TDC

[snakedocpl]

Interesting approach.

Originally Posted by TorpX

Actually, you don't necessarily need the target Aob.

Below, is a geometric solution for timing by wire that doesn't make use of any "stabilized line", or special equipment. In this solution, you do need to know the Aob, and of course, target bearing, and sub speed.
The 'line' moves with the sub, but the angle doesn't change.
The underlined term in the formula accounts for the movement of the line and the space along the target track marked by 'n'.

This one is similar to the German Ausdampfverfahren method.

Originally Posted by TorpX

However, if you had a mechanism to move or "stabilize" the line, there are other possibilities. Below is a diagram illustrating what a solution might look like with the line being moved. This simplifies the calculation of target speed in that the underlined term in the first formula is eliminated.

Note that for the mechanism to know how fast the line is to be moved, the range has to be known.

The initial rate of change of angle a =
(Vu*k sin a) / (2*pi*Range) * (360*60)
I computed an example for a sub moving at 3 kn., timing a target at 2,000 yds., at 45°.
(3*0.563*sin 45) / (2*pi*2000) * (360 * 60) = 2.05° per minute
The problem with the above is that the rate of change of the angle is not constant, so it would have to be dynamically calculated by the TDC, or some mechanism. Of course, the calculation is no more complicated than the other quantities the TDC calculates, so it is certainly possible.
Without some kind of mechanism to calculate the above, I don't really see any point in the technology.
I suspect the reason the feature was not carried over, was that it was rendered unnecessary by RADAR. With a RADAR plot, the target speed could be accurately determined without identification, or knowing the ship's length.

This in turn is similar to the German Auswanderungsverfahren method.

--
Regards
Maciek

[ColonelSandersLite]

Originally Posted by snakedocpl

All this would require small calculating device. I think, that such device was not developed because it would be complicated, its input depended on estimated value of AoB, so it would not give any advantage over plotting or even estimating. I suppose, stabilized line was abandoned because it just impractical.

Originally Posted by TorpX

I suspect the reason the feature was not carried over, was that it was rendered unnecessary by RADAR. With a RADAR plot, the target speed could be accurately determined without identification, or knowing the ship's length.

The more I think about it, the more sure I am that the device was simply ineffective.

AOB isn't actually required as the point of stabilization isn't moving (try shooting at a stationary ship to see what I mean, aob is not a required part of the solution). True stabilization not only requires knowing your own speed but also a specified distance to stabilize to. Sure, you can use assumed values for both, but that would render the device inaccurate. There is also a fundamental problem given the era. Unless you're stabilizing to infinity, the ability to solve the triangle in real time would take an analog computer that surely could never fit in the periscope. US submarines actually did have that computer, in the form of the TDC with position keeper, and it takes up a *lot* of room. Even stripping it down to the bare essentials for this particular job, I very much doubt it could fit.


Given that there is no way to input submarine speed or stabilization distance, and the computer that could do it probably couldn't fit into the periscope, I think it's safe to assume that the line was stabilized to infinity. This means that there is just no practical difference between just using a regular vertical line on the periscope and using the stabilized line so long as the submarine is not turning. In the real world, a 5 knot target will take around (depends on ship length) 50 seconds to cross the periscope line and this scales linearly with speed so a 10 knot target around 25 seconds and 15 knot target around 17 seconds.


I can't speak for everybody, but in my experience, the tactical limitation of not being able to turn while determining target speed is not actually a real issue, regardless of the method used to gather the data.


I think that torpX is right that radar rendered the device a moot point as well, but that doesn't actually mean the device was ever all that useful in the first place. Still, it's a cool idea that was ahead of its time, even if the level of technology at the time rendered it impractical.

[TorpX]

Originally Posted by ColonelSandersLite

Given that there is no way to input submarine speed or stabilization distance, and the computer that could do it probably couldn't fit into the periscope...

This had to be done by the TDC. As you say, the machinery couldn't fit in the scope. But why would it need to? The outputs from the TDC could be fed into the mechanism to move the line. The position keeper already calculates and updates the target position, so not much else is required.

I think it's safe to assume that the line was stabilized to infinity. This means that there is just no practical difference between just using a regular vertical line on the periscope and using the stabilized line so long as the submarine is not turning.

I think this is a further indication that the TDC did indeed calculate the info for the line to move. Otherwise, the whole point is lost.

[ColonelSandersLite]

Originally Posted by TorpX

This had to be done by the TDC. As you say, the machinery couldn't fit in the scope. But why would it need to? The outputs from the TDC could be fed into the mechanism to move the line.

Sure, except that it wasn't. As far as I can make out, looking at the diagrams, the 89KA40/1.414 doesn't actually have any connection to the tdc and the stabilization motor surely isn't receiving any data from there. The sole exception would be possible ad-hock retrofits of the TBT system prior to getting the 91KA40T/1.414HA.

[TorpX]

So, you're saying the navy installed a totally unnecessary piece of machinery that didn't do anything?

Or, if it did something else, besides moving the line in such a way as to help the crew estimate the target's speed, what would that be?

[ColonelSandersLite]

That does seem to be the case. Trying ideas that are hypothetically better than they turn out to be in practice isn't exactly unprecedented. It might have helped a bit with compensating for ship pitching and rolling when surfaced, but given the doctrine when it was designed and installed, I sort of doubt that was the reasoning.

It's explicitly stated as being designed to help in speed estimation, but as far as I can make out, it was only installed in one periscope model so it would seem to me that the navy realized it was a mistake and scrapped it fairly quickly.

[Rockin Robbins]

There's also the fact that they might use the same piece of equipment for a submarine and a destroyer. It would have all the functionality of the DD but not all that would be available on a submarine, so that part wouldn't be plugged in.