Slide Rule Targeting for SHIII/SHIV

[Puster Bill]

Originally Posted by jmr

Well I'm feeling a bit more comfortable practicing your example in this thread but over in this thread you gave a different example where the difference in bearing checks was only 7 degrees. I'm having a bit of trouble duplicating your results for that problem.

I'll have to revisit it when I get a bit more time, perhaps tomorrow.

Although, I notice that I referenced using the A scale against the S scale, but if you have a 'normal' S scale it should go against the C or D scale.

Plus, that was kind of an off-the-cuff first stab at explaining it, so I could have some errors in there.

I'll take a look at it again in the next couple of days (real life unfortunately intrudes!).

By the way, I have been getting more accurate results from the circular rule at the sphere site doing some paper exercises that simulate what you would see in the game, vice using either of my linear rules. Plus, I put the banjo doohickey on the reverse. I still have to figure out how to use it. I don't know that it is necessary, though, because my method gives you an accurate AOB, and you can figure the base course of the target if necessary using the same principles.


Oh, and the *EXACT* conversion from meters per second to knots is 5.144, so 5.15 should be close enough.

The *EXACT* conversion from yards per second to knots is 5.6267, so 5.60 should be close enough.

[jmr]

I have that circular one printed out as well but how do you adjust the S scale since it's fixed on that wheel? Like how would you "fit" 20 degrees between 4 and 7 on A scale?

EDIT: *DOH* I just noticed you don't have to move anything on the S scale as it already gives you the correct value if you use the D scale for your 4 and 7 values (the range at the two bearing points. Is that right?

[starbird]

Yeah, C and D are the same scale. So using C and D you can multiply, using D and S (in your case) gives you the sine. There is no rule for where a scale is located. Some have S on the slide, some on the body. A few have it (and ST) on both the slide and body, so you can do trig and other arithmetic without having to reset your slide.

I picked up a Pickett 500 ES a few months ago, and its a blast to use.

[Puster Bill]

Originally Posted by jmr

I'm just having trouble replicating those steps above to match up 7 degrees between the two bearing marks.

OK, I checked it on my Sterling, and on the circular, and they are in agreement. The angle under the 7300 mark (7.3) should be 38 degrees on the S scale, and the angle under the 6100 range should be 31 degrees.

Does that help?

I re-did the whole problem, and got a speed of 9.4 knots, which is close to my original result of 9.35 knots.

[jmr]

Wow I'm sucking at this.

Ok with the circular slide rule I set the first cursor on 6100 on D scale, then set the second movable cursor on 7300 also on D scale.

Following the cursor down from 6100 it intersects the S scale at 37.6 or we can just say 38. Following the other cursor down from 7300 it intersects the S scale at 47 degrees.

What am I doing wrong?

EDIT: Are you saying you should first have a guestimate of the target's AOB when trying to squeeze in the difference between the two bearing points? The scale is long and just taking a stab at finding X number of degrees between bearing points could take a long time. So by having a guess of the AOB that can give you a ballpark figure for narrowing down the S scale to get your required number of degrees?

[don1reed]

For those of you contemplating the $$$ purchase of an expensive relic...here's the best virtual slide-rule out there. Oh, I have a good collection of the real things; but this is for those who would like the feel of what the WWII skippers had to endure, without spending the big bucks/euros.

http://www.sliderule.demon.co.uk/

May I suggest D/L the newer version 2.1...version 2.0 is good too, btw.

I play SH3/4 in the Windows mode so I keep my virtual sliderule minimized along the bottom of my screen until needed.

...also, the virtual sliderule comes with complete instructions.

cheers,

[Puster Bill]

Originally Posted by jmr

Wow I'm sucking at this.

Ok with the circular slide rule I set the first cursor on 6100 on D scale, then set the second movable cursor on 7300 also on D scale.

Following the cursor down from 6100 it intersects the S scale at 37.6 or we can just say 38. Following the other cursor down from 7300 it intersects the S scale at 47 degrees.

What am I doing wrong?

EDIT: Are you saying you should first have a guestimate of the target's AOB when trying to squeeze in the difference between the two bearing points? The scale is long and just taking a stab at finding X number of degrees between bearing points could take a long time. So by having a guess of the AOB that can give you a ballpark figure for narrowing down the S scale to get your required number of degrees?

Yes, a guesstimate of the AOB will get you there quicker.

One thing you have to remember: With the circular slide rule, ignore the cursor that is fixed to the transparent slide. You want to move the C scale so that the 7.3 (for 7300 yards is over the 38 degree mark on the S scale.

What I do is I put the moveable cursor (not the one fixed to the C, B, and K scales) over my estimate for the AOB at observation B, then move the C scale until the range for observation B is under the moveable cursor. Then I can move the moveable cursor (not the fixed one!) down 7 degrees on the S scale, and see where it lands. It should land very close to the 6.1 (for 6100) if you guesstimated an AOB of 38 degrees for observation B, then moved the cursor down to 31 degrees on the S scale.

One important rule for the circular rule, at least for this part: Ignore the fixed cursor!

If you are still having problems, I can post pictures of it this afternoon (when my 3 year old is in for a nap).

[Puster Bill]

By the way, here is another slide rule that has assembly instructions on the back of it:

http://www.sciam.com/media/pdf/Slide_rule.pdf

[jmr]

I think one more worked example would be nice. I'm the special student that needs extra help

My next question is what do you do about an AOB larger than 90 degrees?

For example, I was messing around with the Torpedoes mission in the SHIII naval academy with the C2 freighter (which starts with an AOB of 110 starboard):

Bearing 1: 345 Range 1700m
Bearing 2: 000 Range 1770m

With a bearing difference of 15 degrees, how do you "fit" 15 degrees between 1700 - 1770?

[Puster Bill]

Originally Posted by jmr

I think one more worked example would be nice. I'm the special student that needs extra help

My next question is what do you do about an AOB larger than 90 degrees?

For example, I was messing around with the Torpedoes mission in the SHIII naval academy with the C2 freighter (which starts with an AOB of 110 starboard):

Bearing 1: 345 Range 1700m
Bearing 2: 000 Range 1770m

With a bearing difference of 15 degrees, how do you "fit" 15 degrees between 1700 - 1770?

Hey, we all need that extra bit of help sometimes.

In the case you cited, it isn't the bearings themselves that are important, but the difference between them.

We have to use our noggin here, and realize that we are describing a triangle. For the purposes of this computation, it doesn't really matter what direction the target is moving, so let us assume it is moving towards us instead of moving away from us.

Between 1.7 and 1.77 on the C scale of the circular, I can fit 15 degrees on the S scale from 73 degrees up to 88 degrees. We can't tell *EXACTLY* where it will fall on the rule because the S scale is all bunched up there, but we know it has to be about 15 degrees from 73.

We get the AOB's by then subtracting those numbers from 180 degrees to account for the fact that he is moving away from us. So, the AOB for OBS 1 would be 180 - 88 = 92 degrees and the AOB for OBS 2 would be 180 - 73 = 117 degrees.

we then slide the cursor to 15 degrees on the S scale, and read the distance off on the C scale, about 4.615. We know he didn't travel 4,615 meters, so it has to be 461.5 meters.

You didn't specify a time between OBS 1 and OBS 2, so I'll assume it was for 2 minutes, or 120 seconds. That gives us a speed of roughly 3.875 meters per second, which equals about 7.5 knots.

I did this on the circular, then checked it on the Sterling. The Sterling gives a slightly closer-to-calculator result, but the difference isn't enough to cause you to miss.

Honestly, I had to draw it out first on paper using a protractor and a ruler so that I understood the problem. That AOB you cited of 110 is off somewhere, it doesn't appear anywhere when I draw the triangle. Unless the ship was zig-zagging, in which case you have to take the BASE course, not the actual AOB. If the ship isn't moving in a straight line, the AOB information generated by this method won't be accurate.

In my defense, It's been a LOOOONNNNNNGGGGG time since I took trig, and this whole slide rule thing is almost as new to me as it is to you.

And truthfully, the proper answer is "Haul ahead of the bastard to you can get a good 90 degree shot at him"

[jmr]

With regards to the problem I gave above, I had auto targeting on so I could verify my results and the 110stb AOB was what the auto TDC was telling me at the of that bearing. It's the torpedo academy mission where you begin facing north and if you move your scope left about 20 degrees you'll see the C2 freighter on a northeasterly heading at 2 knts.


Hey I appreciate you taking the time to help me with this! It's kind of wierd how this all turned out - a thread here and there on whiz wheels and suddenly I find myself with 5 homemade wheels plus 2 wheels purchased from an antique store. It's all deeply fascinating to me being someone who grew up with digital calculators and computers.

[Puster Bill]

Originally Posted by jmr

With regards to the problem I gave above, I had auto targeting on so I could verify my results and the 110stb AOB was what the auto TDC was telling me at the of that bearing. It's the torpedo academy mission where you begin facing north and if you move your scope left about 20 degrees you'll see the C2 freighter on a northeasterly heading at 2 knts.


Hey I appreciate you taking the time to help me with this! It's kind of wierd how this all turned out - a thread here and there on whiz wheels and suddenly I find myself with 5 homemade wheels plus 2 wheels purchased from an antique store. It's all deeply fascinating to me being someone who grew up with digital calculators and computers.

Strange, isn't it? I almost don't care about SHIII anymore, I'm having too much fun with the wheels/slipsticks.

Something has to be wrong with your numbers then. Like I said, I drew it on paper.
Either the first range has to be 1430, or the second has to be about 2300 meters.

[Vandecker]

Ah I get it now thank you very much, Nice work figuring this all out.

Now off to hunting.... once I escape this damn patrol craft

[Capt. S. A. Wood]

New here I guess. I have been reading the forums for a good month or more about DW and SHIV, but never had much to post about, was learning mostly. Have played 688(I) and the two aforementioned games so far.

I am baking here in this dorm room at 5:45 a.m. due to the lack of AC, so I can not really go to sleep. I produced a detailed step-by-step checklist of what Puster Bill put forth in the OP, because even though I suck at mathematics in the purest definition of sucking, I am intrigued by these slide rules. So before I go try out the methods in the game I figured I would just write a little checklist. Hope it is up to par and acceptable.

-----

Silent Hunter 4 - Wolves of the Pacific Slide Rule Targetting Checklist Using Model Pickett N909-ES

http://www.antiquark.com/sliderule/s...l-n909-es.html

Checklist is for two-reading intervals. Intervals can be chained together for more accuracy.
Examples given by OP are in [square brackets], important things are underlined, variables are in bold, and scales are in italics.
Scales used are S, C, and D.

-----

1.a. Obtain range to target and divide by 1000 with precision of 3 as Initial_Range --- [7.000]
1.b. Obtain bearing of target from own ship bow as Initial_Bearing --- [65]
1.c. Start chronograph and wait for 195+ seconds --- [0]

2.a. Stop chronograph and obtain elapsed time divided by 100 with precision of 2 as Time --- [2.40]
2.b. Obtain range and divide by 1000 with precision of 3 again as Final_Range --- [4.000]
2.c. Obtain bearing from own ship bow again as Final_Bearing --- [45]

3. Pause if desired --- [Nap Time]

4.a. Obtain bearing difference of Initial_Bearing and Final_Bearing as Delta_Bearing --- [20 = 65 - 45]
4.b. Align S (Delta_Bearing) with D (Final_Range) --- [S_20 | D_4.000]

5.a. Obtain new S value aligned with D (Initial_Range) and minus Delta_Bearing as Temp_Bearing --- [17 = (S_37 | D_7000) - S_20]
5.b. Obtain bearing difference of Delta_Bearing and Temp_Bearing as Offset_Bearing --- [3 = 20 - 17]
5.c. Adjust S by Offset_Bearing --- [3]

6.a. Obtain new S value aligned with D (Final_Range) as Final_AOB --- [23 = S_23 | D_4.000]
6.b. Obtain new S value aligned with D (Initial_Range) as Initial_AOB --- [43 = S_43 | D_7.000]

7. Obtain new D value aligned with S (Delta_Bearing) as Delta_Range --- [3.500 = D_3.500 | S_20]

8.a. Align C (Time) with D (Delta_Range) --- [C_2.40 | D_3.500]
8.b. Obtain new D value aligned with C (1) as Speed --- [14.6 = D_14.6 | C_1]

9.m. METRIC: Align C (5.144) with D (Speed) --- [C_5.144 | D_14.6]
9.i. IMPERIAL: Align C (5.626) with D (Speed) --- [C_5.626 | D_14.6]

10. Obtain new D value aligned with C (1) as Knots --- [28.2 or 26 = D_28.2 or D_26 | C_1]

-----

Input relevant values into TDC and have a nice day

-----

+ Full credit goes to Puster Bill of course

- Wood

Edit: Changed variable name WTF_IsThis to Delta_Range thanks to clarification from don1reed
Edit: Various changes made to match OP's changes, which should match up now

[don1reed]

Nice job, Woody, and welcome aboard.

...one minor correction... see para 8.c., I believe should be: [6.85 = C_3.5|D_2.40]

@ Bill: Check your PM.