Depth sensor works.... most of the time!

[YorkshireLad]

I have original B&G depth sensor and display unit on my 1994 H40.5, which I have owned for one year. I sail out of Havre de Grace, MD, which is at the very northern end of the Chesapeake Bay. Water depth in my usual cruising grounds rarely exceeds 20 feet, and my depth display is 100% reliable.

BUT..... when I sail further south down the Bay, I have experienced intermittent problems with the depth display. It happened last month when I sailed south to Solomons. Encountered water up to a depth of 100 feet. Depth display worked most, but not all, of the time in shallower waters (20 feet and below), but often the display failed to show a depth when in waters 40 feet and above. Not always though.... I did see depths on the display of 80 plus feet. The display will show the depth correctly for a period of time (a few minutes to a couple of hours), then it will fail and in place of the numbers are a series of dashes. The depth reading will come back on again and read correctly for some minutes, then go off again. When returning to shallower waters to anchor the depth reading usually returns, but not always.

Any thoughts why the intermittent fault? Is the sensor having problems with deeper water? But then why does it work intermittently when I return to shallower water? Water salinity is the only other factor that I can think of that might be playing a part here…. Fresh or slightly brackish water in the northern bay, but more salty further south. Does not make any sense that the salinity could be linked to the problem, but I’m clutching at straws to come up with why the intermittent problem.

 

[Don12364]

Not Necessarily a Fault

The dashes on the display normally indicate "Lost Bottom". This means the sounder is not seeing echoes reflecting from the bottom.
It could also indicate the unit is not functioning but there are many reasons why you might see this even though the sounder is operating properly.
The strength of the echo depends on how good the sea bed will reflect the echo sounder pulses. These are ultrasonic and reflect best from hard rocky and hard sandy bottoms - but hardly at all from soft mud.
Again the deeper the water the weaker the echo.

Having said all that your sounder losing the bottom in less than 100 feet of water appears to indicate that it is not operating correctly.
You don't say which B & G model you have so I can only offer generalisations.

A number of possibilities:-


* Does it have a range switch and is this on the correct range?
* Is there a "Gain" control and is this on Max?
* Is the transducer inside the hull? This invariably reduces the sensitivity as the pulse needs to pass out through the hull and the echo back in again.
* If it is inside the hull is it still securely bonded to the hull?
* If it sits in oil inside the hull, is there any oil left in the pot.
* If the transducer is a through hull type then is it covered in many years worth of antifouling paint. Transducers don't like this and the manual warns not to paint them.
* OK, if it is not painted, then is it heavily fouled as this also reduces sensitivity.
* Is the cable between display and transducer in good condition?
* Try pulling the transducer plug out of the display and reinserting it to combat possible corrosion within the connection.

Sorry to answer your question with a battery of others but if you could check these points and come back we may be able to offer some assistance.

 

[Rick D]

Well, my experience with my ST60+ Raymarine depth hooked to my ST50 Autohelm depth transducer was similar. Of course, the first thing to do is to see that the sender to instrument head connections are clean as is the power. However, in my case, when it was first hooked uo, I would get 400 + feet in depth. Then it would lose it's reading earlier. Then it would just cycle after 40' Then I would get dashes (no signal). Then (now) it is all dashes. I took another transducer and hung it over the side to test it, and it read fine. So, it's the transducer or wiring in between. Regardless, I'm replacing the transducer next haul. I'm only posting because of the similarity in readings as you described even tho I have a different unit.

 

[Bob Poff]

Has it ever worked correctly in deeper water? Or is this a change?

It almost seems like it's running out of signal, with maybe more path loss in the deeper water. Possibly the transducer isn't making enough noise, or isn't sensitive enough.

Could it be that the transducer was thinly painted over?

 

[Pilotcarpenter]

I have a 376 in the upper Chesapeake also, with an ST60, with similar problems. Difference is, mine reads ok in deeper water, goes to 50 or 70 or 90 feet when known depth is under 10'. Even works OK in the ocean. So far, none of the suggestions offered earlier have worked, and the erratic reading is intermittent. Interested in what you find.

 

[Don12364]

Pilotcarpenter - My 376 Replacement Job

My ST50 started doing as yours a couple of years ago. Eventually I had to do something about it because it was reading wrong when I was in very shallow water. This is the time when the sounder is most important.
I took the ST50 instrument back to Raymarine and paid for it to be tested. It tested OK so I had to buy a new transducer (ST60 type).
The point of this note is that Hunters installed my sounder from new and sealed it into the hull with 5200. The nut came off inside quite easily but I was unable to budge the transducer. We could press it down a little and I went outside and put two screwdrivers under the flange, one each side, and levered as hard as I could. The transducer would move down about 3/8" but this would not break the seal and it then sprang back to its original position. We wasted an hour trying to get it out without damage, just in case it could be saved.

I then went home and got a small pair of Stillsons and a Footprint pipe wrench. Fortunately these would fit inside the sounder bay and would grip the thread inside the hull. Then I had to unscrew the transducer.
The original sealant was so elastic that it was necessary to force the transducer round more than 30° before the rubber let go. This ruined the brass/bronze thread so there was no going back.
My boat was on the hard and I was working between tides and did not want to have a 2" diameter hole in the bottom when the water came back!

Eventually I 'unscrewed' it completely out of the rubber sealant. I then discovered that the new transducer was a little shorter than the original and the wooden packing piece inside the hull was too thick to allow the nut to go back on. However the hull at that point was 1½" thick so it wasn't necessary anyway. I used a polysulphide sealant NOT Dow 5200 for the replacement.

Another tip. To the starboard side of the transducer and under the cabin sole there is a conduit which you cannot see. It carries the transducer cable back aft alongside the engine and has an access point in the aft cabin, starboard side under the bunk base. Then it continues back aft and, if you remove the vertical plywood panel in the center and at the aft end of the bed, you will find the outlet of this conduit. From there the cable goes upwards and makes its appearance in the inboard forward corner of the port side aft locker - the curved one you sit on and not the one on the swim platform. From here it enters a piece of slit flexible black plastic trunking which feeds forwards under the removable panel which covers the steering quadrant. From there up into the steering console and to the sounder instrument itself.

I recommend using the old cable to pull through a messenger line and then using this to pull the new cable through. There is no need to remove the plug from the new cable.
BTW:- It is easy to prove the new transducer before tearing the old one out. Just connect it to the back of the instrument and dangle it over the side to get a reading. It is completely waterproof.

 

[Pilotcarpenter]

Re: Pilotcarpenter - My 376 Replacement Job

Thank you very much for the tips. I am sure I will have to go through the same thing.