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Originally Posted by TorpX
I don't know what you refer to when you use the term tachometer.
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It's a device that counts engine revolutions. You can judge your speed by the revolutions. Unfortunately the problems I mentioned earlier make it less accurate the faster you travel
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While the Bendix log would not be as accurate as a timed trial, great care was taken to calibrate it for accurate results. If it had not been accurate, the firing solutions genarated by the TDC, would not have been sound.
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I see. I apologize for being unfamiliar with the instrument, but a careful study here brought me up to date.
http://www.maritime.org/fleetsub/log/index.htm
The first thing I notice is that it operates on a similar principle to the pitot tube. This may affect accuracy at high speeds, or it may not. As I said, I'm not saying it didn't happen, just listing the reasons why I tend to question it.
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Perhaps not, but there are more variables here in a Gato or any sub, than with a battleship. Current displacement, and charge on the battery would affect this. Do timed trials usually involve pushing engines beyond their design limits?
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No, the variables are the same. Any ship trial is conducted with as light a load as possible, and as much power as possible, the goal being to make the ship look as good as possible to the potential buyer (in this case of course the navy). In the case of a submarine it would require the batteries be fully charged of course, and the engines are pushed absolutely as fast as they'll go. With that in mind I would insist that 20.25 knots was the best speed on the best day, maybe getting to 21 if you're lucky.
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Of course you are free to accept whatever sources you choose, but I am inclined to take O'Kane's word for it, as he has spent more time in fleetboats than I. 
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And that's the crux of the matter. On the one hand anecdotal evidence is always suspect, especially given possible variations in measuring equipment. On the other hand anecdotal evidence is vital because sometimes it really is true.
On the other other hand I don't lie and I don't cheat, so when I find something that supports an opposing argument I don't sweep it under the rug. I tracked down Bubblehead1980's mention of Fluckey and
Barb, and sure enough he not only claimed to have made 23.5 knots using "150% overload", however that works with a diesel engine, but was officially credited with a world speed record for it.
http://en.wikipedia.org/wiki/Eugene_B._Fluckey
Again, I'm no engineer, but I do have a basic understanding of how these things work, and while Bubblehead "has no doubt" that it happened, I still do. But you have your statements from the people who were there, and I can't dispute their claims. I can, however, question the equipment, but I can't prove it. You talked about the accuracy during an attack, but an attack takes place at 2 knots, not 20. Are the instruments accurate at higher speeds? Car speedometers and aircraft air speed indicators are not.
So it's an impasse. But I will leave you with one question: If it's realistic to allow the special ability to boost the speed that much, is it still realistic to not have any chance of an engine breakdown at the worst possible moment? To my mind you can't have one without the other and still claim realism.