13 December, 2009

Installing a Depth Sounder

The waters in the lower Chesapeake, Eastern Shore or Coastal Carolina are shallow and in the summer can be very murky due to high algae levels. The charts of the tidal flats are uncharted or out of date. Entering shallow waters I often slightly lower the Newport’s keel to feel my way through. The bottom is sand or mud. I would not try this in New England with granite outcrops.

This summer I decided to upgrade to a depth sounder. At first I debated between a fish finder and depth sounder. I would love to have one of the new GPS/Fish-finder combo units. But I will have to wait until the price comes down some more. My main criteria were cost and power consumption. The electrical system on my Newport 16 consists of one lawnmower battery. I bought my used sounder on E-Bay for $50.

Many of the depth sounders come with a transom mount transducers. This created a problem for me. I need to know where I am going, not where I have been. Mounting the transducer in the hull you loose a little of the signal. This is not a issue since I am interested in the shallow water not the very deep. To reduce the cable runs I decided to mount the transducer under the companionway next to the keel trunk. I mounted the display as far outboard as possible so not to interfere in the cabin.

The working part of a transducer is a round coil in the center. The rest is plastic case and resin to mount the transducer on the stern. To get the unit to sit under the floor pan and as flat as possible I had to reduce the footprint. Using a bench grinder I carefully removed material. The plastic case across the face was popped off.

Using a 3” hole saw I cut through the liner. Make sure the center dill does not extend too far or you may drill into the hull. Previously I have filled this void with foam. Foam was removed. A tube conduit was led to the place where the wire would come out of the liner. The sides of this round compartment were glassed to seal it from the rest of the void.

To mount the transducer I mixed just enough epoxy to fill the circle bottom. When mixing it is important that you do not introduce air bubbles into the epoxy. The unit was paced into the epoxy and gently moved and tapped to remove any trapped air. The wire was led through flexible conduit (Radio Shack) up to the display unit. Power wires were picked up into the same conduit. I twisted the power wires to reduce any interference with the transducer signal.

I test ran the unit in open water. It worked like a champ. Keel down, less than 4’ and it will hit bottom. The unit can not detect less than 2’. The display goes blank. With the keel up I know that I have landed.

At first I wanted to install a cover plate over the transducer hole. After while this did not make sense. If it would leak water would sit in there. The transducer can not be repaired and it is permanently fixed. I filled the space with foam and epoxied a 3mm disk over the top. If I ever have to replace it I will grind off the cover.

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