Holding Bottom at Speed with DFF3D

[ChrisSEA]

Hi everyone, hoping for feedback on what's realistic in terms of holding bottom at speed with the multi-beam frequency and DFF3d.

We just sea trialed a new build with a pocket mount 165T/265LH-PM mounted flush in a custom fairing block--in theory that's about as good an install as possible to minimize interference. We're losing bottom on the multi-beam/165kHz channel at about 22 knots. I have no idea if that is good, bad, or average. We didn't get to try to the L or H bands, and I know the L is likely to hold bottom much better at speed.

I searched and found sidebars on this topic, but nothing dedicated to the question of real-world conditions holding bottom.

Caveats:

• Totally understand that placement/install matters, and that a TM and pocket mount 165t are going to drive different results.
• Not asking about bottom mapping/PBG data, I believe there's a software-driven max speed for that (15 knots or mph?)
• I'm focused on understanding the speed at which people are losing depth/signal return on the multi-beam view(s), using a TZT2/3

What are folks seeing on their own builds using the 165kHz band, whether TM or pocket mount?

Thanks,

Chris

 

[FishTech]

In my testing, 22 knots was right around the high end of what I could hold. I only tested thru-hull installations. I would also like to hear from some users as to what they have been able to hold.

 

[gtstang462002]

My thru hull is good for up to around 20-21 knots with a clean bottom, once bottom growth starts on my hull it causing aeration over the transducer face and I start to lose it around 14-15 knots. My B275LHW has about the same performance.

 

[ChrisSEA]

Thanks for the replies on this.

We tested the other frequencies (50 kHz / 200 kHz) over the weekend and are losing bottom at the same 22 knots (same as the 165kHz performance). Wondering if there are any tweaks (pulse, gain, etc.) to be made that could improve performance. There may not be--we could be facing turbulence issues that can't be overcome. Attaching some pics of the custom fairing block/placement for reference.

 

[Deep Blue]

ChrisSEA,

The installation of your 165T/265LH-PM with the custom fairing block, looks great..!

Keep in mind that the DFF3D is affected by the vessel’s speed. During the slow speeds the DFF3D goes into a slower TX Rate (often referred as the “Pulse Repetition Rate”), and during the higher speeds the DFF3D then switches over to a faster TX Rate. However, when you have speeds of 20 knots or higher (23 MPH +), the DFF3D then fixes that transmission rate at the Maximum TX Rate of “20”.

The 20 knot speeds that you are mapping is typically the fastest speed that I've seen when mapping with the DFF3D.

- Deep Blue

 

[ChrisSEA]

Thanks for the response Deep Blue! The builder (Walker Custom Boats in BC) did a great job on the custom install. Does the 20 knot limitation apply to the other (non-mapping) bands of the 165T/265LH-PM? Totally understand that multi-beam is speed limited, was wondering whether the other bands are as well (by the DFF3D pulse max). In other words, if I'm cruising at 30 knots, is there a way to switch to the H/L frequency on the TZT3 to hold bottom depth at the higher speed (even if I'm not mapping/marking fish very well)?

 

[Deep Blue]

ChrisSEA,

You might give this a try: Set the TZT3's Transmit Rate to: "Manual", then ensure that the TX Rate is set to "20". Also check to see if the Transmission Power is set to "Maximum" I'd then select the sounder for use with the dual frequency screen and then see how the bottom looks between both of these screens.

The Low Frequency has a wider beam width and should show you a good presentation of the bottom. The High Frequency is generally a narrower beam width and is less susceptible to any turbulence.

- Deep Blue

 

[ChrisSEA]

Thanks Deep Blue, will try those changes. I was reading on another thread that one should use the TZT3's "internal" sounder to get better readings at speed--is there any chance that the L/H lead in our install was incorrectly wired through the DFF3d, instead of directly to the TZT3? I don't even know if that's possible, but it's the only other explanation for why all three frequencies are losing bottom at the exact same speed (that I can think of; other than structural turbulence, which seems unlikely given the install).

 

[Johnny Electron]

I noted the weld on forward leading edge has a bit of a lip that could cause some water curling. Next the boat is out it might be worth using some sealant to smooth that out as much as possible or maybe grind it down.

 

[hillman]

ChrisSEA,

The installation of your 165T/265LH-PM with the custom fairing block, looks great..!

Keep in mind that the DFF3D is affected by the vessel’s speed. During the slow speeds the DFF3D goes into a slower TX Rate (often referred as the “Pulse Repetition Rate”), and during the higher speeds the DFF3D then switches over to a faster TX Rate. However, when you have speeds of 20 knots or higher (23 MPH +), the DFF3D then fixes that transmission rate at the Maximum TX Rate of “20”.

The 20 knot speeds that you are mapping is typically the fastest speed that I've seen when mapping with the DFF3D.

- Deep Blue

DEEP BLUE
I heard that dff3d 165khz operating frequency conflicts with 265LH High—CHIRPS from 130 kHz to 210 kHz.
and you have to sacrifice heaving compensation to solve that problem?
Is that true?
Thanks in advance!

 

[hillman]

ChrisSEA,

The installation of your 165T/265LH-PM with the custom fairing block, looks great..!

Keep in mind that the DFF3D is affected by the vessel’s speed. During the slow speeds the DFF3D goes into a slower TX Rate (often referred as the “Pulse Repetition Rate”), and during the higher speeds the DFF3D then switches over to a faster TX Rate. However, when you have speeds of 20 knots or higher (23 MPH +), the DFF3D then fixes that transmission rate at the Maximum TX Rate of “20”.

The 20 knot speeds that you are mapping is typically the fastest speed that I've seen when mapping with the DFF3D.

- Deep Blue

Very useful information! Thanks a lot!
Do you know if DFF3D can accurately mark bottom fish like one or two meters off the seabed 100-200 meters deep when cruising at 8 knots?

 

[Deep Blue]

Hillman,

At that depth, you should be able to detect some fish schools that are off the bottom, but individual fish targets will probably be pretty small targets within the DFF3D's 120 degree beam width.

- Deep Blue

 

[Deep Blue]

DEEP BLUE
I heard that dff3d 165khz operating frequency conflicts with 265LH High—CHIRPS from 130 kHz to 210 kHz.
and you have to sacrifice heaving compensation to solve that problem?
Is that true?
Thanks in advance!

hillman,

You are correct that the B265LH's CHIRP High Frequency (130-210kHz) will interfere with the DFF3D's 165kHz fixed frequency. It all depends on what sounder that you are using with the B265LH Transducer.

If you can utilize this: 001-205-780-00 DFF3D Key Pulsing Kit for use with assorted sounders like the DFF1-UHD and DI-FFAMP. This kit should help stop both of the sounders stepping on one another.

- Deep Blue

 

[hillman]

Hillman,

At that depth, you should be able to detect some fish schools that are off the bottom, but individual fish targets will probably be pretty small targets within the DFF3D's 120 degree beam width.

- Deep Blue

Thanks for your reply.
Does that mean individual fish targets will be smaller on DFF3D than they appear on traditional sonar?

Hillman

 

[Deep Blue]

Hillman,

Because the DFF3D has such a wide beam width, and it's a multibeam system, its going to present smaller fish targets on the screen.

 

[Magnetron]

There's a fantastic video we did in South Florida demonstrating how to interpret fish returns with the DFF3D...

- Maggy

 

[Ktreloar87]

Hi everyone, hoping for feedback on what's realistic in terms of holding bottom at speed with the multi-beam frequency and DFF3d.

We just sea trialed a new build with a pocket mount 165T/265LH-PM mounted flush in a custom fairing block--in theory that's about as good an install as possible to minimize interference. We're losing bottom on the multi-beam/165kHz channel at about 22 knots. I have no idea if that is good, bad, or average. We didn't get to try to the L or H bands, and I know the L is likely to hold bottom much better at speed.

I searched and found sidebars on this topic, but nothing dedicated to the question of real-world conditions holding bottom.

Caveats:

• Totally understand that placement/install matters, and that a TM and pocket mount 165t are going to drive different results.
• Not asking about bottom mapping/PBG data, I believe there's a software-driven max speed for that (15 knots or mph?)
• I'm focused on understanding the speed at which people are losing depth/signal return on the multi-beam view(s), using a TZT2/3

What are folks seeing on their own builds using the 165kHz band, whether TM or pocket mount?

Thanks,

Chris

Just finished up a twin transducer fairing using a b265lh and b54. Holds bottom perfectly to 37knots on broadband and dff3D. I haven’t found what speed it stops working as my boat won’t go any quicker.

 

[Jsubzero]

Thanks for the replies on this.

We tested the other frequencies (50 kHz / 200 kHz) over the weekend and are losing bottom at the same 22 knots (same as the 165kHz performance). Wondering if there are any tweaks (pulse, gain, etc.) to be made that could improve performance. There may not be--we could be facing turbulence issues that can't be overcome. Attaching some pics of the custom fairing block/placement for reference.

I also loose bottom over 30mph on 165t-pm542lm with transducer in the keel center aft. b175h also .200khz and anything else in between when theres a chop in the water. if its flat smooth i will read bottom at 60mph