Stern-drive and outboard boats may have through-hull installations, but transom-mounts can also work well for these applications. Although there may be a performance loss (usually at high speeds, when the boat rises on plane and the transducer comes up near the surface of the water), the installation is easy enough for most people to handle.

AIRMAR TRANSDUCERSTransom-mounted transducers are a project most boaters can install themselves, though through-hull units are generally a job to be left to the pros.What about mounting inside the hull? While this is simple – just epoxy the face of the transducer to the fiberglass hull bottom – it results is a big performance drop as the hull absorbs a lot of the sound wave's power. It can also be disastrous if you mount it over an air pocket in the fiberglass, or on a cored bottom, where performance will be degraded even more. Bottom line: save this type of installation for depth gauges only, where performance and high detail aren't necessary – not fishfinders.

Most of us who install units will be dealing with transom-mounting situations. First and most important in this case will be choosing the transducer location. Crouch behind the transom and look for an area as deep on the hull as possible, with no strakes, intakes, or other items in front of it. Any items like these will disturb water flow and reduce performance. Holding the transducer bracket against the transom, lower it until it's in a position to hold the face of the transducer about 1/8-inch below the running surface of the hull when the transducer is centered on the bracket. Using the pencil, mark the location of the bracket.

WIRING

Before mounting the transducer bracket, run the transducer line to the dash. This is why we left the old transducer in place. Now, we can simply cut the old wire off the transducer, secure the end of the wire to the new transducer wire using masking tape, and then pull the old transducer wire from behind the dash, drawing the new wire through the chase (this usually runs under the starboard gunwale or under the deck in a PVC tube).

If there is no old transducer wire, or if the wire breaks during this process, you'll have to start from scratch by using a wire fish to pull the new transducer wire through the chase. Pull the wire through until the transducer is in approximately the correct position, there is little slack in the line, and excess wire is located behind the helm station. Coil and tie any such excess, and secure it to a bulkhead. Never cut a transducer wire to size. Creating new connections in it can lead to more performance problems.

LENNRY RUDOWJeff Cann holds one helluva yellowfin tuna. Today's technology can help snatch the big catch. Using the marking you made earlier on the transom, drill pilot holes for the bracket's mounting screws with a 5/64-inch drill bit. Then use the 3M 4200 Fast Cure adhesive/sealant to liberally coat the mounting screws. While holding the bracket in place, screw in the mounting screws. Use lots of goop here – the last thing you want is holes in your transom that let water soak through. Once you've got the bracket in place, sit the transducer in the bracket, and tighten it up.

Next, you'll need to follow the transducer wire from the transom to the back of the dash, and use ties to secure it wherever possible. Do not allow any droops or slack in the wire for distances over 6 inches. These areas can rub against fiberglass as the boat runs, causing chaffing over the years.

Next, connect the transducer and power cables to the back of the unit. Then attach the negative and positive power leads to the terminal block. Again, check the wires and secure them wherever possible. Before launching the boat for a test-run, allow the 4200 to thoroughly dry.

Finally, it's time to launch the boat see how the unit performs at rest and on plane. It'll probably work fine when the boat's sitting still, but remember that problems often arise when running on plane. If your unit loses the bottom reading when you firewall the throttles, you'll have to adjust the transducer height on the mounting bracket. Move it down a hair, then launch again and re-test the unit. Continue re-launching and moving the transducer up or down in the bracket until you find the best location.

Now, you're ready to find fish – hopefully, armed with your new, cutting-edge unit, you'll reel in more then ever before.