Why does my sonar look like this?

[Elkins45]

I recently installed a new sonar on my boat and I'm getting a 'grainy' image when running on plane. My guess is that the transducer is a little too low in the water and is causing cavitation and/or air bubbles. Or is it too high? The transducer is significantly larger than my old unit so I couldn't just reuse the mounting holes.

 

[eggs712]

That's normal interference from running. You can adjust 'gain' to minimize clutter like that; the tradeoff would be a little less sensitivity for smaller objects like scattered bait fish.

 

[Chris1956]

Could that be ignition noise?

 

[rolmops]

Having a clean picture from a transducer when running on plane speed is very hard , mostly because at that speed there is simply to much info fed into the sonar
Make sure that the sonar is on autmatic or if manual adjusted for your speed.

 

[Mc Tool]

Yep , thats not to bad for speed , wee bit messy . Transducer is best placed on the starboard side of the prop if it rotates normally and the further away the better . Fiddling with the heigh or even the angle of the transducer can help and make sure its not behind something that creates turbulence like a strake or change of hull profile . You could adjust sensitivity as others have said but personally Id trade a bit of clutter at speed for better performance whilst at slower speeds looking for fish or structure . Pretty much the only thing Im interested in at speed is the depth and maybe what the bottom actually is ...sand gravel or rocks .

 

[dingbat]

Could that be ignition noise?

There is no surface clutter and the "noise" is too consistent across the entire width and height of the screen. Sure looks like electrical interference to me.

 

[airshot]

What kind of boat hull and a couple pics of how the transducer is mounted.
It may very well take some adjusting to get a better picture on your screen. Depth and angle of the transducer can make a big difference as well as adjusting the gain and sensitivity settings. It can take awhile to get the best setup and adjustment. With today's boats running at higher speeds than they did years back, high speeds can be well over 40-45 mph where 30-35 was normal years ago. This high speed can cause interference on the transducer from air bubbles passing over the surface.

 

[Elkins45]

What kind of boat hull and a couple pics of how the transducer is mounted.
It may very well take some adjusting to get a better picture on your screen. Depth and angle of the transducer can make a big difference as well as adjusting the gain and sensitivity settings. It can take awhile to get the best setup and adjustment. With today's boats running at higher speeds than they did years back, high speeds can be well over 40-45 mph where 30-35 was normal years ago. This high speed can cause interference on the transducer from air bubbles passing over the surface.

It’s a 17 foot V hull aluminum G3. This boat tops out at 30 mph.





Looking at these photos (especially the one from directly behind) I think it needs to be raised a bit.

 

[Mc Tool]

That transducer looks a hellava lot like my Lowrance triple shot transducer and I think it needs to be lifted up until the bottom of the transducer is just below level with the bottom of the boat . Apart from that it looks pretty good to me . Lowrance refers to these transducers as a "skimmer " and thats what I had in mind when I mounted it .

please excuse spider webs

 

[airshot]

The pics help...I also think it needs raised up a bit. When I mount a transducer, I use a straight edge coming off the bottom and set the height so the bottom of the transducer is only a 1/4-3/8" below the hull....sort of skins the water as the name implies. I have found that most transducers benefit from being on a slight angle from front to back. The back end being slightly lower than the end closest to the transom. My boat tops out at 31 mph as well and after tweaking those adjustments, I can get a fairly clear picture with very little clutter. The bottom shows up very well at wot on mine and that is what I really look for at higher speeds. Hopefully my tips will get you a better picture, but remember to make tiny adjustments at a time and take notes. Good luck !

 

[mike_i]

I agree with the other guys, raise it up a bit.

 

[dingbat]

The pics help...I also think it needs raised up a bit. When I mount a transducer, I use a straight edge coming off the bottom and set the height so the bottom of the transducer is only a 1/4-3/8" below the hull....sort of skins the water as the name implies.

I agree.
The bottom of the hull should roughly line up with the center of the transducer. Still concerned with the apparent lose of signal.


Testing the transom-mount transducer installation :

1. Drive the boat at a slow speed. If the chartplotter appears to
be working properly, gradually increase speed while
observing the chartplotter.

2. If the sonar signal is suddenly lost or the bottom return is
severely degraded, note the speed at which this occurs.

3. Return the boat to the speed at which the signal was lost,
and make moderate turns in both directions while observing
the display.

4. If the signal strength improves while turning, adjust the
transducer so that it extends another 1/8 in. below the
transom of the boat.

5. Repeat steps 2–4 until the degradation is eliminated.