How to calculate speed without notepad if you do not have gods eye enabled on the nav

CjStaal · 07-28-15, 04:34 PM

I am at 100% realism. How do I find out their speed without the notepad?

CjStaal · 07-28-15, 04:38 PM

I think I know how. Using some trigonometry.

First calculate bearing and range.

Wait about a minute

Calculate bearing and range again.

From there, you know an Angle, and 2 sides of a triangle.

Using a side angle side formula you can calculate distance traveled.

From there, you can divide by the time and you have the speed.

[Best to do this paused, lol.]

I'm hoping there is a better way though.

Kip336 · 07-28-15, 04:43 PM

You're well on your way to the solution. What you said would actually work, but if we can eliminate the math, it's even less prone to error.

Take your bearing/range estimates exactly every 3 minutes and 15 seconds.

The distance between two points per 100 meters is the speed in knots.

Distance 700 meter? speed is 7 knots

Distance 1200 meter? speed 12. etc.

Tupolev · 07-28-15, 11:37 PM

The fixed wire method is good if you know the target's length. Since 1 kt is about .5 m/s, measure the time a ship takes to cross the vertical wire in your scope.

Works best when your own speed is under 2 kts. Also, you can't be turning or pan the scope when this is happening.

My preferred and (in my opinion) most accurate way is to steer a parallel course abeam the target. Match speed so the target stays at the same bearing. Your speed is now the targets speed. May take some fine tuning to get right.

Topp1967 · 07-30-15, 09:20 AM

Thanks! for the 3 min 15 sec tip - elegantly simple . Going to switch to that tonight, up till now I had been measuring distance over a set time ie how many metres travelled in a minute(s) then converting to kmph then dividing by 1.852 to get speed in knots.

Zosimus · 07-30-15, 10:04 AM

I also have a spreadsheet / cheat sheet that I use when stalking a convoy. It tells me how far the convoy will travel in a certain number of minutes. For example, I can look at my sheet and know that a convoy traveling at 8 knots should traverse 15.8 km in 61 minutes.

Obviously, you could say that it will cover 15.55 km in 60 minutes, but I find the .55 awkward to work with. In reality, the convoy will cover 15.81 km in 61 minutes, but that's close enough to 15.8.

I do hourly checks by hydrophone and typically run 15-20 km away from the convoy (depending on the weather). I have noticed that I often get radar contact from the escorts, but they never wander over to check on me. It's early 1943.

07-28-15, 04:34 PM	#1
CjStaal Seaman Join Date: Jul 2015 Posts: 42 Downloads: 15 Uploads: 0	How to calculate speed without notepad if you do not have gods eye enabled on the nav I am at 100% realism. How do I find out their speed without the notepad?

07-28-15, 04:38 PM	#2
CjStaal Seaman Join Date: Jul 2015 Posts: 42 Downloads: 15 Uploads: 0	I think I know how. Using some trigonometry. First calculate bearing and range. Wait about a minute Calculate bearing and range again. From there, you know an Angle, and 2 sides of a triangle. Using a side angle side formula you can calculate distance traveled. From there, you can divide by the time and you have the speed. [Best to do this paused, lol.] I'm hoping there is a better way though.

07-28-15, 04:43 PM	#3
Kip336 Torpedoman Join Date: Jun 2009 Posts: 119 Downloads: 19 Uploads: 0	You're well on your way to the solution. What you said would actually work, but if we can eliminate the math, it's even less prone to error. Take your bearing/range estimates exactly every 3 minutes and 15 seconds. The distance between two points per 100 meters is the speed in knots. Distance 700 meter? speed is 7 knots Distance 1200 meter? speed 12. etc.

07-28-15, 11:37 PM	#4
Tupolev Hauptman Join Date: Mar 2013 Location: FL410 Posts: 174 Downloads: 75 Uploads: 0	The fixed wire method is good if you know the target's length. Since 1 kt is about .5 m/s, measure the time a ship takes to cross the vertical wire in your scope. Works best when your own speed is under 2 kts. Also, you can't be turning or pan the scope when this is happening. My preferred and (in my opinion) most accurate way is to steer a parallel course abeam the target. Match speed so the target stays at the same bearing. Your speed is now the targets speed. May take some fine tuning to get right.

07-30-15, 09:20 AM	#5
Topp1967 Watch Join Date: Aug 2007 Location: Stirlingshire Posts: 18 Downloads: 124 Uploads: 0	Thanks! for the 3 min 15 sec tip - elegantly simple . Going to switch to that tonight, up till now I had been measuring distance over a set time ie how many metres travelled in a minute(s) then converting to kmph then dividing by 1.852 to get speed in knots.

07-30-15, 10:04 AM	#6
Zosimus XO Join Date: Jun 2014 Location: Chorrillos, Lima, Peru Posts: 401 Downloads: 3 Uploads: 0	I also have a spreadsheet / cheat sheet that I use when stalking a convoy. It tells me how far the convoy will travel in a certain number of minutes. For example, I can look at my sheet and know that a convoy traveling at 8 knots should traverse 15.8 km in 61 minutes. Obviously, you could say that it will cover 15.55 km in 60 minutes, but I find the .55 awkward to work with. In reality, the convoy will cover 15.81 km in 61 minutes, but that's close enough to 15.8. I do hourly checks by hydrophone and typically run 15-20 km away from the convoy (depending on the weather). I have noticed that I often get radar contact from the escorts, but they never wander over to check on me. It's early 1943.