DFF3D Questions

[SeanNC]

Thanks C-Bass, instillation location should be all good, followed the procedure, low in the boat, near centre of gravity, not near and metals or electronics.

I think you solved by issue, i wasn't comparing it to the COG of the TZT2, just the magnetic compass. I got on the water today and the heading matched the COG to within a degree or 2 at all times. As long as they align then my marks to the port and starboard from the DFF3D should be pretty accurate right? The error could be with the Richie compass, as it still doesn't match the electronics too well.

On a side note i have a few questions on the DFF3d, i have attached a photo of the multibeam sonar from TM54 and inbuilt TZT2 sonar with TM260. The issue is the depth at which the display starts, the TZT2 sonar starts at 0.2m which is the tm260 draft setting, the multibeam sonar starts at 0.7m approx, even with the transducer draft set at 0m. Applying the transducer draft will only be added to this 0.7m, so adding 0.2m will result in the reading starting at 0.9m. I've been through all the settings that i think could be causing the issue, but no luck. No idea where the 0.7 comes from, any ideas?

Another query was regarding reading the bottom at cruising speed, i had the boat at about 21 knots, the TM260 at 200khz was reading bottom unbroken at a depth of 4-6m. The multibeam however was breaking up at anything over 15 knots. The transducers are at the same depth and different sides of the boat about 0.3m from the keel. Just wondering if there are any reasons on why this is? I was running the beam width and angle on maximum values. Not sure if this has anything to do with it?

Other points to note:
- I noticed that the performance seemed to improve a bit in deeper water (7 to 8m), but was still broken.
- I did some sharp turns and the readings cleaned up and were unbroken, i'm not sure if this is to do with the transducer position in the turn, or just that the loss of speed improves the reading.
- The B54 is attached to an existing plate on the starboard side, but will need to be moved further starboard, as the motor blocks the outermost edge of the swath and is causing minimal noise. Just need another plate welded to make the adjustment.

Thanks for the help!

 

[C-Bass]

Good morning SeanNC,

Yes, believe you are going to be just fine with the PG700 compass. I have been doing this many years now and have yet to see a standard magnetic compass that gets much better than a 10 degree delineation of heading unless it can be calibrated by a professional compass calibrator. You usually find on larger vessels the compass has been professionally calibrated so they match up pretty well with the electronics compasses or ships gyro. A 2 degree difference for the PG700 when compared to COG at a speed where crabbing, current, and wind is minimal is about where you want the PG700. You could probably spend a bit more time putting in manual offsets to the PG700 to bring it in a little closer but you get to a point of diminishing returns.

Regarding the DFF3D, I went ahead and moved the post because we have been able to diagnose your compass issues.

Regarding the draft settings of the two transducers for the system. So a couple of questions. So in the standard Sounder menu you added a .2m draft for that transducer is that correct?

Regarding the draft settings for the DFF3D, you indicated that you did not choose a draft settings for this transducer. Can you confirm that the draft setting for the DFF3D is at 0, the draft setting for the DFF3D can be found in the Menu, Settings, Multi-beam Sonar, Initial Setup, External Transducer Draft?

Can you confirm the following settings:
Menu: Settings: Initial Setup: Depth Display: What is this set to? Under Sea Level or Under Keel

Menu: Settings: Initial Setup: External Transducer Draft: What is this set to?

Menu: Settings: Initial Setup: Keel Draft: What is this set to?

Kind Regards,
C-Bass

 

[C-Bass]

Good morning SeanNC,

Regarding the transducer and reading bottom at speeds. You mentioned that the TM260 holds a good bottom at 200 kHz at 21 knots, what does the 50 kHz look like is it still holding a good bottom?

Typically when a fishfinder is not holding a good bottom it is due to turbulence especially at cruising speeds. The transducers are positioned on the stern, so any bubbles created by the vessel will move to the stern and eventually find their way under your transducers. I attached a photo of a small vessel cruising at speed. Notice the boundary layer on this boat and the amount of bubbles formed from the lifting strakes.




This is likely what is happening for you, the 200kHz frequency is not as affected by turbulence as lower frequencies. This is why I want you to see what the 50kHz looks like at speed?

Also it is good to know that having the transducers on different sides of the vessel is not a true apples to apples comparison due to prop wash and the spin of the prop, what way does your prop spin: Clockwise or Counter Clockwise. This is will affect one side of the vessel more so than the other.

You made a really good observation about how the sounder cleans up during a turn, that is not uncommon because the boundary layer will shift with different vessel movement. When you make the turn it is likely that a layer of turbulence is no longer affecting the sounder on that side of the vessel while the maneuver is being made.

 

[SeanNC]

Thanks mate.

Yep, was aware of the multi-beam transducer draft, just set it to 0 whilst trying to work the issue out, it's now set to 0.2m (tm54)

Depth Display = Under sea level
External Transducer Draft = 0.2m (tm260)
Keel Draft = 0.4m

Altering any of these doesn't remove the issue, like it's seeing 0.7m as 0m, and the transducer drafts get added onto that.

For the other issue, 50 khz always breaks up well before 200, which is to be expected from all reports. I thought the lower frequencies may have been the reason for the 165khz breaking up. Was hoping that being closer to 200 than 50, i might have got a bit more speed out of it. As i mentioned, the transducer will be moved wider anyhow, due to the motor blocking the edge of the swath. It's a single outboard with clockwise prop, so being on the port side i expected to see a bit of interference. Moving the tm54 will get it well outside the prop swing radius, so this should improve things a bit.

Not that i sound on cruising speed or anything, was just curious if there was anything in the settings to tweak that would improve performance at speed. No point discussing the issue further until the transducer is moved.

I appreciate the response,
Sean

 

[SeanNC]

Hi, just checking if there is any update on what my issue may be? I still haven't been able to find the issue.

Sean

 

[C-Bass]

Good morning SeanNC,

Ok, so we have not been able to recreate what you are seeing on our test bench.

If you could please provide a photo with no draft offsets for the internal sounder (B260) and no draft offset for the DFF3D. Please zero out the keel draft as well and post a photo of the internal sounder and DFF3D multi sounder, like the photo you posted originally but with no keel offsets or draft offsets for both sounders.

The top of the screen shows the main bang of the sounder, so the fill at the top of the screen may be different because of the transmit pulse length of the each sounder. The main bang of the sounder shows on the screen, it can be defined by when the sounder transmits it cannot receive. So it does appear the main bang for the DFF3D is a little longer than that of the internal sounder for the TZT2. I am not as concerned with the main bang difference of each sounder because there is not much we can do about that. But we should be able to get the depth number on the bottom of the sounder displays to match up.

Question, the TM54 is mounted on the transom where the B260 is mounted on the hull. Is there a difference in the draft of those two transducers in the water? Or are they on a parallel plane when looking from the water line?

Is there a difference in the depth number?

you may have to only add a draft offset for 1 sounder.

 

[Nick]

Hi,

Just a simple question about Tztouch2 15f anf dff3d.
Is it possible to remove colors on triple beam and cross section views? I can't find color rejection in menus, so probably isn't possible?

Thanks

 

[Snips]

Nick,
Neither of our multi-beam sounders (DFF3D or WASSP) have a delete color option. By using the Clutter Control setting you can increase the threshold of where the blue colors start to appear.

Snips

 

[Nick]

Thank You!