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When I got my Capri 18 last summer, I had planned on eventually installing some type of electronic depth-indicating device. When I saw the Humminbird Wide 100 fishfinder on sale (and with a rebate) at West Marine last winter, I decided to buy it. The Wide 100 is not available any more, but has been replaced with a similar unit, the 100 SX. The 100 SX occasionally goes on special at West Marine and other fishing/boating supply sources. I chose a fishfinder over a plain depthfinder because the fishfinder is less expensive, and it provides more information than the depthfinder.
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I finally got around to installing the unit this last April.
The first part of the installation was deciding where to mount the main unit and the inside-the-hull transducer. I frequent the Trailer Sailor messageboard www.trailersailor.com, and had seen a picture on the website of a unit mounted in the companionway on another sailboat. This place was slightly more attractive (to me) than mounting it on either side of the companionway on the bulkhead, as the external surfaces of the bulkheads are nice places to lean against in a Capri 18 cockpit. After deciding on the mounting region for the display, I then needed to find a good location for the transducer to mount in the hull. The area had to have good access, enough room to place the ‘ducer, and not require a long wire routing to the display. I initially favored cutting an access hole in the bulkhead forward of the porta-potti and below the v-berth. After analyzing the hull contour and other factors, I searched for another location, as I decided that the wire run would be too difficult and the transducer might not be in the best location for a good signal. The Humminbird transducer is made for transom mounting on the outside, but that is not a good location for a sailboat is subject to heeling. The manual indicates that it is acceptable to mount the unit inside a non-cored fiberglass hull, so that it ‘shoots through’ the hull. After a bit of pondering and analyzing the boat some more, it dawned on me that the area behind the ice chest, under the cockpit floor was a large, foam-filled floatation chamber. Furthermore, the area was located behind the keel in a flat-bottomed area of the hull.
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A trip to West Marine brought home a 4” Beckson screw-in deckplate (Beckson DP-40 W / West Marine Model 103598: $8.99), and a tube of Life Seal caulk. While at W.M., I looked at the swing-out electronics mount. Nothing there had the low profile that I wanted and they were fairly expensive ($75-$100), so I didn’t get one. At home, I began to design a simple, swing-away mount for the display unit. After some measuring and cardboard prototypes, I drew plans for an acceptable design and then went out for the parts to make it. As can be seen in the pictures, the main part of the mount is made from 3/16” aluminum diamond plate. I did this because the aluminum is easy to work with, and I thought the diamond plate would give it a special appearance. I will not go into detail about the design and fabrication of the mount, as I can provide some simple plans to anyone who would like them. The pictures give you an idea of the basic design.
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Installing the transducer was the next part of the project. I cut the appropriate sized hole in the bulkhead behind the ice chest area. Using the hole for access, I scooped out a large area of the foam behind the bulkhead, exposing an area of the inside hull surface. The foam was removed up to the top of the hole level and aft, exposing an area of hull approximately 3” wide and 8” long. Before installing the deckplate, a groove was cut in the top inside of the flange. This was to allow the transducer cable to pass between the bulkhead surface and the deckplate flange. The deckplate was then installed using Life Seal, stainless machine screws, and stainless nyloc nuts. Nylon cable clamps and stainless tapping screws were used to secure the cable to the bulkhead. The location for the transducer is approximately 2” aft of the bulkhead, on the inside surface of the hull. The transducer was temporarily mounted in a bedding of peanut butter. No kidding, it works. I did this, as I didn’t want to epoxy the unit in and then find that it was a poor location. The manual says to use epoxy, not silicone to mount the transducer, but many others have had good success using a high-quality silicone like 3M. When gluing with silicone, it is important to push and twist the puck down into the blob of silicone to eliminate any air bubbles. Air bubbles can degrade the performance of the unit. One sailor has actually used plumber’s putty, with success.
Power for the unit is supplied from the ‘Accessory” switch on the electrical panel. A 1 amp AGC-type fuse in an inline holder protects the circuit.
In May, I took the boat out on Folsom Lake. The fishfinder worked very well. The depth alarm is a nice feature, as is the bottom contour display. The transducer is located approximately 4” below the waterline, but in practice, I just figure the depth indication as true depth from the waterline. A simple fishfinder is a great accessory for any keelboat, and it’s entertaining for guests, too.
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