Finding Range

[corsair15]

I have a question about finding range to target without the stadimeter.

First, I wanted to mention that I cannot stand the fact that I can't just input range, speed, and angle on bow with the numpad. It would be so much cooler if I could.

However I actually do not know how to find range without the stadimeter. There was an equation in the instruction manual, and I actually do not know how to use it. I can do math fairly well, but I can't make out what the equation says in the manual. It says something like (Number of degrees divided by [cos] multiplied by [tan] etc etc)

Anyway, I wouldn't actually know how to use that equation anyway even if I did know what it said. So could anyone give me the equation in simple terms that I could do with a calculator or a piece paper preferrably?

I realize that the lines on the periscope represent a specific number of degrees to help you find range. What is the math I'd need to do after I find the degree and bearing to target?

Any replies would be welcomed.

[Diopos]

R=H/tan(φ)

• R - Distance to target
• H - Height from top of mast to waterline
• φ - angle you observe the top of mast through the periscope

You must know H beforehand (identified target or own estimation)
For small φ's you can use R=H/φ as long as φ is in radians not degrees.

[corsair15]

Is that Tangent, multiplied by the number of degrees?

So: Height divided by Tangent multiplied by Angle = Range ????

I'm still not exactly sure (I never took Geometry or Trig in school, I wish I would have though, because now I'm trying to learn it by myself)

[razark]

It's height divided by the tangent of the observed angle (I'm guessing degrees for the angle).

You'll either need to memorize the tangents of angles, have a table to look it up, or have some device for calculating it.

[Pisces]

If you use the "TGT Dial AOB Fix" mod or whatever it is called, then you can click on the range dial an turn it until whatever range you desire lines up with the range indicator. Basically you don't measure the observed height of the target (the two overlaid images of the scope are not used), but force it to use it's default (hidden) heigt angle.

Let me see if I can find a link to it.

[EDIT] It's called the "Easy AOB" mod. Go figure:

http://www.subsim.com/radioroom/showthread.php?t=152945

What I meant was, that to set a range (that I presume you know, like by eyeballing, or I misunderstood) it doesn't matter if the mast is small and the optical size is big, or the mast is large and optical size is small. If you know the range, and just want to set it, just fumble with the dials until it is set.

[EDIT 2]Sorry, I re-read the thread and I obviously misunderstood.

[tomoose]

I must be missing something here. Even with the formula mentioned you're still missing some info, aren't you?

You want to find the range and you've identified the ship and got the mast height from the ID manual. That part is clear enough. How do you determine the verticle (observed) angle without the stadimeter? Which hash mark etc do you use in the periscope/TBT? You need at least two pieces of info in order to solve the equation.

If
Y = mastheight (as given by ship ID book), and
X = angle (observed angle fm sub to mast top, from the horizontal), and
Z = range

Range(Z) = Height (Y)/tan X
How is X determined without the stadimeter or some other device?

[Diopos]

By counting the "marks" on the periscope.

Link


.

[tomoose]

I thought they were not accurate enough for that. I am familiar with the link you posted and as Ducimus says the hash marks are only good for one magnification etc.

I created an .html version of the sliderule omnimeter but Capt Scurvy (IIRC) created an even better beta one although I don't think he's released it as yet as he's doing/done a lot of testing to verify the hash mark accuracy etc.

All that to say that I think the hash marks would be very rough and affect your overall solution. Capt Scurvy's mod may crack this nut.

[Platapus]

They are about as accurate as they were in real life, I am afraid.

One has to keep in mind that most of nature is working against the submarine and its captain obtaining the necessary information.

In this simulation, we often have information far more accurate than was ever available to a WWII Captain.

This is why 100% realism ain't.

[Diopos]

And that's why most torps were fired at a relative close range. To cancel the effect of unavoidable inaccuracies in collecting the relavent target data.



.

[tomoose]

I'll second that. Get in close, 2000yd or less. Even then I still consider myself lucky if I hit what I'm aiming at, LOL.

[CapnScurvy]

Originally Posted by corsair15

I realize that the lines on the periscope represent a specific number of degrees to help you find range. What is the math I'd need to do after I find the degree and bearing to target?

The formula is as follows:
Range in Yards = (76.4 x Height, divided by the number of periscope Telemeter divisions in High Power magnification)

or
Range in Yards = (19.1 x Height, divided by the number of periscope Telemeter divisions in Low Power magnification)

The "Height" figure can be anywhere on the ship, as long as you have a good estimate of its dimension (the stock game uses the mast head heights and are listed in the Recognition Manual). The "Telemeter" divisions are the vertical and horizontal marks seen in the periscopes and American TBT (German UZO).

The game isn't going to give you a correct calculation for two reasons. First, most of the mast height figures given in the Recognition Manual are wrong (a few are close enough to be considered correct but that's only about 1/5 the total ships the game uses). For instance, the stock game lists the Japanese Carrier Hiryu as having a mast height of 102 ft. It should read 123 ft. Or, the Japanese mine layer Okinoshima list its mast height at 69 ft, where it should read 92 ft. These incorrect figures are going to give you wrong range findings if these were the only errors with the equation.

Secondly, the scope Telemeter marks are not correct for the above formula. This formula (used by the Navy Submarine force during WWII) is calculated for a periscope having a 32 degree field of view (FoV). Meaning the scopes view without moving it, covers 32 degrees of angle from the left side of the view to the right (also the same for the view from top to bottom). You may notice the periscope does indeed have 32 small marks from side to side, or top to bottom but; if you check the range of degrees between two non movable points set at the sides of the scopes view, you will find the game has a FoV of 36 degrees not 32!! And, if you use the 1280x1024 game resolution with your monitor, the FoV increases to 38 degrees!!!

So what does a single degree equate to in feet at a 1000 yard distance?

One degree covers 52.356 feet at 1000 yards range. At 2000 yards range the one degree covers 104.712 feet; at 3000 yards, 157 feet and so on. The point is, at 3000 yards range the FoV for a game using the 1280x1024 resolution is a whooping 5968 feet wide where it should be only 5026 feet. Over 900 feet too wide a view!! This means that the targets we see are too small for accurate measurements with a scope Telemeter divisions set at 32 degrees. Having larger FoV makes the objects smaller (having a smaller FoV increases the size of the objects displayed).

I'm working on a mod to correct these two issues. Having correct heights and a correct optical FoV. I call it "Optical Targeting Assist" (I'm going to change the name to "Optical Targeting Correction" since that's exactly what it does), the WIP thread can be found HERE.

Also, to keep from having to do the math, an Omnimeter will be introduced into the game to find correct Range and Angle on Bow of target ships. AoB will be found using the "length" of the target ship and counting the Telemeter divisions, inputted onto the Omnimeter. Just a bit reversed to the way you will calculate range. I hope to have the ships height and length measurements done soon (there are over 100 to check with the stock game).

[corsair15]

Capn'Scurvy......

You're my hero man. I love it, you actually took the time to figure all that out? Kudos to you, and if you had help kudos to those guys too. Major Kudos!

I figured the mast height estimations given in the recognition manual would be off by some amount. Didn't know they would be that large. That makes it almost literally impossible to shoot a target accurately with the information we have. I figured they wouldn't compensate for the pixel differences too, I'm amazed you actually figured out how far it really was. You must have had to do a lot of observing. Good job man. That was exactly the kind of information I wanted.

I wish I had internet at home so that I could help you. Life really blows hard for me right now, and I'm really interested in this.

Thanks for all of your replies everyone, I really appreciate everything,
Corsair

[I'm goin' down]

I get close, close my eyes, push all the butttons, and say a prayer. (then dive to 650 feet.)

[CapnScurvy]

Corsair15, I just noticed you're new to the forums!!

Welcome to the communnity!!

And thanks for the kind words.
Here's a link to a website that has a WWII "Torpedo Fire Control Manual" that could be useful in your study. You say you don't have access to the Internet at home so don't get caught trying to down load this manual at work!!

It explains the procedures of making an attack using the various tools available to a sub "Fire Control" team. This is where the formula I stated earlier can be found (although some of the actual figures don't add up when you do the math, Who proof read these manuals anyway!?!) But, a lot of good information can still be gleaned from it.

Best regards