Quote:
Originally Posted by Vantskruv
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Not necessarily so. The drawing is done in correct fashion. I think your tactical choice of increasing speed along the same initial heading might have been your undoing in getting a reliable fix on it. Getting closer to the target again won't help getting an accurate fix. If you look at ABRG4 and BRG4 they are pretty much the same heading. So, even if showing a graphical intersection, it's position is meaningless. You need a clear crossing, ideally perpendicular. The resolution provided by the periscopes or even the hydrophone does not allow such 1-degree resolution. (technically the TDC dials and compass allows it to be down to a 10th of a degree, and map tools can draw angles with decimals, but accuracy errors add up if you do) If you look at the (range dependent) course lines (A1, A2) across the 2 circles (C1, C2) you used to make the predicted 4th bearing (ABRG4), the general target course could be considered to be close to 130-135. Once you established those you should have chosen to turn in that direction, surface for greater speed (if you did not already) and sprint along the generally parallel course. This would have provided a more clearer intersection of ABRG4 and BRG4, resulting in a more reliable target position and resulting from that a more accurate target speed.
This method is based on difference in drift-rates of the sound/visual bearings. As such you want your speed to initially either not contribute to the relative motion across the line of bearing (which it didn't when you moved slowly along bearing 1) or to contribute as much as possible by moving across a bearing, fast and (for increased effect and to the extent it is known) retrograde with regard to the target course. In the second phase you want to do the opposite of the first. Which to choose first is a gamble. By going slow and along the initial bearing you decided to let the target tell it's direction. Which is fine. As you get to know more, and you are unlikely to force premature detection. But as it turned out, the bearings started to drift slower (measure the differences between the bearings). If the drift of bearings slows down the AOB (at bearing 2) is larger than 90 and you are getting behind it. So once this is known it would have been prudent to restore a position more forward to the target. So to surface and run on diesels for additional overtake speed.
Then there are two choices for the new own course to take to increase that bearing rate and catch up. If the general target course is been established (as you have: 130-135) then turning parallel to that would solve the catching up part. But being somewhat behind would cause your range to decrease first ( as you near the target beam/AOB 90) and risk putting you in danger of detection since you don't know it's actual range yet. Especially in fog conditions this can get you caught with pants down. How much of a daredevil are you, or do you want to play it safe?
If you decide the latter, then turn perpendicular to the last bearing. It is clear right then what heading that is. It is not dependent on drawings or calculations. So immediately executable as first approximation. You can be sure you will not decrease range from that point, at least not on your own account. As you will be going faster and AOB was larger than 90 indicating opening target range. How far can you let it go until you loose the signal/sight? If it was faint (required high gain) to begin with the parallel course might have been more prudent. By moving perpendicular to the bearing the drift will also be as large as possible at the beginning. Whether that is enough depends on your choice of time interval. As it takes a bit of time to rise to surface, and dive again if you need to use hydrophone to locate it. Your average speed will decrease from that.