So lets get those whiz wheel templates out

[Puster Bill]

You can find several different slide rule templates, both circular and linear, in .pdf format here:

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

This picture has a couple of examples that I built recently:



At the top is EtchASketch's venerable WhizWheel, showing the slide-rule side (the other side is a tool for finding AOB). It works, but due to the limitations of the images used to produce it, it isn't the prettiest thing to look at.

In the middle is a simple ABCD slide rule I printed out on cardstock. You can multiply, divide, find squares and square roots with it, but that is about it. It was my first experiment from the website I listed above.

At the bottom is a more advanced (both in for and in terms of construction) Log-Log slide rule. It appears to have all the scales that EtchASketch's WhizWheel has, I just haven't had the chance to try it out in an actual scenario yet. I made it out of cardboard cut from a Revell model kit box (specifically, a German Type XXI U-boat. I assume one made from a Gato class box would work just as well!).

That one is really an 'engineering model'. I plan to print out the scales for the slide rule again, and make one out of sheets of acrylic plastic. I did it in cardboard first to get a bit of experience in building one first. If you are a real stickler for historical accuracy, you could use wood or some sort of sheet metal, like brass, instead.

One note about making the cursors: On the WhizWheel and on the more advanced slide rule, I used black thread, which while fine on the wheel is really too coarse for the slide rule. Being blessed with a wife who has long, fine hair, I am going to use one of her hairs from a brush to make the cursor for my next rule.

[jmr]

Welp I assembled all of Kim Ronhof's tools to the best of my ability and they turned out looking not too shabby.

Ok I'm having one hell of a time trying to use the Mark4B Course Calculator and if anyone can give me a hand with it I'd really appreciate the help.

In the manual under "How to calculate the true course of a target from the angle on bow" I've tried following his steps but I can never get the damn thing to work as advertised. I have auto targeting enabled so I have good target data for testing purposes.

I just need someone to break it down in their own words because Kim's instructions aren't working for me.

[jmr]

Originally Posted by Igorry

Mav97th

Is it possible for you to give step by step instruction on how to use Kim Ronhof's calculator Mark 4B? Maybe have some figures and which wheel to turn. Thanks for the instruction on the mark 3B.

*bump*

Jmr

Ill make a post here about the usage, but im busy in my garden right now. Ill come back later today...

Ok im taking my entry from Kim's own instructions:

How to Calculate the True Course of a target from the Angle on the Bow

Do as follows:
(See figure next page)
1) Turn the middle-disc to the bearing of the target (add clockwise)
2) Mark this point with the alignment tool
3) Add the Angle on the Bow to this mark
4) Mark this point with the alignment tool
5) Turn the middle disk to this point – and read the difference on the middle scale, between target Course and your course at the 180-degree mark on the outer scale.
6) Now turn the middle disc to your course and subtract or add the difference you just found (subtract if the target is moving from east to west , add if it is moving from west to east)

So first you turn the middle disc so the N points to the bearing (relative) of the target. The relative bearing is read on the outer disc. Then you use the alignment tool (on my version is a strip of transparent with a thin line on it) to mark that bearing. Now add the Angle on the Bow to that first mark. Now move the middle disc again so the N points at that new point. Then look at the middle disc at the 180deg mark (or S) and read the difference between target course and your course next to that.

THEN you add or substract that difference to your own heading (true N heading).

Example:

You - heading 005
Target - Bearing (relative) 030 - AOB 40 PORT

First tuen the middle disc to show 030 then add the AOB and mark with the marker at that point (70), move the middle disc to that point. Now read next to the middle disc's South point. Value there should be 250 deg.

Now we either need to ADD that or SUBSTRACT that to our own course to get targets TRUE course.

Turn the middle disc to your own course 005 then use the alignment tool to first substract 250 deg. (turn the alignment tool to counter clockwise untill it comes to 250 on the scale with the WHITE triangle (scale that goes "the opposite way")) and read the value on the outer scale 115 deg. TRUE

Next ADD to 005 - value should then be 255 deg TRUE.

If we have an AOB of 40 PORT and we are going N then he must be coming right to left aka you need to ADD when the AOB is PORT and SUBSTRACT when the AOB is STARBOARD.

TARGET COURSE in the case is 255 deg TRUE.

Make 10 easy examples your self and test it out like that - should be pretty easy after #5.




Now the best thing of this TOOL imo.

Simply friggin awesome

How to Calculate target Speed

It is also possible to calculate the Targets speed, by the reverse operation.
First line up the target at a 90° bearing. Now regulate the submarine’s speed up and down until you hit a speed where the bearing doesn’t change. This may be between speed settings on the sub (1/3, 2/3, standard) – just change the speed up and down and make an assessment of the average speed that doesn’t change the bearing). That speed is actually the minimum intercept speed.

First you turn the alignment tool to that it is on target AOB (middle scale is importent, but PORT or STARBOARD does not matter). Now read the Sinus AOB on the scale inside the two bearing scales (The MOST OUTWARD sinus AOB scale)

EXAMPLE AOB 45 deg. Our own speed neccesary to maintain target at 90 deg bearing is 6 kts.

Sinus AOB is 0.7

Now turn the inner disc in such a manner that your boats speed aligns with the sinus (AOB) you just found, but this time on the innermost Sinus (AOB) scale

At the "SPEED 1" mark the target’s speed can be read off the inner disc. in the example you put 6 kts aligned with 0.7 and should read 8.5 (or 8.55) kts at the "SPEED 1" mark.

The real difficult part - is to assess the Angle on the Bow (AOB). With enough practice you will find it as easy as falling off a log. You can cheat (though in PCT II or III it’s not considered cheat) and just look at the map (F5) and directly read the AOB – the Sonar Bearing Plotter can do this very easily.
From the AOB and your course you calculate the target’s (Co) course – you now have the 2 most important parameters, (target speed and course) which are needed in the TDC. As you also know the minimum intercept speed – your chance of a successful attack has increased significantly.

[jmr]

Mav, thanks a bunch for taking the time out and clearing things up for us. I really appreciate it! I knew I was sort of on the right track but I was a bit unclear on Kim's instructions but thanks to you I know what I'm doing now