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Propulsion Plant

Introduction
Initially I had planned to address ship propulsion plant weight at a single-digit=20 weight level, as most of the data I have for real world ships, and other designs, only have the propulsion plant weight reported at this level.  However, I eventually came across several Undergraduate and Graduate Level Theses on the MIT D-Space website that deal specifically with estimating ship propulsion plant weights at a more detialed level.  

I hope to combine some of the information provided in these Theses with the limited detail propulsion plant weight data that I have on existing ships and design studies, and develop a method suitable for use with the rest of the formulas, equations, and data presented on this site.  I then hope to try and validate this method by estimating the weights for some of the vessels, for which I currently only have a single digit weight estimate for.

I have also found a paper on the intrnet relating ship propulion plant costs to specific propulsion plant components, which I believe will integrate well with this more detailed propulsion weight estimating method.

Hopefully this approach will allow the user to investigate a wider range of potential power plant options, than would be possible if only estimating propulsion plant weights at a single-digit level.

Overview of Plant Layout

For a large number of conventional naval surface combatants the propulsion plant can be viewed as consisting of four main section, including;

   1. The Power Generation Section
   2. The Transmission Equipment
   3. The Propulsor
   4. The Controls, Auxiliaries, and Support Systems

Group 1 primarily consists of items such as the main propulsion diesels, gas turbines, steam plants, and/or other items like fuel cells, which convert the fuel (or stored energy) onboard into power.  For a conventional steam plant this would include not just the boilers, but also the steam turbines, and main condensors, etc.  For a nuclear powered steam plant this will include the nuclear reactor, the primary and secondary sheilding, the steam turbines, and main condensors, etc.

On many vessels with conventional steam plants, nuclear steam plants, and some diesel installtions, the same power generation components are used to generate the required power at both cruise speed and at full-speed.  Examples of ship's like this include the USN's CGN 9, CG 16-24, CGN 25, CG 26-34, CGN 35, CGN 36-37, CGN 38-41, DDG 2-24, DDG 37-46, FF 1037-1038, FF 1052-1097, or the RN's Rothesay, Whitby, and Leander class frigates.

However on many other vessels, different power generation components are used to augment the power generated by the "cruise" plant to provide enough power for the ship to reach full speed.  Examples of ship's like this are the Royal Navy's Steam and Gas Turbine=20 powered "County" Class Destroyers, Type 81 "Tribal" Class Sloops, and Type 82 "Bristol" Class Destroyer, or the Russian Navy's "Kirov" Class Large Strike Cruiser, which is belived to have been configured with a Nuclear Powered Steam Plant for cruising, augmented by conventional oil fired components to provide extra power at high-speed operations. The propulsion plant on the RN vessels mentioned above are described as a Combined Steam And Gas Turbine (CoSAG) plant, where;

  • the first power generation component term ("Steam") signifies what the vessel uses for cruise speeds
  • the second power generation component term ("Gas Turbine") signifies what other power generation components are included on the ship to reach high-speeds, and
  • the term "And" signifies that the Gas Turbines and the Steam plant operate together to provide the power for these high-speed operations

Similarly, for the propulsion plant on the Russian Kirov class vessel is described as a Combined Nuclear And Steam (CoNAS) plant to signify that the ship is believed to have;

  • a nuclear plant for normal cruising operations
  • additional steam plant components for high-speed operations, and
  • these components are operated together in order to provide the power for high-speed operations

Becuase there are complexities involved in operating to different plants on a single shaft at the same time, it can be simpler to instead configure a ship's overall propulsion plant with one set of power generation components for use when "cruising" and a second set of power generation components for use at high-speed.  In such a configuration the cruise power generation components with the only time both sets of components being on line together is when accellerating from cruise speed to higher speeds, where the high-speed components/engines are brought on line to take over the load from the cruise components/engines, which are then taken off line.

Such a configuration, where the cruise-speed and high-speed components/engines are not meant to operate for an extended period on the same shaft allows for less complex/less expensive gearboxes and clutches, etc.  Examples of ship's like this are the US Coast Guard's 378ft WHEC High-Endurance Cutters and the RN's Type 21, Type 42, and early Type 22 vessels.

On the USCG's 378ft WHEC the ship is configured with one diesel engine per shaft to provide cruise power and one gas turbine per shaft to provide high-speed power for a Combined Diesel Or Gas Turbine (CoDOG) plant.  On the RN vessels mentioned above they are configured with a small cruise gas turbine/shaft and a more powerful High-Speed Gas Turbine/Shaft for a Combined Gas Turbine Or Gas Turbine (CoGOG) plant.  Here the term "Or" signifies that typically "either" the cruise engines "or" the high-speed engines will be in use at a given time, rather than having them both on line for high-speed operations as in an "And" configuration.

Because on a ship with an "Or" type configuration, only the high-speed plants is in use to meet the vessel's design speed, while a completely different set of "engines"/components are in use to meet cruise speed operations, the total installed power required on such a vessel is typically more than for a similarly sized vessel with a plant with an "And" configuration, where both the cruise and high-speed (boost) engines combine to provide power for the vessel's top speed.  However, as noted above a vessel with a plant with an "Or" configuration can have a simpler/less expensive gearbox and clutching system.

Group 2 consists of the components that connect the Power Generation Section (Group 1) to the Propulsors (Group 3).  In general the transmission systems on a modern naval surface combatant will either be a mechanical system (consisting of gearing and shafting) or an electrical system (consisting of generators, power conditioning and converting equipment, and motors, etc).  As noted above, for mechanical systems, the gearboxes and other components in this group can be configured to either combine the power output of the cruise engines/components with the high-speed engines/components to provide full power in an "And" configuration, or simpler and less costly gearboxes and other components in this group can be used in an "Or" configuration, where the cruise engines/power generation components only provide power up to cruise-speed, and separate engines/power generation components provide power at higher speed operations.

Group 3 consists of the actual components of the system that convert the energy output from the Power Generation units into thrust.  As such, this group consists primarily of items such as fixed-pitch or controllable-pitch propellers, waterjets, azipods, voith-schnieder type propulsors, or Z-Drives, etc.

Group 4 then consists of all the remaining Controls, Auxiliaries, and Support Systems  associated with the propulsion plant.

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