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Kayak fishing - Installing your fishfinder

November 12, 2019
Kayak fishing - Installing your fishfinder

We all know that fishing is about the catch, but before the catch happens you have to find the fish – so how do you do that? Jason Walker goes through fishfinders for kayaks. There is a wealth of information floating around to help you find the general area where there are fish: fishing magazines such as this one, fishing clubs, mates (the ones you can trust that is), books giving you GPS spots to paddle to, and of course a huge wealth of information on the Internet.

The issue is that all of these will only tell you the general area that the fish should be hanging out in, and they will not put you right on the fish that particular day you are there.

So what can you use to assist you to turn a general “there are fish here” into fish on the table to feed your family and friends? Well it’s technology to the rescue – the fishfinder! Not modern technology by any stretch of the imagination. Maybe some of the recent advances could be called modern, but the basic sonar technology used in modern fishfinders was first used by the military towards the end of World War I, with what we call a fishfinder coming on the market in the late 1960s.

Fishfinders can give you a good understanding of what is in the water, what is under your kayak, the depth, the terrain and structure, and of course the fish.

Almost any fishfinder that has been designed to use on a recreational boat is suitable for use on a kayak. These units are small, sealed fishfinders that come in various sizes with a huge range of features. You can start off with a small basic fishfinder with a black-and-white, low-resolution screen that will show you the depth, the bottom structure, and hopefully some fish. Or you could go the whole way and get a high-end fishfinder that will offer you much, much more; an easier-to-read high-resolution colour screen, the bottom structure, the water column in various different ways, the standard 2D, down-imaging, and even what’s out to the sides with the latest side imaging technology.

Some units are classed as combo units and these contain or link up to a GPS to offer you charting functions, which are great for being able to chart your drift so you can paddle back and re-drift along that same line you just picked up those fish on, or use the marine chart to find the fish-holding drop offs and features. Of course, as with everything, the more you spend the more functions you will get on your unit.

Locate your unit

Where you position your fishfinder will be influenced by several factors, the biggest being the type of kayak you paddle. The latest fishing kayaks all sport centre tackle storage so you can mount your fishfinder on the storage covers; older kayaks will most likely have some flat area or areas for you to choose from. Another factor to take into consideration is whether the installed unit is close enough to reach, should you wish to make any changes to the settings on your unit whilst you are fishing.

Mount it too far away and it may become a matter of having to shuffle forward each time. This is going to quickly become a chore and is potentially unsafe. Also make sure it’s easy to see, don’t be tempted to tuck it away somewhere thinking it will be protected, then find you have to crane your neck to see it every time. Then think about how the unit may interfere with your working space; is it going to get in the way of rigging your gear, your bait, or even how you land and deal with your fish? And if you choose to mount your fishfinder on the side of your kayak, be sure it will not interfere with your paddle stroke.

When attaching the fishfinder or mount to your kayak, don’t scrimp on the hardware. Always use stainless steel for all fastenings, either grade 316 or 304, otherwise you’ll end up with rusty screws and stains on your kayak after just a couple of trips.

Centre tackle storage: The latest kayaks have these handy units for storing your tackle. The benefit of mounting the fishfinder on the staorage lid is you can reach it easily.The latest kayaks have these handy units for storing your tackle.


The most important thing when selecting electronics for use on your kayak is that they are waterproof; you should check that they carry a waterproof rating of IP67 or above. IP stands for “Ingress Protection”, the two numbers relate to the level of protection against solids and liquids. The 6 means “totally protected against dust” and the 7 equals “protected against water ingress when submerged to a depth of 1 metre for 30 minutes”.

So if your electronics are rated to IP67 you should be safe but note it is only a submersion rating; it doesn’t mean you can blast it with a high pressure hose when you are cleaning down at the end of the day. And getting rolled in the surf may exert more than 1metre of pressure, so it always pays to put your electronics safely away before heading in through the surf.

Power Source

Without the ability to simply plug your electronics into the nearest power socket, you need to carry your own power source with you: a battery, specifically an SLA (Sealed Lead Acid) battery. This type of battery operates on the same chemical reaction principles as your car battery but with the safety of the acid being sealed inside the battery’s plastic case. This makes it ideal for use in your kayak as there is no chance of the acid being spilt while the kayak rocks and rolls on the sea.

So what size battery? The size will really depend on the current draw of your electronics. Have a look at the specifications and you should find something labeled “current draw” or something similar, it’s normally measured in milliamps (mA) – a thousandth of an amp. For example, an average-level fishfinder will have a current drain of around 250mA, so once you know this you can look at the battery size you will require.

When choosing the size of your battery, it is important to keep in mind that to ensure you do not damage your battery and shorten its life, you should not take the battery past 50 per cent of the battery capacity.

Battery capacity is measured in Ampere Hours (Ah); an Ah is one amp for one hour, so a 12Ah battery is capable of supplying 12 amps for one hour, 1 amp for 12 hours, or anything in between.
So using our example of the 250mA fishfinder, it needs one quarter of an amp. If we planned on fishing for six hours then we would need at least a 1.5Ah battery, but remembering our 50 per cent capacity limit we would look to purchase a 3.0Ah or higher rated battery.

SLA batteries come in many different sizes but the most common sizes are 7, 12, and 18Ah with 7Ah being the most common and more than adequate for our example fishfinder. You can normally find a 7Ah SLA battery for around $30-40.

Note you will also need a special charger for an SLA battery – DO NOT use your normal car battery charger as this will damage your SLA battery very quickly.

Battery Storage

You should keep your battery away from saltwater, so look to put your battery inside your kayak. Saltwater can short out the battery if submerged, and the saltwater has a nasty habit of corroding the battery terminals very quickly which leaves them unusable.

You can secure the battery by using a specifically designed battery tray or a foam block. Simply cut a foam block about twice the size of your battery, cut a hole in the center to hold the battery, then glue the block into the hull of your kayak to keep it secure.


Getting power to your fishfinder is fairly simple. All you should need to do is run the wire from your battery to your fishfinder. If you need to extend the power cable at all, use a marine-rated cable – head down to your local marine chandlers and they should be able to help you out. Make sure you solder all your connections rather than crimping them where possible, and as with everything on the kayak, you want to seal, seal, seal, to keep that salt water out.

On all your connections make sure you do not leave any exposed cable joints. Give them a quick coat of protectant and cover with some heat shrink to keep the moisture out. For the plugs and sockets, make sure you protect those too with a protectant – personally I have been using Lanocote from CRC with great success. Without some form of protection you will find very quickly that electrolysis will eat up the pins in your plugs, rendering your unit useless and in need of a service.

Solder vs. Crimp

As I mentioned above, where possible you should always solder all your connections. I know this is harder than simply crimping them, but there is a reason I recommend soldering. A soldered joint gives a solid connection, i.e. the solder has flowed around and onto each strand of the wire, creating a solid cable stopping the capillary action drawing moisture into the wire and connection – whereas a crimped connection is only squashing the wire against the connection and does not exclude moisture, which will eventually wick into the wire and cause oxidation over time. This will eventually lead to connection failure and frustration when you have to spend time trying to find the bad connection! So wherever possible always solder your connections.


You should protect your valuable electronics with a fuse. The fuse should be placed in the positive line of your wiring. The correct size fuse should be specified by the manufacturer so have a look into your manual – the most common size is 3 Amp. Also think about putting a spare in your fishing kit just in case.


The transducer is the part of the kit that scans the water under your kayak. It needs an uninterrupted view of the water and again, the newer kiwi-designed kayaks have taken this into consideration with their design and they have specially-designed transducer scuppers. These are scupper holes that have been enlarged on the bottom to accommodate your transducer, which means your transducer will actually be in the water – giving you by far the best view. Talk to your kayak manufacturer/dealer, as most will supply a transducer fitting kit as an accessory to make the job very simple.

On older kayaks you may not have a transducer scupper so you will need to look at another method. The most common tried and tested method is to put your transducer inside the hull of the kayak. You have two options, the first is to stick your transducer to the inside hull of your kayak. The “glue” to use is Selleys All Clear – place a large blob of it on the hull and push your transducer into it. The key is to get no air bubbles under the transducer, as these will interfere with the signal. The second method is a “wet mount”. With this you need to make a well to hold your transducer, the well is then filled with a liquid before you insert the transducer.

After Care

As with everything you take on your kayak, it’s going to get exposed to saltwater during the day, so when you get home you need to remove what will probably now be a crusty layer of salt all over your fishfinder as soon as possible. The easiest way to do this is with some tepid fresh water. The method I use is to half-fill the kitchen sink with tepid water and gently bathe my fishfinder in the freshwater for a couple of minutes. This is all that’s needed to dissolve the salt.

Another method to use is to simply sponge the tepid water over the unit – this will have the same effect of removing the salt and is better if you are unsure about submerging your unit. Once the salt has been removed, put the fishfinder to one side to dry, and once the unit is dry you want to place it in a dry environment – I place mine inside a dry box.

Please avoid keeping your unit in the hot water cupboard, as this environment is not ideal for your fishfinder. The warm air will be moist which is not great for your unit or its connections. A dry box is simply an air tight box with a drying system in it – a mini dehumidifier or silica gel – and all your electronics such as your fishfinder, VHF, EPIRB, camera etc can be stored in it between trips. The issue is that all of these will only tell you the general area that the fish should be hanging out in, and they will not put you right on the fish that particular day you are there.

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