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Brief History of Diesel-Electric Submarines

There is much information in the public domain about the history and development of Diesel-Electric Submarines.  With the advent of nuclear submarines they are now commonly described as ‘Conventional’ submarines.   Briefly, however, Diesel-Electric Submarines made their first significant impact during World War 1.   When surfaced, these Submarines operated a diesel engine for propulsion and to charge the Main Storage Battery.   When submerged, the Main Storage Battery provided the sole source of energy for electrical propulsion, operating of all equipment, lighting and the living needs of the crew.   Hence it is the Battery that allows the Submarine to operate as a Submarine: that is, underwater.

While these WW1 Submarines were designed for underwater operation, the propulsion and energy storage technology of the time meant that they generally remained on the sea surface until they needed to submerge to either attack or evade an enemy.   Typically, a WW1 Submarine, operating at a very slow speed of about 2 knots (4 km/h) and could remain submerged for about 48 hours.   At higher speeds of 6 – 8 knots the WW1 submarine could only operate submerged for about 1 hour.  (A useful historical reference for WW1 submarines is Australia’s own AE2 which has its own dedicated web site: www.ae2.org.au)

Diesel engine, electric motor and battery technology improvement meant that WW2 Submarines could remain submerged for longer periods and/or operate at higher speeds.   Whilst operating profiles varied greatly across submarines of different propulsion and battery size combinations, some WW2 Submarines could remain submerged in excess of 3 days if operating at 3-4 knots.

Today’s Diesel-Electric Submarines are larger, faster, quieter, much more complex and much more demanding for power than their WW1 and WW2 predecessors.  Despite this they operate using fundamentally the same electrical, chemical and mechanical fundamentals of their WW1 forerunners.  

Australia’s geo-strategic circumstances dictates that our Navy operate Submarines that can travel long distances covertly, remain on station for long periods and then return to port safely and undetected.  This requires a large Submarine with a large battery; and the COLLINS Class Submarine operated by the Royal Australian Navy is amongst the largest Diesel-Electric Submarines in the world.

To read more about the history Diesel-Electric Submarines in Australia, the Submarine Institute of Australia website is a good place to start.

 

So Why Lead Acid Batteries in Submarines?

Lead Acid is relatively cheap, very reliable, and well understood from a management and safety perspective.   In recent times newer battery technologies that offer a higher energy density have emerged that show great promise for conventional submarine operations.  Such solutions are currently in their early stages of development and are being carefully evolved to ensure that crucial safety aspects are appropriately considered.

 

What's Special About Submarine Lead Acid Batteries?

There are many information sources available on the subject of Battery technology and theory, however, the most essential characteristics of a Lead Acid Submarine Battery are:

High Endurance  – The battery term for this is Energy Content. The higher the energy content, the greater the underwater endurance of the submarine. This can be measured as:

    • Specific Energy, which is measured as watt hours per kilogram (Wh/kg), or
    • Energy Density, which is measured as watt hours per cubic deci-metres (WH/dm3).

Both of these measures are particularly important due to crucial space and weight factors in Submarine design.

High Speed Capability – The battery term for this is Specific Power (or Power Density) and it is a measure of power available by battery volume or mass and is measure as watts per litre or per kilogram.  Power is the time rate of energy transfer or, the rate at which energy is consumed.   For high speed capability, power consumption will be rapid, therefore the battery will be discharged quickly.  In order to achieve rapid discharge rates, submarine batteries are manufactured such that internal electrical resistance is as low as possible through the use of the highest quality conductors.  

Design Optimisation – Like any electo-chemical device, a Lead Acid Submarine Battery needs to be optimised for its particular mode of operation.   The Battery designers task is therefore to provide maximum energy storage for low and high rate discharges within specific weight and volume parameters.

Charge Acceptance – This term relates to the ease and speed at which a Battery can be recharged.   A Diesel-Electric Submarines needs to operate diesel engines to generate power to recharge their Battery, which intern increases their risk of being detected.   Therefore a Submarine Battery needs to be designed so that it can be recharged as quickly as possible.  

Safety – Hydrogen gas is produced as a result of some battery charging modes which, at certain levels, can be extremely hazardous.    The Battery therefore needs to be designed so that it can be operated at minimal gassing rates.

Shock Resistance – The Battery design and mechanical properties must ensure that the Battery is resistant to an extremely high level of shock force.

Adherence to close Design and Manufacturing Tolerances – As well as being the  submerged energy source, the Battery also provides the Submarines ballast which is an essential design feature impacting on trim, stability, buoyancy and manoeuvrability.    This feature and the fact that the Battery must fit exactly into specifically designed and configured Battery Compartments means that battery weight and size parameters must be very closely controlled throughout the manufacturing process.   To put this into context, the Battery can be 12 – 18% of the Submarines weight.

Reliability – A Submarine Battery is made up of many hundred individual cells, all of which need to perform reliably, equally and consistently so that the whole Battery provides optimal output.   This is achieved through:

  • Consistency of manufacturing.
  • Integrated monitoring systems that provide remote voltage, electrolyte temperature and level information to Operators.
  • Inbuilt temperature reduction features.
  • Electrolyte circulation systems to prevent stratification.
  • Ease of access.
  • Proper electrical and physical maintenance.
  • Longevity – The Battery is installed deep within the Submarine and because of its bulk and mass, it is difficult and time consuming to remove and to install.   So once it has been installed, it needs to be keep there for as long as possible.   A submarine Lead Acid Battery can be expected to be in operation for six years.

 

About PMB Defence Batteries

So what are some of the areas where battery improvement options can be explored by PMB Defence Batteries:

  • Opportunities to lighten the battery and thereby provide greater flexibility for Submarine designers.   This can be achieved by review of the materials used in the battery and the bus bar system used to connect all of the battery cells.
  • Magnetic signature reduction.
  • Improved battery monitoring systems that allow the Submarine operators to monitor temperature, voltage and electrolyte levels more accurately and more frequently.
  • Better ways of achieving the battery cooling and electrolyte agitation and thereby improving performance.
  • Designs that make batteries easier, quicker and therefore less costly to install and remove.
  • Study the complex interdependencies between: Submarine operational requirements, design constraints, energy storage options and electro-mechanical configurations and perform trade-off analysis.
  • Improvements that permit a battery to be charged quicker in a Submarine and thereby improve operational efficiency and reduce detectability.
  • Improvements that reduce the customers maintenance overhead both at sea and alongside.
  • Reduce the total cost of ownership.
  • By forming strong relationships with Diesel-Electric Submarine designers from around the world.

PMB Defence Batteries works very closely with its sister company PMB Defence Engineering in providing quality product and services to our customer.These production and through-life support learning’s are fed back into the companies research and development activities to optimise PMB’s offerings.

PMB Defence Batteries is proudly a small South Australian company employing 40 people.   In addition to the highly trained Trades and Non-Trade people directly involved in manufacturing, PMB employ Engineers covering mechanical, electrical and chemical disciplines, Scientists, a Purchasing team and of course a Finance and Administration group.