Marine electronics evolve as quickly as computers and digital music players – in four or five years, they're totally out-of-date. That includes fishfinders, and if you're still using that old black-and-white bottom machine that can't tell you the difference between a minnow and a marlin, it's time to upgrade.

Just one problem: replacing a fishfinder isn't as simple as removing the old one and mounting the new. You'll also have to deal with new wiring, a transducer and maybe even cutting a hole in the bottom of your boat – what fun!

GARMINNew fishfinders offer color graphics, improved detail, sunlight viewability and better value. If mounting a new fishfinder is indeed this much of a hassle, is it really a worthwhile project? Considering new technology, the answer is yes. Now, you really will be able to tell which readings are baitfish and which are big fish. You will also be able to differentiate the sea bottom from structure, like wrecks and reefs, and distinguish bottom type much more easily. By installing a new fishfinder, you'll be able to see far more detail than you did with one that was made just a few years ago.

What gives? Screen technology has been developing by leaps and bounds. The most important advance in the past few years is the addition of inexpensive, color LCD screens. Sure, color has been around for more than a decade, but it used to be on high-end, budget-busting units only. Not so, these days. Now color units are available for just a few hundred dollars, and color is very important when looking at a fishfinder screen because it allows you to see the density of a reading at a glance. Hot red indicates a very dense reading on most units, while "cooler" colors like green and blue indicate readings that are less dense. So if you see two red readings under a cloud of blue, you know a couple of predators are hunting a school of bait.

Another advance that makes upgrading worthwhile is the level of detail. While most of yesteryear's screens had low pixel counts, today units in the same price range have more pixels. And pixels translate into on-screen detail, plain and simple.

HUMMINBIRDHumminbird's new IS technology offers a whole new advantage when you upgrade your fishfinder.Speaking of screens: those made in the past few years – including new transflective and QVGA screens – work far better in bright sunlight. Older LCD's tended to blank-out from certain angles, especially if you were wearing polarized sunglasses. Most new fishfinders also have features like dual-frequency abilities, allowing you to effectively probe the depths in both shallow and deep waters; ASP (advanced signal processing) which senses and adjusts the best automatic settings; and additional goodies like speed and temperature. Better still, today's screens are larger then those available for the same amount of cash a few years ago. And when it comes to fishfinder screens, bigger is definitely better.

SIDEWAYS GLANCE

Serious anglers may also want to upgrade to the latest and greatest fishfinder feature: side-finding technology. Side imaging isn't entirely new, but it is new to the recreational fishing world. In the past, units costing tens of thousands of dollars with grapefruit-sized transducers were necessary to get an underwater view of the fish and structure off to the sides of your boat. The low-cost side-scanning options on the recreational market consisted of units that turned a down-looking transducer sideways, and the results were less than spectacular. But Humminbird's newest unit, the 1197c SI Combo NVB, paints an image of what's under your boat for 240 feet in either direction on a huge 10.4 inch display. It pumps out a total 1,000-watts RMS through downward-looking 200 and 83 khz beams, and 455 and 800 khz side-looking beams.

What the heck is a khz, and why should you care? It a kilohertz, and it describes the frequency of the beam transmitted by your unit, which in turn determines what you see and how well you see it. Think of it this way: Toss a pebble into a pond and it makes small, fast waves – short frequency, or 200-khz in fishfinder speak – which bounce back when they hit small items. Now think of tossing a boulder into the same pond. It will create larger, less-frequent waves – low frequency, often 50-khz – which roll right over small items without noticing them but continue on for a longer distance. On average in most conditions, that 200 khz wave will travel about 600 feet deep, which is the normal operating limit for a unit pumping out this frequency. A 50 khz unit, however, with its lower detail, may reach thousands of feet.

Side imaging units use a combination of tightly-focused, super-high frequency beams to collect data in an extremely detailed manner, then take that data and "paint" an on-screen picture. "It's like taking an MRI of the water," explains Mark Gibson, senior brand manager at Humminbird. "The transducer reads a very thin slice of very dense, detailed info, then it moves on. The time-distance relationship allows the unit to determine exact distances and depths, and when you consider the overall area you can look at on your unit, you're able to cover literally 50 to 75 times the amount of territory that a traditional down-looker can see."

LENNRY RUDOWFlush-mounting is usually considered superior, and it protects your unit from the elements and from theft.INSTALLATION

Okay, so you know it's time to install a new fishfinder, and you're ready to roll up your sleeves and go to work. What's first? We'll assume you've already taken the old fishfinder off, and a new unit is ready to go. Wait a sec – when you removed the old fishfinder, did you also pull the transducer wire? We hope not. Leave the transducer wire in place, so you can use it to pull the new wire through the rigging tube easily.

Before you go to work, you'll need to make sure you have the following items on hand: a power drill and bits, a jig saw, a Phillips head screw driver, an adjustable crescent wrench, a wire fish, crimpers, a pocket lighter, a pencil, a new fishfinder head unit and transducer, 3M 4200 Fast Cure sealant/adhesive, 4 self-tapping #6 1-inch stainless-steel flat-head screws, 4 feet of 12-gauge tinned-copper shielded wire, with red insulation, 4 feet of 12-gauge tinned-copper shielded wire, with black insulation, two ring connectors, two butt connectors, adhesive-lined heat shrink tubing, nylon tie-wraps and masking tape. Be sure in all cases to use marine-grade materials.

Ready to flush-mount the head unit? Picking the exact location in the dash is imperative, because you need to ensure plenty of depth behind it (a minimum of 4 inches or so for most units) as well as enough space on the dash itself, which will depend on the size of the unit you have chosen. Remember, when it comes to fishfinders, bigger really is better, so take it as far as your dash and your budget allow.

LENNRY RUDOWIf you have to bring wires through the top of the helm when binnacle mounting, cover the hole with a clamshell fitting.The most common mistake people make at this point is failing to ensure that there are no accessories or wires behind the dash, in the spot they're about to cut out. Actually sawing before verifying the clearance can lead to significant damage of the electrical, steering, and/or control systems, so be careful when you measure.

Once you've chosen your spot, use masking tape to secure the cut-out template (virtually all of them have one included in the installation kit) to the dash. Using a pencil, trace the template directly onto the fiberglass. Then, using the power drill, drill a pilot hole for your saw blade in one corner of the template. Use a drill bit large enough to allow the saw blade to pass through the hole. Next, insert the jig saw blade into the hole and cut open the dash hole, following the dimensions of the template. Be sure to run both the saw and the drill at full speed; cutting slowly will only encourage the bit and or blade to grab and splinter the gel coat.

Once the cut-out is complete, you'll need to use a 1/16-inch drill bit to drill the unit's four mounting holes, which will also be shown on the template. Next, run a bead of 3M 4200 Fast Cure adhesive/sealant around the perimeter of the cut-out. (Note: some people prefer to use silicon as a sealant in this situation. Silicon will be easier to remove if need be in the future, however, it's far more likely to deteriorate over time and allow water past the seal. And while 4200 is tough to remove, it's not as difficult as 5200.) Add blobs on top of the mounting holes, as well. Then drop the unit into the cut-out, and use the included bolts to secure it. Tighten the nuts with your crescent wrench, and the unit should be securely in place.

LENNRY RUDOWMeasure twice, cut once. This installation caused problems, because the installer didn't measure the clearance between the throttles and the unit. Now, the port throttle can't be opened all the way.On boats with little flush-mounting dash space, it may be necessary to top-mount (binnacle-mount) your unit. This is far easier – simply drill four holes for the binnacle mount, run a bead of sealant, bolt the binnacle in place, and drill an additional hole to pass power and transducer wires through a clamshell fitting. But this mounting technique leaves the unit exposed to the elements and theft. Plus, it may partially block your view through the windshield. In virtually all circumstances, flush-mounting is the superior strategy.

Once the unit's in place, you'll need to measure the distance from its power leads to a terminal block. Cut one red and one black wire to size, and crimp one end of each to the power leads on the unit using butt connectors. Use your pocket lighter to seal the connections with adhesive-lined, heat-shrink tubing. Then crimp a ring connector to the other ends of each line. Do not, however, attach the power leads at this time.

TRANSDUCERS

Different boats may require you to mount your transducer through the hull, inside the hull or on the transom. Simply put, through-hulls will provide the best performance but require a pro – cutting a hole in the bottom of your boat simply isn't a DIY project. It is entirely necessary, however, on inboard boats, because turbulence created by propwash will ruin the unit's performance if the transducer is aft of the running gear.

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.

Lenny Rudow was senior technical editor for Boating Magazine for more than 10 years, and is currently the electronics editor for Marlin and GoBoating magazines.