Finding Fish: Wide Beam vs. Narrow Beam Transducers

Some anglers prefer peering into the depths with a wide fishfinder beam while others like narrow beams. Which is really best? 

It took you months to settle on the best fishfinder for your needs, and now you have to figure out what transducer would work best with it? Unless you have a PhD in trigonometry and spent the past five years studying piezoelectric crystals and ultrasonic waves, making the decision could be a lot tougher than some people would have you believe. Fortunately, we can boil down a ton of the tech and base the decision on a handful of critical elements like mounting type, range, and critically, fishfinder frequency. Another consideration many of us will grapple with is beamwidth. 

yellowfin tuna caught using wide beam transducer

If you’re focused on finding the tunas, a wider beam will give you a leg up.

Fishfinder Transducer Beamwidth Basics 

Beamwidth is closely related to and somewhat dependent on frequency, because increasing wavelength (which means lowering frequency) increases beam angle, and is one of the two major determining factors in just how wide a fishfinder’s beam will or will not be. The other factor to consider is transducer size, because as diameter increases beamwidth decreases. So, you can’t merely take transducer X with a frequency of Y and “make” it into some specific beam width you’d like — a balance has to be struck between frequency and the physical makeup of the transducer itself. 

transducer frequency plays large role in beamwidth
Frequency plays a huge role in beamwidth. Graphic courtesy of Airmar. 

Remember, decreasing frequency results in increasing beam angle, which widens the beam. But since the transducer manufacturer is the one building the item, and its physical parameters will be out of your control, frequency becomes the key item for we mortal fish-heads to keep in mind. And in a sense, if you have a standard-issue 50/200kHz or similar unit, you already have both wide (50 kHz) and narrow (200kHz) capabilities. 

Of course, those transducer-building brainiacs have the ability to manipulate size on their end of the equation, tilting the balance to create what we would commonly term wide beam or narrow beam units. So, which is best? 

Wide Beam Versus Narrow Beam 

In truth, neither is “superior” and both wide beams and narrow beams each have their own advantages. Wide beams obviously offer more coverage, but narrower beams and their concentrated blast of energy offer far better detail. Meanwhile, lower frequencies and their bigger wavelengths can travel farther, so they offer superior range. When the width/frequency combination is right, and when it comes along with a nice dose of CHIRP action, sometimes a lot more range. A wide beam is also better for picking up pelagics swimming beneath the surface which may not pass directly under the boat, since that beam widens out to cover an expansive swath of the water far sooner than a narrower beam does. On the flip side of the coin, with a wide beam, if you’re looking for structure on the bottom you may not spot it even if you pass directly above. The sharp focus and distinct relief a narrow beam can project to the LCD screen often looks like nothing more than a pancake, from a wide beam’s viewpoint. 

Read Next: Eyes Wide Open: 360-Degree Sonar Views for Recreational Anglers

beam width effects what you will see on your fish finder

This representation by Airmar shows coverage with a 30-degree beam width, in their TM165HW wide-beam transom-mount transducer. Graphic courtesy of Airmar.

What does this mean in practice? If you’re on the hunt for pelagic swimmers like tuna or you’re trying to locate suspended shoals of fish, a wide beamwidth will generally serve you better. But if you regularly enjoy fishing on structure a narrow beam is the way to go. Fortunately, these days there are a wide range of transducers to choose from, including many that have both wide and narrow options. Match them up to the right machine, and you can enjoy fish-finding prowess of all different natures. 

The critical point here? Don’t just buy a unit and accept that the stock transducer is going to be the best one for your own specific needs. Most manufacturers will have a list of compatible transducers you can pick from, and Airmar makes a range of transducers that are compatible with a range of units. (Note for the record that Airmar actually makes the transducers for many manufacturers, in the first place). Weigh your needs by considering the type of fish you go after and the type of fishing you enjoy, then choose the transducer that’s best for your own personal tastes. Hopefully, making that decision won’t require a PhD nor take you a matter of months. 

Leave a Comment