Old Stowe Navsounder Playing Up.

[DJE]

It has worked perfectly for the 10 years that I've had the boat and is now about 20 years old. But since launching this season it won't read depths greater than 10m to 15m. Sometimes it won't work at shallower depths over very soft mud. The display flashes the last reading obtained which the book says is indicating a loss of signal. (It always used to do this when we passed through the wake of a ferry or our own prop wash when going astern.)

I've checked all the wiring and the voltage at the back of the display head and this all seems fine. Next step is the dry the boat out, inspect the transducer and maybe sand off a bit of antifouling but it all looked normal before launching.

Has it just reached the end of its useful life or is there anything else I can check? We're leaving for a long cruise in about four weeks so hauling out to replace the sounder is going to be a bit of a panic.

 

[Searush]

Where are you going? How important is the sounder? Vital in the Fresians or Channel Islands perhaps, but less essential in Cornwall, W Scotland or Norway.

Just a thought, because we tend to assume that it isn't possible to sail without our "essential safety & nav aids" that didn't exist 60 years ago.

 

[theoldsalt]

You say "....sand off a bit of antifouling..."

Surelly you don't antifoul over the trasnsducer...Do you ?

 

[DJE]

We've always antifouled over the transducer and never had problems before. But I was away this winter and SWMBO did it so possibly slightly different thickness this year or uneven edges causing turbulence.

The cruise is to Brittany and the Morbihan probably returning via Channel Islands so I wouldn't like to be without the sounder, although it is working at the depths where we really need it. But the failure to read depths of 2m to 3m over soft Portsmouth mud yesterday was rather worrying.

 

[theoldsalt]

You might get away with one coat or perhaps two thin coats but if there is a build up over several years you may have got to the thickness that affects correct performance.

I would suggest removing the antifouling before embarking on any potentially expensive repairs/replacements

 

[DJE]

Thanks for pointing that out. It's almost word for word what the Stowe owners manual says.
We're putting her on the scrubbing pad tonight to scrape off the antifoul.

 

[Ruffles]

I would look for a loose connection behind the instrument panel. I think though they will measure open circuit when you use a multimeter on ohms setting.

I can't see a layer of anti foul having much affect. I had 20 years accumulation on mine and didn't notice any change when I cleaned it off last year. Don't some people fit them inside the hull?

 

[Pye_End]

Mine had a dodgy power connection and gave similar results (although not quite as severe). It could be the transducer getting tired, but presumably this would be a slower process.

Try Stowe Marine. They are helpful, and have spares if you need them.

http://www.stowemarine.com/support.htm

 

[Seajet]

Stowe is the best respected kit I have ever heard of, and depthsounders are the most simple & reliable.

As you are talking about drying the boat out I presume you sadly have a through-hull transducer on your Sadler, sadly as she is of course grp, no choice if she'd been solid wood.

If in- hull the transducer should be in a non-volatile medium ( which in this case means liquid which won't easily spill ) so castor oil from pharmacists is the traditional choice; just avoid air bubbles between transducer & hull, the No.1 enemy !

One can hear when the transducer is transmitting by listening close with no other distracting sounds, it's a faint rapid ticking sound.

Probably the most useful device on a 20th Century boat before commercial Decca / GPS, but still vital today, it certainly aids sleep at anchor - combined with other precautions such as watching the depth on the way into an anchorage, and amount of anchor warp / chain set etc.

Edited; depth sounders can also be used as major navigation aids, combined with distance log & compass and interpreting chart depth contours, to give surprisingly accurate 'fixes' or steering to harbours in poor visibility, but this is very dependent on the local undersea contours.

In the old days of sailing survey / war / trading ships the 'lead line' with a concave hollow filled with soft tallow brought up specimens of the seabed consistency, still marked on today's charts, which give another aid to a position fix.

 

[jfkal]

Anti foul is not the issue

Paint as such is not the issue. Reason why they tell us not to anti foul is that some volatile contents of paint may attack the plastic of the transducer. There are some water based AF's on the market designed to protect transducers.
However fouling is the most likely cause as a family of barnacles will scatter the outgoing ping so that the return signal is to weak and then get further muffled on the way back in (more so when the barnacles have the TV or radio on high volume at the same time ).
Those ultrasonic anti fouling enthusiasts take note: Yes, barnacles grow even on high power transducers ))