The new DW tma

[Angle]

I have a question about the new TMA errors when turning ownship. What causes that and why doesn't the narrowband display show a bearing error when there is an obvious one on the TMA?

[Hobnail]

I thought that this only effected TA bearing lines when the course of the ship is displaced from the "course" of the TA in a turn. As the sensors of the TA occupy a portion of the wire it "bends" during turns causing the contact bearing to be corrupted.

Also the ownship course differs greatly from that of the sensor in a turn until the array follows the sub through the turn. Not sure if the TA knows it's own bearing in relation to the ship or whether it adopts the ship's, introducing error to the reading.

All of this is my own ramblings, hopefully someone with a clue can correct me where I went wrong.

[OKO]

you both right, let me complete this a bit more, with usable settings for best the TMA process in DW=>

during the record of LOBs, you must not :
- change depth of OS
- change course of OS
- change speed of OS

because all LOBS recorded during this manoeuvers are corrupted.

and

- must be above 6 knts (so, 7 knts or more)
=> because if you go slower than 7 knts, you TA will fall in deeper waters

- need to wait at least 7 not corrupted LOBS before starting the TMA work with only one array, or 3 LOBs with 2 arrays merged.


Of course, sometimes, its VERY valuable to have 2 recorded pattern (legs) to make accurate TMA (with one array).
especially for contact with perpendicular course with you.
this mean sometimes, you better record 3 or 4 legs, then change course, and record 3 or 4 other LOBS, but without using the LOB(s) corrupted during your course change on you TMA.

the more complicated thing is to define which is corrupted LOB, and which is not corrupted.
it's the job of the TMA operator to know that : it' easy to see which one are corrupted on a waterfall (you see a big S at the time the LOB is recorded), but you can't see them on sonar with circular display, so you have to remember (using "show history" on NAV screen could help you ... except for dive change).

Last thing, specific to conformal/hull arrays, is the beam wander effect :
the more the contact is close to the edge of the hull sonar, the more the beam is wandering and lost accuracy.
Only some percent, but some percent mean it become VERY difficult to find out a range for the contact.
So, when using hull (on nuke, it's quite unusual to make a TMA with hull sonar except on very shallow waters) or conformal (with KILO, the more usefull sonar of this platform), you better put your target on your 9/3 o'clock to make the most accurate TMA possible and to avoid the beam wander effect.

[Angle]

Yes. Too bad on the subs we can't remove the corrupted LOBs They clutter up the display pretty bad.

[Fandango]

Originally Posted by OKO

you both right, let me complete this a bit more, with usable settings for best the TMA process in DW=>

during the record of LOBs, you must not :
- change depth of OS
- change course of OS
- change speed of OS

because all LOBS recorded during this manoeuvers are corrupted.

OKO, does that come from testing in DW?...

[Fish]

When making a 90 degree turn, you could wind up your TA, and extend when on new course. It works faster then waiting for the TA is stretched again.

[HydroShok]

if you are doing the tma manually then there is a trick to working around the bad bearings. Long story short, just use the sphere for accurate bearings, and ignore the purple TA lines in TMA.

The sphere is always good, so you can look at the "dots" and see if the TA is off it will look something like this

o.o
o..o
o...o
o....o
o.....o
o......o

you can get the sphere dots perfect, but not the TA(after a turn).



sometimes a quick turn only puts out one or two bad bearing, that looks like this

oo
oo
o.o
o..o
oo
oo



another trick I use alot, is only deploy the TA just enough not full length. To the letter "S" over the word "scope", is all you need and this will work great in shallow waters without dragging so long as you go faster than 3 knots. Because the ta is shorter, it has less bad bearings, it straightens out quicker.

[Kazuaki Shimazaki II]

How far do you have to extend that array to get full (or at least close enough to it the difference is insignificant) sensitivity?

[Fandango]

Originally Posted by Kazuaki Shimazaki II

How far do you have to extend that array to get full (or at least close enough to it the difference is insignificant) sensitivity?

A bit left of the left edge of the TOWED ARRAY label