Mathematical Question concerning Firing Solutions - what am I doing wrong?

HMS Vanguard · 06-14-07, 05:43 AM

Hey,

Okay, so I'm sitting in the training mission for torpedo runs, and I'm attempting to develop the skills in trigonometry to manually work out firing solutions on the Cruiser that sails across my bow. I'm using the process put forward in the excellent thread "http://www.subsim.com/radioroom/show...ghlight=manual" by starvingartist507, but I'm running into a snag with my calculations, and being aware of my general poor maths skills I was wondering if someone could show me where I'm going wrong?

The problem I am having is when I get to Step 4:
"4. Subtract the first total (step 1) from the second total (step 3) 339,860
(8,840,000-8,500,140)"

This is subtracting the total of A Squared + B Squared from the total of "2 x (Cos of Bearing Change) x Range 1 (R1) x Range 2 (R2)". The problem I am having when calcuating the solution is that the total of the former is larger than the total of the latter. As an example:

On the latest time I've attempted the firing solution, my two readings were Bearing 325 at 1,357 feet, and Bearing 342 at 1,242 feet, timed at 45 seconds with a bearing change of 17. The total of R1 Squared + R2 Squared was 3,384,013.

The Cos of 17 turned out to be 0.257, and 2 x 0.257 x 1357 x 1242 = 926,966.7. Subtracting 3,384,013 from 926,966.7 results in -2,457,046, which as a negative number cannot be turned into a square root according to my calculator.

What am I doing wrong here? Any help would be appreciated in this, so I can get to sinking.

Good hunting!

vindex · 06-14-07, 07:20 AM

What the ... holy ... ???

You don't actually need to calculate this stuff. The mechanical computer on your boat does. You just need three inputs:

1) Range (the system is a bit off, but you can get it by trial and error or installing one of the fix mods)

2) AOB (either estimate it visually, which is often flawed, or by protractor -- it's the angle between the target's course and a straight line to your boat)

3) Speed (the stopwatch method is broken, hopefully will be fixed, so better to do it by marking location, waiting a specific period of time, and then marking a second location, then multiplying up to get the distance in nm you WOULD have gotten if the interval had been one hour).

Right now I don't use 100% -- it's really unfair with all the broken range-finding and speed-measurement tools -- I still allow the contacts to appear on the map. If you do this, it's relatively easy to enter a solution then look at your battle map to see how accurate it is (in all three inputs) and make adjustments accordingly.

Unless you LIKE doing math ...

HMS Vanguard · 06-14-07, 08:01 AM

Quote:

Originally Posted by vindex

What the ... holy ... ???

You don't actually need to calculate this stuff. The mechanical computer on your boat does. You just need three inputs:

1) Range (the system is a bit off, but you can get it by trial and error or installing one of the fix mods)

2) AOB (either estimate it visually, which is often flawed, or by protractor -- it's the angle between the target's course and a straight line to your boat)

3) Speed (the stopwatch method is broken, hopefully will be fixed, so better to do it by marking location, waiting a specific period of time, and then marking a second location, then multiplying up to get the distance in nm you WOULD have gotten if the interval had been one hour).

Right now I don't use 100% -- it's really unfair with all the broken range-finding and speed-measurement tools -- I still allow the contacts to appear on the map. If you do this, it's relatively easy to enter a solution then look at your battle map to see how accurate it is (in all three inputs) and make adjustments accordingly.

Unless you LIKE doing math ...

Well, I'm playing on 100% realism myself, and given that the stopwatch system is not working, I was trying to work out the calculations according to the guide I was using in that link I posted. Also, to a degree, I enjoy the idea of realistically trying to input firing solutions in the way that they had to do on the submarines at the time to make it as realistic as possible. It's also quite satisfying to see a fish slam home as a result of your calculations (managed to do it once - JUST caught the rear end of the cruiser, dunno what I did differently that time), but the problem I'm having is that I'm doing something wrong with the calculations. If anyone can help with this, I'd appreciate it.

wetwarev7 · 06-14-07, 08:16 AM

Quote:

Originally Posted by HMS Vanguard

Hey,

On the latest time I've attempted the firing solution, my two readings were Bearing 325 at 1,357 feet, and Bearing 342 at 1,242 feet, timed at 45 seconds with a bearing change of 17. The total of R1 Squared + R2 Squared was 3,384,013.

The Cos of 17 turned out to be 0.257, and 2 x 0.257 x 1357 x 1242 = 926,966.7. Subtracting 3,384,013 from 926,966.7 results in -2,457,046, which as a negative number cannot be turned into a square root according to my calculator.

What am I doing wrong here? Any help would be appreciated in this, so I can get to sinking.

Good hunting!

Multiply by -1, then do your little square root thingie.....

negatives are so easily taken care of with a well placed inverse.....

HMS Vanguard · 06-14-07, 08:25 AM

Quote:

Originally Posted by wetwarev7

Quote:

Originally Posted by HMS Vanguard

Hey,

On the latest time I've attempted the firing solution, my two readings were Bearing 325 at 1,357 feet, and Bearing 342 at 1,242 feet, timed at 45 seconds with a bearing change of 17. The total of R1 Squared + R2 Squared was 3,384,013.

The Cos of 17 turned out to be 0.257, and 2 x 0.257 x 1357 x 1242 = 926,966.7. Subtracting 3,384,013 from 926,966.7 results in -2,457,046, which as a negative number cannot be turned into a square root according to my calculator.

What am I doing wrong here? Any help would be appreciated in this, so I can get to sinking.

Good hunting!

Multiply by -1, then do your little square root thingie.....

negatives are so easily taken care of with a well placed inverse.....

Thankyou.

I will try that out now and post my result.

Good Hunting!

Puster Bill · 06-14-07, 08:40 AM

If you really want the realism, just build a SACF/IS-WAS. That will let you calculate the AOB and speed you need to enter into the TDC (you'll alread have range and bearing).

It isn't that hard, it's basically just two circular slide rules back to back, and there are the original instructions on how to use it at the HNSA website.

SteamWake · 06-14-07, 03:34 PM

You may find this thread http://www.subsim.com/radioroom/showthread.php?t=116612 usefull as well.

Powerthighs · 06-14-07, 04:21 PM

Quote:

The problem I am having is when I get to Step 4:
"4. Subtract the first total (step 1) from the second total (step 3) 339,860
(8,840,000-8,500,140)"

There is actually a typo in this step. If you look at the equation, this step should say:

4. Subtract the second total (step 3) from the first total (step 1)

Because of the restrictions on the values of a, b, and C in a triangle, this will always yield a positive number.

Puster Bill · 06-14-07, 07:22 PM

Quote:

Originally Posted by SteamWake

You may find this thread http://www.subsim.com/radioroom/showthread.php?t=116612 usefull as well.

Just whatever you do, don't link to this thread:
http://www.subsim.com/radioroom/showthread.php?t=112765

06-14-07, 05:43 AM	#1
HMS Vanguard Swabbie Join Date: Aug 2004 Location: England, United Kingdom Posts: 11 Downloads: 0 Uploads: 0	Mathematical Question concerning Firing Solutions - what am I doing wrong? Hey, Okay, so I'm sitting in the training mission for torpedo runs, and I'm attempting to develop the skills in trigonometry to manually work out firing solutions on the Cruiser that sails across my bow. I'm using the process put forward in the excellent thread "http://www.subsim.com/radioroom/show...ghlight=manual" by starvingartist507, but I'm running into a snag with my calculations, and being aware of my general poor maths skills I was wondering if someone could show me where I'm going wrong? The problem I am having is when I get to Step 4: "4. Subtract the first total (step 1) from the second total (step 3) 339,860 (8,840,000-8,500,140)" This is subtracting the total of A Squared + B Squared from the total of "2 x (Cos of Bearing Change) x Range 1 (R1) x Range 2 (R2)". The problem I am having when calcuating the solution is that the total of the former is larger than the total of the latter. As an example: On the latest time I've attempted the firing solution, my two readings were Bearing 325 at 1,357 feet, and Bearing 342 at 1,242 feet, timed at 45 seconds with a bearing change of 17. The total of R1 Squared + R2 Squared was 3,384,013. The Cos of 17 turned out to be 0.257, and 2 x 0.257 x 1357 x 1242 = 926,966.7. Subtracting 3,384,013 from 926,966.7 results in -2,457,046, which as a negative number cannot be turned into a square root according to my calculator. What am I doing wrong here? Any help would be appreciated in this, so I can get to sinking. Good hunting! __________________ "Submariners are a bunch of intelligent misfits that somehow seem to get along, understand each other and work well together. -- submitted by Red Hanley who overheard a skimmer officer say this while talking to a non-navy type

06-14-07, 08:40 AM	#6
Puster Bill Grey Wolf Join Date: May 2006 Location: BA8758, or FN33eh for my fellow hams. Posts: 833 Downloads: 0 Uploads: 0	If you really want the realism, just build a SACF/IS-WAS. That will let you calculate the AOB and speed you need to enter into the TDC (you'll alread have range and bearing). It isn't that hard, it's basically just two circular slide rules back to back, and there are the original instructions on how to use it at the HNSA website. __________________ The U-Boat Commander of Love

06-14-07, 07:20 AM	#2
vindex Planesman Join Date: Apr 2007 Posts: 192 Downloads: 17 Uploads: 0	What the ... holy ... ??? You don't actually need to calculate this stuff. The mechanical computer on your boat does. You just need three inputs: 1) Range (the system is a bit off, but you can get it by trial and error or installing one of the fix mods) 2) AOB (either estimate it visually, which is often flawed, or by protractor -- it's the angle between the target's course and a straight line to your boat) 3) Speed (the stopwatch method is broken, hopefully will be fixed, so better to do it by marking location, waiting a specific period of time, and then marking a second location, then multiplying up to get the distance in nm you WOULD have gotten if the interval had been one hour). Right now I don't use 100% -- it's really unfair with all the broken range-finding and speed-measurement tools -- I still allow the contacts to appear on the map. If you do this, it's relatively easy to enter a solution then look at your battle map to see how accurate it is (in all three inputs) and make adjustments accordingly. Unless you LIKE doing math ...

06-14-07, 03:34 PM	#7
SteamWake Rear Admiral Join Date: Mar 2005 Posts: 13,224 Downloads: 5 Uploads: 0	You may find this thread http://www.subsim.com/radioroom/showthread.php?t=116612 usefull as well.