Undersea Adventure

Adventuring underwater is all about the alien environment, the mystery, the danger. Our real-world deep underwater explorers suffer from extreme risks compared to other types, and could be compared somewhat to space travel or deep caving. Our literature source material is thick with the trials of underwater adventure. I think that should translate well to D&D.

That said, you need to figure out how to balance the danger with the danger-mitigating technology of D&D: magic.

Breathing: A 3rd level Water Breathing spell removes the most important danger, breathing. But can it let you breathe even in especially high pressure? I don’t think it should matter, although Water Breathing as written in 1E/2E (I’m not sure about later editions) doesn’t do anything except help breathing.

Game Mechanics: I say you can hold your breath for twice your CON score in 6-second rounds. You use twice as much air when fighting or other strenuous activity. This lets an average person hold his breath for about a minute. I’d give a longer time if the person was calm, had plenty of time to oxygenate and take in a full breath, and did no activity at all.

Pressure: There is a point below which humans will just be crushed. Does this matter to you? What about the depth below which you need pressurized air and can’t breathe using a long tube? The reason a snorkel is of a pretty standard length is because you can’t inhale unpressurized air if you have too much pressure on your lungs. I would assume if you carried air with you and it was also under pressure (air in a bag, diving bell) it would be okay. Likewise if you came to an undersea air pocket like in a cave or ruin it would be breathable.

Game Mechanics: Based on basic info I found, you can’t metabolize air past about 200′ depth. If you’re in a depressurized container, obviously this doesn’t count. I give -1 to all your rolls per 50′ of depth due to pressure (dizziness, hallucinations, blacking out, etc). If you rise faster than 10′ per round you suffer 1 HP per extra 10′ in the round from “the bends.” A Necklace of Adaptation should compensate completely.

Vision: Water inhibits vision because light doesn’t pass through it as easily. But it also blocks light from the sun and moon, so below a certain depth you should assume that it’s effectively “night” all the time. You can offset this with bioluminescent fish and plants, especially to illuminate the lairs of various intelligent sea creatures and cool things you want PCs to see from far away. The muddiness of the water will be an absolute limit to vision, but even in especially clear water there will be some obscurement.

Game Mechanics: Your vision underwater is normally obscured the same as in Monsoon precipitation. Muddy water may make this zero vision, very clear water may be lighter precipitation level equivalent. I don’t care about light obscurement because that’s taken care of in the precipitation vision rules. A Helm of Underwater Action or any X-Ray Vision should compensate completely.

Temperature: It’s pretty cold underwater. Typically deep ocean temperature hovers just over freezing. If the PC is soaked, that means he’s going to die of hypothermia very quickly.

Game Mechanics: I would count this as exposure to Cold or even Arctic weather without any protection. My exposure rules give -1 penalty to rolls due to Fatigue and 1d6 damage per hour exposed in such weather. Waterproofing magic would help, reducing it to just the fatigue penalty, but a Ring of Warmth would remove the danger entirely.

Movement: You can’t fight as well as you can on land, nor swim as fast as you could run. It’s because you’re not native that that environment; undersea creatures have no penalties.

Game Mechanics: You have normal base movement, but can “jog” to double move only on the surface. You can’t “run” to multiply movement at all, and can’t jog underwater. You can’t fire missiles indirectly (like a catapult). If you’re a surface-dweller, you always lose Initiative to sea-dwellers and you always have -4 to hit and Armor Class. A Necklace of Adaptation might circumvent this, but I don’t remember. A Helm of Underwater Action maybe? Certainly a Ring of Free Action would do it.


Now that we have the dangers put down, and the possible ways around them using magic, there is another problem. If there are no special environmental conditions, what’s the point of adventuring underwater? Instead consider limited magical benefits, such as a reduction in the penalty rather than removing it, or a limit on times per day, charges, or a single-use item that had a duration.

Also consider the Zelda adventure pattern: you have access to Area A, but the way to Areas B, C, and D are blocked. You need Item B to get to Area B, etc. So you explore what you can (Area A) until you find the item needed to access one of the other areas. So it goes until you have access to everywhere.

So we can start with the assumption that the PCs will eventually have access to every undersea area, but they must earn those tools. Begin with diving for Water Breathing items. Then they need to gather items to relieve Pressure so they can go deeper. Then they need Cold Resist items to dive even deeper into the coldest reaches. In all cases they will have movement and vision problems, except that some of them will find temporary, limited efficacy, or even permanent mitigating magic for those two. Now we have three different adventure zones which require various types of equipment to explore.

Note that there are ways around the zone restrictions. They could wrap up in furs, build a big diving bell, and hit the bottom right away. But their exploratory ability will be pretty reduced.

Now we worry about what kinds of monsters and treasure there are to find down there. Try to focus on sea-based things: pearls, coral, shells, driftwood, shark skin, shipwreck goods, etc. Typical weapons will be nets, knives, spears, tridents. This way the treasure is clearly from the undersea adventure sites, and players will remember seizing it from the special undersea monsters they never fight elsewhere.

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One Response to “Undersea Adventure”

  1. Magic Changes Resource Management: 1E AD&D « 1d30 Says:

    […] goes back to my post on underwater adventure as […]

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