Target speed calculation made easy

[scooches]

So...quick question here as I don't have Sh4 yet. The Range tools in this sim measure distance like .8nm vice giving it in yards?! The Navy deals in yards for most everything except air control.

When we would mark contacts on the ship, it always referenced yards, 080 12,000 yards etc...this also worked well with the 3 minute rule. To give inaccurate distance measuring like nm w/ decimals is a bit absurd. It's one thing about SH3 that I didn't particularly care for either. Works well on a large scale chart, but when your talking closer in ranges, specific yards/meters would pay great dividends.

[WernerSobe]

in Real subs there was no magic involved. They used a tool that looked like a logarythmic ruler to find the speed. And it was fearly easy and quickly to use.

Another method was to guess the speed by counting the turns of screws. This only worked with ships they had turncharts for.

[greekfire]

Originally Posted by Shadowmind

Now take an example of a ship that is 1000 yards away, with an AOB of 25 deg, it has moved 2 degrees in 10 seconds:
speed = ((1000 * 0.000493738) * sin(2 deg * pi / 180) * 3600) / (sin(35* pi/180) * 10 sec)
speed = 10.82 knots

I assume you accidently entered 35 degrees into the formula for AOB. In the example, you quoted 25 degree AOB. Or did I miss something?

thnx!

[CableRouter]

Originally Posted by micky1up

why not have the sonar report the rev count of the engine and have a TPK (tuns per knot) for each vessel ie a battle ship has a tpk of 8 and the rev count is 80 therefor the speed equals 10 kts

The max possible rev count in the game appears to be 47. So if you have a freighter with 8 turns per knot, you get the same rev count if the ship is moving 6 knots or 16 knots. SHIII was exactly the same.

[NefariousKoel]

Originally Posted by scooches

So...quick question here as I don't have Sh4 yet. The Range tools in this sim measure distance like .8nm vice giving it in yards?! The Navy deals in yards for most everything except air control.

When we would mark contacts on the ship, it always referenced yards, 080 12,000 yards etc...this also worked well with the 3 minute rule. To give inaccurate distance measuring like nm w/ decimals is a bit absurd. It's one thing about SH3 that I didn't particularly care for either. Works well on a large scale chart, but when your talking closer in ranges, specific yards/meters would pay great dividends.

Yes, it only measures by a tenth of a nautical mile.

I can get by with it as-is using the 3 minute rule. You just have to extend the ruler a bit back and forth to see exactly how far into 0.5nm it is (for instance). If it just gets into 0.5nm but not close to the halfway mark, I know the target is doing 9 knots. I also let the stopwatch run until 6 minutes and mark again, though my speed estimation is perfect every time at 3 minutes using this methodology. The 6 minutes is for a better target heading more than anything.

[greekfire]

Hey guys,

I'm brand new but I wanted to run this formula by everyone to see if it is sound mathematics regarding finding target speed.

I use the law of cosines. a^2 = b^2 + c^2 - 2bc(cosA)

....where a, b, c are triangle sides, with Angles A, B, C. I am solving for side 'a' which is the distance traveled over 60 seconds.

It supposed to be good for when you have 2 lengths and one angle of irregular triangle.

Here are my steps...
1. Identify target and determine initial range to target
2. Start timer for 60 sec while noting initial range and initial bearing
3. After 60 seconds, mark final range and final bearing
4. Determine Angle A by subtracting final bearing from initial bearing
5. Solve for 'a' by using above formula
6. Divide answer by 60 to get speed in knots.

Example:

Destroyer is traveling at approximately 90 degrees AOB at range of 1226 with bearing 335 degrees. After 60 seconds, the range of target is still 1226 but bearing has changed to 347 degrees.

a^2 = 1226^2 + 1226^2 - 2(1226)(1226)cos[347-335]
a = 685.12 (distance traveled over 60 seconds)
speed = 685.12/60 = 11.42 knots

* just figured this out so still not sure how it performs with AOB's that deviate from 90 degrees but seems to work well in game so far.

I have heard about guys using nav map to lay all this out but the ruler is terribly inaccurate using tenths of nm's so I'm at a loss for that approach. If anyone knows how to use map to determine target speed please pass that info on. It would be much appreciated. cheers.

[captainFlunky]

Originally Posted by greekfire

Hey guys,

I'm brand new but I wanted to run this formula by everyone to see if it is sound mathematics regarding finding target speed.

I use the law of cosines. a^2 = b^2 + c^2 - 2bc(cosA)

....where a, b, c are triangle sides, with Angles A, B, C. I am solving for side 'a' which is the distance traveled over 60 seconds.

It supposed to be good for when you have 2 lengths and one angle of irregular triangle.

Here are my steps...
1. Identify target and determine initial range to target
2. Start timer for 60 sec while noting initial range and initial bearing
3. After 60 seconds, mark final range and final bearing
4. Determine Angle A by subtracting final bearing from initial bearing
5. Solve for 'a' by using above formula
6. Divide answer by 60 to get speed in knots.

Example:

Destroyer is traveling at approximately 90 degrees AOB at range of 1226 with bearing 335 degrees. After 60 seconds, the range of target is still 1226 but bearing has changed to 347 degrees.

a^2 = 1226^2 + 1226^2 - 2(1226)(1226)cos[347-335]
a = 685.12 (distance traveled over 60 seconds)
speed = 685.12/60 = 11.42 knots

* just figured this out so still not sure how it performs with AOB's that deviate from 90 degrees but seems to work well in game so far.

I really wish I wouldn't have napped through every math class I ever had at this point.

[Tobus]

Great chart, I was on the verge of shelfing the game until patch 1.4b .
Now tonight I will give it a go once more.

[MudMarine]

CaptFlunky and Others,
Ye Gads! Flunky ya not only one who slept through math. My favorite sim in the past was Silent Service II. The days of those simple sims are over. What we need is a Sub Sim School on line! :hmm: Guess I got to bone up on my math ,YuK! Heck ! I got problems just doin my Taxes! I will have to study this thread a lot and practice , practice and practice till it becomes second nature.

I have some other questions abour SH4 but those are for another thread.

[Powerthighs]

uhm nevermind, that method i just mentioned didnt work, i got too much of a bearing change for the speed to be correct..

So what you are saying, is that I have to check the bearing change by Visual Eyesight? How will I be able to see, with my own eyes, thru a periscope, at 1100 yards, if he changes his course by 3 degrees?

Getting frustrated again.. Ubi.. please fix the auto bearing finder..


S!

RH

RedHerring, not sure if anyone ever answered your question.

The change in bearing doesn't mean how the course of the target ship changes. It means the change in direction you look to see the target.

This is easily measured through the periscope. Let's say you see a ship moving left to right across your periscope view, 2000 yards away. You place your periscope centered on the middle of the ship. You see the periscope bearing is 270, (i.e. the target is directly to your left).

You wait 30 seconds, then move the periscope to re-center on the ship. Now the periscope bearing reads 275.

That means the bearing changed 5 degrees in 30 seconds on a target 2000 yards away. Looking at the chart, that gives you a speed of 10 knots.

[Puster Bill]

Originally Posted by RTKSpiff

Nice table

To get the effect of AOB just divide your answer by sin(AOB), but then
you need a calculator

Heresy! Use one of these:

[Puster Bill]

Here is the thread where I explain how to use a slide rule to get AOB and speed given two range/bearing marks:

http://www.subsim.com/radioroom/show...ght=slide+rule

[NEOCortex]

I figured I'd join this forum and contribute alittle of my own efforts in determining a targets speed and AOB. I've made an excel file which does all my calculations for me.

http://files.filefront.com//;7546056;/

It may help to have some experience with excel to use this, but probably not necessary.

Instructions on this spreadsheet:
Cells in blue are where you input your information, cells in red show the most critical results.
In game, when you want to gather data on a target, set your subs speed and direction, then input your subs speed into the spread sheet.
As quick as possible, get a range/bearing to the target AND start the timer. This will be the range and bearing at time 0 seconds in the spreadsheet.
Keep recording range and bearing data at various times. When you are satisfied or just want results, enter all these readings into the spreadsheet. Extend the formulas in the 6 columns to the right to cover all the entries you just made (if necessary).
Note: DO NOT extend the formulas further then the entered data (w/ the exception of the AOB column), as this will create cells with nonsense values, and these values will screwup the final calculations.

This spreadsheet will take the readings you input and calculate an average speed and heading for the target.
If this is done correctly, then the spreadsheet will calculate the AOB for the all the bearings you took data at, as well as any future bearings you wish to look at.
It will also give you the heading of the target relative to your sub and the targets speed.

Final notes:
These calculations will only work if you use the right units, i.e. meters and seconds.
If you change direction or speed while you're doing this, start over!
If it looks like the target changed direction or speed during this process, start over!
The "averaging" was done by a linear fit of the data provided. See graph in spreadsheet to understand what is going on.
Positive AOB angles imply starboard and negative AOB angles imply port.
The positive x direction was defined as the forward direction of your sub and the positive y direction is defined as right 90 degrees of your sub.

[Gaspode]

Nice work, NEOCortex.

I made a program a few months ago which does nearly the same.
The only thing missing is the calculation of the relative data of the target. But you don't need a huge spreadsheet program to use it, and you don't have to copy the formulas for every contact. Plus you can track as many targets as you want and you can enter imperial or metric ranges

TDC (couldn't resist naming it Target Data Calculator )

[OlegM]

Originally Posted by akdavis

Mk. 14 torpedos are bugged at the high speed setting. The are not travelling as fast as the TDC thinks they are. Use low speed setting on your torpedos and see how you do.

None of you torpedo gurus commented further on this, is this true? TDC overestimates Mk14 speed on high setting?