Ask Sail: Transducer Extraction

I have to replace my depthsounder. The plastic nut that holds the old transducer in place was set in the hull with adhesive. The new transducer will not fit the old nut, which has proven very difficult to remove.
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Weldon Nelson of Winchester, Massachusetts asks:

I have to replace my depthsounder. The plastic nut that holds the old transducer in place was set in the hull with adhesive. The new transducer will not fit the old nut, which has proven very difficult to remove. I am sure that others have had this problem. Your suggestions on how to remove the old transducer holder would be appreciated.

Don Casey replies:

DonCasey

You must remove the plastic nut. You should be able to split it with a hammer and a wood chisel. Once it is split, you may be able to break it loose with a wrench, or you may have to pry it loose in pieces, wedging it free from the hull with the chisel.

With the nut removed, you can extract the transducer housing as you would any through-hull fitting. A solid whack from inside with a small sledgehammer may break it free and drive it out of the hole in the hull. Otherwise, you can pull it out with a threaded rod or long bolt. Pass the rod through a short length of strong wood bridged across the through-hull hole and supported on each end with wood blocks set against the outside of the hull. Inside, the rod passes up through the center of the transducer housing, then through a steel plate or a piece of hardwood set on the inside end of the housing. Fit both ends of the threaded rod with washers and nuts. Hold one nut stationary and tighten the other one, and the housing will pull out of the hull.

Clean away all the old sealant before starting your new installation. You probably don’t need me to remind you that the sealant should be applied around the flange on the outside of the hull only, never inside the hull, and never to the retaining nut. 

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