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Pisces · 01-08-09, 08:56 AM

Running into visual range with a ship is very much dependant on the weather/fog at that moment. It could be they simply went past unnoticed. If the weather was bad visibility could be as bad as 1km or if moderate 8km. That significantly reduces your chances.

Hydrophone is not hampered by that (maybe your crew's effectiveness in detecting is). If you listen yourself you can pick up anything within 34km radius (18.4 nm). That means you get 17 times more surface area of maritime real-estate over the 8km stock unlimmited visual range circle (=(34^2-8^2)/8^2). But only 3.5 more for 16km vis, still not bad. The trouble is you need to dive each time, and kick that lazy watchofficer back up in the end.

The interval depends on the size of the area (talked about later) and the relative speed with which the target crosses your hydrophone coverage, so your own cruising speed and the probable target speed and approach to you. If both you and the target are head-to-head add his (possible) speed to yours. If moving in the same direction take the difference. If perpendicular the Pythagoras equation should be used. The head-to-head situation is the quickest to cross the coverage area so also the determining factor.

Assuming your crew reports everything that comes into visual range immediately, the closest distance of the target-track to your visual range edge determines the interval to listen. The 'maximum' interval to choose depends on how lucky you (think you) are to get a target that crosses your path just outside maximum visual range. Have a look at the below sketch:

The drawn target-track is the most lucky one, just ouside visual range. (direct visual is ofcourse even better: automatic detection by crew) If you are unlucky the target just crosses the outer area of your hydrophone range and so the traverse time could potentially be very short, requiring constant listening. The question comes down to how certain you are of being on a hot traffic-lane. If you think you are on top of the traffic-lane you can use the track-lengths in the image. If not, make a conservative reduction of the time interval we will calculate below.

If you want to catch a target atleast once during his passage through your hydrophone coverage the interval is simply the tracklength (in nm), divided by the relative speed (in knots).

Taking the most extreme case of merchant (medium) speed: 12kts
and uboot cruise speed (i.e. type 7) 8kts
head-2-head relative speed: 20 knots

track outside of 16km visibility: 32.4nm; transit_time=32.4/20= 1.62 hours= 97min

track outside of 8km visibility: 35.7nm; transit_time=35.7/20= 1.785 hours= 107min

track outside of 1km/no visibility: 36.6nm; transit_time=36.6/20= 1.83 hours= 109min

So at the very most do your hydrophone drill every 1.5 hours or 90 mins to make sure a nearby medium speed target has the least chance of escaping your attention.

If you are only interested in head-2-head with slow targets (<8kts) you can do with maximum interval being just under 2 hours. (8+8=16kts , 32.4nm/16kts= 121min)

--------

Aside from that knowledge, I have increased the radius in which map-contactreports can be displayed, from 200-ish to 600km. This means more (distant) contact but not neccesarilly more often (since that is probability driven). So I have more chance to decide for myself if I want to chase them, instead of BdU making it for me. If I cannot be on their central course before they have moved 175km along it (at upper limit of their speed range), I forgo the intercept. At that distance the possible positions due to course uncertainty starts to extend beyond your hydrophone coverage. This way I OWN THEM.

01-08-09, 08:56 AM	#27
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,892 Downloads: 300 Uploads: 0	Running into visual range with a ship is very much dependant on the weather/fog at that moment. It could be they simply went past unnoticed. If the weather was bad visibility could be as bad as 1km or if moderate 8km. That significantly reduces your chances. Hydrophone is not hampered by that (maybe your crew's effectiveness in detecting is). If you listen yourself you can pick up anything within 34km radius (18.4 nm). That means you get 17 times more surface area of maritime real-estate over the 8km stock unlimmited visual range circle (=(34^2-8^2)/8^2). But only 3.5 more for 16km vis, still not bad. The trouble is you need to dive each time, and kick that lazy watchofficer back up in the end. The interval depends on the size of the area (talked about later) and the relative speed with which the target crosses your hydrophone coverage, so your own cruising speed and the probable target speed and approach to you. If both you and the target are head-to-head add his (possible) speed to yours. If moving in the same direction take the difference. If perpendicular the Pythagoras equation should be used. The head-to-head situation is the quickest to cross the coverage area so also the determining factor. Assuming your crew reports everything that comes into visual range immediately, the closest distance of the target-track to your visual range edge determines the interval to listen. The 'maximum' interval to choose depends on how lucky you (think you) are to get a target that crosses your path just outside maximum visual range. Have a look at the below sketch: The drawn target-track is the most lucky one, just ouside visual range. (direct visual is ofcourse even better: automatic detection by crew) If you are unlucky the target just crosses the outer area of your hydrophone range and so the traverse time could potentially be very short, requiring constant listening. The question comes down to how certain you are of being on a hot traffic-lane. If you think you are on top of the traffic-lane you can use the track-lengths in the image. If not, make a conservative reduction of the time interval we will calculate below. If you want to catch a target atleast once during his passage through your hydrophone coverage the interval is simply the tracklength (in nm), divided by the relative speed (in knots). Taking the most extreme case of merchant (medium) speed: 12kts and uboot cruise speed (i.e. type 7) 8kts head-2-head relative speed: 20 knots track outside of 16km visibility: 32.4nm; transit_time=32.4/20= 1.62 hours= 97min track outside of 8km visibility: 35.7nm; transit_time=35.7/20= 1.785 hours= 107min track outside of 1km/no visibility: 36.6nm; transit_time=36.6/20= 1.83 hours= 109min So at the very most do your hydrophone drill every 1.5 hours or 90 mins to make sure a nearby medium speed target has the least chance of escaping your attention. If you are only interested in head-2-head with slow targets (<8kts) you can do with maximum interval being just under 2 hours. (8+8=16kts , 32.4nm/16kts= 121min) -------- Aside from that knowledge, I have increased the radius in which map-contactreports can be displayed, from 200-ish to 600km. This means more (distant) contact but not neccesarilly more often (since that is probability driven). So I have more chance to decide for myself if I want to chase them, instead of BdU making it for me. If I cannot be on their central course before they have moved 175km along it (at upper limit of their speed range), I forgo the intercept. At that distance the possible positions due to course uncertainty starts to extend beyond your hydrophone coverage. This way I OWN THEM. Last edited by Pisces; 02-27-14 at 02:46 PM.