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How does a Pressure Hull work?
A pressure hull is a strong, sealed structure designed to withstand external pressure while maintaining a safe environment inside, commonly used in submarines and deep-sea vehicles. It is constructed from robust materials, such as steel or titanium, and is engineered to distribute stress evenly across its surface. As external water pressure increases with depth, the hull prevents water from entering and protects the occupants and equipment inside from the crushing forces of the ocean. The design includes features like rounded shapes to minimize stress concentrations and ensure structural integrity.
Why are the windows of a submarine so small?
Submarines don't have windows, at least not any that are used for viewing outside of the hull while submerged. They are used in some submarines as bridge viewing windows, but they're subjected to ambient sea pressure when the boat submerges, not direct sea pressure like the hull is.
Why are submarines forbidden to sink beyond a limit?
The hull of the submarine will crush or give way if the pressure of the water is too much.
Why is the hull of submarines specially strengthened?
To prevent it from collapsing from the high pressure of the water outside while submerged. Roughly every 30 feet of depth under water adds another atmosphere of inward pressure on the hull.
What are pressure hulls on a submarine?
Submarines have 2 or more hulls - the superstructure, which is the visible external hull you see, and the inner pressure hull, which contains all the primary equipment and houses the crew. The space between the superstructure and the pressure hull is where the main ballast tanks are located, as well as line lockers, access/weapons hatches, etc. The pressure hull is where the crew lives and works (and keeps on working...). The primary reason there are 2 hulls is that the pressure hull, while optimally designed for maximum sea pressure resistance, isn't designed for optimum speed and maneuverability underwater. The superstructure, built over the pressure hull, streamlines the boat and compensates for this, making modern boats extremely fast and maneuverable underwater. The best analogy is a thermos bottle, which has an outer shell (the superstructure) that protects and insulates the inner thermal bottle (the pressure hull). The Russians are known to use a double-layered superstructure on their larger boats, the theory being to insulate the pressure hull from a torpedo attack. The problem with that theory is that modern torpedoes don't need much proximity to severely damage or sink submarine, and any significant damage
What happen if the hull of submarine ruptured?
All modern submarines are "dual hull" constructed. What you see on the surface is the outer hull, or "superstructure". The inner hull, where the main systems and crew are, is protected by the outer hull. Damage severity of either the outer or inner hulls depends on the boat's depth at the time. If deep enough, it doesn't take much damage to the hull, as sea pressure will be virtually unstoppable, even with the quick-reaction damage control skills of a submarine crew. However, if sea pressure isn't a factor and the flooding can be controlled, then it's possible to survive such a casualty. Again, it depends on the severity of the hull breach, and the depth at the time. Several modern submarines (my old boat included) have survived underwater collisions which produced severe damage.
Why are submarines depressurized?
They're not - they are pressurized upon submergence to maintain a positive pressure in the boat to detect any hull breaches. Any seal leak or breach, no matter how small, will immediately register on the boat's pressure board.
How do submarines withstand deep sea pressure?
The simple explanation of the ability of a submarine to withstand deep sea pressure lies in the mechanical strength of the pressure hull. On modern military submarines (called boats by the crews) the pressure hull is make of steel (except in the case of a few Russian boats which used titanium). This steel basically forms a cylinder and keeps the pressure of the sea water at operating depth from crushing the hull. To gain a tactical advantage, the Russian Navy built some of their boats with titanium pressure hulls. These hulls were designed to allow greater operating depths, and, therefore, increased ability to "hide" beneath the sea. But as is the case with the steel hulls, the titanium hulls used the geometry (shape) and the mechanical strength of the pressure hull and all the fittings to keep the water out at test depth.
Why are submarines always built with very thick and heavy metal?
The pressure hull of a submarine must withstand the pressure of water at depth. Hundreds of pounds of pressure per square inch translates into many tons of pressure around a pressure hull. If that hull doesn't have the strength to stand up to this, the pressure hull will implode. Steel is a "known quantity" as far as metals. We've used it for a long time, and we have a good handle on its characteristics. Steel alloys are extremely strong, fairly easy to fabricate, and won't double the national debt if we use this metal to make a submarine pressure hull. Steel's weldability and its common availability make it a fine choice for submarine pressure hulls. It's really strong, too. That's a big plus. No one wants to be inside the pressure hull of a submarine when it fails.
Can pressure destroy a submarine underwater?
All submarines have a rated "Crush Depth", the depth at which the hull will succumb to external sea pressure. While the actual depths for each class are classified, several submarines were lost during the Cold War to implosion events after major casualties. The most noted for the United States was the USS Thresher (SSN-593) which was lost during sea trials after she suffered a major flooding casualty. It was estimated she made it to within 100' of the surface before sinking to her crush depth and the bottom of the ocean.
Why does a submarine not implode under water?
Submarines will implode very well if they go to a depth past their rated crush depth. All boats are designed to withstand a lot of PSI on the hull, and most boats are designed so that the hull contracts and expands with depth changes. This ability to flex increases the longevity of the hull, though not all navies build their boats that way. In addition to hull design (usually spherical or cigar shaped, the best design for pressure), boats maintain a positive air pressure inside while submerged. This is less about pressure on the hull than it is to maintain a vigil on hull integrity; if pressure in the boat drops, it means there's a leak or flooding somewhere, or a hatch not sealed properly.
What are submarines made of?
Modern submarines, depending on the country, are made of either flexible steel, Titanium or GRP (Glass Reinforced Plastic). GRP boats are used by the Chinese, Titanium by the Russians. Most all other nations use flexible steel (the composition of which is classified) that compresses and expands with the extreme sea pressure as the boat descends or ascends through the depths. The steel used in pre-Seawolf class submarines was HY-80; The Seawolf and Virginia classes are using HY-100, which has a higher pressure rating. Submarine decks are not actually attached to the inner pressure hull - they "float" by being suspended from cables. This is how the decks keep from getting crushed as the boat's hull compresses at deep depths, as the decks don't actually touch the sides of the inner hull. Hulls that don't flex with sea pressure, while being able to have deeper operational limits, don't have the longevity that flexible hulls do. This is because over time, repeated pressure makes the hull brittle - it is akin to repeated pressure on an eggshell. While very strong, over time it will eventually crack.
