How close together have you mounted DI & SI transducers?

[Still Afloat]

Hey, I’m curious how close anyone has mounted two transducers from each other on the stern. I have a couple of Helix 7s, with both transducers mounted on the stern. One is an SI and the other is a DI transducer. Using existing holes I mounted both about 3” apart side to side with the SI about an 1.5” lower. They are both on the starboard (right) side of the stern about 24” from the centerline.

When running both transducers the SI gets a thin dark line in the image every few feet of travel. I didn’t notice any reduction in the SI sensitivity but, it’s possible. The DI works fine with both on. Also, the SI doesn’t have any lines when the DI is turned off.

I’m considering moving the SI down and closer to the center line. This would provide about 18” of side to side separation and maybe 5 to 6” of vertical seperation. This would place the SI in front of the outboard. (I don’t need imaging from this traduced at speed.). Also, this would give the SI a very clear side to side view. Maybe I’ll try it first at trolling speed with the SI transducer mounted with some double sided Gorilla tape.

If you have successfully placed a SI and DI transducers near each other I’d enjoy hearing your experience.

This isn’t anything urgent. If moving the SI near the centerline doesn’t work I’ll just move to the port side of the motor or remove it altogether. Honestly, I can live without three helix 7’s in the same boat. I was just trying to find a use for the older DI unit and I had a big hole in the dash that it filled quite nicely.

 

[FuzzyGrub]

I have never mounted two transducers on the transom, but it does sound like you are getting interferance between the SI and DI. I believe they use the same frequency range. Some of HB units can change the SI freq, so that might be a test you can do. Otherwise I think your tape and test approach is good. On the centerline, might cause some ventilation with your motor, at speed. I would try the port side.

Can your DI unit do 2D? I have used an older DI unit with the unirversal sonor in the MG trolling motor. DI and SI is more for slower speeds, so you could optimize the 2D transducer for the best high speed you could get. The DI units were generally less power than the 2D ones, though.

How about using it as a dedicated GPS graph screen? If it has a NMEA2K port, and motor does, can display more data than the standard gauge sets.

Just my thoughts.

 

[Still Afloat]

Thanks for the reply Fuzzygrub. That’s a good point on possible ventilation when mounting the transducer close to the outboard. This boat is already a bit picky about the prop slipping. When I picked up a new prop last year the prop shop had to add extra cupping. This boat has an 97’ Evenrude 115 and I think the previous owner set up the motor as high as possible since he was primarily fishing a Montana river.

I’ve considered the frequencies of the Helix 7 SI, DI and sonar. The Helix 7 DI unit was set to 2D sonar which uses a much lower frequency. I could be wrong, but I don’t think the Helix is frequency selective based on the viewing mode (DI/2D). In other words, I think it just blasts away at both DI and sonar frequencies all of the time.

Perhaps the Helix 7 can be fooled by selecting a 2D sonar transducer in set-up. Otherwise, I could approach this from hardware and use a transducer that isn’t capable of the higher SI/DI frequencies. I have an older HB tranducer that might do the trick. Need to look up the specs on it.

I’m probably over thinking this but, I want to exhaust possibilities before swapping hardware or drilling more holes in hull.

 

[Still Afloat]

Well after tweaking the frequencies a bit I got it working. However, the SI transducer was a little low and it would rub on the trailer bunk if I cranked the boat on the trailer too far. Rather than risking a broken transducer I moved the SI to the port side. Haven’t tested it since moving it but, it should work fine.

I’m using the DI head unit for 2D low/hi speed plus charting sonar maps. NEMA2000 sounds interesting but, I think it requires a network capable head unit. The DI does not have a network interface but, both SI head units are networked and they talk to the trolling motor for what that is worth.

 

[KevinWI]

So....yeah...as others have said, I wouldn't mount an si and DI transducers.
My rear helix is si/di...so it does both.
My front helix is 2d only.
They are both networkable. So I have ethernet cable going between them.
Now the front unit can display everything the rear unit transducer sees. The front unit uses the US2 transducer of the trolling motor for 2d imaging at the bow.
Originally I had a DI unit at the bow....but that was redundant..so I sold it and bought a less expensive model which can view all the same things.
With this setup, no worries about interference.

 

[Still Afloat]

It works. I just had to tweak the frequencies to avoid interference.

I’ll probably remove the the 3rd non-networked DI at some point.

 

[thill]

I mount multiple transducers on the same transom plate a few inches apart, and have for many years with no issues. Strangely, they tend to read BETTER at speed when there are multiples.

If the units are using the same frequency, they will interfere with each other. I will sometimes use the Garmin, not like what I see and switch to the Lowrance. But since switching to the new Garmin, I rarely turn the Lowrance on unless in deep saltwater. Lowrance is king in the salt, at least the older units I have been running.

 

[Still Afloat]

It was working good for me as well. I’ll be switching boats soon and the non Ethernet Helix 7 will sell with the old boat. I‘ll probably stick with one HB transducer at the transom and maybe one on the bow mount MK.

The boat comes with a Lowrance HDS9. Will see how well it works before deciding what to do with it. Not that I’m in love with my Humminbirds but, I have MK trolling motor. Kinda like cordless power tools, once you get a few batteries it’s more difficult to go to a different brand.

I’m looking forward to trying a different FF.