I am also having sounder issues. The hull transducer is a single
200 khz unit that has been on my hull since 1978. Over the years I have gone through a number of display units but retained the original transducer.
Recently my Navman Depth 1300 unit suffered from screen
burnout and failing digit display, and I am chasing up a suitable replacement as the company, like many, has gone by the way.
In retrospect, I believe that the correct solution is to build a rigid PVC (or other material) tube into the hull that comes well above the waterline internally, something of 60 to 100 mm (2.5 to 4 inches) diameter. A tube is slid down from the inside that has the transducer mounted on the end and is exposed to the water and oriented via a reference mark inside at the top of the larger tube. The internal tube has a standard PVC screw type top to seal it. A snug fitting at the water end or even a coarse screw in assembly may be needed. A blank ended fitting could be inserted for long periods of non use if required. Clearly the placement of such a tube needs careful thought. This can also be done using a large diameter valved skin fitting if needed. The internal tube could be rubber etc. provided it is reasonably straight.
What all this allows is the replacement and or maintenance
of the transducer. from inside the boat.
Over the years transducers have changed from single
frequency models to multiple frequency models and this approach allows the owner to make changes as needed. On larger vessels, the cost of a single lift
out to replace a transducer is usually many multiples of the cost of a built in tube assembly.
It means you can use any transducer (except for the monsters used on deep sea trawlers etc.) and the concept
can be applied to other sensors such as speed paddles and temperature sensors.
If I was in the market for a new boat
, I would be looking for such a an arrangement. Hulls may last forever, but instruments really don't and usually either become obsolete get damaged or just die, so simple replacement seems like a good idea to me.