Stadimeter / Omnimeter

[pdiddy]

My understanding of the Stadimeter in real life is that is was basically a sextant in the periscope; it did not automatically send range to the TDC. I believe the crew had to figure it out using the arc tangent of the angle measured by the stadimeter. Knowing the "opposite" (target height) and the angle, you can figure "adjacent" (range). At least that's what I recall from high school geometry. So the crew had an arctan table or something like the omnimeter (Optical targeting correction mod) and had to manually figure range.

Is this correct?

(Btw, the KIUB in OM+OMEGU models this very well. You have to manually determine range using the AOBF (essentially a round omnimeter) after getting the angle measurement using the stadimeter and then also manually enter it into the TDC.)

[CapnScurvy]

Hi pdiddy, the Fire Control Crew probably had a math wizz working at the chart table, checking/double checking the findings from the Stadimeter (or maybe not....depends on the crew's abilities and who was good with a slide rule). But, for the most part the Periscope's Stadimeter Dial provided the bulk of the information.



The Stadimeter Housing Unit was fastened onto the bottom of the Periscope. The outside view was brought down through a set of prisims, passing through the Stadimeter len's before going to the eye piece. It had two half len's that slide next to each other, giving the double image. Depending on which axis the sliding edge was pointed to, Up/Down, Left/Right.....the Stadimeter would produce either an estimate of range, or an estimate of target course angle (AoB), shown on the Stadimeter Dial. Both could be found well less than a minute by most Captains.

The Stadimeter had two dials, both identical, on either side of the Periscope. It was faster to have a second observer stationed at the opposite dial to make the reading of range or target course, rather than the Captain who kept his focus at the eye piece.

Although there was no direct link to the TDC, the observer usually called out the found range and target course to have the TDC operator input the information. Unlike the TBT (Target Bearing Transmitter), which did have direct input to the TDC for just target bearing. No such direct link was made from the Periscope.

In both devices, the game has taken some creative license in simulating their functions and capabilities. In the Stadimeter's case, the game left out an important function for determining AoB from the real life unit. The game only allows it to work vertically, not horizontally too.

The Omnimeter was a real life tool that helped determine target Range when using the Telemeter hashmarks within the Periscopes lens. It was set with the specific height or length, for whatever reference point you could best use (mast top, funnel, bridge roof, deck etc.) and the calculation was done by counting the Telemeter divisions.

On the other hand, the Stadimeter automatically moved the center Dial Ring (one of three Dial Rings of the Stadimeter Dial), when you possitioned the double image on the corect reference point. The third outer ring of the Dial was manually set to the Targets Length. The inner dial ring was stationary, representing the Targets Height.

[TorpX]

That's a nice diagram, Capn'.

Do you know what the stabilized line elements are for?

[CapnScurvy]

The stabilized azimuth line provides a "line in space" within the field of view. It was used to determine speed of a target. The line was electrically governed by the subs gyro compass which kept the line at a singular position, irregardless of the subs possible changing position.

Once the line was "plugged in" (it was not good to leave it operating for too long because the synchronizing motor could fog up the interior of the scope) the passage of the target over the line was timed with a stop watch, then calculated using the estimated target length to determine target speed.

The "clutch" was used to engage the synchronous motor, that was governed by the compass. You had a cord that really was "plugged in" to make it work.

As you can see, the Periscope gave you Speed, Range, Target Course....all in one easy process. The game missed the actual simulation of this by a large margin. Not only giving us wrong height measurements, wrong scaled viewing, no length measurements (accurate or not), and incomplete simulated features of the devises used in real life.

[Aktungbby]

@ CapnScurvy: We should have a sticky thread for true "pearls o' wisdom" with appropriate diagrams for your two posts which is best I've seen on the subject. Nice sig too!

[pdiddy]

Thanks CapnScurvy!

So, much more sophisticated than I thought! Great information.

[TorpX]

Originally Posted by CapnScurvy

The stabilized azimuth line provides a "line in space" within the field of view. It was used to determine speed of a target. ...

I didn't know US subs had this particular item. I gather it was introduced during the war?

The game missed the actual simulation of this by a large margin.

Quite.

[CapnScurvy]

Originally Posted by TorpX

I didn't know US subs had this particular item. I gather it was introduced during the war?

No, the Kollmorgen Optical Corporation of Brooklyn, New York, has it detailed within their Periscope instruction/maintenance manual of 1940.