I've been playing a whole bunch of Subnautica, and have been thinking about what a Subaquatic Submarine Focused Hexploration/Base Building campaign might look like using Starfinder 2nd Edition rules, and whether there is a planet that would be well suited to such a campaign?
There is a galaxy worth of planets that would likely work on. Especially if you want to do a colonization type campaign or setting up a base. Take something like horizons of the vast and set it on a more aquatic world. Tons of aquatic ancestries are available for it. In the pact worlds one of the pact races the kalo are from a fully aquatic society based on a water moon of bretheda.
But if you are looking more at exploration/colonization super easy to just whip up a world in the vast.
Nice thing about starfinder is basically everybody with tech body armor is effectively wearing a scuba suit rated for moderate depths.
I've been playing a whole bunch of Subnautica, and have been thinking about what a Subaquatic Submarine Focused Hexploration/Base Building campaign might look like using Starfinder 2nd Edition rules, and whether there is a planet that would be well suited to such a campaign?
I don't think any of the central Pact World planets (or space stations, or asteroid belt) are primarily aquatic. You could definitely have a planet of your own design that is aquatic. And put it pretty much anywhere on the galaxy map that you want - as a frequently visited trade planet, or a fringe planet off the beaten paths.
The Hexploration rules are on the Pathfinder side, but are almost entirely system agnostic. You would have no problems using those rules in Starfinder2e. I don't think there are any examples of fully aquatic terrain and hazards, so you would need to use your own creativity to come up with those. The math should all math correctly though.
Like kaid noted, Starfinder has equipment that would easily handle aquatic terrain.
If things do devolve into encounter mode (which probably should happen occasionally) there are the Aquatic Combat player facing rules, and the Aquatic Combat GM Guidelines.
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Hey, SM_aka_SpaceMeister! Dustin recommends Nsis since it's an ice-crusted ocean world in the Diaspora that contains many sarcessian dome cities, submarine fleets, and giant underwater monsters. As you may already know, as well as others in the thread who are avid fans, it was once the fountainhead for the River Between, a cosmic waterway that recently dried up and became ribbons of solar energy for mysterious reasons your players could solve as they explore the depths of this water world. Could be a great fit for your campaign!
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Fantastic advice everyone thank you.
I think I'm going to want to homebrew a planet. Instead of spaceships, the players will build submersibles to explore greater depths and distances from their crash-landing base.
I actively want to discourage or ban natively aquatic races because I want to focus on utilising the planets resources to survive, as well as emphasise the danger and wonder of subaquatic exploration.
Here's the pitch I"m thinking of...
Set during the Drift Crisis:
Genre: Survival Sci‑Fantasy, Alien Exploration, Cosmic Mystery
Tone: Isolation, thalassophobia, awe, gradual empowerment
Primary Pillars: Exploration • Survival • Construction
Secondary Pillars: Roleplay • Discovery • Ethical choices
Combat Philosophy: Sparse, dangerous, environmentally grounded
The party’s starship catastrophically crashes on an ocean world—a planet whose surface appears mostly water, punctuated by alien reefs, abyssal trenches, drifting continents of organic matter, and impossible constructions lost to the depths.
The planet is alive in ways no one anticipated.
CAMPAIGN OPENING: THE DAY THE DRIFT BROKE
Player-Facing Premise:
The PCs are active Starfinder Society agents, assigned to a routine exploratory survey.
Mission Brief:
A newly charted tropical ocean world at the edge of known space.
No signs of hostile sapients.
Long-term potential for trade, research, and possible Pact Worlds interest.
The job is deliberately low-stress:
Survey coastlines
Sample biospheres
Deploy long-range sensors
Open diplomatic channels if sapient life is encountered
Session Zero Guidance
To preserve tone and future thematic resonance, tell the players:
You are not expecting war
You are not prepared for total isolation
Your ship is stocked for exploration, not conquest
Violence is expected to be avoidable, not constant
You are Starfinders—your role is understanding the unknown.
1. Drift Transit
Open in medias res aboard the Starfinder vessel during standard Drift travel:
Normal crew chatter
Briefings reviewed
Passive sensor logs running
PCs getting last prep done
Then introduce something wrong, but subtle:
Navigation instruments desync
Drift horizon “smears”
Comms lag by seconds
A massive, slow-moving object drifting past sensors
A fragment of the Elemental Plane of Water, torn loose and floating untethered in Driftspace.
This is not hostile—just wrong.
2. The Drift Crisis
Without warning:
The ship lurches violently
Drift engines lose harmonic lock
Power fluctuations cascade
External sensors briefly show unmapped gravity tides
PCs are caught.
The water-plane fragment acts like a metaphysical undertow:
Drift vectors collapse
Exit coordinates fail to resolve
Emergency translation engages automatically
The ship is ripped out of the Drift.
3. Transition
Hull stress alarms
Partial system loss
Atmosphere breach warnings
Navigation locked to an unknown gravity well
The ship hits atmosphere too fast and too shallow.
The PCs are conscious. But controls aren't responding correctly due to the Drift scramble.
The Crash: Arrival at the Ocean World
The ship impacts an endless ocean world under storm-heavy skies.
Key details to emphasize:
The water is darker than expected
Scans return contradictory depth data
There is far more mass than a normal ocean planet
The ship skips, tears, and settles into water rather than sinking
It does not sink because:
Subsurface terrain rises
Reefs and planet shift to halt descent
The planet catches them.
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I want to push back on the banning of aquatic ancestries with just this: if not in an aquatic world campaign, when would you play an aquatic ancestry?
We recently played an aquatic starfinder game, and swimming through and breathing in clouds of blood and viscera near drums of unknown fluids contaminating the water was so gross my character opted to use their suit's capabilities.
Just saying, maybe give it another thought.
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Given how many aquatic/semi aquatic ancestries are around in starfinder I don't see much reason to restrict them. In starfinder just about everybody has/should have long lasting environmental protections. It isn't much of an advantage as long as you have some kind of ship/base to recharge your suites as well as lots of magic options to do the same.
Aquatic races and non aquatic ones still will need to do most of the same tasks gathering resources and what not because underwater breathing is unlikely to be much of a help/hinderance but finding food/shelter/equipment effects everybody.
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First, there is a big case made by others for aquatic ancestries, but do whatever is better for you. I'll just weighs some pros and cons from the top of my head.
Pro-aquatic:
* easy to manage, as combat and other things are basically like everyone is flying
* it can be fun to think outside the box for GM-purposes to get hazards there and it's easier to get fantastical and whimsical as basic problems aren't there anymore
* depending on the technology there, non-aquatics don't lose much of an edge anyway
* easier to manage, as it's closer to what Starfinder 2 is designed around, therefore less need to write some subsystems that will actually help (as rewriting hexploration will become a nightmare the moment you realize that a ocean planet is three-dimensional and the party usually need 2 days to have one activity, even if you allow them to swim without exhausting themselves or count water as plains, if you count them as swamps, well... 6 days for one activity :P)
Contra-aquatic:
* Due to a perfect environment, aquatic ancestries are absolutely "normalized" and "unspecial"
* Non-aquatics in the party will feel constantly disadvantaged by their aquatic fellows to get even, even with the technology and other means, as those will use up slots (like upgrade slots, augmentations, spell slots, etc.)
* Survival aspect will fall much flatter, as hunting, harvesting, and gathering doesn't pose as much risk and work, unless everything becomes so hazardous, that it'd be easier and more merciful to hunt down the non-aquatics of the party and eat them than to let them even get outside their crashed ship
So I would probably look at what is important for me as the GM. If I want PCs to struggle and have problems all around they have to work through for several levels (and you got players with the patience for that), then non-aquatic is the way to go. Then maybe around level 5-6 give them some means like a swim speed to open up the world and grow out of the "basic means problems" to lead into more fantastical elements. If it's all about the fantastical elements, the experience of what may lie under the sea, then ask them to play aquatics and if someone actually wants to be non-aquatic, allow some early means to get there with the rest.
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A suggestion: you should actually incorporate that fun real-life fact about aquatic species that never shows up in TTRPGs. Specifically, the fact that basically all species of fish and amphibians have pretty narrow ranges of salinity they can live in without shriveling or swelling to death.
Use environmental hazards like too-salty currents, areas where the water is deoxygenated (like an algal bloom, or what happens in certain underwater caves), the bends (actually terrifying, and aquatic creatures are not immune to it either), or regions contaminated with disease/parasites/chemicals/eldritch god blood/etc. Letting people have the aquatic trait mostly means they can save themselves a feat if they want to use unarmed melee underwater - there's plenty of ways to make it still risky.
(EDIT: Also, this is Starfinder, a Gill Sheath is a level 1 biotech augmentation. Anyone can breathe underwater indefinitely for the low cost of 200 credits and an aug slot. Though, maybe also cribbing the level 3 Hydrojet armour upgrade that grants a swim speed from 1e would be a good idea)
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Thanks for giving such detailed advice about aquatic ancestries. I think you raise a lot of great points about how to challenge even aquatic races and still require submersible/vehicle travel in the campaign for anoxic, radioactive or infected environments, that can lead to a richer aquatic biome diversity and potentially "rope off" more challenging areas until the PCs are able to craft the right equipment.
I'm also thinking of getting a little more granular with UPBs so players will need to track and utilise resources.
- Biological
- Chemical
- Metal
- Mineral
Rather than specify "You collect 10 pounds of titanium, and 100 credits worth of diamond" I just specify you "Collect titanium and diamond increasing your Metal resources by 10 and your mineral resources by 2"
With UPBs being able to act as a "universal" resource when found or scavenged.
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THE SURVEY VESSEL WAYFARER’S GRACE
A crippled Starfinder Society exploration ship
Original Role: Medium exploration & survey vessel
Current State: Crashed, partially submerged, semi-operational
Narrative Function: Home, lifeline, moral anchor
The Wayfarer’s Grace didn’t just survive the impact—it was caught by the shallows and reef‑structures beneath the surface. The hull is breached in multiple places, but key compartments remain sealed.
The ship is now effectively a static base with modular potential.
BASE STAT BLOCK (ABSTRACT)
Use these as tracks, not hit points.
Track
Starting Rating
Meaning
Structural Integrity
2 / 5
Hull breaches, unstable decks
Power Availability
2 / 5
Limited energy, rolling blackouts
Life Support
3 / 5
Stable for now, oxygen rationing
Sensor Coverage
1 / 5
Short-range, unreliable
Crew Morale
3 / 5
Anxious but hopeful
If any track hits 0, the base begins to fail catastrophically.
Upgrades raise the cap or restore points.
HARDPOINTS & MODULE SLOTS
The Wayfarer’s Grace has 6 major hardpoints. Each can be:
Repaired Repurposed Expanded into a new function via downtime
1. Bridge (Command & Coordination)
Status: Damaged but intact
Base Functions
Tactical planning
Crew coordination
Long-term project management
Upgrade Paths
Mission Control: reduces downtime needed for construction
Signal Buoy Integration: limited planetary comms
Cultural Interface: bonuses when negotiating with locals
2. Engineering Bay
Status: Partially flooded
Base Functions
Power routing
Emergency repairs
Fabrication of basic gear
Upgrade Paths
⚙️ Advanced Fabricator: unlocks sub & base upgrades
Bio-Reactor Interface: integrate alien biomass
Pressure-Tuned Systems: safer deep operations
This is the most upgrade-hungry module.
3. Medical Bay
Status: Fully sealed, operational
Base Functions
Stabilize injured NPCs
Treat pressure sickness & alien pathogens
Upgrade Paths
Xenobiology Lab
Long-Term Care Pods (preserve critically injured NPCs)
Neural Recovery Suites (reduce trauma effects)
4. Cargo & Salvage Deck
Status: Breached
Base Functions
Resource storage
Salvage sorting
Upgrade Paths
Automated Sorting Arms
Living Material Containment
️ Modular Construction Frames
5. Crew Habitat Ring
Status: Overcrowded
Base Functions
Housing survivors
Social hub
Morale checks happen here
Upgrade Paths
Hydroponics
Recreation Module (morale buffer)
Diplomatic Quarters (local visitors)
6. Science & Sensor Pod
Status: Mostly offline
Base Functions
Environmental analysis
Limited sonar
Upgrade Paths
Deep Sonar Array
️ Autonomous Drones
Anomaly Detection (Divine/Mystical)
SURVIVORS: SUPPORT NPC CADRE
These NPCs are essential, fragile, and emotional anchors to the home base.
They do not replace PCs in exploration.
Onboard Survivors (Present at Crash)
Chief Engineer Lira Kael (Human)
Brilliant, exhausted, out of her depth emotionally
Keeps the ship alive while PCs are gone
Can restore 1 Power per downtime if supplied
“I can fix anything… just not this planet.”
Dr. Oshuun (Lashunta, Damaya)
Xenobiologist & medic
Fascinated by alien life, cautiously reverent of the ocean
Reduces negative consequences from alien exposure
Quartermaster Bren Vox (Vesk)
Logistics specialist, not combat-trained
Keeps resources honest
Pushes back if PCs hoard or overspend
Loyal, blunt, deeply uncomfortable underwater.
Escape Pod Survivors (ACT I Rescue Hooks)
These pods are side objectives in Act I.
Pod Alpha – Systems Technician Mirea Sol
Found drifting near a kelp forest
Hypoxic but alive
Unlocks faster repairs once rescued
Pod Beta – Surveyor-Scout Dax Thorne
Crashed on a reef shelf
Lightly armed, shaken
Knows surrounding terrain layouts
Pod Gamma – Cultural Archivist Keth-IX
Android, damaged memory core
Holds partial records of lost civilizations
Critical foreshadowing NPC
Recovering Keth-IX reveals the planet once hosted land-based cities.
NPC FUNCTION WHILE PCS ARE AWAY
When PCs leave the base:
NPCs hold the line
They can run 1 base action per downtime
Examples:
Restore +1 to a track
Maintain morale
Prevent random failures
Finish low-risk projects
Failing to maintain relationships or resources can introduce:
Accidents
Panic
Resource loss
Ethical conflicts (“We can’t keep doing this…”)
FAILURE STATES (Pressure Without Punishment)
Use complications, not deaths:
Hull breaches worsen
NPCs injured
Morale drops
Power diverted unexpectedly
Let the PCs feel needed.