Topic: SI/DI Interferance?

[DECIM8]

Hi Guys,

Im interested if anyone can help with this issue, We've got readings like this when under power over 4knots. Can anyone help? The sounder is wired too the boat and I will test without it next week however I doubt this is the issue as I've previously run off a battery with similar/same effect.

I am assuming this is vibration or water from the chine? Best I ask as I could not find much this severe online.


Any help is greatly appreciated. Running under this speed is normally fine, boat is not on the plane.



This is a photo from mild feedback to full blown feedback at high speed.

[sonar2000]

First thougfht is the transducer could be bouncing. Or some other cavitation issue. Is the transducer staying in the water with out aeration or bubbling around it..

Chuck

[DECIM8]

Thanks for the reply, I appreciate it.

Firstly it is Definitely in the water all the time. I would assume that is it moving so I installed a secondary mount alot stronger to prevent the readings however it seems I had the same result. I highly doubt this is movable as its solid aluminum mount. I did note it is inline with a chine and could be the reason I am seeing such readings. As the boat runs duel sounders at the same location (my sounder my friends boat) I had to fabricate this mount. I will attempt to remove this mount and install a single sounder (both are mine however I donated one to him)

For reference at speed what would the readings look like at say 20knots?

[sonar2000]

Let us know the new installation.  It does seem cavitation or aeration.  SI transducers do not as a general rule do not work well above a fast troll. Issues similar to yours.. Also loss of bottom depth...Higher speed can contribute to bubbling/cavitation/aeration issues
Chuck

[DECIM8]

Well.. I dont have the exact problem any more however now have a more intense problem and the transducer is under the water at all speeds. I do think I need to rotate it down a tad more however, looks like crap still.

I believe due to the black lines this may be due to the electrical feedback now?

[DECIM8]

Anyone had this problem as yet? Ive had two transducers two new cables and even now run a direct line to battery. No difference. Can anyone assist? Vibration I assume?

[Rickard]

Hi,
 
I got similar interference above about 4 knots. It's the brand new Suzuki 6hp outboard that causes this. I almost never scan at higher speed than that so this is not a major issue. I'm not sure if it comes from cavitation or from the ignition system.
 
Rickard

[Humminbird_Greg]

Check and see if this is motor interference by taking your motor out of gear and revving the motor to the same RPM level that you are seeing this at.  If that does not show the interference than it is most likely some sort of air bubbles getting under the transducer at the faster boat speeds.  Do you have a Screen Snapshot of this?  I don’t use HummViewer and would like to see it in a form that I am more familiar with.

[DECIM8]

I appreciate the reply guys. I will attempt to find a photo but it looks identical to the screen shot on hum viewer.

I've found some rubber to insulate the hull from the transducer to attempt to muffle some of the vibration. Ill try that and report back. It can't be air bubbles as regardless of its position it happens.

Disappointing but we've learnt to live with it.

Speak soon
Nat

[Rickard]

I'm not sure this helps Nat, but there are observations of interference from cavitation, or at least from something propeller related. I have seen many times that there appears short moments of interference from passing motor boats. The image is affected over the whole range from zero to the max range setting. This happens even when the passing boat is farther away than the range setting. My own new outboard seems to make something similar at 4 knots. I have ruled out the ignition system by running the engine with gear in neutral. The transducer is pole mounted to the side of the boat well below the hull and, as I think, below the sector where air might pass. If the transducer is moved farther away from the propeller the interference vanish. It would not be strange at all if the propeller can make noise at all frequencies, also at the very high frequencies used in a sonar system. Perhaps some hopeless cases of interference can be explained by propeller noise interference?
Rickard

[Humminbird_Greg]

Definitely a possibility Rickard, especially if the propeller is dinged and dented as it will make more acoustical noise.