Time needed to locate convoy with hydrophones?

[jarlemag]

How much time do you consider is required to get a fix on a convoy's position and course using hydrophones only, in "average" and "best case" scenarios? Discuss!

[ljqcn101]

Depends on what accuracy you want to get from hydrophone only methods.

Since hydrophone induces a lot of bearing inaccuracies, you may want to adjust your listen intervals, and/or maneuver your boat to increase target bearing rate in order to reduce the impact of bearing inaccuracies.

I've been doing error analysis on bearing only methods recently with my TMA calculator, which is capable of calculate probability for positional/course error distributions, assuming a random bearing inaccuracy within a range of -0.5 to 0.5 deg. (http://www.subsim.com/radioroom/showthread.php?t=240508)

If you want a high level of accuracy for firing solutions, then you probably want the target positional error induced by bearing inaccuracies to be within 150 meters.

Consider a typical 4-bearing method scenario (constructed with a software called "Maneubo"): Let's say we have a medium-range medium-speed 6km/5kts target with an average bearing rate of 1 to 2 deg/min. And we choose a 10-minute time interval:

time t1 = 0 (sec)
ownship heading at t1 (deg): 0

target bearing at t1 (deg): 322.48

ownship straight direction from last position = 0 (deg)
ownship straight distance from last position = 0 (meter)
*******************************
time t2 (sec): 600

ownship heading at t2: 0

target bearing at t2 (deg): 338.23

ownship straight direction from last position (deg): 0

ownship straight distance from last position (meter): 0

*******************************
time t3 (sec): 1200

ownship heading at t3: 0

target bearing at t3 (deg): 355.6

ownship straight direction from last position (deg): 0

ownship straight distance from last position (meter): 0


target course: 78.12deg

probability of target course error within 5deg: 72.2727 %
probability of target course error within 10deg: 98.9091 %
probability of target course error within 20deg: 100 %

3 bearings when stationary can only get course solution.

*******************************
time t4 (sec): 1800

ownship heading at t4: 0

target bearing at t4 (deg): 32

ownship straight direction from last position (deg): 270

ownship straight distance from last position (meter): 2330


target course: 78.12deg, speed: 5.17377knots, distance: 6583.09

probability of target course error within 5deg: 70.1653 %
probability of target course error within 10deg: 98.9256 %
probability of target course error within 20deg: 100 %

probability of target positional error within 75m: 13.4711 %
probability of target positional error within 150m: 29.1736 %
probability of target positional error within 300m: 56.4463 %

Looks like we got a roughly 60% confidence of target positional error to be within 300m, when we consider a -/+ 0.5deg bearing inaccuracies. Looks marginally acceptable if we want a firing solution, but further increasing time intervals will improve the score.

If you only want a rough estimate of course and speed, you can decrease the time interval to 5 or 7 min maybe.

In this case when I'm about to take the 4th bearing, I moved to the opposite direction of
the target course because this will maximise bearing rate. You may want to avoid the following situation since the bearing rate is low and the solution is very error prone to bearing inaccuracies:

[jarlemag]

Thanks for the very detailed post. A good start!

To further specify the question, the expectations for the "fix" I had in mind is one good enough to plan an intercept course.

The motivation for asking this question is the disagreement between people who say, "Find the convoy's position and course by hydrophones first, then plot an intercept course" and those who say "forget about determining course, just go flank speed on the surface in the direction of the convoy".

In my experience, visual contact can usually be made within 15 minutes of travelling flank speed on the surface on the initial contact bearing, with a dive to correct course halfway, (after about 5 km), while 15 minutes is also commonly cited as the "minimum time" for a triangulation by the 4 bearings method. Therefore, I'm currently leaning towards the first method (immediate flank speed run on the surface.)

[Pisces]

Currently, with the closeness of the convoy at spawn you really do not need to go through the whole 3/4 bearing procedure to get to it. Just move towards the sound direction and trail it, with another hydrophone check if you feel unsure or excessive fog conditions apply. The current spawn condition is very forgiving in that.

But when you reach it, you are likely in an disadvantageous position and know nothing about where it is going. You shift the workload of gathering target movement to the visual contact phase. Doing the complicated method at a standoff can be considered as a time-investment into knowing roughly where he is going before you reach it. There is no rule that says which method you should follow. Some people like to keep things simple and do no-brainer actions to get a job done. Others simply like to use their wits and limited mount of information available to still get the end result. It's a choice.

But maybe in a future version of the game the developers introduce a more challenging situation where a convoy, or more likely an armed taskforce, moves much more rapidly (your surface speed now is 3 times faster than the average convoy speed) and from a further distance. (I hope!) Then it might prove more effective to use a systematic method of tracking the the contacts whereabouts, rather than to just dive-listen-sprint-repeat.

p.s. Has anybody even traced back the target course from a visual (verified) sighting to the moment of spawn?

Would be nice if we had the tools in game to do this. I mean, atleast with SH4 you can somewhat attempt this sort of thing in game. Just another big question mark as to who this game is really geared at.

[Pisces]

Have you even played the game? Have you even tried the navigator station? In what way is it different or lacking to SH3/4/5? Aside from the ability to drag circles, it is equal if not better overall than in the Silent Hunter (4) games. Try using the odometer in the SH games for proper dead-reckoning. (it's there, but cumbersome) Try finding the precise timestamp on the clock of an event. Try writing text. Try drawing tangent circles to a line. You can do the exact same and more compared to those games. Stop talking BS.