Depth Sensor

We have a Raymarine ST60 Tridata instrument that reads our Airmar P319 depth sensor.  It worked fine for about a year, then began working intermittently for a few months, then just quit altogether.  By “quit” I mean it was obviously giving us wrong depth data.  The depth would go from 80 feet to 112 feet to 328 feet and then cycle down.  It was just giving random numbers until it would sporadically throw out a number that would be correct.  I felt that the most likely cause of the malfunction was fowling of the sensor.

The water here in the marina is notoriously yucky.  (That’s an official yachty term for disgusting.)  I’m reluctant to go in.  One day I had to go diving for a piece that I dropped in the water.  That’s a story for another time.  While in there, I figured I might as well clean the depth sensor.  It’s about 2 feet below the water line and at this depth it’s pitch black and I can’t see anything.  I was groping around until I felt what I thought was the depth sensor.  It had what felt like a raised lip on one edge and I knew this was not good.  I went to scrubbing and had Jodi in the cockpit seeing if my work made any difference by watching the Tridata.  It never did, so I gave up and figured I might need a new sensor.

That was several weeks ago.  Then today I was filling the forward water tank.  I installed a pressure gauge at the outlet of the tank that measures inches of water and I use that to tell me when the forward tank is full.  It’s right by the depth sensor.  As I was looking at everything I realized (hoped) that I was probably never cleaning the depth sensor.  I was most likely cleaning the plug for the speed sensor.  I pulled the plug out of the thru hull and sure enough there was flat barnacle skeletons where I had scraped the growth off.

Well, crappers.  That means I have to go back into the muck and try again to clean the depth sensor.

I suppose this all comes from not really KNOWING the underside of our boat AND.  In my defense, we got to see it for about 30 minutes while hauled out for the survey.  Since then, it’s been submerged in murky water.