By David Heinke

One of the most effective tools you can have on your boat is a graphic depth sounder also called a fish finder by many. For years the sonar devices available did little more than let you know how deep the bottom was, along with an indication of something that might lie in between the bottom and your boat. These devices referred to as "flashers" really helped fishing, but compared to today's units with fish icons and temperature readings, dual frequency transducers and so on, they seem crude. Nonetheless, the basic principle is the same and the parameters that dictate good performance have remained consistent since the first units were developed.

Despite the recent advancements in computer technology that allows simple sounds waves bouncing off objects to be translated into graphic imagery, how effectively your unit works depends on the installation. Installation of a fish finder is relatively simple and doesn't require much time to perform the labor. However, sometimes the location of the transducer might need to be changed a few times to achieve optimum performance. The bottom line is that the positioning of the transducer is THE most critical part of the installation and performance of your unit, so lets start with the transducer first.

What is a transducer?
The function of the transducer is to convert electrical energy from the transmitter into sound energy. The transducer then picks up the sound after it reflects off of an object. The transducer is one of the most important parts of a sounder system and it is sometimes the most neglected. The transducer can be compared to the speakers of a stereo system. A high quality speaker placed in the ideal location will deliver the best results. The same is true with transducers. Transducer can also use a paddlewheel that will send a signal to the head, translated into speed and in addition a thermometer sensor can also be imbedded in the transducer.

Almost all transducers are made by one company and regardless of the brand name; all depend on a mounting location that allows the transducer to work well. The transducer must remain in contact with the water to hold a signal and the water passing under the transducer must be free from air bubbles or any item that might hinder the signal, for instance, bottom paint containing metal. Many times people will say that they want a fish finder that will show the depth while they are running at higher speeds. I will personally guarantee that all sounders will give you depth readings at speeds up to and over sixty mph as long as the transducer maintains contact with the water and is mounted in a location that receives a steady flow of water clear of turbulence.

If you look at the bottom of boats, you will notice that very few are perfectly flat. There is almost always some "V", and many boats have stepped chines or lifting strakes to improve performance. The problem is these devices will disturb water flow along with any thru-hulls. In addition, you need to keep your transducer at least a foot away from the centerline of the boat if you have an outboard motor and plan to use a transom mount transducer. The transducer will produce turbulence as well and can cause your propeller to cavitate. When you boil it all down, there is usually only one or two possible places you can mount your transducer without negative effects.

To aid in finding a location to mount your transducer, there are several styles of mountings available. The most common type of transducer is the transom mount and is the simplest to install and gives excellent performance on smaller planing style hulls. Many times the transom is the only part of the boat that remains in contact with the water consistently when planing. It is far easier to drill two to three small #10 holes in the transom than a one and a half inch hole in the bottom. Sometimes what I like to do is to attach a piece of Starboard material--cut into a rectangle four by twelve inches--to my transom where I think might be the best place to mount the transducer. Then I attach the transducer with short screws to the board and can then reposition, or later add other transducer without adding new holes to my transom.

The thru-hull style mount is useful and most effective on displacement hulls. The boat must be hauled and a hole must be bored through the hull and the transducer installed per instructions with the recommended caulking. An advantage to a thru-hull mount is that you can get a "tri-ducer" a transducer that will send depth, speed and temperature signals to the head unit.

If you can't bring yourself to drill a hole in your hull and just don't like the look of a transducer on your transom, you might be able to use an "in-hull" or "puck" style mount. These are the simplest devices and resemble a small hockey puck. They shoot the signal directly through the hull material and work very well. The drawbacks are that they can be mounted only in glass non-cored hulls, will only give a depth reading, and will lose some sensitivity compared to a direct water connection.

There are also "trolling motor" mounts and transducers that can be attached to a stick and pointed where you want the signal to go-a poor man's scanning sonar! There are many mounts because there are so many different hull shapes, types, materials and applications. Every boat is different and the greatest challenge is to find a location that will give you good clean contact with the water. Find that, and you are golden and the envy of every fishermen.

How do I route my cable?
Depending on the transducer mount type, I will usually locate, but not install the transducer immediately. I will run the cable that connects the transducer to the head unit first, so I can really be sure of the mount location later. This is the most time consuming part of the installation. Depending upon your boat, this can either be a quick painless procedure or a brutally lengthy aggravating process. Don't blame the fish finder or me - blame the boat manufacturer!

How you decided to route the cable many times is predetermined with a rigging tube, but on some boats, panels might need to be removed and/or a "snake" device used to pull the cable through the boat. There is no correct procedure; you should get the cable routed in the best way for you. Personally, I use a combination of snakes and twine to do most of my installations. I like using soft metal bailing wire in about an eighth of an inch in diameter. I bend the tip over on itself about an inch and then wrap the base with duct tape. This allows the snake to push through and not get snagged up and stuck. After I have successfully pushed my snake to where I want, I then use duct tape to attach the cable to the snake with along with some poly-twine.

After I pull the cable and twine through to the head, I have a way to add another cable without using the snake. The twine can be used to pull another cable in the future. On routing the cable, you do not want to kink the coax and be careful not to cut any of the insulating cover or crush a connector. Many times, you will have more cable than you need, DO NOT CUT THE CABLE! Coil the excess cable and secure to the boat, preferably in a location that will not interfere with any radios or compass. Use plastic cable ties to secure the cable to the boat placing the ties approximately every four to six inches.

We are finally to the head unit and this is where we get to have fun and call it work at the same time. Sit or stand in the position you normally drive your boat. Determine from that position where you want to mount the head unit. I will spend up to an hour on average just eyeballing different mounting locations before I make a decision and drill that first hole. Think about your electronics in a priority manner. Put the device you use most often directly in front of you. Many times both the GPS and sonar deserve the front row and as a result that is why you see so many GPS/sonar combo units--in my opinion it's a great idea.

Before you mount that head unit, you will need to make sure you can run your transducer cable and power harness to the location. First run the transducer cable and then run the power harness because usually the cable will have a bigger connector than the harness. I like to have a dedicated switch for my electronics, but as long you use an in-line fuse, you can jump power off any twelve-volt source including the battery terminal. However, make your power connection, use heat shrink waterproof electrical connectors. These will increase the life and performance of your electronics. It is very important not to power your head unit on until the transducer is also connected. Some sonar units will fry their components if you do this, just like some stereos will die if you apply power without the speakers hooked up.

If you have a transom mount transducer, it is now time to, at least temporarily, mount the unit. You can always change the location relatively easily, but if you have a thru-hull mount, then you will want to follow the procedure for a "shoot thru the hull" type mount. Contact your manufacturer for specific instructions, but the idea is to move the transducer around while the boat is in a known depth of water and bottom composition. Once you have found the best spot or the location that gives you the most accurate readings then mark that location for mounting. It takes a lot of guts to drill large holes through the hull, so it is best to try to reduce the number of potential holes by getting things right the first time.

By this time you should have a mounted transducer, a routed cable and a head unit that has been connected to a power source. Other than learning how to use your sounder to catch fish, you have just completed an install. You might have to tweak the transducer location over time, but that is the nuts and bolts of a fish finder install. Of course I'm putting myself out of work telling you this, but you can save some money installing your own unit. If you have a free Saturday afternoon, you could install your own in the same amount of time it takes to play nine holes of golf or less.

Hope this helps and you'll go out and install that new fish finder you got for this season. If you don't, then come see me, I'll put it in for you…but it'll cost ya!

Until next time,
Bon installation!

This article is printed with permission from West Marine. Visit their website, http://www.westmarine.com for more boating supplies and information.