Fish Finder Installation

Selecting a fish finder and installing in a kayak is a problem solving and decision making exercise. If you're a newbie, there's a ton to learn. And it crosses multiple disciplines - sonar and GPS technology, electronics, engineering, fabrication, etc. Getting a handle on it is like peeling an onion - every layer you remove reveals a few more. But if you don't learn it, you risk buying the wrong device for your purposes, hampering its performance by botching the installation, or being disappointed in your investment because you don't know how to use it. And the manufacturers provide surprisingly little assistance! (And sometimes they even mislead you...) There's a ton of information on the Internet but it's scattered everywhere and is of widely varying quality. If you're like me and you want to feel confident before spending your money or tampering with your boat, you'll end up reading a lot of stuff before you feel ready to take it on.

As part of outfitting it for fishing, I installed a Garmin echoMAP CHIRP 43dv on the SS Guacamole. I'll save my impressions of the 43cv and why I chose it for another post. For this one, I wanted to talk about the install. I know that when I was researching fish finders and how to install them in a kayak, I treasured every decently-written piece of advice I could find. So here's my contribution to the web's collective wisdom on the subject. Giving credit where it's due, I would be neglectful if I didn't mention that I took a great deal of the ideas for this from The Kayak Fishing Blog's post on the topic. In particular, KFB turned me on to the Pelican case and the Mad Frog transducer arm. KFB is a terrific site and great resource. Definitely check it out and bookmark it!

Portable Installation

My kayak is a tandem+1 kayak, which means that I could be sitting in the front, middle, or rear seating position depending on how many people are on board. Therefore one unique requirement I have is that the fish finder display must be movable between all three seating positions. Because of this, I opted to do the install as a "portable system" which can be easily mounted and dismounted from various locations on the boat, or even onto a different boat.

Parts List

Here's my parts list with links to where you can buy everything I used. [By the way, I've no vested interest in any of these products other than the fact they're what I bought. As always, your mileage may vary.]


Pelican 1120
The Pelican case is the hub of the system. Everything is either mounted on or placed inside the case, which is then mounted on the kayak's gunwale. The case holds the battery and wiring, and the fish finder display and transducer are mounted on the outside.

Submersion in water could short your battery, potentially destroying your fish finder or even causing a fire! So you need to protect the battery from getting wet, even if the kayak capsizes. A high quality case is essential for this application. The Pelican 1120 case is small, light, rugged, waterproof, and the ideal size.

One decision you have to make is how to orient the case relative to the kayak. I oriented mine so that the long side of the case was perpendicular to the length of the kayak, with the handle facing the paddler. This increases the odds of my leg or foot bumping into the case, but it also projects the transducer arm a bit further out over the water in order to clear the side of the kayak. You should probably dry-fit it on your kayak to see which way works best for you.

Transducer arm
As part of the portable install, I used a Mad Frog Transducer Deployment Arm to mount the transducer. One end of the arm attaches to the Pelican case, and the other end attaches to the Garmin transducer. The arm extends over the gunwale of the kayak and holds the transducer in the water, just under the surface. Mounting the transducer on an arm is not only portable, but it also sidesteps some of the issues with installing the transducer in-hull or in a scupper hole. In-hull installation gives inaccurate water temperature readings, can degrade sonar signal strength, and causes performance problems if air bubbles get in the sealant. Having accurate water temperature readings is really important to me because it's essential for patterning fish. Installation in a scupper hole can subject the transducer to damage since the transducer will be exposed on the bottom of the boat.

Hole saw
You have to drill a lot of holes for this. A regular power drill works great. Use can use regular twist bits for small holes and hole saws for bigger holes (say, larger than 3/4").

Before bolting anything on the Pelican case, I put a dab of marine sealant on the drilled holes. You need to do this carefully, preferably on both the inside and outside of the case. Otherwise, the waterproof case that you paid a lot of money for will no longer be waterproof! A lot of people use Goop Marine Sealant, which is an excellent product. I used DAP marine sealant because it's more sealant than adhesive, which means I can pretty easily get the part off again if I need to. With Goop or something like 3M 5200, it can be difficult or even impossible to remove the part without damaging something. I figure the screw's job is attachment and the sealant's job is waterproofing. But if you're sure you want the part permanently mounted (and a lot of these parts certainly can be), then feel free to use something stronger.

Save the plastic debris!
Pro tip: Save all the plastic shavings and hole pieces from your drilling! Put it somewhere safe in a zip-lock bag (I keep mine in one of the hatch nets on my kayak). It'll come in handy if you ever need to repair your kayak by plastic welding. Even if you don't know how to plastic weld, save it anyway. You can give it to your repairman if needed or you might decide to learn how to plastic weld yourself one day. In any case, it will be color-matched to your kayak better than the repair blanks you buy.

Battery and Charger

Batteries are a surprisingly complicated topic! You'll be making several decisions about battery type, charging capacity, size, weight, connectors, chargers, and so on. The two best sources of information I found on the topic of batteries are below. I won't bother to reproduce the information they provide. But I highly recommend reading both of these sites as between the two, you'll be armed with all the information that you need.
I picked a standard AGM lead acid battery. It's the most economical choice. The Garmin fish finder that I bought has a pretty low current draw, so I settled on a 5 amp-hour battery. Fully charged, I've gotten 10 hours of continuous use from the battery powering the Garmin and it was still going fine. I have yet to run the battery out of juice on a single fishing trip. For that reason I suspect that a lot of people over-do it on the battery and lug around a lot of excess weight and volume. On the other hand, larger display screens definitely consume more power. 
For a charger, I got a Battery Tender Junior. There are cheaper chargers out there, but many of them greatly shorten the lifespan of a battery by continuing to charge after the battery is full. So I spent the extra money to get a charger that managed that intelligently. A long time ago I had a Battery Tender to keep my motorcycle battery charged during the off-season and it worked really, really well, so I trust the brand. By the way, the charger doesn't actually go on the kayak. I keep it in my garage and top off the battery when needed before a fishing trip.

Mounting the Transducer on the Arm

Fish finder transducers are generally packaged for installation on a power boat. My Garmin for example came with transom and trolling motor mounts, but nothing purpose-built for mounting on a kayak. After doing a bunch of examining, measuring, and mulling over the included mounts, I figured out a way to adapt the Garmin transom mount to the Mad Frog transducer arm.

Transom Mount
The Garmin transom mount has one bracket that attaches to the transducer and a second bracket that attaches to the transom. The two brackets then attach to each other with a pair of bolts that act as a hinge so you can adjust the angle of the transducer relative to the boat. My plan was to ditch the transom bracket and attach the transducer bracket to the transducer arm using a single, longer bolt. I measured everything carefully to figure out what I needed - a 2 inch long, 1/4"-20 stainless steel machine screw and matching locking nut, which I got from Home Depot. By the way, any hardware you buy needs to be stainless steel to prevent rust and corrosion from water exposure. Failure to do this could mean that something expensive winds up at the bottom of the lake one day!

Fabricated spacer
Mounting the transom mount onto the arm also required a couple of 3/8" spacers to hold the arm firmly in the mount. I was planning to use wood for this. Then I found a cutting board at Walmart that was exactly the right thickness (3/8") and since it was made from polyethylene (i.e. the same stuff most sit-on-top kayaks are made of) it won't get damaged from water exposure. Bonus! I cut my spacers from the cutting board using a miter saw (a regular hand saw would work fine too) and smoothed the cuts with a little bit of filing and sanding. I drilled 5/16" holes in the spacers to run my bolt through. The transducer mount attaches to the arm through a sandwich of the spacers plus the washers that came with the Garmin unit. It's a bit odd looking, but it works well. There was a pre-drilled hole at the lower end of the transducer arm to mount the transducer, but it wasn't big enough to fit my 1/4" bolt. It would be easy to drill out except that the hole wasn't perfectly centered on the arm and I was worried that drilling it out would put the enlarged hole too close to the edge of the arm and compromise its strength. So instead of drilling it out, I used a rat-tail file to enlarge the hole, keeping it centered.

Sandwich of spacers, washers, and transducer arm

Mounting the Arm on the Case

Upper arm trimmed to size
I attached the other end of the transducer arm to the Pelican case using the bolt and nut that came with the arm. The arm is designed to attach to a horizontal surface, but I couldn't do that on the Pelican case without grinding off some decorative ridges molded into the top of the case. So I mounted it on the side of the case instead, which is fine so long as the bolt that forms the arm's elbow joint is oriented bow-to-stern relative to the kayak, which means the lower arm will rotate port-to-starboard when deployed in the water. When paddling in the water, the current will flow from the bow to the stern and push on the transducer. If the joint rotation is not port-to-starboard, the arm joint will rotate in the current and move your transducer out of place. This is all kind of complicated to write down as a description, but if you look at my photos below, it should make sense.

Arm folded up for transport
Arm extended
I also had to trim off part of the upper arm so that it fit onto the case nicely and allowed free rotation of the arm joint. The arm is polyethylene so it's easily cut with a saw and finished with a file/sandpaper. The arm also came with a set screw that you screw into the Pelican case next to the upper arm to keep it from rotating out of place when the arm is extended.

Attaching the Fish Finder Display

Oddly, the Garmin doesn't come with bolts to attach its tilt/swivel base to a boat. So I measured things out and bought some stainless steel #8-32 5/8" machine screws, washers, and locking nuts. I bolted the base to the top of the Pelican case making sure to seal the holes well with the sealant. I decided to place mine centered, near the case handle, which is the front of the case when mounted on the kayak.

The Garmin tilt/swivel has a lot of parts: the base bolts to the case, the tilt/swivel screws onto the base, the cradle attaches to the tilt/swivel, and finally the fish finder display snaps into the cradle. It sounds complicated but it's an assemble-once-and-forget-about-it system. Functionally, it's terrific because it's sturdy, it can be oriented in any direction, and the display is easily mounted and dismounted from the cradle without futzing with the cables.

Base, tilt/swivel, and cradle
Fully assembled
Base attached

Wiring Conduit

Conduit for routing wires from inside to outside
The battery and excess transducer wiring go inside the Pelican case, so I needed some way of routing the wiring out to the Garmin display and transducer. For this, I installed a 1/2" liquid-tight conduit fitting (like you would use in an electrical junction box) on the top of the Pelican case behind the fish finder tilt/swivel base. I sealed the mounting hole with marine sealant, and sealed the inside of the conduit itself after the wiring had been run through. I basically filled the entire inside of the conduit with sealant. The conduit is, without a doubt, the weakest part of the system from the standpoint of waterproofing. If I find a better solution, I may switch it out (if possible). If you have ideas on that, I'd love to hear them in the comment section...

Mounting the Fish Finder on the Kayak

To mount the case (and everything else) onto the kayak, I used the Scotty mount system which is what I've standardized on for my kayak.

I installed a Scotty Post Bracket to the bottom of the Pelican case using the bracket's included machine screws and locking nuts. Then I installed a Scotty Locking Flush Deck Mount on the gunwale of my kayak. Scotty's Flush Deck Mount comes in both locking and non-locking versions. I recommend getting the locking version in case of a tip-over. To install the Deck Mount, I used 3/16" marine rivets. You can also use stainless steel nuts and bolts to attach the Deck Mount and in fact that is a more secure way to do it. But I think the rivets are fine for this purpose.

Post Bracket
  Riveting the Flush Mount to the gunwale

The Post Bracket mates with the Deck Mount to mount the Pelican case on the kayak. I installed two deck mounts so that the fish finder would be down near my feet on the starboard side when seated in either the middle or rear seat positions on the Guacamole. I wanted it well out of the way of my paddle stroke, but still reachable by hand.


Once it's all put together, the fish finder is deployed by: 1) mounting the case on the deck mount, 2) locking the deck mount, 3) extending the transducer arm into the water. To remove the fish finder, you just do the 3 steps in reverse. I have an old padded Cordura case that I used to keep a Game Boy in (yep, it's that old!) that I now use to store and transport the fish finder display. To charge the battery, I just open the Pelican case, clip on my charger cable, and plug in. If I want to use the fish finder with a different kayak, it's simply a matter of installing another deck mount.

I hope this helps with your fish finder install. Unless you have the same model of kayak and fish finder that I do, there will undoubtedly be differences in your install. But hopefully this gets you far enough along to work out what those differences are and how you'll deal with them. Good luck!

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  1. So finally I got the guide that I was looking for desperately. I found it more detailed than other articles I read. I recently started learning this skill and also bought the garmin fish finder but didn't know how it can be installed. Thanks to your detailed article for helping me.

    1. You're very welcome! Thanks for visiting and thanks for leaving a note.


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