Barotrauma Extended Engineering Guide - Undertow Games Forum (2024)

Barotrauma Extended Engineering Guide - Undertow Games Forum (1)

This guide is made for BTE, or Barotrauma Extended, the mod. If anything substantial changes, I will update this guide.
I'm making this since I'm tired of people blowing up my subs as I shout at them "DID YOU PUT COOLANT IN THE REACTOR" and they go "YOU ONLY NEED ONE ROD"
I've done my best to color code it and liberally use bold and italics to keep it from getting boring. If something is bolded or coloured, I strongly suggest you read it, as it's probably important. See the bottom for some ADVANCED TIPS

Part I: The Reactor (or, "the part of the guide that triples in size of the rest of its contents")

The Reactor is the most important part of the submarine. Without the reactor, there is no power. Without power, there is no oxygen, no engines, and no railguns.

In Vanilla barotrauma, setting up the reactor is as simple as throwing one fuel rod into the thing and being done with it.


In Barotrauma Extended, the reactor system has been entirely revamped. Fuel rods now damage the reactor over time, slowly leading up to an explosion. You can see the current status of your reactor by looking at its sprite.
If the control panel on the front of it is blue, you're golden! A blue control panel means that the reactor is at 100% health.
If the control panel is green, watch out! A green control panel means the reactor is slightly damaged.
If the control panel is yellow, work quickly! A yellow control panel means the reactor is at 50% health.
If the control panel is red, all hands on deck! A red control panel means the reactor is about to explode.

Not to worry, however, because keeping the reactor from exploding is simple as can be! For every two Uranium Fuel Rods, add one Sulphurite coolant rod!
Sulphurite coolant rods heal the reactor over time. There is one other better type of coolant, as well as another type of fuel, but I won't be covering those here, as they are uncommon.

Now that we know how to keep the reactor from exploding, how do I turn this thing on? Well, the first thing you need to do is check the box which says Automatic Temperature Control, and raise the Shutdown Temperature. The number you need to raise it to varies, but we'll get to that later.

Now that that's done, how much fuel should I put inside this thing? Well, this part varies. Different subs use different amounts of power. Many subs can be powered with just one fuel rod, but this is not always the case. Depending on how many fancy gizmos are on this thing, you may need more.

To figure out how much fuel you need, start by adding just one fuel rod (as well as a coolant rod to counter the damage). This will allow the fission rate of the reactor to reach up to 25%. The red line will slowly rise on the monitor, and the red listing at the top which reads Output will start to rise in number.

Barotrauma Extended Engineering Guide - Undertow Games Forum (2)

Note the Yellow Line on the monitor, as well as the yellow text which reads Grid Load. The Grid Load is the amount of power the submarine currently requires to function at max capabilities.

Your goal as an Engineer or Mechanic is to keep these two lines as close together as possible. The Automatic Temperature Control will not do this for you.

Note the two controllable options for Fission Rate and Cooling Rate. The Fission Rate is the speed at which the Fuel Rods in the reactor heat up. Each fuel rod raises the maximum Fission Rate by 25%.

The Cooling Rate, as the name implies, cools off the reactor. This has nothing to do with the coolant rods which you added earlier (although they may increase the efficiency at which you cool the reactor down, I haven't tested it, but it's not important).
The higher the Cooling Rate Percentage, the less heat you will generate in the reactor. less heat = less power generated.

The Automatic Temperature Control option will do its best to keep the Fission Rate and Cooling Rate balanced in a way that will keep the reactor from overheating. It is extremely slow, however, and leaving the reactor to sort itself out will more often than not lead to disaster.

As the submarine begins to move, the Grid Load will spike rapidly with movement, as the engine and ballast activate and deactivate rapidly. As the lines spike, adjust the Fission Rate and Cooling Rate to accommodate. That is, if your Output is higher than your Grid Load, lower the Fission Rate and increase the Cooling Rate (and vice versa).

Finally, the Shutdown Temperature. I would argue that this part is what most engineers have the least understanding of. As the name implies, the number at which you set this to is the temperature that the reactor will shut down at. That much is simple. What isn't quite as simple, however, is what number it should be, or how to tell what temperature the reactor is at.

Every submarine technically can answer differently here, however most subs stick to the default values.

By default, every reactor will:
Generate 1 degree of heat CELSIUS per kW of power (this thing runs HOT)
Light on fire at 9000kW (9000 degrees Celsius)
Meltdown/Explode at 9500kW (9500 degrees Celsius)

With this in mind, it's perfectly reasonable to set the reactor shutdown temperature at 8999kW. At this number, (unless there is a glitch with heat generation) you will never run into problems with your reactor, as long as you are adjusting the Fission and Cooling Rates. That being said, you may not want to do this. If your submarine uses less power than that on average, you can set the shutdown temperature to a lower number safely. The reactor shutdown temperature doesn't expel all of the heat remaining, but simply stops it from generating any more heat past that point. With this in mind, if a submarine averages 6000kW while moving, a smart number to have the shutdown temperature at would be around 6500-7000kW. You want to leave extra room for things like pumps to remove water if there is a flood, or anything else on the sub that uses power, but is not always active.

If there is a flood on the ship, be sure to check and see if the shutdown temperature needs to be raised. Pumps use a lot of power, and when all of the pumps on the sub are active, it can be a huge toll on the system. (I've seen sub's Grid Loads going as high as 10,000kW)

Speaking of floods

In the event that the reactor is flooded with water, its heat production will be severely hampered. In vanilla Barotrauma, all one would need do is add three fuel rods to the reactor, and it would generate heat again. This is not the case in BTE.

In BTE, fuel rods generally produce less heat, and so it is far more difficult to generate any power if the reactor is flooded, as the water is freezing cold. You have two options here.

The least favorable option: Remove all coolant rods, and fill the reactor completely with fuel rods.
If you have 5 fuel rods in there, you will slowly but surely begin to generate heat, and thus, power. The issue, however, is that without coolant rods, the reactor will rapidly begin to break down. and EXPLODE

The more favorable option: Use the Diesel Generator

Most submarines in BTE are equipped with a Diesel Generator. It has the ability to generate heat, and isn't hampered by floods.

To use the Diesel Generator, simply throw in a couple of diesel cans. The more diesel cans you add to it, the faster it will generate power. The main problems with the diesel generator, however, is that you have no way to control how much power it generates. This means that, after not too long, it will end up generating too much power, blowing all of your junction boxes. To top it off, the Diesel Generator will break down after not too long, so be sure to have a mechanic handy to fix it back up if this happens.


Last part of note about the reactor is the batteries. Not all subs have these things charging automatically, so make sure you turn them on! If your sub has a lot of batteries (like 6) set them to 50% charge. If there's only a few, set them to 100% charge. If your reactor isn't putting out enough heat, the batteries will pick up the slack and pump out the rest for you. Keep in mind, the higher the charge rate of the batteries, the higher your Grid Load is. Batteries are essential to prevent power flickers while moving. They typically won't be able to keep the ship powered if the reactor dies, as they don't push out very much power. It's primarily to assist with matching Grid Load.

And that's it! Remember: Your job on this submarine is to be an engineer. If the sub is moving, you should always have somebody watching the reactor. If the sub is idling, it should be fine, but be cautious anyways.

Remember to keep an eye on your fuel reserves as well. The Fuel Rods and Coolant rods will eventually run out of juice, and you'll need to replace them.

Part II: Junction Boxes (or, "why am I not pumping out any water? and why is the grid load so low?")

Junction boxes are any Engineer's nightmare. If a junction box is either submerged in water while powered or has 4,000kW more than it needs it will begin to rapidly take damage, and eventually explode/catch fire.

Junction boxes typically won't be a problem until there's a flood. Once the sub begins to flood, however, any powered junction box will begin to take damage on contact with water. Once a junction box takes enough damage, it will explode. Have no fear, however, because fixing these is a piece of cake.

Only Engineers are able to fix junction boxes. No other job can (except for a prisoner who spawned with lucky stats). That means it is imperative that at least one engineer stay alive at all times. Theoretically, an engineer could make an entire expedition on their own.

You can tell how damaged a junction box is by looking at its sprite. As it begins to teeter towards its demise, black soot will start to form in the vent on its sprite. Pictures below.

To fix a junction box, simply have a screwdriver and a piece of wire in your inventory, then press E on the broken junction box. A menu will appear, which shows in green or red text to confirm that you have all the materials and necessary engineer skill to fix it. Assuming you have everything, a small button which reads Fix will be available to you. Click it, and the junction box will instantly repair itself.

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A junction box at approximately half health

Barotrauma Extended Engineering Guide - Undertow Games Forum (4)

A broken junction box

On top of fixing junction boxes, an engineer will also need to occasionally fix terminals. This can be anything from the Captain's navigation terminal, to the hull integrity monitor, to the kitchen refrigerator. To fix these things, simply interact with them in the same way you would with a broken junction box.

Part III: Mechanics (or, "LEAK!")

A mechanic's sole purpose is to fix big things, like the engine, the nuclear reactor. or the hull of the sub.

In order to fix one of these machines, you take a similar approach to the engineer. You bring one welding tool and a wrench to what you wish to fix, and hit the fix button. Simple as that.

Fixing walls, on the other hand, is both one of the simplest and hardest parts of Barotrauma.

Anybody can fix a breach in the hull, but you're the best at it, and you need to be on TOP of things. As soon as there is a breach in the hull, you will hear water pouring into the sub, and you will feel yourself lurch as the sub plummets downwards. Your job, first and foremost, is to patch up the holes and get the water OUT of the sub. If you don't do this fast enough, the sub will crash into more ice and rocks, causing more holes to appear on the sub, potentially at the cost of many innocent lives. Worse yet, if you don't patch the holes, and there's no ice to catch you, you may end up falling for a long, long time, until the pressure of the ocean crushes the entire submarine you're inside of.

Essentially, what this boils down to is, always have a welding tool on you, and keep an eye on comms. People will usually yell pretty fast if there's a leak, but if nobody yells, use your ears, and follow the sound of flowing water! Some subs even have Hull Monitors which can tell you which room has a leak, but if the junction boxes blow, that won't help you much.

A fast mechanic can save hours of repair-time. Be careful, though, because if the water has been leaking into an area for too long, or the hull is completely breached, the water pressure may completely crush you within seconds. If you're being crushed by water pressure, the screen will shake and zoom in towards you. If this happens, open the NEAREST door to relieve yourself of the pressure, and don't come back without an exosuit.

Part IV: Advanced Tips (or: "sorry I blew up the sub, cap, I was trying to speedrun the reactor")

1 - In BTE, the engine takes a mighty long time to start up. If you're an impatient asshole (like myself), you can load 4 uranium fuel rods and just one coolant rod into the nuclear reactor to match Grid Load in seconds! be VERY cautious doing this, however, because if you don't take the extra fuel rods out in time, the reactor will explode rather quickly.

2 - Did a flood just happen in the room next to you, but you have no oxygen mask or exosuit available? Run in there anyway, champ! If the leak is small enough, you can get in and out without running out of breath, potentially saving the whole sub! But don't bother if the leak was caused by hostile aquatic life....

3 - Tiger Thresher tearing your hull a new one? Get in an exosuit and repair the wall while yelling at security to get a harpoon and kill that thing. If you repair the wall consistently, you may be able to prevent the sub from sinking! Just be sure to yell about it on comms.

4 - Engineers: You have the most powerful tool of all. A screwdriver. Every single button, piece of electronic, wire, etc. in Barotrauma are connected through a dense wiring system. Think redstone in minecraft. With a screwdriver, you can pretty much rewire anything on the sub, giving you access to areas you wouldn't otherwise be able to access. This can help you get to a leak if nobody else is there to open the door, or to access other, more nefarious items. You could even rig a detonator up to a door button, causing an explosion as soon as somebody tries to open the door! The possibilities are quite literally endless. Just don't get caught!

5 - Engineering usually has a Tool Box which can be used to craft makeshift weapons. Throw some old useless equipment (or the doctor's medical hud he "misplaced") into the decontructor to get the materials, then throw together a sawblade gun, or flamethrower!

And that's it! You should be a master of engineering, now. If you have any questions, or I missed anything, please reply! I'd love to make this guide as comprehensive as possible.
Want to test out your new Advanced Abilities? Join the discord for my BTE server, SwimZone! - - Just @ me if you want to play, and (if I'm around) I'll pull up the server! Or, if you'd rather play single player (like a WEIRD, IRREGULAR person), download my sub!

Barotrauma Extended Engineering Guide - Undertow Games Forum (2024)
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