[jmr]

I had to dig around in the 2002 Subsim forum archive and found this info regarding Ekelund range formula:

Here's the full thread link http://www.subsim.com/phpBB_2002/vie...c=4518&forum=2

Brief summary:

Single leg

xDMHr
------- all that times K.
DBy inst


Double leg

xDMHo 1 xDMHo 2
-------- +/- -------- all that times K.
DBy 1 DBy 2

K = 1.934 (2 is good enough for government work)

xDMHo = ownship speed across LOS
DBy = bearing rate
xDMHr = relative speed across the LOS

TopTorp '92 gives an example:

Given:
Ownships course: 075
Speed: 8
True Target Bearing: 120
Bearing rate (Dby): 1.5 degrees per minute

Compute:
Relative bearing = 120-075=045
xDmho

sin(045)X8kts = 5.7kts across the LOS.
Range = 5.7/1.5 = 3.8KYDS

Initial detection ranges yield bearing rates frequently less than one, like .5. So, when OS changes course across the LOS and yields a change in bearing rate less than one, that mean the range to target is likely beyond 10KYDS.

Although not a part of the Ekelund formula, you can compute ownship speed IN the LOS and estimate a rate of closure, normally expressed in yards per minute.

For this example, that means you take the cosine of the angle and multiply that by OS speed. In this case the sine and cosine of a 45 degree angle is the same. So, OS speed in the LOS - expressed as yDmho using Treeders notation - is computed as 5.7kts.

If you convert the NM (nautical miles) to yards (there are 2000 yards per NM) and the time from hours to minutes, you get a closure rate of 190 yards per minute.

When I was a Fire Control Technician, our skipper didn't feel comfortable tracking another sub with closure rates above 300 yards per minute. Some skippers and XO's design a trip wire. That is, the FT is responsible for making a verbal report to the OOD (that's Officer of the Deck for you non-bubble heads) to that fact. In such a case, a reasessment was in order.

I hope I havent thoroughly confused the community with this thread. But the delicacies of TMA are indeed delicate as well as intricate. But if you are really motivated in TMA & Sub Command, you can perfect these techniques and be sure to stay outside of counterdetection range. Of course, it's all fun and games on the computer, but this is the way sub business is done.