Nautikin Adventures – How to Submarine

This guide will cover the basics of building a submarine.

Guide to Submarine

Core Concepts

In order to build an effective submarine, you must master the following concepts related to buoyancy.

Vessel mass

The mass of your vessel will dictate the ease at which your vessel can submerge in the water, the heavier the vessel is, the harder it will be to float and the more likely it will be to sink.

Center of mass (COM)

In terms of building a boat, your COM is extremely important for keeping a boat balanced while floating on the surface above water. For submarines, it is a magnitude more important because 100% of the surface area of your vessel will be submerged and subject to underwater forces. The best way to keep your COM happy for a submarine is to incrementally test your vessel at each stage and start out with a very basic design (just the hull in the shape you want). Once you have perfected the initial stage for floating on the surface, you can start creating ballast in regard to COM.

Surface area

This is directly tied to the size of your vessel and the surfaces of the hull that are touching the water. The larger your vessel’s hull is, the more surface area and buoyancy your vessel will have to keep the mass above water. By the same respect, the more surface area you add (hulls) the harder it will be for the ballast to submerge your vessel by overpowering the forces attributed to surface area / buoyancy. The smaller you make your vessel, the less surface area it will have. With less surface area the affects of COM become more sensitive and the buoyancy becomes less effective.

It is recommended that in your first attempt to make a vessel you start with something large and stable before attempting to make a small highly tuned submarine.


By physical requirement, in order to submerge your vessel while remaining buoyant you must create a vessel that has more ballast (water in a tank) than surface are can displace the water and otherwise affect buoyancy forces. For submarines, buoyancy does not just mean floating on top of the water and being stable, it means being stable while completely submerged and making underwater maneuvers. The larger your vessel is, the more ballast you need in order to submerge. Additionally, in order to submerge your vessel to the sea floor or desired depth between the floor and the surface you must have more ballast than required to submerge your vessel just below the surface. It is extremely important that ballast be centered, otherwise your vessel will not remain stable when attempting to submerge or return to the surface.

Note: Depending on your design it is probably unwise to dump ballast all at once and return to the surface too quickly. This can result in unstable movement especially if you are currently maneuvering your vessel.

Step by Step

Step 1 – Get a working hull

For this first part, we want to make something extremely simple, that floats. In order to simplify this guide, I will be using a very basic design / parts to demonstrate the core concepts (ugly submarine).

As we can see, this hull is seemingly perfectly flat in terms of COM and floating on the surface, so we can probably move onto trying to make it submerge. Depending on the hull you choose as your base, you may need to test out different scales to determine what works best for your design. If you need to make something a certain scale but the hull no longer has the proper amount of surface area, you may have to attach additional hulls as stabilizers. This is just the default steel hull.

Step 2 – Get it to submerge

For this part we need 2 things:

  • A temporary steering wheel (will will want an airtight one later).
  • A large ballast tank to overcome buoyancy of the hull.

So, I have haphazardly attached a giant ballast tank to the lower section or the hull. I have filled the ballast tank to around 9% of its capacity and I can already see my vessel sinking. Great! There are a couple problems that may not be apparent though.

  • The vessel is not completely centered / balanced in terms of COM, we can see that my submarine is starting to tilt backwards.
  • I have too much ballast, this is somewhat obvious visually, but the real indicator is that 9% of my ballast is already going to send me to the sea floor, so I really don’t need the rest.

Note: Attaching ballast tanks near the bottom of your vessel or below the COM will help reduce top heavy instability with regard to buoyancy (falling over).

Step 3 – Make it stable

So now I basically want to address the 2 issues from the last step. These will continue to be a problem every time I make a change to the vessel without balancing everything. Balancing the ballast will be more difficult and may require some trial and error because COM will change when I start to fill the tanks with a variable amount of water. Changing the amount of ballast though simply requires scaling the tank itself.

Here I have moved the tank slightly forward based on my visual observation of the tilting and dramatically reduced the size of the tank. Again, I want to check to make sure that my vessel floats on the surface before submerging again.

After submerging, we can see its a lot more stable in terms of being buoyant. I could meticulously adjust the COM to get it perfectly center, but first I am going to add more parts. Another note here is that we are using 23% ballast now instead of 9% so it is significantly more efficient.

Step 4 – Make it move

Now obviously I need some engines and a fuel tank. I will need to be careful to consider everything from the previous stages when choosing the size of the fuel tanks and where to balance the engine to push the vessel underwater. Ideally we should have a smaller fuel tank near the COM. For the engine placement we need to consider how we move through the water when completely submerged. The propellers must be pushing directly on the axis for COM, otherwise it will tilt. For this example I am using racing engines because they work underwater. Submarines can use any engines that work underwater.

So there are a couple things I did here to make the submarine move.

  • Added engines that are more or less even with the center of mass.
  • Increased the size of my hull to account for the thrust from the engines.
  • Increased the size of my ballast tank to account for the larger hull / amount of surface area.

At this point, I have a very basic and probably ugly looking submarine. If I want to improve it further I will need to patiently iterate over steps 2 – 4 for every part I want to add. But for this guide I am going to stop here and move onto oxygen.

Step 5 – Give it oxygen

When underwater, Nautikins need oxygen. This means 2 things:

  • Airtight seats.
  • Oxygen tank.

Nautikins in airtight seats will automatically breath using the air in the oxygen tank. When the oxygen tank is depleted, they will begin to drown once out of breath. To refill the oxygen tank, simply return to the surface.

Here is a version of the example submarine with air tight seats and oxygen.

So we can see that I have replaced the temporary steering wheel with an airtight submarine driver seat in white and a oxygen tank in a cyan-ish color. At the top of the HUD we can now see an oxygen bar indicating the remaining oxygen across all tanks.

That is basically how to make a submarine. A more complex or perhaps better looking submarine would require the same iteration of steps until you have a a submarine that matches your desired design.

Useful tips

  • The more ballast tanks you use, the harder it will be to balance.
  • The more hulls you use, the more surface area you will have to overcome with ballast.
  • Bigger is usually easier.

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