Q&A: Can We Install A Bronze Transducer In Our Aluminum Boat?

Question: We want to replace the current inoperable depth sounder on our aluminum boat with a forward looking type (EchoPilot or Interphase), but we have run into the dilemma that the transducers suitable for our hull have bronze stems.We have been advised that bronze stems can be installed in aluminum hulls if the stem is well isolated from the hull and an aluminum donut is installed as well. We would appreciate any information you could provide us and what your experience has been, especially if you did install a bronze stemmed transducer on Morgan’s Cloud.

Answer: I would not recommend installing a bronze through hull on an aluminum boat, even if it is isolated from the aluminum; there is just too much risk of electrolysis. Also, if there is any dampness, and there will be, copper salts will form on the bronze and drip into the bilge…not good.

When we bought our EchoPilot FLS II, EchoPilot provided a custom aluminum through-hull at additional cost. This is not a cheap solution, but definitely the way to go. Once we had the aluminum through-hull we had an aluminum donut machined that compensated for the angle of the hull since it is vital that the transducer be installed absolutely vertical.

The next challenge is to get all this installed and safely watertight. You could weld the donut in, but this is messy and it is very difficult to get everything lined up perfectly when welding, due to heat distortion of the surrounding plate. To get around this we used Plexus adhesive to glue the donut down before drilling the hole. The cool thing is that Plexus sticks to aluminum brilliantly, particularly if you use the Plexus aluminum primer, and it will gap fill up to ½” so you can use it to make any small adjustments to the leveling of the donut. Once the Plexus is dry, drill the hole through the donut and the outside plate making sure it is absolutely vertical.

Before starting this project make sure the boat is level on the ground, both fore and aft and side to side. Remember, you are trying to level the actual water line (scum line) since you want the beam from the sounder to be parallel to it. If you want to get really anal retentive about it you could rent a self leveling laser that surveyors use to line up buildings. We rented one for a recent project for about US$100 and it was great, although it is probably overkill for this. This process will drive your travel lift operator crazy, but is the only way to get things right.

Your next issue is to fair-in the transducer through-hull on the outside, since it won’t lie flush. The answer here is to cover it in mold release wax and then install it onto a pile of epoxy putty on the outside of the hull (we make our own putty from WEST SYSTEM resin and micro-balloons). Tool the putty to a fair shape while wet. Once dry, remove the transducer through-hull, clean off the mold release wax with acetone, sand the epoxy putty to a final smooth and fair shape and make the final installation with a good underwater sealant.

It’s a lot of work, but well worth it; once you have a forward scan sounder you won’t be able to imagine how you got along with out it.

For the high latitudes, I would recommend the new EchoPilot Platinum model which replaced the FLS II that we have and, as I understand it, fixes most of our criticisms of the older model. I would also recommend having a spare transducer aboard since they seem to lose their sensitivity after a few years and can die suddenly.

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John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 18 years, as co-editor/publisher of AAC.

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