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    Categories: ColumnsElectronics

Fish Finders and Transducers

Raymarine CP570 Professional CHIRP Sonar Module

Why it’s time to take a closer look

By Brian Kelly

There have been a number of advancements in the world of fish finders and transducers in the last five to ten years. Anglers are better equipped to catch more fish and boaters are better able to navigate through rocky passages due to the development of technology. As you’ll soon learn, there’s a lot more to all this than the little puck that protrudes through your hull!

Identifying your needs is the first step in deciding what type of equipment is best for you. Are you going to be installing the products yourself? Will you be using the equipment primarily to track fish? Do you just want to know the depth of the water? If the latter is all you’re looking for, a simple depth gauge may suffice, but with all that technology has to offer, it might be tough to pass up on some of the neat products out there.

Nowadays, most chart plotters are considered multi-function displays because they have the ability to act as radar, a fish finder and can display your engine information all in one place. Having the capability to plot a course and track fish at the same time is a great feature, especially when real estate on your dash is limited. Let’s take a look at the various transducer technologies available and how to install them.

For fishing, you just can’t beat the power of a CHIRP. I don’t mean some kind of call you make to get the fish to jump out of the water, I mean CHIRP, short for Compressed High Intensity Radar Pulse. It’s a relatively new technology for the recreational market, but dates back as far as World War II.

Before CHIRP, sounders were designed to interpret a continuous amplitude modulated wave (AM). This created a tone-burst acoustic signal. With AM, noise interference is present and creates clutter on the screen. CHIRP technology, on the other hand, produces a frequency modulated (FM) sound signal and creates virtually no noise because the signal is carried in the changes in frequency. No noise equals better fish targeting and the ability to pick up wrecks or contours of the bottom.

Traditionally it has been difficult to pinpoint fish when there is only one beam angle to rely on for information. Now, with newer systems developed by Raymarine, Furuno and Simrad, it’s harder for the fish to hide.

Raymarine has a very accurate (and affordable) system with their Dragonfly line. The Dragonfly uses CHIRP DownVision technology to view fish and structures from wide angles. When mounting two transducers with this system, you can catch wide views from both sides of your hull.

Navigating through uncharted waters can definitely put you on edge. Not knowing where the next shoal will pop up is something that can make you sweat a bit. Simrad has a system in which the transducer is pointing forward. This allows you to view upcoming shoals, or just shallow water in general. ForwardScan will fire the elements in the transducer from the top to the bottom, creating an image of what’s approaching. Its main purpose is collision avoidance, not detecting fish.

Furuno has developed a BDS (Bottom Discrimination Sounder) that indicates what type of bottom you are looking at. The sounder will identify whether the bottom is mud, sand, gravel, or rock. This can be quite handy for larger boats looking to secure a safe anchorage as well as for choosing the proper anchor.

Now that we have a better idea of the types of fish finder technologies out there, we can look at installation and what is key to optimal performance. There are three ways to mount a transducer: through-hull, in-hull and transom mount. Through-hull is the preferred and most accurate mounting option. It allows for minimal interference and the sensor will have direct contact with the water. Mounting of the through can be complicated if you don’t know what you’re doing.

First, if you already have a transducer mounted in the boat, make sure the new one is approximately three feet away. Next, determine what material your hull is made from – straight fibreglass or cored. With a cored hull, you will have to dig out some of the core and apply some epoxy. The transducer has to be mounted as vertically as possible. In some cases, a high-speed fairing block – a type of shim that compensates for the deadrise of the hull – will have to be installed to get the proper alignment.

In the past few years, Airmar has designed a transducer with the element floating in an oil bath. This allows you to install the transducer flush to the hull and still compensate for the hull’s deadrise.

Be mindful of anything in front of the transducer. Make sure there are no steps, other through-hull fittings or intakes. Aeration going past the transducer will cause significant loss in performance as well.

If you have a performance boat, or just don’t want a hole going through the bottom of your boat, an in-hull transducer may be the way to go. Mounting in-hull lowers performance and accuracy because there is always a slight signal loss. The options for mounting are also limited, with fibreglass hulls being really the only possibility for an in-hull mount. To do the installation, a special silicone or epoxy is applied to the element that then rests in an oil bath.

The final option for mounting a transducer is the transom mount. This is the easiest installation of all the methods since it doesn’t require drilling a hole in your boat. You also retain all of the performance. It is usually the preferred mounting method for smaller boats. Location is critical, though. Mounting it too close to the propeller will cause aeration and too far below the hull might affect the propeller.

Because technology changes so quickly, it’s best to educate yourself on what is out there before making that big purchase. Talk to your friends and see what they are using, ask your local marina or marine electronics company what the popular products are and why. With all of this high-tech fish finder technology available, making excuses on why you didn’t reel in the big one should be a thing of the past!

This article is featured in the Fall 2015 issue of Boats&Places.

Brian Kelly:

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