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Transducer Tribulations

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I've got Advansea S400 Wind and Multi instruments on my boat, hooked up to a B&G Vulcan 7 plotter/Autohelm via NMEA Backbone.


The S400 was chosen as a direct replacement for the old Navman units as they can use the Navman transducers.


All has run well for 2 years however the water speed stopped reading about 6 months ago (thought maybe transducer).


But after coming out of the water for a keel reset and hull scrape/coat when we fired the instruments up the Multi display up and quit.


Got a new one, put it in for the Enduro however on the way to the start the screen started showing a black spot and was extremely hot to the touch. When I checked the solar mppt display I could see that something was drawing about 6 amps... felt the power wires to the multi and they were scorching so cut them and draw went back to .2 amps.


Took the unit to Absolute Marine who tested it and found no fault.


Refitted yesterday and changed the fuse from the original 15 (!!!) amp to a 3 amp and plugged it all up, checking the draw at each stage. 


Power wires connected - 0.1- 0.2amp


NMEA wires connected - 0.1- 0.2amp


Speed transducer - 0.1 to 0.2 amp


Depth transducer - Fuse go bang.


So its looking like transducer or transducer wiring. Nothing was done in the area that the transducer is mounted or wiring routed whilst out of the water so I doubt its damage.


But - the thru hull Navman depth transducer has never been mounted through the hull. It was glued directly to the inside of the glass hull in what is supposed to be a thin area (Is there any thick areas on a 930's hull???) under the galley bench. It has read depth fine through this hull for many many years.


But when out of the water I painstakingly scraped the hull back to glass, rolled on two coats of Altex Carboguard, sanded that back then sprayed a tie coat of epoxy primer and 2 or 3 passes of Petit Antifoul.


My question is - have these layers of coatings somehow proved a bridge too far for the transducer to read through or is it just a coincidence that the transducer has decided to fail at the same time as we did the bottom job?


Is there any test I can do with transducer in place to find the fault?



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This will boil your biscuit - for Saturdays SSANZ I ran the Multi unit (with the depth transducer unplugged of course) purely as a SOG repeater.


It was also displaying depth, and based on a few checks against the plotter throughout the day... seemed to be reading pretty accurately.


For the life of us, we could not ascertain where the unit was getting its data from!


Is there a possibility, that when connected to the Vulcan but not getting a transducer signal, the depth according to the plotter and tide info is calculated for your position and displayed?


Was weirding us out a bit 

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