The U212 submarine is
capable of long-distance submerged passage to the area of operation. The German
Navy has ordered four of the submarines.
The Type 212 is being
constructed by Howaldtswerke-Deutsche Werft GmbH (HDW) of Kiel and Thyssen Nordseewerke
GmbH (TNSW) of Enden. HDW is responsible for the bow sections and TNSW for the
stern section. HDW is assembling the first and third vessels, TNSW the second
and fourth. U31, the first of class, was launched in March 2002 and
commissioned in October 2005.
The propulsion system
combines a conventional system consisting of a diesel generator with a lead
acid battery, and an air-independent propulsion (AIP) system, used for silent
slow cruising, with a fuel cell equipped with oxygen and hydrogen storage. The
system consists of nine PEM (polymer electrolyte membrane) fuel cells,
providing between 30kW and 50kW each.
For higher speeds,
connection is made to the high-performance lead acid battery. An MTU 16V-396
diesel engine powers the generator from Piller GmbH for charging the battery
installed on the lower of the two decks at the forward section of the
submarine.
The diesel generator
plant is mounted on a swinging deck platform with double elastic mounts for
noise and vibration isolation. The propeller motor is directly coupled to the
seven-bladed screwback propeller.
What has made a major difference to the SSK in recent years
has been the emergence of workable AIP systems. The threat from maritime patrol
aircraft is now so severe that in a hostile environment (eg, the North
Norwegian Sea or the Mediterranean) an SSK cannot afford to use her schnorkel
for more than 20 minutes. What is known as the submarine's discretion- rate,
the period between battery-chargings, must be extended if the submarine is to
regain the advantage. The purpose of AIP systems is to 'float the load' on the
batteries, using the AIP system to run the 'hotel services' such as
air-conditioning, hot water, auxiliary electrical power, etc, and so keep the
batteries fully charged for any emergency.
THE AIP SYSTEM
During World War II the Kriegsmarine had experimented with a
closed-cycle diesel system as an alternative to the Walter perhydrol-fuelled
turbine. Postwar, the Americans and British experimented with high-test
peroxide, but the Soviet Navy was more impressed with the Kreislauf system, and
designed the Project 615 'Quebec' class coastal submarines around the concept.
What the Soviets called a 'single propulsion system' ran submerged on an
internal supply of liquid oxygen (LOX). The oxygen was added after the exhaust
gases were filtered through a lime-based chemical absorbent. The boat could
also run its Kreislauf diesel in the normal way, using a schnorkel.
The 'Quebec' had three engines, a 32D 900bhp diesel on the
centre shaft and two M-50P 700bhp diesels on the outer shafts. In addition a
l00hp 'creep' motor was coupled to the centre shaft and a back-up
diesel-generator aft. The boat could be run at slow speed using the centreline
diesel only. Soviet records suggest that experiments had started before 1941,
probably with the small coastal boat M.92, and other closed-cycle designs were
prepared after the 'Quebec'. Because LOX cannot be stored for any great length
of time these 467-tonne (460-ton) boats could not operate far from a base. It
was also a dangerous system; at least seven suffered explosions, and one of
these, M.256, sank after being flooded during firefighting efforts. One boat
with the Walter turbine AIP system was built, the 965-tonne (950-ton) Project
617 S.99, known to NATO as the 'Whale' type. The 5.99 made 315 dives using her
Walter system, in 1956-9, but in May 1959 she was badly damaged by an
explosion, and was never repaired. After these boats were decommissioned in the
early 1960s interest in AIP lapsed, but recently the Russian Rubin Bureau
announced that it can offer an AIP system for the new 'Amur' type SSK.
Information released shows that it is a fuel-cell system (see below).
The most successful AIP system so far is the Stirling
engine. Developed from a patent dating back to 1816, the Stirling cycle burns
diesel fuel in pure oxygen, in a pressure vessel. The Swedish submarine
builders Kockums AB of Malmö own the rights to the Stirling engine, and tested
its V4-275R 75kW engine in the serving submarine Nacken. This proved
successful, with less vibration than a conventional diesel-generator, and
considerably lower noise levels. In fact it is possible to conduct a
conversation while standing alongside a running Stirling engine. Since then the
A 19 type 'Gotland' class have been built from the outset with Stirling
engines, and the system has been evaluated by a number of navies. Despite
rumours of submarines running entirely on four Stirling engines, Kockums denies
this, pointing out that the amount of LOX required would be impossible to fit
into the submarine's hull.
The German Navy followed a different route, funding Siemens
and HDW in the development of a Proton Exchange Membrane (PEM) fuel cell
capable of generating 40kW. As with the Stirling principle, the idea is an old
one, dating back to 1839. In essence a fuel-cell reverses the process of
electrolysis, using a chemical reaction to combine hydrogen and oxygen, thereby
producing electrical energy, heat and water. The heart of the PEM system is a
solid polymer electrolyte in the form of an ion exchange membrane in contract
with a platinum catalyst and carbon paper electrodes. The membrane is
positioned between the fluid flow field and the cooling units in such a manner
that hydrogen ions pass through it and combine with hydrogen anions. As long as
hydrogen and oxygen are supplied the fuel cell will continue to produce power.
A single fuel cell cannot produce more than 1.48V and
therefore several must be stacked to form a module. The main drawback to the
system is the cost of materials, and HD W has so far not offered it for export.
The Federal German Navy tested a lOOkW prototype installation in the old Type
205 boat U.I, and the Type 212 boats currently under construction will have a
400kW version.
OTHER AIP SYSTEMS
After the fuel cell trials the U.I was made available by the
Navy to TNSW for trials of a closed-cycle diesel AIP system (CCD). This has the
advantage of being simple, the most complex part being the water absorption
system developed by Cosworth Engineering. The engine exhaust gas is 'scrubbed'
with water to remove the carbon dioxide, and in the same process the water
vapour is condensed. Surplus carbon dioxide is eliminated by adding a small
quantity of argon gas. The great virtue of the CCD system is its use of the
same diesel for schnorkelling or as an AIP unit, a great saving in cost. The
system is being marketed by TNSW and RDM (as the Spectre system). The TNSW
trials with U.I had the rare benefit of comparing like with like: both the fuel
cell and the CCD being tested in the same hull.
The only other AIP system available is the French (Module
d'Energie Sous-Marin Autonome [MESMA]) system, which uses an oxygen-ethanol
fuelled steam turbine. Conceived in the early 1980s by the Bertin company, it
was taken up by DCN, the French Navy's design and procurement bureau, in
collaboration with Empresa National Bazan in Spain. Although the French Navy
has not installed MESMA in a submarine, it has been sold to Pakistan for
fitting to new Agosta-90B type SSKs.
The excitement over AIP has led to exaggerated claims about
its potential. Some commentators claim that the advent of AIP has created a
third category of submarine, the SSK+AIP, but the fact remains that only one
navy has a modern AIP system operating. Three more will have systems in service
after the turn of the century (counting Italy's acquisition of the Type 212
design), but a number of experienced operators are still not sufficiently
convinced to commit themselves.
FUTURE DEVELOPMENTS
AIP enthusiasts point to potential developments. The CCD
system has great promise, with such improvements as electronic fuel-injection
and electronically actuated valves. These improvements will allow the operator
to select engine-characteristics from a menu of choices. The Solid Oxide Fuel
Cell (SOFC) would use natural gas as fuel, resulting in a single propulsion
system for surface and submerged propulsion. Siemens is also known to be
working on a fuel cell using methanol as the base fuel to generate hydrogen.
In theory none of the weapons and sensors which equip SSNs
are unsuitable for SSKs, but size is critical. A large internal volume is
required to accommodate modern electronics and the fuel and batteries needed
for reasonable endurance. As U-boats found in World War I, the number of weapon
reloads is also critical in deciding how long a submarine can remain effective.
As the number of sensors has increased, so has the demand for processing power
and displays. Even automation is not the whole answer, because a minimum number
of people are needed to cope with battle damage and system failures.
Over-reliance on automation results in crew-fatigue on long patrols. During and
after the Falklands War the Royal Navy's 'Obérons' were spending 42 days in
transit and on patrol, 14,816km (more than 8000 miles) from a dockyard. The
strain on the crew after such a long patrol has to be seen at first hand. Even
after the Argentine surrender and the formal end of military activity some
'Obérons' had to avoid Argentine SSKs, not knowing what their opponent's rules
of engagement might be. This meant that the British submarine had to behave as
if her opponent was hostile, but without the ability to take any offensive
action to remove the threat.
The prestige of submarines and their undoubted deterrent
value means that more navies will acquire them in the next decade. But the
enormous throughlife cost of SSNs and their unsuitablity for inshore operations
means that the SSK will remain a much more attractive option for the lesser navies.
US Naval Intelligence predicts that many more SSKs will be in the hands of
non-aligned or unstable countries. Iran's acquisition of three 'Kilos' since
1988 caused something close to panic in Washington, although the Iranians seem
to be interested only in safeguarding their coastal waters from hostile
incursions. It is a chilling thought that if Saddam Hussein had possessed
submarines in 1991, the Coalition naval forces could not have operated with so
much freedom in the Northern Gulf.