4-Bearings Technique Tool

[Pisces]

@Thecoroner: You can't get a solution from 4 lines (or more) by going constant speed in a straight line. You either need to make a course change or a speed change at some point, or both.

[Captain_AJ]

There are so many methods for hydro hunting,, I have discovered a few that are less time consuming and are somewhat accurate. the trick is to train your ear for pounding water propeller sounds and learning distance by the sound. I recommend trying a few that are easy to remember and easy to plot in the map& and less time consuming, and will not expose your boat .. these are the methods I use

Bstankos

[Thecoroner]

Originally Posted by Captain_AJ

There are so many methods for hydro hunting,,

Yeah, you can quite quickly tell if the ship is going towards you or else. I guess only by playing with the gain you could get a range estimation (I can't ^^)
I bet the best can even roughly id the ship like that. (telling if it's a merchant or warship for example).

But it's really hard to pick a point in a convoy and be sure to follow exactly that one to take bearings marks.

I'll check your videos. I watched a lot by stoianm if i recall correctly like 10 years ago. I found some pdf explaining how to 4B running at constant speed (and taking turns) too. I'll try to add that in the tool some day.

Thanks for feed back :-)

[ljqcn101]

You can open up an audio recorder and watch the waveform. But that's cheating anyways.

I think there may also be a way to estimate the speed by counting propeller turn per minute and then multiply by a constant number (something like TPK in Dangerous Waters). But we got over 160 types of merchants and those sound signatures may all be different.

[Thecoroner]

Originally Posted by Pisces

@Thecoroner: You can't get a solution from 4 lines (or more) by going constant speed in a straight line. You either need to make a course change or a speed change at some point, or both.

Yeah, I know. But you can still get infos and estimations but the solution won't be unique unless you take a turn or else. As with 3 bearings at stop, you can get the course but not a unique solution.

[ljqcn101]

Originally Posted by Thecoroner

Yeah, I know. But you can still get infos and estimations but the solution won't be unique unless you take a turn or else. As with 3 bearings at stop, you can get the course but not a unique solution.

Yes, but you can get a bunch of solutions starting from 1000m to 5000m for example. (This is the range I set multiple starting point for optimisation. There could be more solutions.) Course solutions can be in a certain range though. But if bearing lines have intersections, you could get course solutions in totally different directions.

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

target bearing at t1 (deg): 90

ownship straight direction from last position = 0 (deg)
ownship straight distance from last position = 0 (meter)
*******************************
time t2 (sec): 120

ownship heading at t2: 0

target bearing at t2 (deg): 85

ownship straight direction from last position (deg): 0

ownship straight distance from last position (meter): 300

*******************************
time t3 (sec): 240

ownship heading at t3: 0

target bearing at t3 (deg): 80

ownship straight direction from last position (deg): 0

ownship straight distance from last position (meter): 300


target course: 358.88deg, speed: 6.26725knots, distance: 999.996m
target course: 358.16deg, speed: 7.67643knots, distance: 2000m
target course: 358.17deg, speed: 7.66992knots, distance: 1995.38m
target course: 357.67deg, speed: 9.08642knots, distance: 2999.99m
target course: 357.68deg, speed: 9.07374knots, distance: 2991m
target course: 357.31deg, speed: 10.4969knots, distance: 3999.99m
target course: 357.04deg, speed: 11.9077knots, distance: 4999.99m

probability of target course error within 5deg: 13.6364 %
probability of target course error within 10deg: 23.0909 %
probability of target course error within 20deg: 49.2727 %

probability of target positional error within 75m: 3.81818 %
probability of target positional error within 150m: 13.6364 %
probability of target positional error within 300m: 27.9091 %

*******************************
time t4 (sec): 360

ownship heading at t4: 0

target bearing at t4 (deg): 75

ownship straight direction from last position (deg): 0

ownship straight distance from last position (meter): 300


target course: 358.34deg, speed: 6.26019knots, distance: 1000.58m
target course: 358.37deg, speed: 6.23728knots, distance: 984.243m
target course: 358.35deg, speed: 6.25775knots, distance: 998.846m
target course: 358.36deg, speed: 6.24476knots, distance: 989.58m
target course: 358.39deg, speed: 6.21228knots, distance: 966.41m
target course: 357.3deg, speed: 7.66408knots, distance: 2001.17m
target course: 357.32deg, speed: 7.63115knots, distance: 1977.72m
target course: 357.31deg, speed: 7.64557knots, distance: 1987.99m
target course: 356.57deg, speed: 9.06974knots, distance: 3001.76m
target course: 356.59deg, speed: 9.02861knots, distance: 2972.5m
target course: 356.58deg, speed: 9.0449knots, distance: 2984.09m
target course: 356.04deg, speed: 10.4765knots, distance: 4002.35m
target course: 356.06deg, speed: 10.4307knots, distance: 3969.78m
target course: 356.05deg, speed: 10.4356knots, distance: 3973.29m
target course: 355.64deg, speed: 11.8839knots, distance: 5002.94m
target course: 355.65deg, speed: 11.83knots, distance: 4964.62m
target course: 355.63deg, speed: 11.8987knots, distance: 5013.45m

probability of target course error within 5deg: 24 %
probability of target course error within 10deg: 48 %
probability of target course error within 20deg: 81.3333 %

probability of target positional error within 75m: 4 %
probability of target positional error within 150m: 16 %
probability of target positional error within 300m: 34.6667 %