Fishfinders – are they worth it ?

There are a lot of kayaks out there with various electronic gadgets fitted to them. People often ask what are the benefits?, are they worth the additional expense?, how effective are they?, etc.

Well firstly, do you really need any electronic equipment to catch fish off a kayak?, the simple answer is no. Though what it can do is to enhance the fishing experience and ultimately improve your catch rates. I’m going to specifically look at fishfinders in this article.

So how do they work?, well it’s not something I’m going to go into great detail about. Basically it uses sonar with the transducer transmitting sounds waves into the water. These sound waves will reflect off fish or structure, the reflected ‘echoes’ being picked up by the transducer with the relevant information being processed and displayed on the LCD display.

The display will show the depth of the water, water temperature and the type of structure beneath the kayak (model dependent). The temperature sensor detects and displays surface water temperature. Since many fish species are found in specific water temperatures, a temperature graph or digital readout can be helpful in finding them. Remember, this is the surface temperature and has little relationship to the water temperature where the fish are holding!

From time to time the display will show fish, though it’s generally limited to displaying larger or shoaling fish clear of the bottom. That being said, I’m generally not looking for fish returns at all, in fact it’s a rarity to see a fish return in the areas I tend to fish. It’s the depth indication and the structure detail that is invaluable to any angler.

565 display

So what do they consist of?. Well the basic kit will contain a transducer, a display, a mount and assorted cabling. I’m not really intending to go into the ins and outs of fitting one here, there are multiple articles of a number of forums covering specific model fits to particular kayak models.

The sound is transmitted in a cone shape, some models produce multiple cones operating at different frequencies such as my Humminbird 565. Multiple beam models will produce a better definition return and will generally cover a wider area.

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     Single Beam Transducer                                     Dual Beam Transducer

The cone angle will dictate the amount of coverage the cone provides. As can be seen above, a 60 degree cone will cover far more ground than a 20 degree cone.

Below is a quick reference chart for the area covered by the specific cone angle listed.

For example, if you are fishing in 10 feet of water and the cone angle on your transducer is 20 degrees, the area across the bottom is 3.5 feet.

  • 20 degrees - 0.35 or roughly 1/3 of depth
  • 24 degrees - 0.42 or roughly 2/5 of depth
  • 30 degrees - 0.53 or roughly 1/2 of depth
  • 40 degrees - 0.72 or roughly 3/4 of depth
  • 50 degrees - 0.93 or roughly 9/10 of depth
  • 60 degrees - 1.15 x depth
  • 70 degrees - 1.4 x depth
  • 73 degrees - 1.48 x depth
  • 80 degrees - 1.68 x depth
  • 90 degrees - 2 x depth
  • 100 degrees - 2.38 x depth
  • 110 degrees - 2.85 x depth

Sonar Returns

Fish returns can be displayed in two basic formats. Either as an unprocessed sonar return called an "arch", or as a Fish ID symbol (software derived). You can generally choose either presentation, though this is dependent on the model of fishfinder.

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                      Arches Display                                             Fish ID Display

To display "arches", the fishfinder relies on the characteristics of sonar. When a fish passes directly through the transducers beam, it can form an arch on the display screen. The size of the fish arch is affected by the sensitivity setting of the unit, your kayak speed, the depth of the water as well as the location of the fish within the sonar beam. Often only partial arches will be displayed because the fish does not travel directly through the centre of the beam.

If the signal doesn't encounter anything along the way, it reaches the bottom. Soft bottoms like mud and weeds tend to absorb the signal. Hard bottoms such as rock reflect a stronger signal back. These subtle differences in sonar reflections appear on the display screen. That's how a fishfinder "reads" the bottom and everything in between. Experienced users will be able to differentiate between mud, sand, and rocky bottoms.


The resolution of a fishfinder's display is what determines its ability to see fish near the bottom, separate closely spaced targets from one another, and to give an accurate picture of structure and the sea bed. Display resolution is determined in two ways: the vertical pixel (Pixels are the small dots that make up a liquid crystal display. Smaller pixels, and more of them, produce a more detailed image) count from the top to the bottom of the display, and the number of pixels per square inch.

A large number of pixels vertically will show target depths more accurately. More pixels per square inch will provide better detail of structures, a better representation of what's below you, and improve split screen images. But remember: the contrast of the display must also be sharp in order to use the resolution.


                     High resolution display                                        Low resolution display

Displays are available in colour or black & white dependent on the particular model. I personally prefer black & white displays as they use far less current than the equivalent colour model. I personally feel that colour displays are not really worth the additional expense, though it’s down to personal preference at the end of the day.


                   Monochrome Display                                            Colour Display

Transducer Types

Thru-Hull Mount - In this installation, the transducer is generally bonded to the inside of the hull with epoxy (I used ‘Marine Goop’). Ideally, the transducer is placed close to the centre line. The signal "shoots through" the hull with some loss of signal strength. This installation must be made in an area of the hull that is made from solid material, with no air bubbles or separated layers. There are alternative methods to mounting this type of transducer to the inside hull of a kayak, these include mounting it within Vaseline/water filled ‘container’. I’d highly recommend taking your time and researching what will best suit your model of kayak.

Humminbird offer a kayak specific through hull transducer which actually passes through a scupper hole. This offers a simple to fit transducer which isn’t open to de-bonding from the hull over time unlike some transducer installs. Note the transducer is visible protruding from the scupper hole in the photograph shown below.



Thru-scupper mounted transducer

There are yet more considerations, such how to power your fishfinder. Some people use small re-chargeable batteries whereas others (including myself) use a larger SLA type battery. Again it depends on the model of fishfinder as well as your own personal requirements. For example, my battery also powers my GPS, navigation light and baitwell.

There are a huge amount of models out there. Prices vary greatly from under £100 to well over a £1000 for high specification side scan models. Clearly you have to weigh up what your requirements are against your budget.

But is it worth it?, for me the answer is definitely yes.