Hydrogen and bioethanol-driven subs fight in the Indian Ocean

The competition for India’s contract for six new P75I submarines is in its final stages, with Spain and Germany emerging as front runners. 

Spain unveiled the S-80 sub with air-independent propulsion [AIP]
Photo credit: Navantia

Spain is vying for this contract with the sophisticated S-80 model—an ingenious creation from Navantia set to debut in the Spanish Navy. Germany is putting forward the reliable Type 214, manufactured by Thyssenkrupp Marine Systems [TKMS]. This model is already employed in various navies worldwide. 

Interestingly, both of these submarine models incorporate air-independent propulsion [AIP] systems, allowing them to stay submerged for extended periods—usually a feature reserved for nuclear-powered submarines. 

The competition has not been without contenders. Other competitors include Russia’s Rubin with the Amur 1650 submarine, Korea’s Daewoo Shipbuilding & Marine Engineering [DSME] with the Chang Bogo class—which takes inspiration from the German Type 209—and France’s Naval Group with the Scorpene, a model that’s already utilized by India through a former program. 

Hydrogen and bioethanol-driven subs fight in the Indian Ocean
Photo credit: Navantia

A detailed comparison by Navy Recognition brings insightful observations to light. One aspect under scrutiny is the displacement and size of the submarines. 

The S-80, being slightly larger at just over 80 meters and displacing 2,200 tons, offers more room for onboard systems and crew, a key advantage in an environment where space is a luxury. Conversely, this advantage might lead to a larger acoustic signature. The S-80 can comfortably house 32 crew members compared to the Type 214’s 27. 

The Type 214’s propulsion system is powered by a diesel-electric system from two diesel engines and utilizes Siemens hydrogen fuel cells for its AIP. The Spanish S-80 relies on three diesel engines for propulsion and incorporates an AIP system powered by bioethanol processors. 

Hydrogen and bioethanol-driven subs fight in the Indian Ocean
Photo credit: DAPA

The German-made Type 214 stands to benefit from the performance of its propulsion systems and boasts 20 knots underwater speed and a maximum surface travel range of 12,000 miles at eight knots. The S-80, despite its impressive specs, falls slightly short at 19 knots underwater speed and an 8,000 miles range on the surface, at an identical cruising speed of eight knots.

Weapons and acoustic signature

Our analysis delves into the contrasting weaponry specifications present in the Type 214 and the Navantia ship. The former is equipped with eight 533mm torpedo tubes, allowing for a variety of offensive options including torpedoes, anti-ship missiles, and mines. In contrast, the Navantia vessel houses six guns of equal caliber with a mirroring weapon storage capacity. 

Both submarines prioritize stealth in their operations, featuring reduced acoustic signatures to maintain a low profile. The detection proficiencies of these seaborne combatants further deepen the dissimilarities between them. Some advantage is credited to the German’s Type 214 due to its incorporation of advanced sonar technology. However, the Spanish Navantia vessel counters this with its meticulously designed hull and cutting-edge sonar systems.

More about the Spanish AIP

Powering the S-80 is an air-independent propulsion [AIP] system that relies on a bioethanol processor. This processor, compromised of a reaction chamber and several Coprox intermediate reactors supplied by Abengoa’s Hynergreen, converts bioethanol [BioEtOH] to high-purity hydrogen. Serving as the primary energy source is a suite of fuel cells furnished by UTC Power. 

This intricate system, known as the Reformer, utilizes bioethanol as fuel, and oxygen [stored as a liquid within a highly pressurized cryogenic tank] which subsequently produces hydrogen and carbon dioxide. Additional oxygen and the resulting hydrogen supplement the power generated by the fuel cells. 

The bioethanol processor is also tasked with creating a heavily concentrated stream of carbon dioxide and other trace gases that the combustion process does not fully burn. Coupled with seawater within one or more venturi ejector scrubbers, this gas stream transitions through a new system, SECO2 [or CO2 removal system] engineered by Bionet. The intended purpose of this system is to dissolve the CO2 ‘bubbles’ in water until they become undetectable. 

Determining the input of oxygen and fuel are energy demand levels. The AIP in the S-80 submarine possesses at least 300 kW [400 hp] strength, powered by a permanent magnet electric motor. The motor drives a fixed propeller distinctly designed, avoiding cavitations even at high velocity. 

Due to resonance effects stemming from the motor, a highly resilient RATO-S G-561W coupling provided by Vulkan is integrated. 

December 2020 saw the Spanish Ministry of Defense declare it would be spearheading the efforts to develop a Spanish fuel cell. This decision results from the current SPC’s escalating costs and the aim to remove reliance on foreign manufacturers. A robust program plans to birth a 300 kW prototype within a six-year timeline. 

The enlightened design of the S-80 Plus class submarines serves to excel in threat scenario missions. Their advanced mobility capabilities make operating in far-flung regions feasible while maintaining  high-speed undercover travel. 

Their newly developed technological Air Independent Propulsion System [AIP] ensures their prolonged presence in a targeted area without detection, providing a significant advantage in possible conflict zones.


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