Intercepting

Pisces · 05-31-08, 10:23 AM

To get a target's course based on (hydro) 'bearings only' look at the following from a guy named Redwine. Because of his language (I think he's from argentina) it may be difficult to follow, but the formula works.

http://rotteufel.iespana.es/htdc_tut...ualtdc_009.htm

I found a sliderule ages ago that works by the same math but handles it in an easy way. Take 3 bearings, with equal time intervals (think long, not 3m15s, bearings move sloooowwww), line up the difference between the bearings of time1 and time3 with time1 and time2 and read off the AOB of the target at time1. BUT this is ONLY the true AOB if you are stationary. If you move (with significant speeds) the angle is NOT the AOB but skewed so-to-say by relative motion. So then it should be called 'Angle On Relative Motion'. Which is very difficult to correct for. (needs two sets of these 3 bearings while the sub is on 2 different courses or speeds and some vector-math for desert) Also, accuracy is very much hampered by the fact that Silenthunter (series... the slideruler was made back in the sh1 days I think) do not supply fine bearings (like with tenths of a degree). Bearings are all given in round degrees which makes the outcome very fuzzy/unprecise. Try it adding halve a degree either side on both bearing differences. You'll see what I mean. Also, you can't tell how fast it is, or the range it is at. But target course is a whole lot allready. You just need the time to wait for the bearing to move enough.

Here's a webcam image showing my poor attempt to make this thing (bad quality):

Let's say I took 3 bearings with 2 equal time intervals inbetween with my hydrophone (but periscope or whatever works just the same) B1=087, B2=081, B3=072, the bearingdifferences (6 and 15 degrees) result in a Target AOB at time of bearing 1 being 26 degrees. Since the target was moving from your rightside to your leftside (passing in front of you) he was 'showing' his left/port bow. Draw the angles out on paper and you can see the target's course.

I don't know who made it so hopefully they won't mind I uploaded it to my homepage, for availability sake. The .zip file contains a .htm file with information on the assembly and use of the tool by the original maker. The drawing for the tool can be print from a (autocad vector format) .dwg file, or an ordinary .gif image.

http://ricojansen.nl/downloads/gizmos.zip

05-31-08, 10:23 AM	#10
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,904 Downloads: 304 Uploads: 0	To get a target's course based on (hydro) 'bearings only' look at the following from a guy named Redwine. Because of his language (I think he's from argentina) it may be difficult to follow, but the formula works. http://rotteufel.iespana.es/htdc_tut...ualtdc_009.htm I found a sliderule ages ago that works by the same math but handles it in an easy way. Take 3 bearings, with equal time intervals (think long, not 3m15s, bearings move sloooowwww), line up the difference between the bearings of time1 and time3 with time1 and time2 and read off the AOB of the target at time1. BUT this is ONLY the true AOB if you are stationary. If you move (with significant speeds) the angle is NOT the AOB but skewed so-to-say by relative motion. So then it should be called 'Angle On Relative Motion'. Which is very difficult to correct for. (needs two sets of these 3 bearings while the sub is on 2 different courses or speeds and some vector-math for desert) Also, accuracy is very much hampered by the fact that Silenthunter (series... the slideruler was made back in the sh1 days I think) do not supply fine bearings (like with tenths of a degree). Bearings are all given in round degrees which makes the outcome very fuzzy/unprecise. Try it adding halve a degree either side on both bearing differences. You'll see what I mean. Also, you can't tell how fast it is, or the range it is at. But target course is a whole lot allready. You just need the time to wait for the bearing to move enough. Here's a webcam image showing my poor attempt to make this thing (bad quality): Let's say I took 3 bearings with 2 equal time intervals inbetween with my hydrophone (but periscope or whatever works just the same) B1=087, B2=081, B3=072, the bearingdifferences (6 and 15 degrees) result in a Target AOB at time of bearing 1 being 26 degrees. Since the target was moving from your rightside to your leftside (passing in front of you) he was 'showing' his left/port bow. Draw the angles out on paper and you can see the target's course. I don't know who made it so hopefully they won't mind I uploaded it to my homepage, for availability sake. The .zip file contains a .htm file with information on the assembly and use of the tool by the original maker. The drawing for the tool can be print from a (autocad vector format) .dwg file, or an ordinary .gif image. http://ricojansen.nl/downloads/gizmos.zip Last edited by Pisces; 03-05-14 at 04:32 PM.