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Mar 20 12 5:58 PM
Mar 20 12 6:06 PM
On the other side, France to the Gulf of Mexico is only about 4000 nm as well and they always seem to have refueled on route as well. Been a few cases where German U-Boats ran out of fuel as wellAny cases where U-Submarines ran out of fuel on Pacific Patrols?
Mar 20 12 6:35 PM
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Mar 20 12 6:40 PM
Mar 20 12 9:25 PM
Kitsune wrote:Many times, German U-Boats would refuel twice, once inbound and once outbound, from either a tanker submarine or another U-Boat with some spare fuel.Did US Submarines ever refuel each other?
Mar 20 12 10:17 PM
Mar 21 12 1:25 AM
sergeante wrote:US boats certainly didn't have an overboard fuel pump. The only way fuel could be expelled out of the tanks was by blowing it out with compressed air. But the boat would have to ship fuel transfer lines and connecting gear that fitted the fuel filling connections on deck. I doubt that was standard equipment. I'd also question whether that was standard equipment on German boats.
Mar 21 12 1:49 AM
Mar 21 12 6:30 AM
Kitsune wrote:Trying to do some calculations hereA US Gato appears to have about 420 tons of fuel (using gallons and converting to weight as diesel fuel) at wartime load?A German Type IXC/40 seems to have 214 tons of fuelIt looks like they require similar power for similar speeds - 21 knots at 5400 HP (Gato) and 19 knots at 4,400 HP (Type XI) Both are listed at around 11,000 nm at 10 knotsUnless the US engines are very inefficient, it would appear as if something does not fit hereOpinions?
Mar 21 12 6:48 AM
Mar 21 12 6:56 AM
Mar 21 12 7:28 AM
Mar 21 12 8:11 AM
Mar 21 12 8:26 AM
DCJ wrote:I didn't bring up the Gato/Balao issue and I don't have any interest in it. I agree that it's an issue of "poorly vetted sources and slipshod editing."
Mar 21 12 5:45 PM
I've been turning this over in my head, because it does seem anomalous. Using some terribly crude estimates from Springsharp, it appears that, at 10 knots, a Gato class hull would require about 20 percent more power. That comes just from hull size, since the Gato was 60 feet longer and 5 feet wider in beam than a Type IX. So that's at least part of the explanation.As for the rest, my guess is that US engines were not so much inefficient, but rather that the MAN diesels used by the Type IX were very efficient. This description is taken the US postwar evaluation of the Type IXC: "The diesel engine selected for the IXC has several interesting compromises in design. In order to obtain the high power desired in each of the two engines for the limited direct drive RPM it was necessary to highly supercharge the engine. This was accomplished effectively by the exhaust turbine supercharger. However, in so doing, design limitations in engine size required the acceptance of high exhaust temperatures for a submarine installation. The resultant mean effective pressure and power for each cylinder are high, and the fuel rate over a wide range of operation is low." So, perhaps the Germans achieved very high fuel efficiency by supercharging the bejeesus out of their MAN diesels. Furthermore, it seems possible to me that the diesel-electric arrangement on the Gato class allowed it to develop power at higher RPMs than would be permissible in a direct-drive arrangement. That in turn would make it more practical for the Gatos accomodate less efficient engines that simply ran faster to produce the necessary power. As best I can tell, the MAN M9V operated at about half the RPM of a Fairbanks Morse 38.
Mar 22 12 6:03 AM
sergeante wrote: Supercharging probably did make the German engines somewhat more fuel efficient in some operational situations. But it's a self-limiting technology. You can only run the engines so hot before they break. And running engines any hotter leads to a higher parasitic load for running cooling water pumps. Also, blowers are themselves a parasitic load, whether run directly by mechanical power takeoff from the engine or through exhaust turbines (exhaust-driven blowers create higher exhaust pressures, which in turn creates more resistance on the exhaust stroke). In any case, they weren't 40-60% more efficient. Diesel was a fairly mature technology, even back then.WRT the engine efficiency of US boats, remember that one of the advantages of decoupling the egnines from the propulsion motors was that the engines could be run at optimum fuel efficiency most of the time. Only during speed runs or fast battery charging would they be operated at lower efficiency. Being able to run 1 to 4 motors independent of speed aided this.
Mar 22 12 6:58 AM
Yes, I understand those things. Feel free to tell me your idea for how the Type IX went the same distance on half the fuel. Obviously my idea was too stupid to be the answer.
Mar 22 12 6:59 AM
Mar 22 12 7:21 AM
I would argue that there is a problem with the ranges with one, the other, or both.
Mar 22 12 7:37 AM
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