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BigWalleye · 05-22-17, 09:38 AM

Here is another consideration:

If you search in a barrier pattern (180 degree turns at each end) for 3-hour legs at 10kt cruising speed, with a 16km horizon you will cover roughly 2100 square km. At the center of each leg, a target traveling at 10 kts and moving perpendicular to your search will have a 2 in 3 chance of being in your search area. At the ends, this drops to 1 in 3.

Now consider the same search pattern, but every hour, you dive to 20m for a hydrophone search. Hydrophone detection range is about 30km. Now your search area is 4200 square km, almost double. The chance of a 10kt target being in your search area at the end of each leg is rises to 1 in 2, and in the middle, virtually 100%. (These numbers are all just for the mathematical case. RL, all probablilties would be reduced, but would all stay in the same relative order.) So a search with periodic hydrophone checks should be significantly more effective than a purely surface search. But, particularly in SH3, it is significantly more work, too.

If you search instead in a zigzag pattern, with 60-degree turns at each end, then you get much better coverage (about 100% at the ends) - but only when the target is moving in the same direction as your search. (This is sometimes called a retiring search.) For a target moving the other way, it's about the same as a straight pattern. So zigzagging is helpful, if you know which way the traffic is heading, or don't care.

IAC, adding hydrophone checks to your searches will significantly increase the likelihood of finding contacts. It is more work. If you are in a rich hunting ground, like the Bristol Channel, it may not be necessary. But if you are having a dry patrol, hydrophone checks may just produce some more action.

05-22-17, 09:38 AM	#19
BigWalleye Sea Lord Join Date: Jul 2012 Location: On the Eye-lond, mon! Posts: 1,987 Downloads: 465 Uploads: 0	Here is another consideration: If you search in a barrier pattern (180 degree turns at each end) for 3-hour legs at 10kt cruising speed, with a 16km horizon you will cover roughly 2100 square km. At the center of each leg, a target traveling at 10 kts and moving perpendicular to your search will have a 2 in 3 chance of being in your search area. At the ends, this drops to 1 in 3. Now consider the same search pattern, but every hour, you dive to 20m for a hydrophone search. Hydrophone detection range is about 30km. Now your search area is 4200 square km, almost double. The chance of a 10kt target being in your search area at the end of each leg is rises to 1 in 2, and in the middle, virtually 100%. (These numbers are all just for the mathematical case. RL, all probablilties would be reduced, but would all stay in the same relative order.) So a search with periodic hydrophone checks should be significantly more effective than a purely surface search. But, particularly in SH3, it is significantly more work, too. If you search instead in a zigzag pattern, with 60-degree turns at each end, then you get much better coverage (about 100% at the ends) - but only when the target is moving in the same direction as your search. (This is sometimes called a retiring search.) For a target moving the other way, it's about the same as a straight pattern. So zigzagging is helpful, if you know which way the traffic is heading, or don't care. IAC, adding hydrophone checks to your searches will significantly increase the likelihood of finding contacts. It is more work. If you are in a rich hunting ground, like the Bristol Channel, it may not be necessary. But if you are having a dry patrol, hydrophone checks may just produce some more action.