SUBSIM Radio Room Forums - View Single Post - target speed: the eighty-ten method

tomoose · 08-13-10, 07:14 AM

I don't get it either. I've read the above but there seems to be a leap of faith involved plus "situating the estimate" (as RR has implied). Getting a good AOB is a bit of an art at the best of times using the VISUAL method! Despite the method described above I still can't see how one can possibly "assume" the 10D AOB just by placing the target at 80D when the target is completely out of sight with range/speed unknown and given that the degree of error varies with the range (i.e. the further away the target the greater any error or assumption will compound the situation, if you get my meaning).

I'm trying to understand the method but can't get past the distance and AOB aspect. For example; as indicated above, I detect a target at 120D starboard, range unknown, and sonar says he's closing, fine. I turn my boat to put the target at 80D bearing. Target is still closing. I adjust speed to keep target on 80D. Target is still closing but regardless of my speed, how do I know he's at an AOB of 10D? He could be at 0D AOB and proceeding at .5knots or at 25D AOB proceeding at 4knots (I'm exagerrating to make my point). I can adjust my speed to keep him at 80D but I don't see how that means he's definitely at 10D. He's still closing and depending on his approach angle to me it would take quite some time to determine his speed but that would still not give me his range (which 'could' be 19nm but then again could be 25nm etc ad naus). With a lot of sonar hits I should be able to determine his course (over time) which in turn would give me a rough AOB but I'm still not sure how that could definitely be 10D!?!?
Perhaps some still map shots with the trig etc could clarify things?

08-13-10, 07:14 AM	#11
tomoose Grey Wolf Join Date: Aug 2005 Posts: 930 Downloads: 23 Uploads: 0	Puzzled I don't get it either. I've read the above but there seems to be a leap of faith involved plus "situating the estimate" (as RR has implied). Getting a good AOB is a bit of an art at the best of times using the VISUAL method! Despite the method described above I still can't see how one can possibly "assume" the 10D AOB just by placing the target at 80D when the target is completely out of sight with range/speed unknown and given that the degree of error varies with the range (i.e. the further away the target the greater any error or assumption will compound the situation, if you get my meaning). I'm trying to understand the method but can't get past the distance and AOB aspect. For example; as indicated above, I detect a target at 120D starboard, range unknown, and sonar says he's closing, fine. I turn my boat to put the target at 80D bearing. Target is still closing. I adjust speed to keep target on 80D. Target is still closing but regardless of my speed, how do I know he's at an AOB of 10D? He could be at 0D AOB and proceeding at .5knots or at 25D AOB proceeding at 4knots (I'm exagerrating to make my point). I can adjust my speed to keep him at 80D but I don't see how that means he's definitely at 10D. He's still closing and depending on his approach angle to me it would take quite some time to determine his speed but that would still not give me his range (which 'could' be 19nm but then again could be 25nm etc ad naus). With a lot of sonar hits I should be able to determine his course (over time) which in turn would give me a rough AOB but I'm still not sure how that could definitely be 10D!?!? Perhaps some still map shots with the trig etc could clarify things? Last edited by tomoose; 08-13-10 at 07:48 AM.