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 The charts of the tidal flats are uncharted or out of date.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.

Main Locker Bulkheads

The two main watertight bulkheads that divide the aft lockers from the main cabin were placed a few inches aft of the keel winch board bolts. I did this for two reasons. The lockers hatches are prone to damage. In case one flooded I wanted a small volume. Working on the locker from the top is also difficult. On the cabin side the extra area behind the berth makes for a large, dry storage. A small 4” clear screw in deck plate directly under the winch board allows in light and ventilation. The board bolts and hardware on the cockpit coaming are all accessible from the cabin.

To reduce gear noise I use Wal-Mart Camping Pad Foam in the storage area and bulkhead. This is a great product that can be put on with contact cement. And it looks good too.

When I filled the aft cockpit coaming with foam I inserted a light plastic pipe through the center. With a clip on the other end I have a great 7’ fishing pole storage on each side. The pipe is large enough to fit the pole tip with lures attached. No fishing hooks to snag on.

The bulkheads were built using my polystyrene sheets with glass cloth sandwich. The shape was cut from a cardboard template. The bulkheads were set in place and small gaps filled with foam spray. Then a large lightweight epoxy fillet was applied around the edges and covered by 3” glass tape to spread the load on the hull. This bulkhead reinforces the hull, seat and keel winch support.

Under Cockpit Foatation

On a Newport 16 the area under the cockpit can be a black hole. Equipment stored in the stbd locker drifts to port when sailing. Any water that leaks into the boat stays in this area. The Newport has a drain plug in the stern to drain this water. I consider this area unusable. My solution was to fill this space with flotation foam and encapsulate the area with fiberglass.

The first step was to remove the drain plug and seal the hole. Then I cut the original Styrofoam blocks to fit tightly into the space. Due to the V – shape in the hull this was done in two layers. The gaps around the block were filled with household expanding foam. This foam also acts like glue. I spread a layer on the hull before setting the Styrofoam blocks. Once the foam expanded the fit was very tight.

To seal the foam in fiberglass I had two choices. Either lay fiberglass cloth directly on the foam or use rigid panels as bulkheads. Polystyrene insulation that comes in 4x8’ sheets from Home Depot can be laminated. Working under the seats of this small boat can be very tight. Any fabrication outside the boat is preferred. Using a cardboard template I cut the styrene and laminated a glass cloth on one side. These were glued in using the spray insulation to the side of the Styrofoam blocks so that the vertical line is flush with the cockpit side. Using glass tape it was bonded to the hull and cockpit. Added benefit is the additional hull strength. The original half pipe stiffeners can be removed.

You have to work from the stern forward. This is why the rear is painted and finished off. Note: The hull deck joint is faired with epoxy filler and glass tape. Cockpit coaming is also filled with foam and glassed. Once the space was finished I installed a transverse bulkhead creating two watertight storage spaces.