Nick's problem with his depth sounder

[Rowana]

My last reply was to Ash. This one is to Nick.

How is your transducer fixed?

Mine is in a tube in one of the under bunk lockers. To get a good seal with the hull, I put a little castor oil in the tube first before inserting the transducer. It works OK at fairly shallow depths, but then starts giving some silly readings as the depth increases. I just ignore it as once I'm past 1.5 meters, I'm not going to hit anything anyway!

[sahona]

OK. The xducer is through-hull, which I assume means there's a blob on the outside of the hull with a nut (not you) and cable on the inside.
The symptoms are : Perceived loss of sensitivity over a period - increasingly unable to display deep water.
Erratic display with engine running fast enough for the alternator to be 'pushing amps'
Both these symptoms could be the result of a poor connection somewhere in the transducer cable, whereby the receiver is straining to hear the pings and hears any interference at a similar level.
Also consider the possibility of the transmit ping being weak for the same reason. In either case the signal to noise ratio could be too low.
So, number one - follow the cable from beginning to end looking for ANY damage. Ingress of water to a split bit of plastic will cause problems as the xducer and cable (at original manufacturers length) form part of the tuned circuit for the transmitted pulse. This is where the transistor radio comes in. It should hear "ticks" of interference when tuned to 200kcs (the light programme, long wave). There should be no difficulty hearing these.
If the boat is out of the water and you have sensitive fingers, you may even be able to feel these pulses by touching the xducer (although I haven't tried that one!).
Number two - can you take the instrument to a neighbour's boat and try his transducer? Dry or wet doesn't matter - it's the comparison we want.
Doing the above will isolate the problem to xducer , cable, or instrument head.
Notice I've deviated from the alternator this time? - finally the customer started to tell me the whole story, and I bet there's more pertinant stuff if we keep pumping....

[Nick]

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Will investigate along these lines.

More hopeful now - a new NASA Target 2 Depth Sounder, with transducer, is only £85 so I reckon its got to be worth a splurge.

[sahona]

what model is the old one . The transducer may be compatible etc.

[Nick]

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Old one is NASA Target. NASA Clipper is a direct replacement. Will carry out more investigation and if it looks like the transducer/cable will see about getting that separately.

Good grief, maybe we will know how much water is underneath us for the first time in 7,000 miles!

[Rowana]

Nick,

I have a spare transducer for my NASA Clipper which you are welcome to borrow to do any tests/comparisons you like.

Say the word and I'll chuck in a jiffy bag and post it to you, but it will be next year now !

Jim

[Nick]

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Thanks a lot Jim, much appreciated - but hold off on that until I have had a chance to at least check the whole cable run on ours.

HNY when it comes . . .

[Clyde_Wanderer]

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Will investigate along these lines.

More hopeful now - a new NASA Target 2 Depth Sounder, with transducer, is only £85 so I reckon its got to be worth a splurge.

No Nick, its not worth the splurge, I would recommend you look further than Nasa, and definatly not the Targa/Target.
Mine is the Nasa Clipper duet, which could be very soon going over the side, for good, Frankly they are rubbish, if you could stretch to something like a Raymarine unit you would be well adviced to do so, far better.
C_W

[Nick]

if you could stretch to something like a Raymarine unit you would be well adviced to do so

Can't and anyway it wouldn't match the others . . . the Target worked perfectly OK for two years and all the way round Ireland, so I will be quite happy to get that level of performance back again.