Digital depth sounders display depths as numbers: 125.6, 23.9, 45.7, and so on—one number at a time.

Flasher depth sounders, often called flashers, display depths as flashes of light around a gradated circular display. The gradations come in various scales: feet, fathoms, and so on; and often it’s possible to select between them. More often than not, flashers display multiple “depths” simultaneously.


Isn’t there only one depth?

No, actually, there isn’t.

Hang tight and I’ll explain.

A Flasher Showing a Depth of 15 Feet

The flasher depth sounder creates a flash representing the depth from which each “significant” echo has returned, and as indicated above, often multiple flashes, that is, multiple depths, are displayed at the same time. The operator can determine what is and what is not “significant” by adjusting the instrument’s gain and sensitivity controls.

The picture to the right shows a flasher indicating a depth of 15 feet.

Usually, the strongest echoes come from the bottom and make the brightest flashes. Weeds and fish return weaker echoes and make duller flashes.

This isn’t really as confusing as it might at first appear to be.

For example, if the bottom is at 45 feet, the top of the weeds are at 35 feet, and a fish is cruising along at 24 feet, then a flasher will display flashes at 45 feet, 35 feet, and 24 feet. If you don’t want see the weeds and the fish, you can, mostly, adjust the unit so that it doesn’t display them.

With a minimal amount of experience, it’s duck soup to tell what’s important and what’s not and to adjust the depth sounder accordingly. I’ve almost always been able to adjust flashers so that the only echoes reported are the ones coming from the bottom. Yes, there can be stray flashes, but it’s easy to tell whether or not they can be ignored.

Also with a bit of experience, it’s possible to tell what sort of bottom is down there: rock, mud, sand, and so on. Often there’s a layer of mud or debris over a hard bottom. With more experience it’s possible to figure that out, too, and how thick it is, using the intensity and pattern of the flashes.

On the other hand, current-generation fish finders use the returning echoes to paint a picture of the entire water column and, to some extent, the bottom. They display that picture on a television-like screen.

Some fish finders display a fairly abstract image, while others display detailed renderings. Some are so fine-detail oriented that they can show the wheels on Junior’s discarded bicycle, the position of a lure in relation to the fish, and, I guess, whether or not the fish look hungry.

Which is all the good, but what I’m primarily interested in is, how stinking deep is the stinking water? And I need to know that reliably, time after time, regardless of turbulence, kelp, algae, plankton, jellyfish, and changes in water temperature.

In and of itself, however, depth often isn’t the whole story. Many beautiful anchorages were at one point log-booming areas or built-up in some way. Depending on how long they’ve been abandoned, the bottoms of such areas can be littered with deadheads, broken-off pilings, and other debris.

In such places it would be nice to have a fish-finder’s rendering of what is on the bottom: deadheads, pilings, outlying rocks, etc.—things that can foul an anchor or punch a hole in the boat’s hull.

In such situations, I don’t know of anything that is quite as good as a high-quality fish finder.

On balance, however, I’ve decided that my next project will be to install a flasher depth sounder on my boat. No, it won’t tell me whether or not the fish are smiling or where the remains of the wrecked docks are lurking, but it will tell my how deep the water is . . . time after time after time. And therein lies its value.


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