Newb question: target speed.

[rune711]

I am not understanding why my speed estimates are always so far off. I'm using the standard method of plotting several sightings of the target, measuring and then using these figures to compute the speed. Distance = rate * time. In this case I need to figure rate, so it's Distance/time = rate.

For example if I see that the target has moved 1.5nm in 3 minutes that should give: 1.5/3 = x knots. A knot is measured in nautical miles per hour, so thats

1.5/3 = x/60 equals 20 * 1.5 = x or 30 knots.... which is twice the actual of 15 knots. The ruler IS in nm, right? Or is it in 1000s of yards or meters, or what???

What am I goofing up?

[Gargoyle]

Conversions:

1 knot = 1nm/hr = 1.852 km/hr = 2025.37 yrds/hr


Depends on what you have your measurements set up as in the options (metric or imperial). Your math is correct, but there are two things that could be messing you up: 1. incorrect units of measurement; 2. are you measuring travel based off of contact plots or angular change.

As long as you units are correct and plots are damn close, then your speed should be good. If you are using angular change, then your values could be a bit on the slow side.

[FinnN]

If the target has travelled 1.5nm in 3min (1/20th of an hour) then it will indeed be going 30kts (1.5 x 20). And the map distances are shown in nm...so your speed calculations are correct (unless I'm totally wrong!).

Have fun
Finn

[rune711]

Well... I've tried it with my own boat.. Cruising at standard speed of 15 knots I mark the map and wait for 3 minutes to elapse. Mark again and measure. Distance is 1.5. Because it doesn't tell me the units I'm assuming it's Nautical Miles. 1.5 x 20 = 30 knots, not 15. What gives?

[rune711]

Originally Posted by Gargoyle

Conversions:

Depends on what you have your measurements set up as in the options

Huh? Where is this option?

[ijozic]

Originally Posted by rune711

Well... I've tried it with my own boat.. Cruising at standard speed of 15 knots I mark the map and wait for 3 minutes to elapse. Mark again and measure. Distance is 1.5. Because it doesn't tell me the units I'm assuming it's Nautical Miles. 1.5 x 20 = 30 knots, not 15. What gives?

15 nm/hr * 3 / 60 hr = 0.75 nm

I guess 1.5 stands for 1500 yards.

[jdski]

1.5 nautical miles = 3000 yards.
I don't do the math myself, I use my nautical slide rule.
You can pick one up from $13.95 to $20.95 online. Applying the distance/time to it works out to be very accurate.

Originally Posted by ijozic

15 nm/hr * 3 / 60 hr = 0.75 nm

I guess 1.5 stands for 1500 yards.

[Puster Bill]

Originally Posted by rune711

Well... I've tried it with my own boat.. Cruising at standard speed of 15 knots I mark the map and wait for 3 minutes to elapse. Mark again and measure. Distance is 1.5. Because it doesn't tell me the units I'm assuming it's Nautical Miles. 1.5 x 20 = 30 knots, not 15. What gives?

Congratulations!

You have inadvertently stumbled upon the "3 Minute Rule". The distance you measured as 1.5 is actually 1.5 kilometers, or 1,500 meters, not 1.5 nautical miles.

Now, the "Three Minute Rule" (Which should really be called the "Three Minute and 15 Second Rule") states that whatever distance in kilometers you travel in 3 minutes and 15 seconds, multiply by 10 to get the speed in knots. If you are just using meters, you have to divide by 100. Either way, you are just moving the decimal point.

Using the Three Minute Rule is the fastest, easiest way to get the speed of a contact, provided you can accurately measure the distance between two observations.

[jdski]

If your set to imperial units you'll see 1.5nm next to each number. That's nautical miles. If it says 1.5km that would be kilometers and you must be set on metric.
Yes, traveling at 15 nautical miles per hour (nm) in 3 mins will take you .75nm or 1500 yards.

Originally Posted by ijozic

15 nm/hr * 3 / 60 hr = 0.75 nm

I guess 1.5 stands for 1500 yards.

[rune711]

I must be missing something. Where is this setting to change from imperial to metric?

Its in the game options screen.