Slide Rule Targeting for SHIII/SHIV
 

Did you ever want to increase your game immersion, and your accuracy, without using modern technology? I certainly did when I got the GWX upgrade for SHIII. I had been using this wheel for targeting:



http://img164.imageshack.us/img164/113/image001zs5.jpg


It worked well enough, but it took me ‘out of the game’ because it looks like it was printed on an old dot matrix printer.

After trying to make a couple of slide rules (and succeeding, somewhat), I decide to just go ahead and buy one. I checked some local antique shops until I found this:

http://img78.imageshack.us/img78/3018/image002ku2.jpg

A Sterling “Precision” slide rule. I put the word precision in quotes because Sterling has just about the worst reputation for accuracy. However, that doesn’t really matter for the job we have to do, and I was able to get it for $5. A good condition, more accurate, and more authentic slide rule would have cost a lot more. No matter whether you buy one or make one, it has to have the C, D, and S scales on it. It would also help if it has the A and B scales (just about every rule does). Any rule that has the word ‘trig’ in the name will work fine.

Anyway, down to the business of sinking ships…

In order to get the information that you need, you will have to make two observations. Let us call them A and B. We need to know the distance to the target and the bearing for both observations, and the time between those observations.

Let us suppose that the distance for our first observation is 7000 (don’t worry about whether it is meters or yards yet), on a bearing of 65 degrees. Start the stopwatch, lower your scope, and go get a cup of coffee, take a leak, apologize to your wife, or whatever. Let’s just say you missed the opportunity to use the 3 Minute and 15 Second rule to get target speed, so your next observation, B, occurs at 4 minutes. When you take the B observation you get 4000 yards at a bearing of 45 degrees.

I write this stuff down on paper, and this is what it would look like:

O RNGE BRG AOB TIME (seconds)
A 7000 065 ??? 0
B 4000 045 ??? 240

You now have everything you need to determine AOB and speed of the target. We whip out our handy-dandy slipstick, and note that there are 20 degrees between 65 degrees and 45 degrees. I move the slide until there is 20 degrees difference on the S between the 4 and the 7 on the A scale. I have to use the A scale on this particular rule, as it has a ‘double length’ S scale that goes from about 45’ to 90 degrees. Most rules have a regular S scale that goes from a little under 6 degrees to 90 degrees, and an ST scale to handle the smaller numbers. If your slide rule has a 'regular' S scale, you have to use the D scale instead of the A scale.

You will note here that it works out that when 23 degrees on the S scale is under the 4 (for 4000) on the A scale;

http://img133.imageshack.us/img133/3743/image003zh8.jpg

That 43 degrees on the S scale falls directly underneath the 7 (for 7000) on the A scale:




http://img133.imageshack.us/img133/2359/image004sa8.jpg



We now have our two AOB observations. Strangely enough, the AOB for observation A is actually under the distance for observation B, and vice versa. We then fill the information in on our paper:

O RNGE BRG AOB TIME (seconds)
A 7000 065 023 0
B 4000 045 043 240

If you are pretty good at guessing the AOB, align your guess of the AOB from observation B on the S scale with the distance from observation A on the A (or D) scale. That should save you some time fiddling around, as you are close to where it should be.

Now that we have the range and AOB, we have to figure the target speed to input it into the Vorhaltrechner/TDC, as the case may be. As a side note, I usually pause the game right after the second observation so that I can make the calculations. On a real submarine, the captain wouldn’t be making the calculations, so I am in effect doing two jobs! You don’t have to, though. If you leave the periscope at the heading of the last observation, you will be able to enter all the information, then swing the ‘scope back on target, with the information all updated by the TDC.

To calculate the target speed in units per second, we need to find the distance the target has traveled between observation A and observation B. Without moving the slide, we move the cursor of the slide rule down the S scale until it is right above the difference in degrees between the bearings of observation A and observation B. For this example, that is 20 degrees. We read the speed off of the A scale (or D scale, if you have a ‘normal’ S scale). In our case, it reads 3.5, which we know will be 3500 units (either meters or yards):




http://img259.imageshack.us/img259/6743/image005zr5.jpg



We now have to find out how fast that is in units per second. On this particular rule, I have to flip the slide over the get the B and C scales:




http://img339.imageshack.us/img339/6380/image006xh8.jpg




The following section has been changed on edit from the original to correct an egregious error. Thanks to don1reed for pointing it out!


To find the target speed, we have to align the 2.4 (for 240 seconds) on the B or C scale with 3.5 (for 3500) on the A or D scale. It should look like this if you are using the C + D scales:

http://img250.imageshack.us/img250/4...ture022mt4.jpg



We then read the speed in units per second on the D scale right underneath the index mark of the C scale, in this case 14.6 units per second:

http://img260.imageshack.us/img260/7...ture023jz0.jpg




Now, to find the target speed in knots we have to know whether our distance unit is a yard or a meter. If the distance measurement is in yards, you have to align 5.6 on the C scale with the speed in yards per second, or 14.6, on the D scale:
http://img409.imageshack.us/img409/5...ture024nc0.jpg

We then read the speed in knots on the D scale directly below the index on the C scale, in this case just about 26 knots:

http://img341.imageshack.us/img341/9...ture025fh5.jpg



The calculation is the same if your base unit is meters, except that instead of using 5.6, you use 5.15. In our little exercise, that would give you a target speed of 28.2 knots.


You can now plug the distance, bearing, AOB, and speed into the TDC in manual mode. Don’t forget to switch it back to Auto!


Happy Hunting,

Puster Bill

Sliderules in antique stores!!! <sad>

Might just as well bury me now or put me on an ice flow.

Anyway for us dinosaurs that STILL OWN a sliderule. Thanks very much for these instructions.

Antique stores indeed Haruumph!

Thanks for the excellent instructions. I have a question about the two observations. Does the sub have to be at a stop or can you creep along at around 2-3 knots in between the two measurements? I'm just curious if I need to be on the surface or can remain at periscope depth (which would require some form of movement to maintain depth).

Thanks,
Ron

interesting post. If I could pull myself off this freakin computer, I'd go out and look for one. meh....checking ebay.







btw...I luv your font size. it fits perfect on 48,0681 x 32,253 resolution. :)

I find that if you are creeping at steerage, ie. 1 to 2 knots, it doesn't introduce enough error to matter as long as you aren't taking very long shots.

If you were going faster than that, it would introduce more error.

Well, as for the font size, well, I wanted it to be easily readable.

If you can't find a slide rule locally or on Ebay, you could always make your own from the templates available here:

http://www.sphere.bc.ca/test/build.html

I built the Yokota Log-Log rule at that site, and it works well for this. Don't build the first one (unless you want to just for fun), because it lacks the S scale.

There are also some nifty Java slide rule simulation pages here:

http://www.antiquark.com/sliderule/sim/index.html

Slide rules and whiz wheels rule! Here's some I made from various posts on these forums.

Kin Ronoff's Range Calculator Mark 3B and Course Calculator Mark4B

http://img89.imageshack.us/img89/435...angevg4.th.jpg

Target course calculator and nasmith director

http://img101.imageshack.us/img101/4...torahc6.th.jpg

Banjo

http://img341.imageshack.us/img341/2856/banjofo0.th.jpg

I remember playing around with one when I was a kid, right when electronic calculators became cheap enough to replace them. I ended up busting it. What did I know?

As soon as I can, I'm going to pick up a couple of Picketts. I want an N600T or N600-ES, and either an N500-(T or ES) or a N1010-(T or ES).

Great Post Puster Bill!

Cheers :arrgh!:

Here's my tutorial for the Banjo:
http://www.subsim.com/radioroom/show...=108931&page=2

I adapted the instructions for that wheel (first picture in my post) to a linear slide rule. I did find that he uses 5.70 for converting from Yards per Second to Knots, which is incorrect. It's actually about 5.64, which I round down to 5.6.

Hey, I appreciate you posting these links. I'm checking them out as soon as I get done typing this. Always excited about trying out alternative tools and methods for plotting. Too fun. Thanks again. lol about font. :)

EDIT: That sphere website sells them. I'm gonna buy one but I need you to tell me which kind is best. From your posts, I assume an A/B scale with S?

Yeah the graduations are a bit sloppy as well which is why I hardly used that wheel. I'm going to have to shopping around my area antique stores for a slide rule. I made my own from this page but I'd like to have the real deal and not a laminated card stock one ;)

Actually, all you really need is the C+D scales, and the S scale, although just about every slide rule has an A+B scale (except for circular ones, they don't need it because the scales are 'wrapped around').

I checked out the sphere site, and they do indeed sell them, but you could probably pick one up cheaper on Ebay.

If you want to go even cheaper, call around to your local antique stores (sorry Platapus!). Or just ask some of the people who are older than 45 or 50. They might have one sitting around and will give it to you. My father has a circular one that he's currently trying to find for me, and a guy I work with was going to give me his, but he couldn't find it (he thinks he lost it in a move).

If you want to build one, try the circular rule at the sphere site. It has to be the first circular one, because that is the only one with an S scale. Print it out on cardstock and laminate it. Print out the cursor on an inkjet transparency (10 sheets for about $7 at Wal*Mart), then just pin them together.

Yep. That's why I went looking for one.

Although, I think I am going to have my father build a wooden, brass, or acrylic base for that Yokota Log-Log rule. He's handier at that kind of stuff than I am.

I built one out of cardboard, and I love it, I just want a sturdier one.

Damn, this slide rule thing can be addictive!

A slide rule in game map tool would be rather useful methinks...