External Transducer

External Transducer Mount Fish Finder

Prowler 15

Project: Rig a fish finder on a Prowler 15, so it can be quickly and easily removed for use on other boats from time to time, without sacrificing tackle box space….and while you are at it, mount a portable GPS.

Materials: Fish finder; 1 inch by 1/8 inch, by 3 feet Aluminum flat bar; aluminum rivets and washers; one inch stainless steel bolt and wing nut; 12 volt battery or eight 1.5 volt (AA) batteries; Velcro straps; lock tight or gasket cement; a few feet of 14 gauge electrical wire and quick disconnect electrical connectors ( I used a four prong trailer wiring plug) ; one piece of ½ inch inside diameter pvc pipe about 15 inches long with 2 matching female threaded adapters and 2 matching threaded male plugs; two battery springs stolen from the battery compartment from one of your kid’s discarded toys that ran on AA batteries; rubber 3/8 inch grommet and 3/8 by 1/2 inch rubber stopper that fits snugly in the grommet; silicone rubber, marine goop, or epoxy glue; one plano tackle box with a flat lid surface ( I used a five inch plano spinner box which fits perfectly in the prowler tray); one piece of plastic cutting board, plexiglass, or similar material about 7 inches by 10 inches; a few stainless steel screws (1/2 inch and 3/8 inch); electrical shrink wrap and electrical tape; a closed cell foam block (to make a battery “nest” if you go with a 12 volt battery); (optional) portable GPS and mounting bracket ; miscellaneous other stuff I forgot to mention including an occasional cold beer or other refreshment.

Tools: The usual…. including soldering gun, rivet gun, drill, drill bits, screwdriver, wire strippers, sharp knife, vice, tape measure, bottle opener (for the beer).

Summary: Having two boats and one fish finder, I wanted to have a moveable fish finder for use in either boat. So I used a piece of aluminum to build a transducer mounting bracket connected to the boat where the rudder would be attached. Then I mounted the transducer on a separate piece of aluminum which could easily be attached or removed from the mounting bracket with one bolt and a wing nut. The fish finder (screen) itself was mounted to the lid of a portable tackle box which can also be moved easily from one boat to the other. For power, I used a sealed rechargeable 12 volt battery mounted inside a closed cell foam “nest” wedged snugly into the front hatch compartment. As an alternative to the heavy 12 volt battery, I made a battery pack out of ½ inch pvc pipe with threaded fittings on the ends which holds eight removable 1.5 volt (AA) batteries in series ( 8 batteries times 1.5 volts each equals 12 volts). Wiring from the transducer to the fish finder is external to the bow and held to boat fittings with easy to remove Velcro straps. The battery is inside the front hatch and the leads (+ and -) go through a small hole drilled in the yak near the fish finder screen. The hole is lined with a rubber grommet and the wires go thru a rubber plug that makes a removable water tight seal inside the grommet.

General guidelines: Measure twice and cut once. Solder all electrical connections and protect them with heat shrink tubing or use butt connectors with heat shrink tubing. Use goop, epoxy, or silicone rubber liberally when you need a water tight connection. Use gasket cement or locktite on all nut and bolt connections so they will stay tight but still be removable. A little light bulb grease on the electrical disconnects can deter a lot of corrosion and make the disconnects easier to disconnect.

Details: A picture is worth a thousand words so let’s walk through the pictures and explain each, one at a time. In pretty short order, you can stop reading and start rigging.

Figure 1 Mounting Bracket. Using a vice or other tool, bend two sections of the Aluminum into L shapes, one long section for the rudder mounting screws on top and one short for the rudder mounting screws beneath. Rivet the two sections together so that they fit the boat snugly. Drill holes for the rudder mounting screws and attach to the boat with locktite but be careful not to overtighten or the nylon screws will strip or the brass female inserts molded into the boat will loosen. The longer piece should not extend to the bottom of the hull but only to the point where the transducer will skim the water surface. Otherwise you risk damage to the bracket, the transducer, or the boat when you hit dry land.

Figure 2 Transducer Mount. Mount the transducer on the factory provided transducer mount and then mount that component to a short piece of Aluminum with two small bolts, nuts and locktite or gasket sealant. This component is then bolted to the Mounting Bracket with a single wing nut. Note, to prevent the transducer from spinning on the bolt, I shot a rivet through the aluminum so that it extends beyond the thickness of the aluminum. This little protruding “nub” is then inserted into a hole lined up and drilled into the Mounting Bracket to hold the transducer parallel to the water when the wing nut is tightened…you could also use two bolts to accomplish the same thing but since the aluminum is only one inch wide, there is not much room for two wing nuts.

Figure 3 shows the completed transducer mount.

Figure 4 Mounted Fish-finder and Figure 5 Tackle Box Lid. A five inch Plano spinner box fits perfectly in the molded-in flat tray of the Prowler. First, glue (with goop or silicone so it is water tight) and screw (with 3/8 inch screws and washers) a small section of plastic cutting board to the top of the tackle box. I used a Coleman camping cutting board which was the perfect size for my needs. Then with ½ inch screws, screw the fish-finder mount (and GPS mount if you are doing one) to the top of the cutting board. To hold this all in place on the yak when underway, I modified the bungee cord that comes with the yak by moving one end to the other side of the molded in tray. It is then stretched over the top of one corner of the cutting board and can be easily undone to open the lid of the tackle box.

Figure 6 Battery and Nest and Figure 7 Battery in Nest. An old boat cushion contains many layers of closed cell foam which I cut and glued together to make a snug compartment for my battery. You can also use pieces of a blue closed cell camping sleeping pad (Walmart 6 bucks). The foam was sized and cut so that when it is put into the front yak hatch and slid aft, it wedges tightly in the interior molding contours of the yak foot rests but is still removable. To keep the battery from dislodging in case of a yak rollover or rough water, I used a cheap inflatable beach ball and blew it up enough to wedge it in snugly on top of the battery adding additional stability. The closed cell foam and beach ball also add additional flotation if things get really hairy and your yak interior gets swamped. As you can see I also soldered additional connectors to the battery so I could later power other things from the same battery (like a live well, navigation lights, big screen TV, etc).

Figure 8 Battery Pack Apart and Figure 9 Battery Pack Assembled. As an alternative power source, I used a section of ½ inch pvc pipe to hold 8 AA batteries in series giving me enough 12 volt power to run the fish-finder. First I found some battery springs from one of my son’s discarded toys and soldered a length of wire to each. Then I drilled a small hole into the end of a ½ inch male pvc pug and ran the wire through it so the spring was tight against the end. Both ends of the plug were then smeared generously with epoxy glue to keep it water tight. Female adapters were then glued to the ends of the PVC pipe so that batteries can be inserted and the two ends screwed shut. This makes a watertight sealed battery pack which still allows fresh batteries to be added as needed (or you can use rechargeable AA batteries). The only tricky part was measuring the PVC pipe length to make sure that the battery springs were slightly compressed giving good contact when the batteries are inserted and the male plugs are screwed into the female adapters. I suggest you first assemble all parts without glue to make sure you have good electrical contact before gluing it all together.

Figures 9 and 10 Wiring Plug. The battery leads go through the yak in a small hole lined with a 3/8 inch rubber grommet. To make it water tight and removable drill a small hole through the center of a 3/8 by ½ inch rubber stopper, run the wires through the stopper, and glue them into the stopper hole with goop or silicone. Obviously, you do this before you solder the electrical disconnects to the ends of the leads or you won’t be able to fit the wires through the hole. If you make this mistake, just slice the stopper lengthwise and press the wires into it. As the picture shows, an in line fuse was installed on the positive lead, and a connector was added to the fish-finder wires so that the unit can be plugged and unplugged. I also added a similar plug disconnect to my battery charger leads so that I can unplug the fish finder and plug the battery into the charger and charge it without removing the battery.

Conclusion. The fish-finder can be completely removed and used on a different boat when desired. The battery is snug but still removable. The tackle box tray still holds an accessible tackle box. As a bonus, there is room for a portable GPS, other gear, or a convenient cutting board for cutting bait. And the best part…only one new hole drilled into the yak !