[Pisces]

Originally Posted by ljqcn101

Interest myself to see how much impact it has to those 3-bearing AOB or 4-bearing methods.

Bearing accuracy has a BIG impact on these methods, in particular AOB accuracy! And range and speed depends on that. The longer the time interval the lower the impact the bearing errors will have. My experience is that this AOB error vs time is inversely proportional. Because of the bearing drift size vs error size you will get more accuracy.

I'm using this tool to quickly work out the AOB vs bearing differences for the stationary 3-bearing method: http://www.subsim.com/radioroom/showthread.php?t=147719

It is based on the following math formula: cotangent (AOB) = cotangent (B2-B1) - 2*cotangent (B3-B1)

Let's say we start taking bearings when a target happens to show an AOB of 21 degrees to it's course at the first bearing. Starting with the a time taken for an initial bearing difference of 6 degrees then the 3rd bearing will be around 16 degrees from the first.

If you consider the edge cases of 0.5 degree bearing inaccuracies you would end up with the 2 situations that show the biggest variation to AOB:

B2-B1 -1 degree ; B3-B1 +0.5 degree
B2-B1 +1 degree; B3-B1 -0.5 degree

This results in a AOB range of 35 degrees:
5 vs 16.5, AOB = 12 degrees
7 vs 15.5, AOB = 47 degrees

This range of possible AOBs might be acceptable. But you are not always as lucky to find a target this far away still on the horizon. In these situations, but also when it is moving away, the AOB convergence goes quickly. But the nearer the target is to the horizon, the slower the bearing drift becomes. Ultimately a snails pace.

The closer you are to the point where the target starts with an AOB of 90 the harder it becomes to notice a change in bearing drift. It is pretty constant in that area. For example, with an AOB of 70, and a time interval worth 6 degrees the 3rd bearing would indicate 12.35 degrees of drift. We are not able to measure to such precision, but let's assume we were. Then with the above mentioned bearing difference errors this would entail an AOB range between 21 and 145 degrees. That is certainly not very useful. But with periscope sightings instead, and measuring using the heading dial on the TDC this situation will have much better results.

We have several options to increase the change in bearing. First, to double up the interval, meaning we would have to stay listening stationary for a total of 4 original time intervals. If the target started again at 70 degrees AOB at bearing 1, but we instead listen at the double duration then bearing 2 was likely recorded as 12 degrees. And subsequent the third would come around 25 degrees from the first. This would lead to a AOB-range of 46-91. That is substantially narrowed, but still pretty wide.

We could also re-use the 2nd and 3rd bearings and wait for the 4th from a stationary position. Then we can verify our first three bearings for correctness. If we additionally listen half-way through the 2nd interval we can use B1, B2.5 and B4 to get AOB based on a wider bearing change range. The latter one will have the possible AOB range narrowed down.

With the superior speed on the surface vs the convoy it would seem using the moving 4-bearing method, as described by Kuikueg and Neuro, is more effective. As one is able to move perpendicular to the bearings to either side in order to increase the bearing changes. But perhaps this only becomes necessary when the game provides more challenging convoy spawn distances. Simply moving towards the sound, with a intermediate hydrophone check is still the simplest option.