Random Encounters: Roll Days Between Events, Not Daily

 "I wouldn't want to track how far you get in a day, I'd want to track how far you get or how many days until you encounter something."

- Commenter, Signs in the Wilderness

Let's. 

I intend to apply this to maritime adventure, so we will work an example at sea. This can obviously also be applied to the howling emptiness of terrestrial wasteland. 

1. Split your AOI based on density of traffic. I call these EDZ, Encounter Density Zones. Each is associated with a die size, representing the days between encounters. 

2. On departing town or port, roll the EDZ die: This is how many days until an encounter. 

3. When the day of an encounter is reached, roll to determine its type. Nothing notable happens in the intervening days aside from the consumption of rations and other downtime activities, like healing. 

- If passing into a new EDZ (eg. leaving sparse EDZ d30 ocean to EDZ d16 banks trafficked by fishermen), use the equation (Days Remaining)/(Old EDZ die)*(new EDZ die). In this example, if 7 days were remaining til an encounter, the equation would be 7/30*16 = 3.73 rounded to 4. On the 4th day of this leg, there will be an encounter.

- The nature of the encounter is based on the traffic in the area. It may be external (encountering fishermen, merchants, whales) or internal (mutinous grumblings, mechanical breakdown).

This allows long voyages to be handled quickly by skipping uneventful days. It must be rolled secretly, which may be a demerit, but it does give the DM time to embellish and rationalise a random encounter before it occurs. 

Worked example

 

A. PC Ship puts to sea from 49 15' N 124 15' W. Being in EDZ8 the DM secretly rolls a d8 result 3. The DM rolls to determine what the encounter is also based on the EDZ.

B. 3rd day of voyage. Encounter resolved, next EDZ roll d8 result 4. 

C. Vessel changes EDZ. (3 days remaining til next encounter)/(old EDZ size 8)*(new EDZ size 10) = 3.75 rounded to 4. 

D. Fourth days of second EDZ leg. Encounter resolved. EDZ10 rolled result 10. 

E. EDZ change. 7/10*6 = 4.2 rounded to 4. 

F. Fourth day of third EDZ leg. Encounter before entering port. 

 

(Note1: The relationship in the map between travel speed and scale was selected thoughtlessly, pay no mind to it.)

(Note2: I didn't pay attention to the half baked prevailing wind sailing speed system visible in the photo. Some more interesting scheme for resolving speed and wx is TBD).

This system does make it certain that an encounter will occur, which may be undesirable. The system could be embellished to avoid this in two ways:

Simple: On max roll, the die is rolled again. (eg. Roll d6 result 6. Roll again result 3. Encounter in 9 days). This has the undesirable effect of making encounters likely to take longer in very dense EDZs, wuch as those using a d4 or d6, while making long periods without encounters unlikely in sparse EDZs like those using a d24 or d30. 

Elaborate: Odd results in the upper half of the die's results prompt a reroll. Eg. roll d8, a result of 5 or 7 would see the d8 rerolled and that result added to the 5 or 7. This could 'explode' or 'chain' to see a long interval without encounters.  

Note that even if an encounter is determined, spotting distances, lookout alertness, wind orientation, the relative performance of different vessels, and terrain make engagement far from certain, if one or both parties do not desire it.