Depth finder problem with...

[Hightower]

...shallow depths. It's my day for having electrical gremlings today. Now this has been happening on and off for a little while, but a close shave with a shallow bank earlier today has prompted me to get to the bottom of this.

When using the depth finder in anything deeper than 35 feet it works fine. Go shallower than this and it stops reading the bottom and displaying depth. The transducer is sikaflexed in the hull and I've used ever manual and auto setting on the unit.

Is there anywhere else I could start looking?

[Channel Ribs]

I would check the cable for kinks or pinches.

[Hightower]

I wasn't sure of the model before, but I am now, it's a Raymarine A65 and DSM25 depth finder module which shows no faults.

[Hightower]

Originally Posted by Channel Ribs

I would check the cable for kinks or pinches.

I'm very confident that this isn't the problem as I'm very particular on cable runs etc. That said however there is a large coil of excessive cable in the console (perhaps about 15'), perhaps I'll unravel it and might pull a bit more into the hull before my next trip out.

[Leapy]

Originally Posted by Hightower

...shallow depths. It's my day for having electrical gremlings today. Now this has been happening on and off for a little while, but a close shave with a shallow bank earlier today has prompted me to get to the bottom of this.

When using the depth finder in anything deeper than 35 feet it works fine. Go shallower than this and it stops reading the bottom and displaying depth. The transducer is sikaflexed in the hull and I've used ever manual and auto setting on the unit.

Is there anywhere else I could start looking?

I'm having the same problem with my Garmin 550S, except it's critical depth is around 15ft. Below that, zilch.

The conclusion from trying a new plotter and new transducer is that the new transducer fixes nothing ... and the new plotter fixes the problem.

After checking and rechecking this several times clearly the plotter is at fault. The marine engineer I used is of the view that either the 50Hz function of the plotter is kaput, or, the plotter is not switching to or processing the 50Hz signal.

Garmin Technical agree this is a possibility and they're having the plotter back next week for investigation.

[jyasaki]

Leapy: Not working deep, or not working shallow?

The HF side should work well beyond 15 ft; my Lowrance is a HF only unit and I can read reasonably solid to 270 fsw, occasionally (when stopped) to as much as 400 fsw.

jky

[Leapy]

Originally Posted by jyasaki

Leapy: Not working deep, or not working shallow?

Not working shallow

[Hightower]

Checked all cables and are looking in good condition.

I just don't understand why when reading depths greater than 35' it works fine. I wonder if it's something to do with too much power overloading the transducer or something? I've turned gain and power down with no results. I'm probably going to reposition the transducer in the hull and see if this works better.

[two stroke mick]

Garmin 160 c fish finder.
My FF often drops out at 3-5m if I am driving at circa 18 kn plus

[Chris]

Andy if the transducer was angled wrong this could be the reason. as the water gets deeper the signal would cover a wider area and the bounceback would also give a wider signal so would hit the transducer. However as you get shallower the signal would narrow and the bounceback might be missing the transducer.

However I will say that I am guessing and this might all be complete bollix ;-)

Before you moved the transducer into the hull did you have the same problems?

Is it a dual frequency transducer. If so can you try setting it to just one frequency to test?

Chris

[neil.mccrirrick]

Originally Posted by Chris

Andy if the transducer was angled wrong this could be the reason. as the water gets deeper the signal would cover a wider area and the bounceback would also give a wider signal so would hit the transducer. However as you get shallower the signal would narrow and the bounceback might be missing the transducer.

However I will say that I am guessing and this might all be complete bollix ;-)

Before you moved the transducer into the hull did you have the same problems?

Is it a dual frequency transducer. If so can you try setting it to just one frequency to test?

Chris

No I'm with you Chris, mines a Garmin 178c, dual frequency. If the transducer isn't lined up so its horizontal I lose the depth in shallow water, if it is its all good

[Hightower]

Originally Posted by Chris

Andy if the transducer was angled wrong this could be the reason. as the water gets deeper the signal would cover a wider area and the bounceback would also give a wider signal so would hit the transducer. However as you get shallower the signal would narrow and the bounceback might be missing the transducer.

However I will say that I am guessing and this might all be complete bollix ;-)

Before you moved the transducer into the hull did you have the same problems?

Is it a dual frequency transducer. If so can you try setting it to just one frequency to test?

Chris

That's a good idea Chris.

Yes it is dual frequency and I have tried it on both frequencies. The transducer is sat on the inside of the planing pad, so I would have thought this pretty horizontal whilst underway and at rest.

From memory the transducer emits an elliptical pattern and on the transom mounted bracket this was originally mounted to, had the facility to turn up to 90 degrees so that the pattern could go front to back or side to side. Perhaps it's worth turning this to see if I can get a better result.

[jyasaki]

Originally Posted by Hightower

I just don't understand why when reading depths greater than 35' it works fine.

Most likely a timing issue. Your system probably isn't handling the signal returned with little delay (i.e. shallow water.) give it enough time to recover and it works OK. Why that would be may be due to a lot of things, and I couldn't make a guess as to which is most likely. Doubt it's a power issue, as that's the same no matter what depth (though the return signal isn't.)

Leapy: The LF side is used for deep water. might want to think about a new marine engineer.


jky

[Hightower]

So if it's a timing issue I guess I have limited options.

[Pikey Dave]

Have you checked to see if there's a firmware update for either the DSM 25 or the head unit? I have a DSM 300 which had loads of gremlins which were sorted with updates.

[Hightower]

I'll look at the firmware over the weekend.

What I have found out is the transducer I've got installed says it shouldn't be used at 50 khz and as my sounder is dual frequency 50 and 200khz and I've been using it on auto settings I might have fried my transducer a little.

what do you guys think?

[Chris]

I would get the right transducer and start there. Sounds like it is the problem.

[Hightower]

Originally Posted by Chris

I would get the right transducer and start there. Sounds like it is the problem.

Yes, that's what I'm thinking.

Out of interest, does anyone know what the effect would be by pumping in the the wrong frequency?

It's obviously working to some degree, it's pinging out sonar and as it's working in deeper water.

[Leapy]

Originally Posted by jyasaki

Leapy: The LF side is used for deep water. might want to think about a new marine engineer.

More likely is I need to remember what he and Garmin say rather than transpose their diagnosis ;-)

[jyasaki]

Originally Posted by Hightower

Yes, that's what I'm thinking.

Out of interest, does anyone know what the effect would be by pumping in the the wrong frequency?

It's obviously working to some degree, it's pinging out sonar and as it's working in deeper water.

If I remember right, the heart of a transducer is just a crystal. Converts an electric signal to mechanical, and vice versa. Wrong freq shouldn't do much to it, I'd think (but I may be wrong here), just wouldn't work as expected.

jky