Real navigation target motion analysis cheatsheet

McDonnel · 11-06-21, 09:17 AM

I am sorry to resurrect this old thread, but I would really like some help here with the target course determination.

Let me use my example, encountered in the game - "stationary" 4-bearings method, readings taken at the same time interval of 10 minutes:

Co = 287° (my u-boot course)
b1 = 48°
b2 = 59°
b3 = 70°

So, if I start calculation using the easiest formula:
1) Cot(DRM - B1) = 2*Cot (22) - Cot(11)
2) Cot(DRM - B1) = 2*2,4751 - 5,1446
3) Cot(DRM - B1) = 4,9502 - 5,1446
4) Cot(DRM - B1) = -0,1944 (this is negative, so I take absolute value, determine angle of 79 from the tables provided and put it further as (90-79+90 = 101) according to your instructions)
5) DRM - B1 = 101 degrees
6) DRM = 149 degrees (correct? or do I use here the true bearing of b1t = 335° (= Co + b1 = 287+48) already, which gives different DRM = 436 (-360?) = 76 degrees?)

How do I get from here to the target course?
Ct = Co + DRM according to your instructions, but no matter if I use 149 or 76, (resulting in either Ct = 287+149 (-360) = 76° (??) or Ct = 287 + 76 (-360) = 3°

For the Poseidon´s beard, I am unable to get to that correct target course of cca 91°, which I get with graphic resolution.

Thank you very much for any help.

Btw: Spiess line formula comes out to 80,24°, which is pretty close to expected 81° (and later verified 82° from graphic solution).

11-06-21, 09:17 AM	#13
McDonnel Watch Join Date: Nov 2016 Posts: 19 Downloads: 17 Uploads: 0	I am sorry to resurrect this old thread, but I would really like some help here with the target course determination. Let me use my example, encountered in the game - "stationary" 4-bearings method, readings taken at the same time interval of 10 minutes: Co = 287° (my u-boot course) b1 = 48° b2 = 59° b3 = 70° So, if I start calculation using the easiest formula: 1) Cot(DRM - B1) = 2Cot (22) - Cot(11) 2) Cot(DRM - B1) = 22,4751 - 5,1446 3) Cot(DRM - B1) = 4,9502 - 5,1446 4) Cot(DRM - B1) = -0,1944 (this is negative, so I take absolute value, determine angle of 79 from the tables provided and put it further as (90-79+90 = 101) according to your instructions) 5) DRM - B1 = 101 degrees 6) DRM = 149 degrees (correct? or do I use here the true bearing of b1t = 335° (= Co + b1 = 287+48) already, which gives different DRM = 436 (-360?) = 76 degrees?) How do I get from here to the target course? Ct = Co + DRM according to your instructions, but no matter if I use 149 or 76, (resulting in either Ct = 287+149 (-360) = 76° (??) or Ct = 287 + 76 (-360) = 3° For the Poseidon´s beard, I am unable to get to that correct target course of cca 91°, which I get with graphic resolution. Thank you very much for any help. Btw: Spiess line formula comes out to 80,24°, which is pretty close to expected 81° (and later verified 82° from graphic solution).