Calculating Speed Method / Question

FT2/SS · 04-11-07, 04:19 PM

This question is mainly for those of you that have been in the submarine community (like the real one). Kinda embarassed to be asking this, seeing as I was once an FT, but if someone could doublecheck or correct my formula it would be awesome. Would provide a really nifty way to rapidly get speed off of all other observation data (its really much more simple than it seems).

Rg = Range
xRS = relative speed across the line of sight
xOS = ownship speed across the line of sight
xT = target speed across the line of sight
OS = Ownship Speed
T = Target Speed
TAoB = Target angle on the bow
DBy = Bearing Rate
K = Magic Constant (1943?) ***not sure if this value is right, pulled it off a google for Ekelund Ranges, think all the conversions are there, but not sure... I always just used 2 anyways...

Best I can remember for calculating for Dby from Rg and xRS is:

DBy = K (xRS / Rg)
(not sure if this is right, but if it is...)

therefor

DBy / K * Rg - xOS = xT

Giving us

(DBy / K * Rg - xOS) / sin(TAoB) = T

I'm not sure if this is right, but I know there's a way to do it that doesn't involve pulling out the ekelund range formula (which irronically, I have memorized). I tried to re-derive it but I seem to have forgotten too much calculus somewhere along the way. And the numbers I'm getting plugging in stuff seems to make sense.

If so there's a REALLY easy way to get speed, as long as you have your sin tables memorized anyways (or a calculator / BRC you can print out online).

Any help is appreciated on checking this.

edited: for clarity... sort of :O

04-11-07, 04:19 PM	#1
FT2/SS Swabbie Join Date: Apr 2007 Posts: 5 Downloads: 0 Uploads: 0	Calculating Speed Method / Question This question is mainly for those of you that have been in the submarine community (like the real one). Kinda embarassed to be asking this, seeing as I was once an FT, but if someone could doublecheck or correct my formula it would be awesome. Would provide a really nifty way to rapidly get speed off of all other observation data (its really much more simple than it seems). Rg = Range xRS = relative speed across the line of sight xOS = ownship speed across the line of sight xT = target speed across the line of sight OS = Ownship Speed T = Target Speed TAoB = Target angle on the bow DBy = Bearing Rate K = Magic Constant (1943?) **not sure if this value is right, pulled it off a google for Ekelund Ranges, think all the conversions are there, but not sure... I always just used 2 anyways... Best I can remember for calculating for Dby from Rg and xRS is: DBy = K (xRS / Rg) (not sure if this is right, but if it is...) therefor DBy / K Rg - xOS = xT Giving us (DBy / K * Rg - xOS) / sin(TAoB) = T I'm not sure if this is right, but I know there's a way to do it that doesn't involve pulling out the ekelund range formula (which irronically, I have memorized). I tried to re-derive it but I seem to have forgotten too much calculus somewhere along the way. And the numbers I'm getting plugging in stuff seems to make sense. If so there's a REALLY easy way to get speed, as long as you have your sin tables memorized anyways (or a calculator / BRC you can print out online). Any help is appreciated on checking this. edited: for clarity... sort of :O Last edited by FT2/SS; 04-11-07 at 04:31 PM.