Having a lot of trouble calculating speed

[ricardo]

So, I'm on an escort mission trying to hit a corvette. I have it locked and identified, distance and AOB calculated, but my chronometer doesn't do anything. I start it and stop it, but no spped is calculated. Do I have to do the math with pen and paper? How is this supposed to work?

Luckily, so far almost all convoys move at 7 knots, so before they are alerted I know the speed. If I didn't know that I wouldn't be hitting a darn thing.

However, this is a corvette moving in to attack my fleet, and it's going much faster. I can't come up with a spped.

Alot of times the seas are too rough to use the chronometer at all because all you see is smoke. Calculating speed has been the main mystery for me throughout the game.

[Rick Rawlings]

Couple of ways:

Run alongside the convoy at top-of-mast seeing distance. Put a ship at your 90° or 270°. Increase your speed until the ship is losing ground on you. Then decrease speed until the ship starts to overtake you. You have now bracketed the convoy's speed. You can do the same thing in front of or behind the convoy so they catch up to you or fall behind.

and/or

With the ship locked and recognized, open the chronometer tool. Place the vertical wire just in front of the bow of the ship in question. As the bow passes the wire, start the tool. When the stern of the ship passes the wire, stop the tool. Be sure to update the speed in the torpedo targeting dialogue with the speech bubble.

and/or

Open the stopwatch. Do not lock the ship but look up its length. Place the vertical wire just in front of the bow of the ship in question. As the bow passes the wire, start the stopwatch. When the stern of the ship passes the wire, stop the tool. Use your phone calculator to divide the length of the ship by the time. This is in m/s. To convert to kph, multiply by 3.6. Enter this number in the torpedo targeting dialogue and then update with the speech bubble.

For the last two, make sure you are not yourself moving.

[ricardo]

Thanks. I was frustrated because the second method has never worked for me.

I like the third method just in case the second never works for me.

[Mouse Rat]

I've used the 3m15seconds method coupled with an effective distance and bearing plotting.
It's by far the most reliable method i know and .. it works from ALL povs.. even from directly front or at weird AOB angles. It does require you to know which type of ship is in the catalogue.

All the others require at least 70° AOB or higher to get accurate estimates.

The distance estimate is using the mast height coupled with the amount of miliradians it occupies in the periscope.

The formula is sufficiently accurate to get speed estimates.
(mast * K) / miliradians = distance

mast .. from catalogue
K .. is 1700 for 0.6x and 17000 for 6x

EX: 33.34 tanker being around 155 miliradians on the 6x (around middle between 150 and 160)

(33.34 * 17000) / 155 = 3656m so 3.7km

Since only the miliradians count you can look at it directly from the bow and still get accurate distance predictions.

Then you plot the current enemy location, with the distance plus the bearing.
.. wait 3mins15seconds
Take second measurement.

The distance in between the plots is the speed.

753m is 7.5kn

While the periscope dial doesn't work with decimals being 8 for a 7.5 measurement, BUT the TDC does.
(I also use the "normal" speed measurement and it says 8kn but in the TDC is set up on 7.5kn as you can see from TDC view. so they are both accurate being on 7.5kn
at 55:02 in the video)

Using these methods you can get accurate estimates without locking the ship or using any cheating tools available, while on high realism.

(using the intercept tools with zero speed you can get course and speed measurements and do hydro kills without even having to see the enemy ship. and that works in any realism settings. but that's a different method. different video)

This method is used directly in this video from 44mins in
This is unlisted so should be no ads.

The YT compression fuggs up with the night time so you can't clearly see the miliradians, but the method described above is directly used to get speed measurement and a high ° solution set up for a test.(while on high realism)

And if you have means to write them down irl(the bearing and miliradians) you don't have to pause.

The described method is from 44mins in

https://youtu.be/_Q0Wc29Xb7c?t=2641

[wntu4]

Use the 3:15 method. Most accurate.

[Mouse Rat]

You can also use the "cheating" tools as mentioned above.
Talking to myself loudly while playing the game feels weird, BUT hopefully the video drags the point across.

It's a mini patrol where i find a ship using the cheat tools.
And kill it with a perfect 90° shot, from 50m deep without having seen it once.

It also changes course mid tracking , BUT thanks to the cheat tools , we get easily past that and get the kill.
All due to the incredibly accurate predictions of the ingame tools easily available even on high 90% realism.

Video is unlisted , should be no ads.
Can safely skip the first 7 mins , till the report of the ship that is getting hunted and ultimately killed.

https://youtu.be/KDmdpZHpDjw

[japp_02]

Originally posted by wntu4:

Use the 3:15 method. Most accurate.

^This.
But you must use mixed measurement options km / knots in the options.

Procedure:
Put a marker immediately ahead of the target;
let the chrono run 3 minutes 15 seconds,
reput a marker ahead of the target,
measure the Meter distance of the 2 makers.

distance in Meters / 100 = speed of the target in knots.

[Mouse Rat]

Originally posted by japp_02:

Example:
Measured distance = 5.23 km
Target speed = 5230 / 100 = 5.2 knots
Enter 5.2 in the TDC UI and press Return, do not enter 5 rounded.

can't be 5km , 5kn is 500m


5kn, 5 * 1.852 = 9.26 km/h

3m 15s (3x60 + 15)/ 3600 = 0.054167 hours

distance(km) = 9.26(km/h) * 0.054167(h) = 0.501 km = 500m

Didn't mean to diss you , its just when i see 1km+ i know it's wrong measurement.
And it's a good choice for anybody reading this.. to double check a 1km+ reading.

In the "cheating tools" video from earlier in the thread on the turn the distance for 3.15 was 1.1km which i ignored, waiting for it to go in a stable course then 3.15 and was 832m so around 8kn which ended up being the TDC speed for the kill.

I've had 13kn (1.3km) only two times in my campaign .

One was a crazy chase , turns out was a fake GB tanker under portuguese flag i chased for 600km+ since i wasn't at flank.
Normally they don't go that fast , at least none that i've encountered in my campaign.

https://youtu.be/zDTbEu0_H1o

OR this one when i was chasing a friendly sub and assumed the speed estimate was wrong
18km in 45m 18/.75 = 24km/h 24/1.852 = 12.9 = 13kn

https://youtu.be/OD_B7JPcgZU

[Rick Rawlings]

Originally posted by Mouse Rat:

I've used the 3m15seconds method coupled with an effective distance and bearing plotting.
It's by far the most reliable method i know and .. it works from ALL povs.. even from directly front or at weird AOB angles. It does require you to know which type of ship is in the catalogue.

All the others require at least 70° AOB or higher to get accurate estimates.

The distance estimate is using the mast height coupled with the amount of miliradians it occupies in the periscope.

The formula is sufficiently accurate to get speed estimates.
(mast * K) / miliradians = distance

mast .. from catalogue
K .. is 1700 for 0.6x and 17000 for 6x

EX: 33.34 tanker being around 155 miliradians on the 6x (around middle between 150 and 160)

(33.34 * 17000) / 155 = 3656m so 3.7km

Since only the miliradians count you can look at it directly from the bow and still get accurate distance predictions.

Then you plot the current enemy location, with the distance plus the bearing.
.. wait 3mins15seconds
Take second measurement.

The distance in between the plots is the speed.

753m is 7.5kn

While the periscope dial doesn't work with decimals being 8 for a 7.5 measurement, BUT the TDC does.
(I also use the "normal" speed measurement and it says 8kn but in the TDC is set up on 7.5kn as you can see from TDC view. so they are both accurate being on 7.5kn
at 55:02 in the video)

Using these methods you can get accurate estimates without locking the ship or using any cheating tools available, while on high realism.

(using the intercept tools with zero speed you can get course and speed measurements and do hydro kills without even having to see the enemy ship. and that works in any realism settings. but that's a different method. different video)

This method is used directly in this video from 44mins in
This is unlisted so should be no ads.

The YT compression fuggs up with the night time so you can't clearly see the miliradians, but the method described above is directly used to get speed measurement and a high ° solution set up for a test.(while on high realism)

And if you have means to write them down irl(the bearing and miliradians) you don't have to pause.

The described method is from 44mins in

https://youtu.be/_Q0Wc29Xb7c?t=2641

Just out of curiosity, I thought the scale on the periscope was not really in miliradians, but was just for show? Has that been changed? Are you using a mod? Also for the OP, the 3:15 method is just so you don't have to do any further calculations. But if you don't have three minutes, like if the destroyer is racing out of sight, you can measure any time amount and just divide the distance travelled in meters and divide by seconds to get m/s and then convert to kph or knots as you like. One of the silent hunter mods had a nice little tool with three scales arranged vertically. You drew a line through the distance travelled and the time and it gave you the speed.

[Mouse Rat]

Originally posted by Rick Rawlings:

Just out of curiosity, I thought the scale on the periscope was not really in miliradians, but was just for show? Has that been changed? Are you using a mod?

No mod. ATM i don't use any mods.
It does work.
It's in tens like 150 to 160 so you have to eyeball the % like 152
But the differences between 155 and 152 is still in the ballpark that is useful to get good distance measurements.
After that is plotting it. On bearing and distance.

And there are relative errors but they are small to be ignored ish..
Like in a 3.15 sequence can be introduces 20-30m error
like 830 or 780m .. that still 8kn.
That depends if you estimate more or less.. like 155 or 150 for a 152

Even the map tools are using hundreds of meters past 1km so ..you have to eyeball it,

Like when trying to draw 1580m , thats 1.5km but first move to 1.6km then move slightly back to switch back to 1.5km

Still it's sufficiently good for estimates especially if you set up within 1km in a high 80/90 °

Then the error introduced by the measurements have no huge impact.
It's obviously different if you try to snipe at 3.5km.

Still have to try a sniper shot on a moving target using this.
But it's easily usable for CQB.

I've never got good distance measurements using the periscope tool, so i had to figure out if the miliradians are good.
Also i think there was a guide that has a link to a site that did basically the same thing.

The formula is
(mast*K)/miliradians = distance(m)
and the K is based on the zoom. 1.7k for 0.6x, 17k for 6x.
It does require you to know the ships mast, as from the catalogue.

But once that is figured out you can get distance even from directly in front or behind.
Which would be impossible.

Once i've started using this the distances became accurate that i could easily switch to a no maps contact campaign and be effective without using any intercept cheat tools.

[Mouse Rat]

Originally posted by Rick Rawlings:

Just out of curiosity, I thought the scale on the periscope was not really in miliradians, but was just for show? Has that been changed? Are you using a mod?

Continuation of the above response.. i made a quick video to showcase the accuracy.
Unlisted, should be no ads.

https://youtu.be/Cot7pDNEFa8

[birusmax_83]

and why do you need to multiply by 1.7k or 17000? where did this coefficient come from?

[Mouse Rat]

Originally posted by birusmax_83:

and why do you need to multiply by 1.7k or 17000? where did this coefficient come from?

as far as i understand it , there is a formula in trig
Distance(m) = Object Height(m) / tan(θ)

object height is the mast of the ship we looking at.

for small angles ..like the ones in periscopes tan(θ) can be approximated to θ
so the formula can be switched to

D = OH / θ

θ(radians) = θ(miliradians) / 1000

and for "miliradians"
the formula ends up being

D(m) = (mast(m) * 1000 ) / miliradians

So technically K is 1000.

But due to calibration and zoom levels.. it ends up being 1700 to 17000
determined by ingame testing.

You can determine the precise distance from the map with contacts on , then the miliradians so it's relatively simple to figure out K for various zoom levels.

1700, 17000 are easy to remember.

I'd also argue there are probably more precise K factors ..but these are simpler to remember and clearly accurate as you can see in the video.

Is this simpler to use than the ingame tool?
idk , but its clearly more accurate, i could never get good estimates until this.

[birusmax_83]

Is this formula true for all mods, or only for vanilla?

[Mouse Rat]

Originally posted by birusmax_83:

Is this formula true for all mods, or only for vanilla?

I don't play with mods so don't have much experience..but i'd assume it works with anything that doesn't directly modifies the miliradians or the zoom etc.

[Rick Rawlings]

Originally posted by Mouse Rat:

Originally posted by Rick Rawlings:

Just out of curiosity, I thought the scale on the periscope was not really in miliradians, but was just for show? Has that been changed? Are you using a mod?

Continuation of the above response.. i made a quick video to showcase the accuracy.
Unlisted, should be no ads.

https://youtu.be/Cot7pDNEFa8

Very cool! Thanks for taking the time to make the video!