Here we go again! And some old questions on plotting and Maneuvering boards

[Kpt. Weyprecht]

I've been far from virtual submarinning for years anj just jumped back into the old rabbithole. Frankly, I'm glad to be back here.


Now, I've always been an eternal newbie, between ailing computers, system crashes and RL work, I've actually spent more time reading naval manuales than playing the sim. But fot the moment, Proton works good enough and I can fire both Silent Hunters on my working laptop, although SHIII only works without H.sie's or Stiebler's patches.
At the same time, I dusted off some of the old reading stuff. These are things I was wondering about since my last time in SH.

I read through the ols US Navy manual on plotting, but then realized German subs (or British ones for that matter) didn't have a DRT. Ben Bryant insists on Royal Navy's distrust of gyrocompass. So how could a world-centric plot be accurate enough to put torpedos in a terget while navigational errors were sometimes massive?

I know Wolfpack pages feature several methods for plotting turning radiuses and inertia. But even in Wolfpack, dead reckoning is only required when submerged. On top of it, actual manuals don't seem to linger on that aspect. I finally tracked down most of the techniques for accounting of the advance and translation to the Admiralty manual of 1938, but that is meant for groups of surface ships, not for fire control. Here I fond an example of an exercice plot made by a French submariner in 1968: the submarine's changes of track as just squared... but I hope by then they had a proper DRT: http://www.sousmarinvenus.com/Plot_SM.html
A good solution seems to be the maneuvering board. Back in the day I used Aaronblood's MoBo (sadly it doesn't run under Wine) and I will probably end up ordering a pad of paper boards. But they actually aren't mentioned that often, I'm not sure they were used by other navies. Even Dick O'Kane mentions it as "old fashioned" in Clear the Bridge, I failed to find anything on this technique in French, aside from radar plot exercices, or German. I did notice a moboard in the footage from the control room of the Delta III class Russian SSBN.

So... did they just use MoBoards? Or routinely accounted for inertia and turning radiuses (but then, what about currents and so on?) Or just considered that error induced was not important enough and avearged out somehow?


Oh, by the way, I was intrigued to find this: https://info.publicintelligence.net/...rineManual.pdf

The table(s) 3-5 are "Submarine Course and Speed Diagrams". I'm almost sure this could be of use but I can't see what to actually do with it... _

[Aktungbby]

Kpt. Weyprecht! Nice 9 year silent run!

[Sean C]

If you go to the Maritime Safety Information website, you can select Chapter 6 of the Radar Navigation and Maneuvering Board Manual and download it for free. (Or download the whole manual and many other resources.)

Also, I can PM you with a link to a high-resolution scan I made of the standard U.S. Maneuvering Board, if you like. It's about 12½" x 14"; 150 pixels/inch.


Cheers!

[derstosstrupp]

“Or just considered that error induced was not important enough and avearged out somehow?”

This right here.

German U-boats used 2 primary methods of data gathering on the surface while at a safe distance: matching course and speed (called “Ausdampfen”), and plotting (called “Koppeln”).

Ausdampfen was much more prevalent. When a target was spotted, they’d immediately put it astern to ascertain its bearing change. Then, based on the dispersion of its masts etc they’d get a rough idea of its AOB and turn to what they thought was a parallel course. Then, by watching the mast tips and the bearing change, they’d adjust own course and speed until a) the masts stayed about the same size, and b) the bearing stayed steady. At that point, the submarine’s course and speed are the target’s - the data has been “ausgedampft”. Since targets in real life zigzagged more than not, this was typically relied on only for speed, the AOB being estimated prior to the shot.

Koppeln, or plotting, was also done. You are correct about the lack of a DRT. They did have a pit log, like an odometer, which could be reset by the helmsman in the tower. The navigator plotted the U-boat and target movements on millimeter paper (like graph paper on steroids). Plotting was done at 5-minute intervals. Every 5 minutes, the commander would call down bearing and rough range. I say rough range because the UZO had no rangefinding capability - range was estimated based on how much mast was showing above the horizon. Over time, errors tended to average out. Plotting was much more common in situations when the U-boat was following a convoy as a “contact holder”, providing convoy course and speed data to assist in the gathering of a wolfpack.

Ultimately, data gathering was an art more than a science. If you get close enough when firing as they did, under 1000 m, you minimize the impact of estimation errors, often to the tune of a knot of speed and 10 deg of AOB if close enough.

The focus on inertia and turn radii is a game concept. Wolfpack players like to focus on that when in real life this minute accuracy wasn’t cared about. Data was gathered on the surface and, if that was impractical or impossible, simply eyeballed underwater prior to the shot.

[Kpt. Weyprecht]

Thanks for your replies!
So my thinking wasn't that bad. I had noticed the use of millimeter paper. I used to draw archaeological plans on it, I suppose they did that to simplify scale calculations. By the way, do you know what sort of scale they used for fire-control? I only remember the US dead reckoning maual specyfying that in case of a Man Overboard, the plotters are to switch to a scale of 200 yards per inch, so something between 1:10 000 and 1:25 000.
There was also the emergency procedure of the "Halifax plot", very Wolfpack-style byt not suitable for combat.


So, for dead reckoning and tactical plotting, they would just draw a new course line, and possibly round the corners somewhat out of experience? Very much like in the case of my archeaological drawings, beginners tended to take lots of measures while experienced people were able to deal with much fewer measurements and just freehand draw the rest?


As for the maneuvering boards, it seems to be an incredibly convenient way of getting around the difficulties of a world-centric plot, but then why didn(t everybody use them all the time?

[derstosstrupp]

Here’s an example of a historical one, this is from U-47 under Prien.

http://www.uboatarchive.net/U-47/KTB47-6Sketch.htm

These were more for situational awareness and were often appended to the KTB (logbook of the patrol) when handed to BdU. In rarer cases they were used for the actual data gathering (in these cases you’ll read in the KTB “Schussunterlagen erkoppelt” - shooting data obtained by plotting).

As mentioned before, Ausdampfen (matching) was more common, BUT that also could involve plotting own boat movements.

Here’s an example:

U-625 (Hans Benker) mentions in the KTB of its first patrol having missed a steamer, and wanting to remeasure its speed:

“Place myself in its wake and match him again using the radar. This works very well and is more accurate than when I only plotted along with him. First of all much quicker. He now runs at 10 knots”.

What’s happening here is he’s using the generated range from his radar to make sure he stays the exact same range behind the target and keeps the target on his bow, then he knows he has matched course and speed. However, certainly not all boats had radar, hence why he mentions the plotting; had he not had radar he would have plotted his own boat’s movement, keeping the target visibly at about the same range in front of him over a certain period of time, and then averaged his speed as the target speed over that measured length of time. Inherently less accurate, which is why he mentions that. This type of plotting was more common, made easier by the fact the boats had a pit log (odometer).

To answer your question about why plots like a maneuvering board plot (in other words a relative motion plot) weren’t used ubiquitously, that I’m not sure about. The unreliable range problem, the lack of surface rangefinding capability is probably a factor, which made the matching of course and speed actually more practical than plotting in many cases. That’s why most commonly in these logbooks you see them either doing this in the target's wake, or overhauling to directly in front of it and doing it in front, traveling along at the target speed and just matching its maneuvers.