White Plume Mountain Aquarium Hydrodynamics

(Updated 6/29/17)

The aquarium room in the dungeon White Plume Mountain is a very complex encounter that will quickly have DM’s trying to figure out hydrodynamics of water flow and volume. Last night I had the pleasure of co-DM’ing a nearly disastrous attempt on the room in an Adventurer’s League game at Giga-Bites Cafe. The players, through recklessness and bravado, started to try to take on all of the room’s creatures at once. In the end, they managed to withdraw from the room and their actions probably set them up for an easier take on the room later. This experience got me thinking that maybe I could help out with some volume and flow calculations.

  • Water Volume of Area B: 34,000cu ft (34 10’x10’ cubes)
  • Air Volume of Area C: 26,000cu ft (26 10’x10’ cubes)
  • Water Volume of Area D: 18,000cu ft (18 10’x10’ cubes)
  • Air Volume of Area E: 10,000cu ft (10 10’x10’ cubes)

If the glass wall at B is broken, water will flow into area C, fill it and then flow into D and finally overflow and flow into area E, filling it to a depth of 8 feet (if the drains are blocked somehow). This will take about 25 minutes (250 rounds) to complete. If left alone, Area E will drain in about 30 minutes, resulting in very little water actually accumulating in Area E for any length of time.

If the glass wall at C (once filled with water or B and C at the same time) is broken the water will flow into D, overflow and flow into area E, filling area E to a depth of 22½ ft, Filling Area D to a total depth of 12½ ft and 2 ½ ft of water will remain in Area C. This will take about 12 minutes (120 rounds) to complete. If left alone, the extra water will drain in about 2 hours, resulting in water only in Area D.

If the glass wall at B is broken and the party waits for the water to drain out, and then the glass wall at C is broken, C, D and E will fill completely and E will fill to a depth of about 21 feet, D to 11 feet and C to 1 foot. This will take about 15 minutes (150 rounds) to complete. This water will drain from Area E & C in about 90 minutes, leaving 10 feet of water in area D.

If the glass at D (but not at B) is broken, the water will flow into Area E, completely filling it to a depth of 12 ¾ ft and 2 ¾ ft of water will remain in area D. This will take about 12 minutes (120 rounds) to complete. If left alone, this water will drain from area E & D in about an hour.

If the glass at B, C and D are all broken the whole mass of water will drain in about 3 hours.

For simplicity’s sake opening a second hole will halve the drain time.

Trying to climb up through a hole where water if pouring out is extremely difficult, the DC should be at least 25. Trying to act under a flow of water should require a STR check at DC 15 and all actions should be at Disadvantage. However, this will only be the case for the first few minutes of drain time, the flow will get weaker over time and after about half the time, will be slow enough that it will not impede heroes from action. Unless you want it to.

A quick Google search reveals that an ASU biologist says that some Scorpions can survive for up to 2 days under water. In that case, I’d rule that these scorpions can swim. That should freak out the players. However, these are all unintelligent, hungry animals. The Manticores are a little smarter, but the rest of the animals will try to eat each other given the chance.

The Manticores have learned that shooting spikes at the Sea Lions is useless, even if they killed a Sea Lion, the body would just sink to the bottom of the tank and they would not get any food.

But the Scorpions, Crayfish and Sea Lions will all attack each other given the opportunity. The Manticores will also attack anything that they can reach and eat. Nothing will drown in the event that their enclosure fills with or drains of water.

The Manticores can theoretically reach any part of the room with their tail spikes, except that the glass walls prevent them hitting targets not standing in a gap in the glass or on top of a glass wall. (The red line in the diagrams indicates the attack angle on the Manticore’s spike attack.)

In the event that the players break the glass wall at B, the water will flow into C, the Scorpions and Crayfish will co-mingle and kill one another, with the exact results being dependent on the exact situation. In the water, the Crayfish will likely get the better of the Scorpions. The water that flows into E will drain out in about 30 minutes. The Manticores will be well and truly pissed off wet cats.

In the event that the players then break the glass at C, any surviving Crayfish will probably be OK and will stay away from the Sea Lions, meanwhile the Sea Lions and Manticores will fight one another, with the Manticores trying to get out of the water and fleeing up into the dry area at A. They should be able to jump from the top of glass wall to top of glass wall to escape. Its likely that the Sea Lions will kill one and eat it given time. The excess water will drain out in about 90 minutes.

Edit: Upon reflection, the drain times from one level to another have been updated. Since the rate at which water drains is kinda based on the square of the height difference between the top of the water and the bottom of the hole, the water will drain 100 times slower at the end of the drain time than at the beginning, not 4 times. Oops. So I have made the drain times 25 times slower than they were in version one. This ends up having a pretty significant effect given the published drain time of all the water (3 hours), which is probably way too fast but it’s a given in this physics problem.

Episode 85: Gamemastering 101 Panel

This episode is a recording of a panel on gamemastering at the Atlanta Science Fiction and Fantasy Expo on March 11th, 2017.

God Told Me To by Gumbel is licensed under a Attribution-NonCommercial-ShareAlike License 

Trail of Cthulhu game aid

I created a LibreOffice spreadsheet to keep track of the players’ spends on investigations and general activities. It’s very similar to the ones available on the Pelgrane site and elsewhere. I like mine because it is ‘form fillable’, you know, being a spreadsheet and all.

It could be expanded to automatically calculate point allocation during character creation, but that is definitely beyond the scope of use of this document.

ToC Abilities Record

Using Dramatic Beats in RPGs

I’ve been reading Hamlet’s Hit Points (HHP) by Robin D. Laws (available here) recently and thought it might be interesting to try to use the concept of dramatic hope/fear beats at the table. If you haven’t read it, the basic idea is that stories consist of beats of various kinds that move to audience toward hope that the hero will succeed or fear that they will fail.

dramatic-tension-chartTo do that I drew the chart to the right and used the chips to keep track of whether we were going down towards fear or up towards hope. For our game hope was positive/solving the mystery fear was negative/scary/deepening the mystery. HHP talks about Dramatic beats, Procedural beats, Gratification beats and a variety of other situations that can result in a move toward hope or fear. This system doesn’t distinguish between the various kinds of beats, just whether the story was moving up or down. Any movement up, moved all of the chip to the center line and one chip up to hope, and the reverse happened for movement toward fear. A rule of thumb from Hamlet was Shakespeare never had more than three beats in either direction in a row, while Dr. No had as many as five or more. As a GM, I could look at the status and say, it might be a good time for an up or down beat now, depending on where we were.

This done, we sat down to play game of Trail of Cthulhu using a home made investigation. We play over Skype, we’ve been doing that for about 4 years now, so the issues of Skype are familiar to us. Particularly the issues of not playing with even video, it’s just audio.

In practice I found two interesting things and underlined a truth that I have known for a while. First thing I found was that my sense of how things were going tracked pretty closely with where the chips told me it was. If I felt the mood was dark and worried, I’d see that we were 3 or more chips in the Fear. If we were joking and light hearted, sure enough we’d be more than 2 chips in the Hope. I was probably less careful about tracking up beats.

gratificationThe second thing I found was that the players had more control over the progression than I imagined. In HHP, gratification beats are generally followed by a free floating up arrow. Which is great for movies, plays and literature, but in games, every participant has the opportunity to make a joke at any time which lightens the mood and clearly works to reverse direction on the chart toward Hope. I found that my players would routinely make a joke after 4-5 down beats, which effectively allowed me as GM to not worry about providing a break in the tension, the players would do that themselves. Alternately, you could look at it as robbing the GM of the ability to control the tension. As we got closer to solving the mystery, the up beats came fast and furious. It will be interesting to see how the chart works during an action scene.

The truth that was underlined by considering the flow of the story as procedural beats was that I don’t know enough about what makes a compelling story as I should. I feel that If I knew the structure of a story I would be better able to use where we were in manipulating the tension and story. I feel like this is an area that I need to learn more about to improve my games.

(Thumbs Up graphic from Gameplaywright available under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License)

Episode 64: Workshop: Dark Heresy followup

img_3509 img_3510In this episode Tim and I discuss how the first session went and where to go next with his Dark Heresy game. His players definitely shouldn’t listen to this one. Until later.


Pictures by Tim Williamson


Dark Heresy is by Fantasy Flight Games


God Told Me To by Gumbel is licensed under a Attribution-NonCommercial-ShareAlike License

Episode 63: Workshop Dark Heresy Campaign Kick off

_dsc8389In this episode Tim and I discuss how to kickoff his Dark Heresy game. His players probably shouldn’t listen to this one.


Photo by Dan Williamson


Dark Heresy is by Fantasy Flight Games


God Told Me To by Gumbel is licensed under a Attribution-NonCommercial-ShareAlike License


Episode 35: Bonus Episode 2, GM 101 Panel from ASFE

We did a panel on Game Mastering 101 at the Atlanta Sci-Fi and Fantasy Expo on March 5th, 2016. This is a recording of that panel. Pardon the bad sound quality.


Happy Halloween (The Vivisectors) / CC BY-NC-SA 4.0