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Naval Propulsion Plants

Posted: Thu Jan 13, 2005 1:06 am
by José M. Rico
Different types of naval propulsion plants:

1. Steam propulsion plants: This is the oldest type of naval propulsion and it is still used today by many ships. It comprises a series of boilers where coal (up to WWI) or fuel-oil (after WWI) is burned to heat the feed water and produce high pressure steam that is delivered to the turbines that turn the propellers. This derived of the force generated from the impact of the high pressure steam on the turbine blades.

2. Diesel propulsion plants: In these type of plants the fuel is injected and burned inside the cylinders of the diesel engines that move the propellers through a reduction gear. Since there are no boilers nor turbines, weight and space is saved. This system has higher efficiency, and because of its lower rate of fuel consumption provides ships with longer range than steam propulsion plants. However, diesel powered ships are generally slower than those powered by steam. Another disadvantage is that diesel engines are too noisy making them easily detected by passive sonar.

3. Gas propulsion plants: This system is similar to that used in jet aircraft and it became widely used in the 1950's. The fuel combustion generates gas that rotates the gas turbines and turn the propellers. It requires high fuel consumption and it is not efficient as diesels, but provides higher speed, quicker response time, faster acceleration/deceleration and weight reduction.

4. Combined propulsion plants: These plants are used to take advantage of both diesel and gas systems. Main arrangements for combined plants:
  • a) CODAD (COmbined Diesel And Diesel). Usually comprised of 2 diesel engines for cruising speed, adding the power of 2 other diesel engines for high speed operation.
    b) CODOG (COmbined Diesel Or Gas turbine). The cruising speed is attained with the diesel engines and the gas turbines are used for high speed operation.
    c) COGOG (COmbined Gas turbine Or Gas turbine).
    d) COGAG (COmbined Gas turbine And Gas turbine).
5. Nuclear propulsion plants: These plants are basically a steam turbine with a nuclear heat source. The first nuclear powered surface warship in the world was the USS Long Beach (CGN-9) commissioned in 1961. Nuclear propulsion offers significant advantages. Unlike conventional ships that require refuelling every few days, a nuclear powered ship has a much greater operational range and can go for years without refuelling since consumable fuel is not needed. Nuclear plants are bigger than those on conventional ships, but they require less space overall because of the lack of fuel bunkers. The biggest drawback of nuclear propulsion however is the initial cost.

Posted: Thu Jan 13, 2005 9:18 am
by foeth
I think you forgot the reciprocating steam engines; the compound and tripple expansion engines (IIRC, single cylinder engines weren't a success due to weight).
This derived of the force generated from the impact of the high pressure steam on the turbine blades.
Perhaps in early turbines, but it's usually the expansion of the steam resulting in a lift over turbine blades that generates the force (lift based vs less efficient drag-based)
However ships are usually slower
Lighter and more efficient makes a ship slower? I don't think so. WWII warships had a power plant with an enormous capacity. Economy forced "small" diesels. Diesels are the most efficeint type of engine (ok Stirling engines are better but are not used).

Gas turbines are very very small for their power output and quite light. Except for the lower efficiency, they cannot run on heavy fuel oil but lighter and more expensive fuels.

I'm also missing the diesel/turbine electric drives :(

Posted: Thu Jan 13, 2005 8:06 pm
by José M. Rico
Thanks for pointing that out Foeth. I tried to give only a general overview of how the steam propulsion functions. But you are right, I forgot about the old steam reciprocating engines. I was thinking of modern steam systems with geared turbines. By WWII standards anyway reciprocating engines were totally outclassed, although some old ships still had them and the battleship TEXAS BB35 is a good example of that. During the 1925-27 modernization this battleship was retrofitted from coal burning to fuel-oil but still kept the reciprocating engines! If I am not mistaken steam driven turbines began replacing the reciprocating engines in ships during World War I.

Regarding diesels, perhaps I did not explain myself correctly. What I tried to say is that diesel powered ships are generally slower than those powered by steam. We have a good example in the German "pocket battleships" of WWII which used diesels, and although they attained a considerable good speed of about 28 knots, they always fell short against heavy cruisers mounting classical steam propulsion plants which could easily surpass 30 knots. The German diesels gave much more range however.
foeth wrote:I'm also missing the diesel/turbine electric drives :(
Are you referring to the CODLOG (COmbined Diesel, eLectric Or Gas turbine) and CODLAG (COmbined Diesel, eLectric And Gas turbine) systems?