CHIRP Sounders

Installing a CHIRP sonar system will provide professional quality sounding for anglers who are serious about fish-finding.

Do you ever wonder whether the equipment on your boat is the best it can be? Is there something better, faster, or more useful on the market? What about technology that previously was only available to the military? CHIRP sounding (Compressed High Intensity Radar Pulse) has been used for years in military sonar systems and is now available in recreational fish-finding units. Let’s take a look at why this is great for recreational boaters.

What Does it Do?

CHIRP sonar systems are all about getting the best quality images and adding detail that isn’t possible with conventional sonar systems. This is very exciting because you no longer have to choose between depth or detail—you can have both. Serious sport fishing anglers can see individual fish and features near the bottom and throughout the water column, as well as underwater bottom contours and features. Even at depths up to the stated maximum of 10,000 feet (3,000 metres), individual features are visible (albeit, in less detail than shallow-water images).

With older sounders, you are locked into which frequency you are using. Experienced sport fishers will know that different species and sizes of fish are picked up best at specific frequencies. This sparked the invention of the broadband sounder, with a selectable frequency giving you better images of the fish that you are targeting. CHIRP sounders do more than this. CHIRP operates by changing the frequency (more on that later), and will pick up all the fish species under your boat.

While all these features don’t come free, and some devices suffer from lower gain and hence a shallower maximum depth, the latest and greatest for fish-finding is certainly very cool. Let’s take a look behind-the-scenes at how this technology works.

Traditional Fish Finders

Sounders work by bouncing a pulse of sound off of objects, much like using a fog horn to gauge your distance from the shore. For traditional fish finders the pulse is transmitted at a single fixed frequency, typically either 50 kHz or 200 kHz, and generally for a very short time period. There is a trade-off between target resolution and target depth. A shorter pulse provides clearer images, but will only show shallow details. A longer pulse will emit more energy, which is necessary to show results from deeper depths, but will result in a loss of detail. Hence, the fish and features blur together at depth, and on the typical display it is difficult to differentiate fish that are swimming close together or those that are close to the sea floor.

Why does the resolution drop for longer pulses? If the pulse is longer, the echoes from two objects close together merge into one long echo. It is like trying to use a foghorn by sounding it for a full minute. Usually you can time a short echo to figure out the distance from shore, but if you sound the horn for too long once you stop to listen the echoes are confused.

Instead of hearing a series of short echoes from targets at different distances, you’ll hear a long echo for each target, and chances are they will overlap. You won’t know if there are multiple targets, or one big target. It’s impossible to tell what the details of your surroundings are.

CHIRP Fish Finders

With CHIRP the former trade-off is no longer an issue. Your sounder can identify details on objects much better even at depth, providing much higher resolution images, and showing you where the fish are. This is possible because a CHIRP pulse changes frequency as it is transmitted, so the echoes no longer merge together into one if they overlap from different targets. This is like saying “hello” loudly instead of blowing a foghorn; even when the echoes overlap you can distinctly hear “hello” echo multiple times and know it bounced multiple times. Hence, distinct targets are visible.

Choosing a Unit

If you’re wondering where to get a CHIRP unit, keep this installation information in mind. A CHIRP sounder will run you anywhere from $2,000 to $2,500 for a Garmin GSD26 or Simrad BSM-2 black box. But that is only half the story. To activate CHIRP you’ll need a special broadband CHIRP transducer from Airmar, priced anywhere from $1,500 to $4,500 each.

Ensure the transducer explicitly describes being used with CHIRP sounders; a standard broadband transducer isn’t enough. This is a solution geared toward people who make a living from catching large fish and if you’re serious about fishing it is certainly worth it. As any technology, we can expect prices to come down in the future if demand rises, so keep an eye on this if it’s on your wish-list.

Before purchasing the sounder equipment, check to make sure your multifunction display is capable of showing the data from the black box unit; staying with the same manufacturer is a must, but not enough to guarantee your system will be compatible. Finally, transducers come in thru-hull, in-hull and keel-mount varieties, which should be selected for your budget and to optimize performance on your boat.

Installation

While the parts are unique, installation is similar for any sounder. Install the black box unit, and connect it to your multifunction display first. Importantly, never connect or disconnect a transducer when the black box unit is powered.

Check to make sure it’s all working, and then choose the location to mount your transducer. Location is critical, and different for sailboats and powerboats. The goal of selecting a transducer location is to minimize nearby obstructions and thru-hulls that will create turbulence and bubbles, and to ensure the transducer will always be in the water. For example, one typical location on sailboats is in front of the keel, while for planing powerboats you want it aft and centre, so it stays in the water when you’re planing. A poor location will result in very poor performance, so do some research and make sure it’s right for your boat!

Next, it’s a good idea to test your transducer before you permanently install it to make sure there aren’t any issues. Once the bedding compound is set it’s going to take a lot of work to repair or move it to a better location. Installation may also require a haul-out unless you select an in-hull transducer model. And of course, follow the manufacturer’s instructions to avoid voiding your warranty.


About the author: Jeff Cote is a systems design engineer and owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. This is the first in a new series of columns on thechanging world of technology and boating.