1. This is NOT meant as a faithful diving simulator. Just an upgrade to add more challenging water effects. Remember there's a LOT of design options between 0% and 100% realism!
   
2. I haven't yet worked out the rates of pressure damage to inflict upon an exposed deep diver. Accepting suggestions from any number crunchers.
   
3. There may still be a few unforeseen consequences. Please let me know in the comments what I've overlooked.
   
4. Special request not to announce "Who wants to wait around for an airlock?"

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Diving at great depth is bad for your health! We can acknowledge this without going the Full Sim (e.g. without including narcosis and 'the bends')

• Beginning at 100m a swimmer receives some slight damage over time (rate to be decided)
  
• Every 10m deeper below adds to this rate of damage
  
• By about 900m pressure damage becomes brutal enough to make swimming unsustainable. To survive deep down in the inky depths you're gonna need a titanium hide!

Notes:
- Ideally with the addition of 'Ntrox' Tanks' and other mixed gases to mitigate pressure damage.
- The starting depth for taking damage is up for debate, due to implications for Seamoth pilots

3 classes of habitat can be built to cope with increasing depth and water pressure:
Ambient Pressure, Hybrid, and Single Atmosphere.

Use: Shallow-water base
Range: 0-100m deep
System: Ambient Pressure (Internal pressure = surrounding 'ambient' water pressure).
Access:
- Floor hatch (for continued easy access)
- Wall and ceiling hatches (but this now triggers the habitat flooding effect)
- Moonpool (when attached)
Notes:
- Floor hatch access won't cause flooding because internal and external pressures are balanced
- Below 100m the ambient pressure is too great to open conventional hatches

Use: Middle-depth base
Range: 100-900m deep
System: Hybrid (Habitat pressure = surface pressure, Moonpool = ambient water pressure)
Access:
- 'Wet Airlocks' (these replace wall hatches in Multipurpose rooms during construction)
- Alien Containment Airlock (see concept art below)
- Upgraded Moonpool with built-in a 'Dry airlock' (see location pics below)
No Access:
- Floor, ceiling and wall hatches (will not open against the extreme water pressure)
- Standard Moonpool (uncontrollable flooding will continue while one is attached)
Notes:
- Wet airlocks should be user friendly (single click use, rapid purging of about 3 seconds)
- Moonpool's dry airlock prevents high pressure water flooding into lower pressure base
- Pressure damage effects are experienced within moonpools below 100m (as for divers)

Use: Deep-water base
Range : 900-2000m depth
System: Single atmosphere (all compartment pressures = surface pressure of 1 atm)
Access:
- Wet Airlock' wall hatches (but now high pressure damage incurred when exiting)
- Alien Containment Wet Airlock (but now very high pressure damage incurred when exiting)
- Cyclops 'docking tube' (existing mod pictured below)
No Access:
- Floor, ceiling and wall hatches (cant be opened against the water pressure)
- Standard Moonpool (uncontrollable flooding will continue while one is attached)
- Upgraded Moonpool (functions, but high ambient pressure damage makes it impractical here)
Notes:
- Cyclops now becomes essential to access the smaller subs at great depths

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Use: Shallow & medium depth transport (without air supply)
Range: 0-900m depth
System: No cabin (ambient pressure vehicle)
Access: Unrestricted
Note: Below 100m the pilot experiences ambient pressure damage as for 'Free Swimming'

Use: Shallow & medium depth (with air supply)
Range: 0-900m depth
System: Wet sub (internal pressure = ambient pressure)
Access:
- Unrestricted
- While Docked (in moonpool or Cyclops)
Notes:
- Cockpit that freely fills with water during use, then drains out when docked
- Air supply is provided by the sub's on-board re-breather mouthpiece (animation required)
- Below 100m the pilot experiences ambient pressure damage, as for 'Free Swimming' above.
- Suggest new Seamoth module 'IV Drip' to counter ambient pressure damage.

Use: Deep-water pressure protection (with air supply)
Range: 0-1700m depth
System: Single atmosphere 'dry sub' (internal pressure = surface pressure)
Access:
- While afloat immediately after construction by Mobile Vehicle bay
- While docked (moonpool or cyclops)
- When out of water
No Access:
- While submerged (hatch will not open)
Notes:
- The opportunity for surface entry into a newly made Prawn must be extended
- Warper teleports on a Prawn pilot can be deadly now. Don't stray far from your Cyclops when drilling and you should be OK. Use drones to scout ahead for Warper patrols n the Lava Zone.
- Alternatively, tweak the warp mechanic for the Prawn so you warp 'as one' , and stay inside the suit.

A bit tricky this one. Now you're sealed inside this can, tool use is limited to drills and grapples.
Couple of options:
- Several additional 'tool arms' as modules (Builder, Scanner, Cutter)
- Existing Prawn claw arm can just use any tool in your inventory. A mini 'tool airlock' allows this (that could just be commented on by the PDA without having to show it).

Use: Deep-water dock for smaller vehicles
Range: 0-1700m depth
System: Single atmosphere 'dry sub' (internal pressure = surface pressure)
Access:
- Via the existing wet airlock 'Diving Chamber' (non-functional, and pictured below)
- Via vehicles docked in its onboard dry dock (pictured below)
- Via a docking tube with a habitat (existing mod pictured below)
Notes:
- Now much more than just a floating Winnebago, it's now a vital partner for the smaller vehicles.

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Three 'Precursor Tech' blueprints can be found the Primary Containment Facility, hidden in the
small rooms adjoining the Antechamber (Precursor forcefield pictured below)

Appearance: Replaces any hatch with a Precursor green force-field disk
Function: Allows free access to a habitat, at any depth, without need for a wet airlock

Appearance: Replaces interior water surface with a Precursor green force-field
Function: Modifies any moonpool to operate at surface atmosphere pressure
Notes: Eliminates need of any moonpool 'dry airlock' below 900m

Appearance: Replaces top hatch with a Precursor green force-field disk
Function: Allows free entry/exit underwater to the Prawn without need for docking.

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@Catalytic - Troubleshooting & mixed gas idea.
@EleventhStar - Troubleshooting 
@Bionerd1999 - Brainstorming. Troubleshooting (Prawn tools)
@KC_RadishRipper - Warper effects on Prawn drivers. 
@Radio - Prawn arm tool use

Cyclops Docking Tube mod:
https://www.nexusmods.com/subnautica/mods/554

Modding Documents: (PM me if you want to access these)
https://steamproxy.net/sharedfiles/filedetails/?id=3023474038&preview=true
https://steamproxy.net/sharedfiles/filedetails/?id=3023447963&preview=true