Squirrelly Depth Finder

[Kate]

I have a fairly new Hummingbird depth finder that's acting squirrelly: 5', then 105', then correct feet -- all in the blink of an eye, repeatedly. The transducer seems to be mounted properly.

Any thoughts? (And, no, BB. I do not need a new jet engine.)

[sailor55330]

I've seen this before- Does it happen after crossing through the wake of another boat or in very silty areas where the bottom might be stirred up? I've seen fine bubbles in the water or silt from the bottom cause wacky readings. Usually once you clear the area it settles down. Does any of that sound like when it's happening? Remember, the transducer basically bounces a signal off the bottom, so if there's enough surface area in the water, even bubbles, it can give a false reading. I used to get this all the time in Galveston bay after crossing behind a shrimp boat or crossing the ships channel. You would be in 40ft of water, then a cargo ship would go by and it would read 2-3 ft or less and then go right back to normal.

If it's doing it in places where you know the depth and turbidity to be a non factor, then it's either a bad transducer or cable.

[AsLan7]

.
Is it an external or internal transducer? Air may be interfering.
Back when we had a different boat with an external hummingbird transducer depth finder, a similar thing happened. I mounted it in a way which caused a slight aeration. Remounted it so it would not aerate and the problem went away.

On an internal thru the hull transducer, we had a similar issue as well. The anti freeze fluid had depleted. Fixed the issue, filled the cup and the problem went away.

Something to check anyway.

.

[Kate]

"Does it happen after . . .?"

It happens everywhere and under all conditions, which makes me think there's something hinky with the device.

"If it's doing it in places where you know the depth and turbidity to be a non factor . . ."

Yes, but now you mention it, I'll triple check that.

Thanks for the input.

[Kate]

"Is it an external or internal transducer?"

External.

"Remounted it so it would not aerate and the problem went away."

Did you remount the transducer or just change its angle? If remount, where to?

Mine's mounted about a foot to port of the outdrive. Now you've got me wondering if maybe prop wash is causing the aeration and thus the squirrelliness.

Thanks for the tips.

[AsLan7]

"Is it an external or internal transducer?"

External.

"Remounted it so it would not aerate and the problem went away."

Did you remount the transducer or just change its angle? If remount, where to?

Mine's mounted about a foot to port of the outdrive. Now you've got me wondering if maybe prop wash is causing the aeration and thus the squirrelliness.

Thanks for the tips.

.
Yes we remounted it further to the starboard side and slightly higher on the transom to avoid “turbulent “ water. That did the trick.

.

[Kate]

Thanks, A7. If I try that. I'll report back.

[Kate]

sailor: "I've seen fine bubbles in the water or silt from the bottom cause wacky readings. Usually once you clear the area it settles down."

I just noticed that the squirrelly behavior is only at low speeds in shallow depths. Once at cruise in deep waters, it's operates fine. That sounds like the point you made, above.

That's particularly annoying since those shallow areas are where the depth finder is most important. Did you have a fix?

[bruceb58]

Post a picture of your transducer mounting. We might be able to tell what is going on. Is there a strake on the hull that is directly in line with the transducer?

Ideally, you want to look at it while you are driving the boat at the offending speed but that is tough on a boat with a large swim step.

[Kate]

b: Mounting is about an inch from bottom of transom; 4" to port from odrive housing. No strake in line. Ttab plate 4" to port of transducer. Could that plate cause bubble-interference at low speeds?

Thanks for your input.

[bruceb58]

b: Mounting is about an inch from bottom of transom; 4" to port from odrive housing. No strake in line. Ttab plate 4" to port of transducer. Could that plate cause bubble-interference at low speeds?

Thanks for your input.

Does it behave differently with the tab up or down?

The entire bottom of the transducer needs to be in the water at all speeds. Do you think it is?

Does it behave this way with engine on just sitting in neutral? How about when the engine is off?

My next question is how you routed power to the head unit and how you routed the transducer cable. When I install the transducer, I make sure I run it away from other power wires.

[Kate]

B:

Don't know, will check.

Good question. I'll check.

More good questions. Will check those, too.

My mechanic installed it. Would interference from other wires cause squirrelly behavior at low depths/speeds but not at deeper waters/high speeds?

Thanks for the excellent diagnostic check list.

[bruceb58]

Would interference from other wires cause squirrelly behavior at low depths/speeds but not at deeper waters/high speeds?

Probably would have interference at all speeds.

[capn272]

My stock depth finder is going to find itself at the business end of a pair of wire cutters, probably today..

[Kate]

c: May I borrow your wire cutters? What are you replacing it with?