A submarine design uses many engineering and scientific design principles. This page is to help those (especially school students) who wish to understand the complexity of various scientific principles affecting submarines. Including physics, ergonomics, mathematics and chemistry.

A submariner is highly trained and educated. No other naval vessel requires more training than the crew of a submarine. When you see a submariner wearing their dolphins it means they have passed the stringent requirements to understand and operate a submarine safely. Every “qualified” crew member must know their job, the critical parts and the limits of the submarine’s operation to ensure the safety of everyone on board. That means if you got by with a 60% grade at school you WILL NOT survive on a submarine. You must be almost 100% correct all-of-the-time when operating underwater in a submarine.

On the surface, nature is very forgiving. Underwater, nature can kill quickly. That is why we must design a submarine to be able to travel underwater safely.

1 • Specific Gravity
2 • Buoyancy
3 • Trim
4 • Stability
5 • Pressure
6 • Friction
7 • Change
8 • Sound
9 • Reliability

10 • Valves
11 • Smells
12 • Snorkel
13 • Crew bunks
14 • Batteries

15 • Hatch
16 • Masts
17 • Diesel-Electric Power System
18 • Sonar
19 • Air
20 • Nuclear Propulsion
21 • Navigation
22 • Seals
23 • Pumps and Piping
24 • Gauges and Instruments
25 • Air Independent Propulsion

Specific gravity is the weight of a substance compared to water. (Water = 1) If it floats it specific gravity is less than one. If it sinks its specific gravity is greater than one. A modern submarine functions best at exactly one (neutral buoyancy) because its hydroplanes can easily control its up or down movements like the wings of an aircraft.

Water weighs about 62.4 pounds per cubic foot.
Sea water weighs about 64 pounds per cubic foot.
The denser sea water (S.G.=1.025) can support 2.5% more weight than fresh water. Fresh water enters the sea via rivers and streams along the coast.

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Negative buoyancy Sp. Gr. is greater than 1
Positive buoyancy Sp. Gr. is less than 1
Neutral buoyancy Sp. Gr. is equal to 1 (water)
A body floating in a liquid is buoyed up by a force equal to the weight of liquid displaced. (ARCHIMEDES principle)
To float, an object must displace its own weight of water without sinking. For a submarine to sink it must displace its own weight plus about 18% more. The 18% extra weight comes from allowing seawater to enter the sub’s “ballast tanks”. Blowing air into the top of the ballast tanks forces out the water and lowers the S.G. below 1 forcing the submarine to the surface.
During WWII most submarines had a reserve buoyancy of about 30% because they spent most of their time travelling on the surface. Today the reserve buoyancy of a submarine is about 18% since they spend most of their time submerged.
- - - - - - - - - - - - -
A can of
diet pop weighs 14 grams in air and displaces 375 grams of water.
It contains about 227 grams of soda giving it a weight of 241 grams.
That can displaces 375 grams of water, therefore it will float.
BUT, a can of regular pop containing sugar weighs 385 grams, which is 10 grams more than it displaces, therefore it sinks in water. (try it)
If you add enough salt to the water, the salt water will become more dense and the regular Coke can containing sugar will float.

A submarine must also be “balanced” while underwater. To control this balance the submarine is “trimmed”. That is, its specific gravity (1.0) is maintained in its optimal “balance” position in the centre of the boat by moving water or fuel to various tanks around the sub to counteract changes in weight around the sub. A record (log) must be maintained at all times on the weight distribution (tons) in each of the various fluid tanks on the sub. To check on the subs trim it may use various “bubble levels” to see that the sub is level.
Flow meters and tank gauges can help indicate what volumes are in various tanks. An average diesel-electric submarine may have over 20 tanks containing sea water, fresh water, lubricating oil, hydraulic fluid, sewage, and fuel. It also may have over 20 cylinders of compressed air to blow the sea water out of the ballast tanks to lower its S.G. bringing it to the surface.

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A bubble level or “Clinometer” from a submarine
Once the submarine is trimmed for dive it can surface by “blowing” out with pressurized air, or pumping out, some of the water from the tanks to lower the subs specific gravity to less than one, allowing it to float to the surface.

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Fluids are distributed to keep the subs centre of gravity in the centre.

A submarine must also keep its top-side up while underwater. To help this, almost all of the heavy weight (engines, batteries, fluid tanks) in the submarine are placed as low as possible in the boat. The lower the centre of gravity, the more stable the submarine.

A submarine’s hull and every part penetrating the hull must strengthened to resist the external pressure placed on it by the sea water above it. The hull is only as strong as its weakest point. The testing and inspection of the submarines steel thickness, welding, seals and piping is extremely important to ensure its safe design diving limits.

A submarine completes regular test dives at various depths before going on patrol to ensure the integrity of the sub.

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For every 1 foot of depth there is about 0.47 psi (pounds per square inch) of pressure on the hull. A submarine at 500 feet has a pressure of about 235 psi on its hull.
The best hull design is spherical. This resists the most pressure. That is why the pressure hull of a submarine is round. As a submarine submerges in water its hull begins to shrink from the pressure.

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Depth gauge (actually a water pressure gauge)

A submarine has various depth categories...
Snorkel or periscope depth (65 feet)
Operating depth
(40% of test depth e.g. 270 feet)
Safe maximum depth
(70% of test depth e.g. 540 feet)
Test depth
(70% of design crush depth e.g. 900 feet)
Design crush depth
(Theoretical hull collapse e.g. 1286 feet)
- Actual crush depth
(Actual hull collapse e.g. 1410 feet ??)

Below is a chart of atmospheric pressure safety levels.
A diesel engine sucking the air out of a submarine hull can be dangerous.

internal pressure levels
Note: Oxygen masks on an aircraft only deploy if the plane depressurizes.

When water moves across the hull of a submarine it creates friction. Friction increases as the speed increases. The faster you wish to go the more energy you need. That is why a nuclear submarine has the energy advantage to cruise underwater at speeds of over 30 knots ( 34.5 miles per hour), while a diesel-electric submarine has a maximum cruise speed of 20 knots, but because it uses less operating equipment it’s quieter. A streamlined and smooth submarine will have the least friction and can go faster using less energy.

Older WWII submarines were faster on the surface than underwater because they were designed to travel on the surface to their patrol area to save fuel, then dive using batteries while on patrol. Today it’s different, diesel-electric submarines will come up near the surface to snorkel once a day to recharge its batteries or just travel at snorkel depth. A very smooth and streamlined hull of a submarine can increase its underwater speed by 6 knots (6.9 MPH)

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Objects released simultaneously sink at different speeds in a tube of water

A submarine moving underwater in the different parts of the ocean is under constant change of pressure, stability, buoyancy, current, speed, depth, salinity, temperature and specific gravity. This requires the submarine to constantly change its dynamics to counteract these changes. Sea temperatures, salinity, depth, and speed will keep changing the submarine’s neutral buoyancy. The submarine must also continually change its controls and trim to ensure its neutral buoyancy. When a submarine is not at 100% neutral buoyancy, it takes more energy to push the sub through the water using more fuel or battery power.

In water, sound travels 4.3 times faster than in air and over 500 times further than it does in air. A submerged submarine must be silent to prevent being detected by an enemy. The quietest sound (ultra-quiet) is at the lowest optimal speed on battery power which is usually around 4 knots (4.6 miles per hour).

The noisiest part of a diesel-electric submarine is the diesel engine. The diesel engine is only used to charge the subs batteries then it goes silent, goes deep and sneaks around the depths of the ocean.
Equipment is installed on special isolation or insulation pads to prevent motor sounds being transmitted from the sub. Even the propeller is designed to prevent making noise.
Listening devices (SONAR) are installed in submarines to be able to hear what is going on around the sub. Different frequencies of sound travel further underwater. By listening to a sound from different locations, a submarine can triangulate the approximate location where the sound originates from.
Since a submerged sub has no eyes, it must rely on its SONAR system to be able to hear noises from ships and especially other submarines. Submarines operating at the same depth have been known to collide because they were both operating on an “ultra-quiet “mode.

A submarine must have extremely reliable equipment and a reliable crew. There is no way it can be repaired underwater. Each piece of equipment must be reliable and the most important equipment must be able to have a manual operation or one or maybe two back up systems. This reliability puts a great demand on a submarines operational ability.
As a rule, a submarine is being maintained at least 30% of its life. Newly designed submarines are “prototypes”. That means all the equipment on the submarine may have not been “field tested” so equipment may require to be maintained more frequently.
The lives of a submarine crew depends in the reliability of the subs operation. There is not much room on a sub to carry spare parts, so it must be reliable.

All submarines have valves. They control the flow of fluids. If you look through the interior of various submarines on this website you will see hundreds of valves. Each valve has a purpose to allow flow into a tank, isolate a tank, or isolate a pipe. Modern submarines have solenoid valves which are operated by an electro-magnet instead of by hand. By installing reliable solenoid valves a submarine requires a smaller crew.


Submarine high pressure solenoid activated valve with its exterior cut away.

valve handwheel colors

Valve handles are designed to be easily recognized in the dark


All submarines have smells, just like your home. The main odour inside a diesel-electric submarine is the diesel fuel which is usually limited to the engine room. The three other most common smells in a small space where a group is located are: sweat, cooking, and toilets. The sweat is controlled by daily washing, the cooking smell tells you when dinner is ready, the toilet odours are (hopefully) contained in the toilet area. Some submarines have “scrubbers” to absorb odours.

All diesel-electric submarines have a snorkel. A snorkel intakes and exhausts air to and from the diesel engines. The submarine must come up near the surface of the ocean and extend the snorkel mast (pipe) above the water while going at a slow speed to prevent water from entering the intake. There are valves to shut off the snorkel pipes while the submarine is submerged.

Snorkel exhaust and intake masts

Each member of a submarine crew has a place to sleep. Sometimes the bunk is rotated with another crew member because of the lack of bunk space (called “hot bunking”) for each crew member. The bunk is compact and may have a light for reading.


The battery is the life of a diesel-electric submarine. The diesel engines power an electric generator to charge the batteries on board a submarine. A submarine battery may cost over $100,000 each. Each cell gives off 2 volts and a bank of cells provides the submarine 440 volts. Since the weight of the battery cells are about 1,000 pounds each they are positioned in the lowest part of the submarine to provide ballast which keeps the centre of gravity low making the sub more stable.

good view here_9300
BATTERY CELLS (looking through deck opening

All submarines have water-tight hatches and doors. Hatches are the access openings on the deck and water-tight doors are to separate a submarine into various water-tight compartments. All modern submarine doors are round. Round doors and hatches are the best design for the high pressures exerted on it from the depths of the ocean. The round design distributes the stress equally around the opening to prevent a build-up of stress at any one point which could lead to a failure.


Masts on a submarine provide sensors that extend up from the fin or sail to reach above the water line to prevent the whole submarine from surfacing while locating vessels or sending radio communication.. The masts may be used for radio antennas, periscopes, radar and snorkels. Masts are raised and lowered by a hydraulic system.


Diesel-electric submarines are powered by a diesel engine which is connected to an electrical generator which can run an electric motor or charge the batteries, or both simultaneously via a control system. Diesel engines must intake combustion air and exhaust fumes to the outside. While fully submerged intake and exhaust isolation valves are closed to prevent water entering the sub.

submarine power system

Listening devices (SONAR) are installed on submarines to be able to hear what is going on around the sub. Different frequencies of sound travel further underwater. By listening to a sound from different locations, a submarine can triangulate the approximate location where the sound originates from.
Since a submerged sub has no eyes, it must rely on its SONAR system to be able to hear noises from ships and especially other submarines. Submarines operating at the same depth have been known to collide because they were both operating on an “ultra-quiet “mode.
SONAR may be active (Pinging) or passive (listening only).
It is rare that a sub uses active sonar because it can be heard by other submarines and ships.

19. AIR
A subs crew need air to breath. Air is 21% oxygen and 78% nitrogen with some argon and carbon dioxide. Compressed air is stored on a submarine in high pressure steel bottles. Compressed air is also used to force the water out of the ballast tanks to lower the sub’s specific gravity giving it enough bouyancy to bring the sub to the surface.
Carbon dioxide is removed from the air on a submarine by an absorbent chemical filter (soda lime) system called protosorb.
In an emergency, oxygen is generated by burning special “candles” containing sodium chlorate and iron filings that give off oxygen.
Steel air cylinders on a submarine are filled by an air compressor operated by an electric motor or a diesel engine while the sub is on the surface.

O2 generator

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O2 Generator flow diagram

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CO2 Scrubbers

Some submarines are nuclear powered. They have a pressurized nuclear reactor that provides heat to steam generators to supply steam turbines that power electrical generator that powers an electric motor that turns a propeller. This gives the advantage of being able to operate for up to 35 years without refuelling.
The most common nuclear fuel used is uranium which give off neutrons (radioactive). If enough neutrons are brought together they create a reaction causing heat.
A simple example is rubbing your hands together creating friction that causes your hands to heat up. Heat is controlled within a reactor by a continuous pumping of a liquid coolant that transfers the heat to steam generators outside the reactor to make steam and to prevent the nuclear reactor overheating.

sub reactor flowsheet
The NUCLEAR REACTOR heat up water that circulates from PUMP pressure
to the PRESSURIZER which controls the pipe pressure to the STEAM
GENERATOR. The CIRCULATING pump returns the
cooled water to the NUCLEAR REACTOR for re-heating.

The hot water from the REACTOR heats up a separate water system into
STEAM which is sent under pressure to the STEAM TURBINE. The STEAM
enters the STEAM TURBINE under high pressure (HP). The TURBINE uses up
some of the energy which changes the steam to a lower pressure (LP) then
returns to the STEAM GENERATOR via a STEAM CONDENSER which
condenses the steam to water which returns to the STEAM GENERATOR.

The STEAM TURBINE turns a shaft to power an ELECTRICAL GENERATOR
which produces electricity and sends it to the SWITCHBOARD that sends the
electricity to the MOTOR that drives the propeller of the submarine.


closed-loop pressure reactor

Future design of a closed-loop pressure reactor with built-in steam generator and the reactor fluid not requiring pumps. All control rods enter from bottom via cables to prevent problems due to expansion and contraction from temperature changes.

Navigation is an important part of operating any ship. Reading marine charts, using GPS positioning systems, using radar and sonar are all part of knowing how to navigate a ship’s through a narrow bay or inlet without colliding with a rock or grounding on a shallow bottom. You can calculate when you will arrive at a destination, what course to take, what speed, and how much fuel it takes to get there.

Modern submarines use an inertial navigation system (INS) that calculates an accurate position of the sub while it is underwater for long periods.


A marine chart (North is always at the top of a chart)

Pipes, cables, shafts, hatches or wiring penetrating a submarine’s hull or compartment must have a watertight seal to prevent water from entering the submarine when it is dived underwater.

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Cable seals through compartment bulkhead.

Pipes and pumps are a major part of every submarine. Pumps are used to transfer fluids from tank to tank or to remove water due to small leaks. Modern submarine use hydraulic pumps, centrifugal pumps, vacuum pumps, turbine pumps and compressors (air pumps) all connected to various pipes and tanks.

The crew judge what the submarine is doing during operations by reading various gauges or instruments. Such as,
- Depth, Speed, Course
- Rate of dive, Dive angle, Heel angle
- Battery voltage and amperage
- Tank pressure
- Fuel depth gauge
- Engine temperature, RPM (revolutions per minute)
- Percent Carbon Dioxide
- Hydraulic pressure
- Waterproof hatches open or closed
- Torpedo tube loaded and ready

Non-nuclear submarines must recharge their
batteries to stay underwater for longer time periods

Air Independent Propulsion systems allows recharging of batteries without surfacing for air
A -
Hydrogen Cell Power - Liquid Oxygen and Hydrogen Fuel

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B - Closed Cycle Diesel Engine - Diesel and Oxygen Fuel

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C - Closed Cycle Steam Turbine - Ethanol and Oxygen Fuel


D -
Stirling Engine - Liquid Oxygen and Diesel Fuel

This page is still under construction.....
More science to come....
• Propulsion
• Electricity
• Motors (Electric)
• Engines (Diesel)
• Hydraulics
• Inspection and testing
• SCUBA diving
• Fire fighting
• Radar
• Radio