1930s: German navy switchs to diesel power?

Discussion in 'WW2 General' started by tomo pauk, Nov 24, 2012.

  1. tomo pauk

    tomo pauk Creator of Interesting Threads

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    German navy received, in 1930s, 'pocket battleships' that were powered by diesel engines. That practice was not followed in subsequent classes. Wonder if there is merit to apply diesel power (either full, or partial) in other KM ships, from destroyers up to battleships?
     
  2. Shortround6

    Shortround6 Well-Known Member

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    #2 Shortround6, Nov 24, 2012
    Last edited: Nov 24, 2012
    The light Cruisers had mixed power. Diesels on some shafts and Steam Turbines on others. Plans were made for Diesels in later ships that were never made.

    State of art at the time was that diesels required more volume (hull space) that a steam turbine installation of equal power and many have been heavier.



    127-560x368.jpg

    Boilers had made a lot of progress between 1916 and the early 30s. reducing the size and number of boilers needed. Power plant size helps govern hull size and in the case of armored ships, the size of the area that needs armor protection so a bulky power plant, even if economical ( and fuel oil can be but in double bottoms and used as part of the torpedo protection), may require a larger ship than a more compact but thirstier power plant.
     
  3. Shortround6

    Shortround6 Well-Known Member

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  4. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Thanks for the feedback :)

    1: shafts
    2: main diesel engines
    3: reduction gears
    4: diesel generators
    5: chambers for 150mm ammunition
    6: auxiliary diesel engines
     
  5. davebender

    davebender Well-Known Member

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    Diesel power would be technically interesting but it won't change the war. For that to happen German capital warships would need to leave port once in awhile to attack the enemy.
     
  6. Readie

    Readie Well-Known Member

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    Steam turbines were the power plant of choice.
    Diesels did not have the power to shift WW2 battleships/ battle cruisers at 28 - 31 Knots.
    I bet they were a sight at full chat...wow.
    Cheers
    John
     
  7. davebender

    davebender Well-Known Member

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    That misses the point.

    Diesels were very economical for cruising. WWII era surface warships typically cruised at 15 knots. Diesel(s) on the center shaft only need enough power for economical 15 knot cruise which constitutes about 95% of warship operations.

    Steam turbines on the two outside shafts provide 30 knots or so for the 5% of operations when high speed is required.
     
  8. Denniss

    Denniss Active Member

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    This arrangement may be viable for three-shaft ships but RN usually had four-shaft capital ships.
     
  9. Shortround6

    Shortround6 Well-Known Member

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    The alternate power works up to a point. Battleships could need 20-30,000 more hp for an extra TWO knots. The difference between 28 and 30 or 30 and 32 knots. Even with Steam turbines there is a limit as to how much power you can put through each shaft (or through each propeller?). The Diesels need more foot print or volume per horsepower than steam turbines and battleship power plants were built "heavier" than cruiser power plants for both reliability and durability. Reliability for combat operations and durability because it is a much bigger project to replace battleship power plants. More decks and more armor have to be removed to get major power plant pieces into and out of the ship once it is built. Battle ships also have much heavier armor over the machinery spaces so an increase in power plant size causes a disproportionate increase in armor weight which causes the hull to be bigger to "float" the armor which requires more power for the same speed.
    As with many other things, technological advances came in fairly short order so comparing a 1950s ship to a 1930s ship (or engine) doesn't tell us much.
     
  10. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Was it a custom, in steam-powered ships, to install the diesel generators and/or auxiliary engines in the main boiler/turbine rooms, within the armored 'citadele'?
     
  11. Readie

    Readie Well-Known Member

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    Dave,
    Diesels had their uses of course but, not as battle ship / battle cruiser main power units. Steam turbines were the most powerfull unit available whether maximum speed was used or not.
    The big change was from coal to oil as the boiler fuel.
    Cheers
    John
     
  12. Shortround6

    Shortround6 Well-Known Member

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    It depends on the ships, Most ships with an 'armored citadel' had the diesel generators and/or auxiliary engines within the citadel or at least the majority of them. In some ships they had their own compartments within the citadel, in others they were in the main machinery rooms. Some had a mixture. Some ships had some of their diesel generators outside the citadel, it depended on how "tight" the design was and/or if/when the electrical load changed during the design process.
    Battleships, in general, had much better sub division (more compartments) than cruisers. In some cruisers the main machinery compartments were not sub divided side to side. That is to say an engine or boiler room extended from one side of the ship to the other because flooding just one side of the ship brought more danger of capsizing than the greater flooding but sinking on an even keel (little or no list to one side) that flooding the full width of the ship would bring.
     
  13. Shortround6

    Shortround6 Well-Known Member

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    Other big changes were small tube boilers (less weight per ton of water turned to steam), Higher pressures and lots more super heat (some navies carried it too far) which also reduced the boiler weight per pound of steam. Together with the oil fuel it meant one big boiler could do the work of 3-4 smaller ones but be lighter and require much less crew. Throw in double reduction gear sets between the turbines and the props and the weight per HP of an early 1930s steam plant was waaaay lower than even a 1916/7 steam plant of the same power. AND more compact which means less armor.

    As far as speed goes please not that although there were other improvements the extra 4-5 knots that a Missouri had over a South Dakota were bought with most of the 10,000 ton and 200ft differences between the ships. Also please note that a Missouri was supposed to be able to hit 27kts with only 1/2 of it's boilers lit.

    That is where the Diesel powered large warship runs into trouble. It cannot quite match the steam powered one in speed and that last 2-4knots require so much weight and volume. If you think the Diesel powered ship can be slower and use it's guns/armor to fight it's way out of trouble that is a different argument.
     
  14. Readie

    Readie Well-Known Member

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    The armoured citadel must also include the magazine. No point in armour protecting the engines and not the magazine...look what happened to HMS Hood.
    Speed was vital as it gave sea room to fight or run. Steam boilers pretty much reached the peak of their development as shown with locomotive technology in the Mallard.
    Capital ships were not used lightly as the Germans showed with theirs. All much too much to risk?
    The downfall of the capital ship was the aircraft but, that is another story.
    Cheers
    John
     
  15. Shortround6

    Shortround6 Well-Known Member

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    The Mallard was pretty much low tech. Try checking the British WW II Steam gun boats. 8000hp in a ship that weighed about what the Mallard and tender did.

    8000hp worth of WW II diesels that could run at that level for 8 hours or so at time would be a pretty complicated engine room.

    The Diesel powered American DEs had about 6000hp.
     
  16. delcyros

    delcyros Well-Known Member

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    The biggest issue, and the prime reason for dropping Diesel propulsion from the german perspective was not the weight of the plant nor the spacial requirements for their installation (Diesels are rather compact compared to boilers). KM ship designing practice required excessive length of the waterline to be put under armour in the "armoured citadel", so both, armour weight and space are no issue here.
    The reason for this was their desired protection scheme, moving from all-or-nothing alike Panzerschiffe with inclined main belts to a more sophisticated system incorperating belt and armoured slope + splinterbelt /ATB schemes to fit their specific anticipation of intended battle ranges. This system required a rather low placed main armour deck, which in it´s own required excess stability charackteristics to make worth the tradeoff in more appaerent risk of the flooding of it´s wingtanks through penetrations of the main belt. Their armour system was not to make these ships invulnerable but to keep the embedded vitals intact from even short range belt-penetrating fire.
    In order to attain large enough protected buoyancy and volume despite the low armour deck, the "armoured citadel" was taken intentionally further fore and aft than would be necessary.
    Thus, Diesels would indeed fit nicely their choice of armour protection philosophy.

    Another problem is definition. When Germany signed AGNA 1935, it eventually was bound to the definition limits of Washington and London naval treaties. These treaties defined that fuel oil was not to be counted in standart displacement but all weight of the engine was. This is what eventually killed the Diesel choice. Diesel propulsion is MUCH more economical but You will require more dead weight buildt into the powerplant. Since the fuel weight doesn´t count but the machinery weight does, the choice of lightweighted, high pressure, superheated boilers and turbines was made.

    You need to realize that Diesel propulsion was indeed always LIGHTER than boiler/turbine if You factor in the weight of fuel oils/diesel. The Panzerschiff DEUTSCHLAND had just 4,962 t of machinery and fuel weight for a plant capable of producing 54,000 SHP design and a max range of 10,000nm at 20 kts. SCHARNHORST´s weight was 9,990t (including fuel oil) for a plant capable of producing 134,000 SHP design but a max range of only 6600nm at 19 kts. Corrected for identic range, the machinery + fuel oil weight of SCHARNHORST would have to be drastically increased, to ~14,000t, resulting in a specific weight of ~104kg/SHP for steam turbine and 92kg/SHP for Diesel plant´s with a design range of 10,000nm @ 20 kts.
    Corrected for the higher (=134000 SHP) power of the SCHARNHORST´s, the DEUTSCHLAND´s plant (including Diesel fuel weight) would be 6,875t heavy, resulting in a specific weight of ~75kg/SHP for steam turbine and ~51kg/SHP for Diesel plant´s with a design range of 6,600nm @ 20 kts (same as SCHARNHORST).

    But since the Treaties are ignoring fuel oil weights, the lightweight advantage of Diesel is gone. On any Washington displacement, a Diesel driven variant will be correspondingly less powerful than a boiler/turbine driven one.

    Mixed propulsion plants were tried in the various interwar CL but none actually worked well. Part of the problem is that You can´t run the boilers cold. Thus, they need to be lit up in order to have action reserve, meaning that in actual service condition in wartime a relatively high fuel consumption unaccounted for in peacetime has to be factored in.
     
  17. Readie

    Readie Well-Known Member

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    Shortround, We'll have to agree to differ about Mallard's tech spec being 'low tech', she was the first A4 to be fitted with a Kylchap double blast pipe and her WSR, which is held to this day, speaks for itself.
    The steam gunboats were turbines not compound pistons. Great performers in heavy seas but, having to be kept 'in steam' was a disadvantage.
    The British Gun Boats etc with 4 × Packard 4M 2500 petrol engines, total 5,000 hp went well but, the thought of sitting on all the petrol is eye watering....
    A pretty explosive choice really....superheated steam or petrol.
    Cheers
    John
     
  18. Shortround6

    Shortround6 Well-Known Member

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    The Mallard's WSR was a notable achievement but 250lb boiler pressure in a fire tube boiler, single expansion pistons and the rest of her "specs" were certainly not the latest word in steam power plants, either afloat or on land. Railroads were a world unto themselves and the steam plant had to survive extreme vibration and banging about which ship and stationary power plants (electrical generation) did not have to deal with. Attempts to use water tube (or flash in some cases) boilers at 300-600lb pressures in railway service were usually costly failures. Attempts to use geared turbines usually failed too, but that does not mean ship owners were going back to fire tube boilers and reciprocating steam engines for high powered ships in the 30s and 40s.


    Technology did not stand still and a 1928 Diesel installation may have been different than a 1938 Diesel installation. But steam technology was not standing still either. Late WW I technology required 8 oil fed boilers to produce 65,000hp on the last Hawkens class cruisers built. By the late 30s the twelve 6in gun cruisers were getting 80,000hp from just 4 boilers. In between 72,000hp was gotten from 6 boilers. Granted the later boilers may have been larger than the early boilers but 4 big boilers means fewer boiler rooms, less piping (fuel, feed water, and steam) and a more compact layout. Some Italian 10,000ton "treaty" cruisers were supposed to have 150,000hp. Try that one with Deutschland type diesels.
    US Baltimore class cruisers got 120,000hp from four boilers.
     
  19. Readie

    Readie Well-Known Member

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    Points taken SR but, the A4 was the last word in steam locomotive power and although steam lasted longer here than in the USA, no steam locomotive bettered Gresley's designs.
    If you want the ultimately useful steam powered vessel, I would suggest these...warship: ww2 Liberty ship Specifications
    Cheers
    John
     
  20. davebender

    davebender Well-Known Member

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    When I was on U.S.S. America boilers were never completely cold when at sea. Only a couple minutes were required to bring an idle boiler into service. This sort of thing happened when an aircraft had a flap / slot problem that required a higher landing speed or more wind over the flight deck.

    If the USN could find a solution I suspect other nations could also.
     
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