How do fishfinders work?

In 1948 (the same year Smye-Rumsby started!), a device for detecting fish underwater was developed in Nagasaki, Japan. Kiyotaka and Kiyokata, the Furuno brothers, owned a small marine electrical company in a small port in Japan.

One day, an experienced fisherman talked to the brothers “I know where fish are. And I can guess its quantity, too!” This private talk between the Furuno brothers and the fisherman provided Kiyotaka with the inspiration for developing a fish finder. “Air bubbles.” said the fisherman, “When air bubbles rise to the sea surface, it means there is a fish school down below.” – This was the secret for fishing.

It was a well-known fact that a sound wave reflects when it hits against a bubble, what Kiyotaka instantly thought was that it can be used for detecting bubbles in order to find fish. This conversation with the experienced fisherman had become an important trigger for developing fish finders.

A fish finder provides underwater information by transmitting ultrasonic waves into the sea and receiving its reflection. Part of sonic or ultrasonic waves reflects back to the source when they hit an object – fish schools, seabeds etc. A fish finder uses this ultrasonic reflection characteristic and displays the readings on a screen.

Furuno have a fantastic section on their website dedicated to fishfinders, their history as well as how to read a fish finder screen. Click here to check it out.

A fish finder consists of two parts: the main unit (with a screen) and the transducer. The main unit should be located where it can be easily accessed. The transducer should be mounted on the boat’s bottom either through-hull or in-hull installation. A poorly mounted transducer may result in failure in capturing reflected waves or other serious defects, giving you inaccurate readings.

Different fishfinders and transducers are suitable for different installations. If you’re not sure what would be suitable for your vessel, our specialist marine engineer team are here to help you find the right solution and fit it where required. We have a range available in our online store, if you can’t find what you’re looking for please call us on 0800 975 6444.