Raymarine ST50 - Designed to Leak?
Gene,
VC 17 is a very thin antifouling and I would not expect a single coat to have any effect on the transducer performance. Indeed I always give my xducer a single coat of whatever I am using with no affect on performance at all - (if it can shoot through a hull then what is a thin layer of paint - unless it softens the plastic surface).
My recent experience is that it is difficult to discover whether the problem is the xducer or the instrument. Having a spare xducer to try is the best check.
The xducer ST60 is compatible with the ST50 Instrument and still available, either from Raymarine or Airmar who are the manufacturer. Even another make will probably do if on approx the same frequency.
My ST50 failed over the winter and I was lucky I had a spare xducer to dangle over the side of the boat and so verified it was the instrument at fault. (My xducer was from an old Raytheon sounder they supplied to an Americas Cup defender some 35 years ago when I worked there.)
I opened the instrument and discovered a 'high tide line' about 1/2" up from the bottom of the printed circuit board. Clearly the case had leaked and the components at the bottom of the PCB were corroded away.
Upon examination I noted that the sexy red rubber seal went around the outside of the case but the four screws which held front to back were INSIDE this perimeter seal. Thus any water dribbling down the gap between bulkhead and instrument could leak in down these 4 screws. Then again the four rubber push buttons are only a light 'push in' fit and can also leak.
ST50 Instruments are like hens teeth to get hold of these days so I went to an 'Aladdins Cave' locally. They provided a used instrument head. It didn't work so I opened it up - same tide mark at same height. The water would fill the casing but it leaks OUT through the two lower case fixing holes described above so the level only reaches 1/2".
I took the second unit back and they found me a third. This worked but, out of insatiable curiosity, I opened it up and, sure enough, a similar tide mark. I guess the difference being the instrument was not running when the flood came so the corrosion was much less.
Three leaking instruments - can't be just a coincidence!
So, then I put four small squares of PVC tape, one over each of the case fixing screws and finished off with a turn of black tape right round the whole casing covering the aforementioned sexy red seal.
To protect against water ingress in the future I drilled two 2.5mm drain holes, one in each lower edge of the case right at the outer corners (1/8" dia. would do). There is a small part of the moulding just there so, with care, the drill only penetrates enough to go through the case and stops against this post and does not damage the PCB. The casing already has a breather hole in the back of the round projection at the rear so I don't feel my holes are making anything worse.
It should be noted that ALL ST50 instruments use this case and are similarly at risk.
Next time I go to the boat I shall drill weep holes in all the other cases - no need to open them up - and put a turn of tape round each.
See photos below:-
BTW:- Years back, after a very rainy day at sea, my ST50 Log was seen to be full with water swilling half way up the LCD display. On arrival we opened the unit and rinsed it out in a bowl of warm soapy water. Then thoroughly air dried it and put it back. Has worked perfectly ever since except the distance run had increased by 5,000 miles. Luckily a boat's second hand values are not measured like a car's!
