Marc
Posts: 280
Joined: 9/5/2000
From: Braunschweig, Germany
Status: offline
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Hi Mike,
first you are absolutely correct not to trust every figure or statement that you read somewhere.
So I again took a look in the cruiser book and here are some passages that (in my opinion) describe quite well the figures I already stated and shows that the authors didn't just throw in an endurance value but commented them, as I think, very well.
Here the data for the Myoko and Takao classes:
Myoko-class as built: 8000nm/14 knots (designed), 7000 nm/14 knots (effective), 2470 tons oil
Myoko after first reconstruction(1936): only 4,000nm at 16 kts !!!!!
Myoko-class 1940: 2,214 t oil 8,500nm at 14 kts (planned), 7,463nm at 14 kts (effective) and 5,000nm at 18 kts.
Takao-class as built: 8000nm/14 knots (designed), 7000 nm/14 knots (effective), 2645 tons oil
Takao/Atago 1939: 8500nm/14 knots (planned), 5049 nm/18 knots (effective), 2318 tons oil
Myoko class as built:
"The maximum fuel capacity was 2470 tons of oil, and the designed endurance was 8000nm at 14 kts, which was considered the normal cruising speed in the early 1920s. The effective endurance was expected to decrease to some 7000nm as a result of the weight added before completion. Compared to the British Kent and the American Pensacola class, which carried about 3400 tons and 3000 tons of fuel oil, respectively, and had effective endurances of more than 10,000nm at 14 kts, the endurance of the Myoko class was more than 30% less. However, it should be remembered that when the Myoko class was designed, the Japanese assumed that the IJN would engage the U.S. Navy within about 1500nm of Japanese home waters..."
Takao class as built:
"The output of each of the cruising turbines proper was 3100 SHP at 5439 rpm, reduced to 1600 rpm by the cruising gear between the cruising and outer HP turbines. Over the whole turbine set, i.e. the cruising turbine plus the outer HP and LP turbines, the output reached 7,050 SHP at 170 rpm after reduction in the main gear, or 14,100 SHP for the port and starboard sets. This power yielded a cruising speedof 18 kts. A crusing speed of 14 kts could be obtained with 140 rpm and 3,750 SHP over the whole turbine set, 7,500 SHP for both shafts. In crusing conditions the main steam passed through the cruising turbines, whose exhaust steam was passed to the first stage of the common-use outer HP turbine, then over the outer LP turbine to the condenser; the inner HP and LP turbines were decoupled. In these conditions the turbine sets of the after engine rooms ran freely or could be disconnected at the main gear wheel. In other than cruising conditions, main steam was admitted simultaneously to both outer and inner HP turbines, the cruising turbines being bypassed and decoupled at the cruising gear...
The maximum fuel capacity was 2645 tons of oil, and the designed endurance was 8000nm at 14 kts. Because of the excess displacement, the actual maximum range was some 1000nm less. By the early Thirties, the Naval General Staff had concluded that a cruising speed of 18 kts was more acceptable than 14 kts. However, the power needed for 18 kts was about twice that for 14 kts, and the fuel consumption was correspondigly doubled. Thus, the maximum endurance at 18 kts was expected to be reduced to some 4000nm."
Myoko-class after second modernization:
"The boilers were retubed, and six of them were given steam preheaters. New burners were fitted, and the power of the blowers was increased. These measures reduced the fuel consumption...
The induction turbines fitted during the First Modernization were removed since they caused a lot of trouble. The revised cruising arrangement that was adopted allowed the steam from the cruising turbines, located in the forward turbine set, to be admitted directly to the aft HP turbines. Thus, cruising power was available on four shafts, facilitating transitions to higher speeds. Because of the increased displacement, a further drop in maximum speed was expected, the designed speed being 33.3 kts at 132000 SHP. The Myoko reached 33.88 kts with 132830 SHP at 14,984-tons displacement during trial run ... on 31 March 1941.
The maximum fuel capacity was reduced from 2472 tons to 2214 tons oil. Moreover, some 480 tons of fuel capacity were redistributed, mainly in the outer part of the original bulges and in the new bulges. Originally it had been expected that the boiler improvements would increase the radius of action to some 8500nm at 14 kts, notwithstanding the reduced fuel capacity and the increased displacement. However, more realistic predicitions brought that value down to 7900 nm at 14 kts, and the Myoko consumption trials yielded an effective radius of 7463 nm at 14 kts, or about 5000nm at 18 kts."
If I am not missing something the Maya and Chokai were the only two cruisers of the two classes that only used two shafts for cruising until their end. This was quite less effective than using all four shafts.
Since the book states for the Takao class only the endurance for 18 kts I would make a bet based on the known values from the Myoko class:
Myoko 5000nm - 18 kts , 7463nm - 14 kts
Takao 5049nm - 18 kts , 7500nm?? - 14 knots??
Marc
Finally here a scan from the book that shows some trial results of Myoko and Haguro after completion:
 Attachment (1)
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 IJN Chokai
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Printable Version
Preliminary Japanese Class change summary. - 
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