Depth Finder Problems

Having problems with my Humminbird 565.
It's a long story, but bear with me.

I've had my depth finder mounted on my Hobie Quest since 2007.
Every few years I need to remount the transducer (through the hull) I have it mounted with silocone. It's always worked fine this way.

This year I accidentally left the head in a place where it got submerged in water for a few days. (I know I know!) anyway, I got the head out of the water and dried it out with a hair drier. It worked fine for a couple days, but then it wouldn't read the bottom. would show 1.2' no matter what depth I was at.

Remounted the transducer and then it worked fine, but then "Low input Voltage" message started to appear as soon as it was turned on.

Eventually got a new battery and this message went away.

Then it started working great up to 25', but then any deeper and it reads 1.2'.
Removed transducer and tried directly over the side and all works properly.

Remounted trans and I'm back to 1.2' after 25'

Not sure if my mounting is flawed or the head is damaged after being submerged.

Any thoughts or ideas?

On my now dead Eagle I found a couple of failure modes that created the same issues you're seeing. 
- The most profound and easiest to remedy was corrosion of the wires at my power connection.  Checking the cables with a multi-meter I found a significant voltage drop between the battery and the connector for the head unit.  Trimming the cables back to get rid of the corrosion did the trick and gave me full depth capability.
- The second issue I found was corrosion of traces and presumeably dendritic growth between terminations on the sonar PC board itself.  My unit had gotten flooded by sea water and the salt immediately set to work.  The GPS portion was isolated and sealed so it had no effect there.  A little clean up with IPA and an acid brush helped a bit but the unit never operated the same after the salt intrusion.

-Spot-

Since it works over the side in water, but not mounted in the yak, I would suspect the mounting or the connector which presumably is disconnected and connected during the switch over.  Humminbird once told me their units could withstand 30 minutes of total submersion.

When you say mounted in silicone, do you mean you glue it down to the inside of the kayak?  Any bubbles underneath?  I see you only have a couple posts, so I have to ask if you have checked out the transducer mounting sticky thread in Drillin' & Cuttin'?

I know this is puzzling me, figured since it worked over the side I would just have to remount the transducer. Yes I've glued it to the hul the same way I've always done it. (and this way always worked before) I don't put the foam block down first with the cutout for the trans. I didn't see the need for it nor could I find any.

As far as bubbles, I think its one of those things you can never be sure of, but I hold the trans down with a block of wood wedged between the trans and the cockpit, so there shouldn't be bubbles in between.

I'm at a loss and can't get past the evidence - works in the water not in the yak.  You could try some electronic contact cleaner on the connector.  Spray both sides wet, then connect/disconnect a dozen times.  Might just be some oxidation on the gold plated contacts. 

If you know any IT folks or live close to an electronics store, many electronics, particularly networking gear, is shipping in closed foam cutout blocks.

Just as a point of information.  If your silicone seal produces a vinegar smell, then it is acetoxy caulk which is VERY common.  The prepolymer chains in the caulk are capped with acetate. When exposed to moisture in the air, the acetate groups hydrolyse to give acetic acid (vinegar) and the short chain prepolymers link up to give longer polymers curing/hardening the caulk.  Acetoxy caulk gives off acetic acid for over a week.

Acetic acid is corrosive to metals so if your transducer has a temperature button you might check it next time to see if it has corroded any.  It is stainless steel and should be fairly resistant. 

I never thought about the "Silicone" that I used to attch to the hull.
This is a different brand than I've used in the past.

I thought I made sure it said "100% Silicone", but maybe it isn't.
I'll take a look at the tube when I get home.

I mounted the trans twice with ths stuff and both times had this happen.

Good observation! I never even considered that might be the problem!
I'll try cleaning the connections (again)

I'll let you know what happens. (might be a few days if I remount with a different brand of adhesive.

Note, I've seen battery connection (corroded wires) issues cause similar problems.  My theory is that the transmitting causes transient IR drops (V=IR) causing the receiver to lose sensitivity, which can also mean lose bottom lock.  With the 'ducer mounted in the water, you don't have the same signal lose as through hull and the difference alone may explain the behavior.

When mounted inside, it is finicky at both 83 and 200 kHz?  Does increasing the gain/sensitity change the performance?

-Allen

Latest Update (not fixed)
Looked at the tube of adhesive I used, It's 100% silicone by Liquid Nails.

Sprayed the connections with CRC contact cleaner and connected and disconnected
the head many times, went out on the water to test: same result, works fine up to 25' then went to 1.2'

Took the trans out to see if there were bubbles, I was very surprised to see this...

Must have slid it around enough to wipe the silicone completely off the corner.
Cleaned off all the silicone and tried it holding it over the side, worked great up to 79',
(that's as deep of water I had right now) event turned it to the side to break contact with
the bottom and then pointed down again. It reconnected with the bottom again.

Felt very hopeful, so I tried mounting the trans with duct seal (I'd recently read a lot of
positive reports about mounting the trans with duct seal)
Went back out on the water, worked great to 25' and then went to 1.2'.

Without touching the trans or anything, it will reconnect with the bottom when I get back to 17'

I'm tempted to by a humminbird 561 (looks like same electrical connections as my 565)
and plug the new head into my existing setup and see if it works or if I have the same Issues.

When you say you used duct seal, what was between the transduce and the bottom of the kayak?  Did you use a water bath?

-Allen

Now that you have the Duct Seal ...

Create a ring of Duct Seal and stick it to the bottom of the kayak forming a reservoir.  Put the transducer in it, then fill with fresh water, and test function.

I'll give the wet well a try.
Itried mounting it with tthe duct seal between the trans and hull.

Finally had time to get back to the depth finder problem.
I did have the trans mounted dry with duct seal.
Pushed the trans down onto a duct seal pancake and then added
Some duct seal around the sides of the trans.

Result of reading well to 25' . Any deeper and it reads 1.2'.

Tried making a well with duct seal and putting water in it.
Same result.
Now when I hold trans over the side it won't find the bottom until
I get into water around 25-30', but then will read the bottom up to
80' (that's as deep as I went)

I'm guessing there's some corrosion on the PC board that taking
Away Fremont the trans voltage.

My next step (unless I hear of a better idea) is to spray the PC
Board with contact cleaner and scrub with a soft tooth brush.
Don't think I can make it any worse at this point!

I would be surprised if the circuit board is not coated with polyurethane or humiseal or something like it to give it some protection from the elements.....I know my old Humminbird LCR 400 had this coating....so trying to scrub it is a moot point.
Having said that, I think the issue is in the connector/wiring or the transducer has gone bad.
Have you called Humminbird technical to see what they think based on your extensive trouble shooting?

Before you start taking drastic measures, know anyone with a Humminbird that you can try you can switch head units with to try to isolate the problem the the transducer or the head unit?

-Allen