Navigating Submarine Emergencies: Redundancy and Alternative Propulsion Techniques

Underwater missions often rely on precise and redundant systems to ensure the safety and successful completion of missions. However, what happens if the submarine's propulsion or power systems experience a major malfunction or even complete failure? This article explores the methods and systems in place to address such scenarios, focusing on two critical situations: severely damaged propeller blades and engine breakdowns.

Severely Damaged Propeller Blades or Engine Breakdowns

While submarines are designed with redundancy in mind, the failure of primary propulsion systems can pose significant challenges. For instance, if the propeller blades are severely damaged beyond repair or the engines break down, leaving the submarine dead in the water but otherwise functional, what options are available?

In most cases, the engineering officers can implement workarounds to ensure minimal propulsion. For example, in the context of an engine breakdown, the engineering teams can often find a workaround to operate with reduced speed and range. However, the destruction of propeller blades is a different matter. Since deliberate sabotage is the most likely cause, the outcome can be irreversible, leading to the effective loss of the submarine.

Nevertheless, some submarines are equipped with secondary propulsion motors that can help them limo home. These systems, although not as powerful, can significantly extend the mission's lifespan, allowing the submarine to operate at a reduced speed and range until it can return to a friendly port. Additionally, these secondary motors may need to contend with leaks in the shaft seals, further complicating the situation.

Redundant Propulsion Systems and Drives

Modern submarines are designed with multiple layers of redundancy to ensure minimal downtime. For example, most current Western nuclear-powered submarines employ dual sets of main engine steam turbines. This is due to the reactor having two cooling loops, meaning one set of turbines is sufficient if the other fails. All submarines have battery backups and diesel generators to further secure power. In newer designs, the switch to electric drives eliminates the need for main engines, relying on turbo generators instead.

Moreover, US submarines boast an electric motor connected to the same propulsion shaft as the main engines. As long as the shaft, screw, and associated components can still rotate, the electric motor can be used to maintain movement. This may not achieve the full speed but is effective for prolonged underwater operations. Additionally, these subs have a secondary electric motor designed for mooring, which can move the boat at a very slow speed, typically just a few knots, depending on the current speed.

Emergency Propulsion Mechanisms

Below a certain depth, blowing the ballast tanks has minimal effect, as it's the use of hydroplanes that are most effective in bringing a submarine to a shallower depth. If the submarine is within a specific depth range, an Emergency Propulsion Mechanism (EPM) is deployed to bring it to a shallower depth. From there, the ballast tanks can be blown to bring the boat to the surface. However, the mission's initial parameters might prioritize returning to a friendly port as quietly as possible, depending on the situation.

Isolation of failed systems is another vital aspect of submarine design. This enables other systems to maintain as much functionality as possible, preventing the boat from being "dead in the water" due to a single propulsion or power fault. Consequently, the ability to switch to alternative propulsion methods at any time is highly critical during training and maintenance.

Conclusion

Submarine design and operation are intricately dependent on redundancy and alternative systems to ensure the safety and successful completion of missions. Strategies such as secondary propulsion motors, electric drives, and emergency propulsion mechanisms are essential components in addressing the challenges posed by propulsion failures. Understanding these systems and their implementation is crucial for the safe operation and survival of modern submarines.