Transducer interference

[MyEscape]

Hello,

Not sure if this is a similar problem to some other recent posts however my sounder (Lowrance X47) gives a clear picture at slow speeds, however as soon as I a moving at say, more than 8 knots I have interference on the display. Can still read the depth, however screen is not clear.

I thought the transducer was not deep enough in the water, however I've moved this as low as it can go, with the transducer clearly lower than the hull.

After inspecting th hull (a Seajay 4.15PRO) there is a ridge of weld on the hull where it joins the transom.

Do you think this might be the problem? Causing rough water at speed under the transducer.

Steve

[blaze]

I would think any small weld/ scar is going to cause turbulence/air bubbles and cause interference, faster you go the worse it will be.
Can this weld be ground off or at the very least smoothed out and any edges removed. Maybe some of that alloy putty/ liquid steel or the likes can be applied and sanded/filed to a smooth surface.
cheers
blaze

[MulletMan]

Think Blaze (again) is on the mark.
The "V" part of the transducer should be the only bit facing into the water.
If any of the bracket attachment is below the keel skin, you will get interference.
A lot of guys tear their hair out with this problem and my boat looks like a sieve from punching holes in it to get the transducer right.
You can also but a sliding type SS bracket that can be easily adapted to hold the transducer and then you can fiddle about with the various heights till you get it right.
Also make sure the angle of the bottom of the transducer is exactly in line with the under keel of the boat.
If it is not secured tightly, the water flow at speed can push it up and then the angle to the bottom will be much more shallow and you will lose the picture. There are normally two SS screw bolting the transducer into its holding bracket and if they work lose, you will have problems maintaining the correct angle relative to the boats keel.

And I guess you have it perfectly horizontal to the water flow? On a strake or rib is usually the best but if it is on the sloping part of the transom bottom, then the transducer will of course not be exactly aligned and also cause a problem.

Think I have confused myself now! #[smiley=hammer.gif]

[fishn-ads]

A couple of questions how far from the engine is it mounted? What depth does the transducer sit below water line? Does the sounder have a Chart speed control &/or fresh/salt water selector? What is the power output (i think you'll find it only 100 watts RMS single chanel 200 Khz)?

You may find that the sounder could be working to the best of it's ability being a budget sounder, i've had a couple of cheaper sounders and while they don't give a good picture of the bottom at speed, they will still let you know when your about to beach.

I got a Humminbird Matrix 27 on the new rig $800 for dual chanel sounder 500watts RMS and GPS, she keeps a good picture at 25 knots on 200Khz.

As the old saying goes more power!

Ads
Ads

[Angla]

Can you adjust the gain on the fishfinder while you are under way?

I tend to use a Gain of 17 or 18 while stationary. But during travel, I just change it to 14. Try adjustin it by 1 initially to see each change it makes to the scene.

Angla

[MyEscape]

OK, thanks for the valued advice so far. Obviously from the replies I have I'm talking to the right people with lots of knowledge on the subject.

So, I'll post a couple of photos today to give you more of an idea.

Thanks for your time.

Steve

[outsiderskip]

seajay
i run a independent battery and i installed a inline filter which i bought from bias boating for 14.95
Make sure your tranducer is not on a plainning stroke also u can adjust the angle of tranducer

cheers pete

[outsiderskip]

seajay
i run a independent battery and i installed a inline filter which i bought from bias boating for 14.95
Make sure your tranducer is not on a plainning stroke also u can adjust the angle of tranducer

cheers pete

[MyEscape]

OK here we go with a photo from the rear of the sounder to show the depth below the hull

Steve

[MyEscape]

And another from below, showing the weld ridge, which I though might have caused some turbulance around the transducer.

Steve

P.S
Got the hang of posting photos too on the first go!

[blaze]

Hi
I would get some aliminum putty and smooth that weld out for a start, may not be your problem but it would be a good thing to eliminate for a start. I think that would be creating some turbulence/airation.
cheers
blaze

[MyEscape]

Thanks Blaze,

I think I'll try your idea with the putty and perhaps fill to the weld if you know what I mean, rather than attack it just yet with a grinder.

Would prefer to tread carefully and try something each time I go out (usually just the creeks or river so it's not much of a problem), rather than rush it like a bull at a gate and have to call in an aluminium welder to patch a hole.

Hope the photos made sence to you.

Steve

[blaze]

photos make perfect sense, trying one thing at a time is the way to go. There are a lot of products that will do what you require.
Devcon make an alloy putty (quite expensive)
Maybe just a bit of auto body putty primed would do as a temp to test a theory
cheers
blaze
ps
you may well need to go from the weld foward for about 50mm to form a smooth flow of water.