Excel target speed calculator

I've put together a little spreadsheet for calulating target speed, does anybody know a way to upload the file if anybody wants it?

All it needs is:-

your current speed (knots)
initial bearing and distance to target (degrees & yards)
the time between sightings (seconds)
second bearing and distance to target (degrees & yards)


It will may need some testing, it's worked okay so far for me. (touchwood)

[Puster Bill]

Originally Posted by mr darcy

I've put together a little spreadsheet for calulating target speed, does anybody know a way to upload the file if anybody wants it?

All it needs is:-

your current speed (knots)
initial bearing and distance to target (degrees & yards)
the time between sightings (seconds)
second bearing and distance to target (degrees & yards)


It will may need some testing, it's worked okay so far for me. (touchwood)

Nice, but you should really use one of these instead:



Actually, either the top one or the bottom one. You can find the template for the bottom one at:

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


Here is how it works:

You take observation 1, say, 7300 yards at bearing 220
Then, a few minutes later, observation 2, 6100 yards at bearing 213.

Subtract 213 from 220, giving 7 degrees.

Fiddle with the S scale on the slide against the A scale until the distance between 6100 and 7300 on the A scale matches 7 degrees. In this case, it comes to about 52 degrees matching with 6100 (actually, 6.1 on the scale). That is the AOB at the second observation.

Without moving the slide, move the cursor along the S scale down to the 7 degree mark on the S scale. This will give the distance traveled on the A scale, in this case about 1,480 yards (it will actually read 1.48).

Now, you remembered to time the observations, right? If you are using a variant of the 3 minute 15 second rule, you are golden, as you can convert directly to knots.

However, if you had to go take a dump or whatever between observations, and couldn't do it exactly, don't sweat it.

Lets say that you had to wait for 4 minutes, or 240 seconds, between observations. Align the distance, 1,480 yards on the A scale (again, actually 1.48) with the time in seconds on the B scale (actually, 2.4). We then read the speed in yards per second on the B scale under the 1's on the A scale, in this case 16.2 YPS (actually, it will read 1.62).

To get knots, simply align the middle '1' on the B scale with 5.7 on the A scale. Slide the cursor to the speed in YPS, or 16.2 (1.62) in our example, on the B scale. You can then read the speed in knots on the A scale right under the cursor, or in this example 9.35 knots.

If you are doing your calculations in meters instead, you would use 5.2 on the A scale to give speed in knots.

You now have everything you need, distance, AOB, and speed in knots. You could print up a chart with common YPS/Knot equivalencies if you are lazy.


I know it sounds like a horrendous procedure, but it is easier to do than it is to describe. And, it is authentic: This is how those calculations were done (although probably with a circular slide rule, which are available at the link above. For our purposes, the C and D scales on a circular rule work just as well, but you *MUST* have an S scale on it).

Good god that's scary sounding stuff!

not making any promises, but i'll look into it.

[Puster Bill]

Originally Posted by mr darcy

Good god that's scary sounding stuff!

not making any promises, but i'll look into it.

If you are smart enough to make an Excel spreadsheet, you are smart enough to use a slide rule.

Don't let it intimidate you. The hardest part is actually making the bugger.

Hell, I went from not knowing delta india charlie kilo about slide rules to figuring out how to make one, making it, and using it in about a week. And I have a full time job, a wife, and a 3 year old son at home.

[flintlock]

These are all very handy and much appreciated solutions, though personally I would be elated if Ubi simply fixed that faulty chrono. Still, this offers variety for those interested.

I'm using this pattern:-

http://www.sphere.bc.ca/test/build/yokota-loglog.pdf

Originally Posted by Puster Bill

Here is how it works:

You take observation 1, say, 7300 yards at bearing 220
Then, a few minutes later, observation 2, 6100 yards at bearing 213.

Subtract 213 from 220, giving 7 degrees.

that makes sense.

Originally Posted by Puster Bill

Fiddle with the S scale on the slide against the A scale until the distance between 6100 and 7300 on the A scale matches 7 degrees. In this case, it comes to about 52 degrees matching with 6100 (actually, 6.1 on the scale). That is the AOB at the second observation.

you say the distance between 6100 and 7300, do you mean 1200? (1.2 on the A scale)

where do you get the 52 degrees from? If i line up 7 on S with 6.1 on A i can find ~52 on the T2 scale. If i line 7 on S with 1.2 on A then i can't see anything like 52 (or even 5.2) lined up with 6.1

Originally Posted by Puster Bill

Without moving the slide, move the cursor along the S scale down to the 7 degree mark on the S scale. This will give the distance traveled on the A scale, in this case about 1,480 yards (it will actually read 1.48).

Now you've lost me totally. I haven't moved the slide (as requested) so as far as i can see, 7 on S still lines up with 6.1 on A. Where do i get the 1.48 from.

Originally Posted by Puster Bill

Now, you remembered to time the observations, right? If you are using a variant of the 3 minute 15 second rule, you are golden, as you can convert directly to knots.

14.8 knots in this case?

Originally Posted by Puster Bill

However, if you had to go take a dump or whatever between observations, and couldn't do it exactly, don't sweat it.

Lets say that you had to wait for 4 minutes, or 240 seconds, between observations. Align the distance, 1,480 yards on the A scale (again, actually 1.48) with the time in seconds on the B scale (actually, 2.4). We then read the speed in yards per second on the B scale under the 1's on the A scale, in this case 16.2 YPS (actually, it will read 1.62).

gotcha

Originally Posted by Puster Bill

To get knots, simply align the middle '1' on the B scale with 5.7 on the A scale. Slide the cursor to the speed in YPS, or 16.2 (1.62) in our example, on the B scale. You can then read the speed in knots on the A scale right under the cursor, or in this example 9.35 knots.

this is using the 1.62 to the Right of the middle "1", yes?

Originally Posted by Puster Bill

If you are doing your calculations in meters instead, you would use 5.2 on the A scale to give speed in knots.

You now have everything you need, distance, AOB, and speed in knots. You could print up a chart with common YPS/Knot equivalencies if you are lazy.

or make an excel spreadsheet to do it for me!


Thanks

[Puster Bill]

Originally Posted by mr darcy

I'm using this pattern:-

http://www.sphere.bc.ca/test/build/yokota-loglog.pdf

that makes sense.

you say the distance between 6100 and 7300, do you mean 1200? (1.2 on the A scale)

No. You are sliding the 'S' scale so that the number of degrees between 6100 and 7300 on the A scale is about 7 degrees worth on the 'S' scale. In other words, you will align the slide so that 52 degrees on the 'S' scale is directly below the SECOND 6.1 on the A scale, and 7 more degrees up on the 'S' scale (right about 59 degrees, although it won't be *EXACT*, I get about 59.4 or so, close enough for our purposes) should fall right under the second 7.3 on the 'A' scale.

Then, you take the cursor and slide it down to the 7 degree mark on the 'S' scale. You can then read the distance off of the A scale.

In effect, what you are doing is solving for the third side of a triangle: Given the length of two sides of a triangle (in our example, 6100 and 7300 yards), and the angle they form (7 degrees), find the length of the third side.

This time when I did it, I got about 1,463 yards. However, I put a new cursor on my rule over the weekend, and it (or the previous one) might be a little off. Still, it is within a small margin of error (in this case, less than 17 yards off).

You can also do it with the D scale and the S scale. It works the same. But this time it works out so that when you move the slide so that there are 7 degrees between 6.1 and 7.3 on the D scale, 30 degrees on the S scale is above 6.1 on the D scale, and 37 degrees on the S scale is above 7.3 on the D scale. Then, you slide the cursor down to 7 degrees on the S scale, and read the distance travelled on the D scale. Checking mine, I get 1.485, or 1,485 yards. Using the D scale is more accurate, but in my case maybe not quite, as I said I may have a misaligned cursor. In any case, the ship itself is larger than the 22 yard difference (I hope!).

By the way, if the angle change had been *REALLY* small (less than 6 degrees), you would have to use the 'ST' scale. You would also use it for really large (over 80 degrees) angles, but if that is the case the target is moving *VERY* fast, or you just weren't paying attention for a long time.

It might be easier to manufacture one of the circular slide rules at the site. All you need to do is print out the base on regular paper (I use cardstock myself), then use inkjet transparency for the cursor/scale overlay. Pin them together using a thumbtack to a piece of cardboard or a piece of wood. I'm planning on doing that when I can get some transparencies. It would also be more accurate, because the scale length on an 8 inch circular slide rule is just over 25 inches, compared to 10 inches at best on the rule we are both using. That means greater accuracy.

If you get serious about it, check some local antique shops for a real slide rule. You can find them cheap quite often. You could also check EBay. They have *TONS* of slide rules for sale, some of them brand new. Just make sure that one you buy has at least A, B, S, C, and D scales on it (anything with 'Trig' in the name will have it, the 'S' scale is the sine function). A circular rule would only need the C, D, and S scales (The A/B scales essentially duplicate the C/D scales, but they are doubled. This is necessary on linear slide rules, but not on circular).

I hope that clears it up for you.

Originally Posted by Puster Bill

No. You are sliding the 'S' scale so that the number of degrees between 6100 and 7300 on the A scale is about 7 degrees worth on the 'S' scale. In other words, you will align the slide so that 52 degrees on the 'S' scale is directly below the SECOND 6.1 on the A scale, and 7 more degrees up on the 'S' scale (right about 59 degrees, although it won't be *EXACT*, I get about 59.4 or so, close enough for our purposes) should fall right under the second 7.3 on the 'A' scale.

Thanks again.

I see now how the cursor works. However (there's always a but, isn't there!) where do you get 52 to ~59 degrees from? Is it just a case of trial and error to find the best fit or is there a more scientific method?

[Puster Bill]

Originally Posted by mr darcy

Thanks again.

I see now how the cursor works. However (there's always a but, isn't there!) where do you get 52 to ~59 degrees from? Is it just a case of trial and error to find the best fit or is there a more scientific method?

It's a bit of trial and error. It is easier to do with a circular rule (which is how I actually learned how to do it).

It might be an interesting project to make a slide rule just for targeting and such, although I don't know enough about it to feel comfortable making one from scratch.

What I may do, however, is to do a little tutorial with pictures (using both linear and circular rules, and a manuevering board) to make it clear, and post it, but it's gonna be a few days, or even a couple of weeks, before I have the time to sit down and grind one out.