for each half of the night.
11. If there's an encounter, resolve it. If really crappy weather happens, resolve it.
12. Wash, rinse, repeat.