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Kayak Modifications: Installing a Depth Finder

Resident fishing expert Trevor Bellrichard begins a series of Do-It-Yourself kayak modifications to turn what would be a run-of-the-mill sit-in kayak, into a rather credible and comfortable fishing vessel. Canoe and kayak modifications are likely to become an ongoing series, but initially we’re focused here on fishing mods in what was lovingly called “From Crappy to Crappie” as a working title. We hope these DIY hacks inspire your next offseason project, or save you some money at the very least. First up, “Episode one: Installing a through-the-hull depth finder.”

Installing a depth finder on a kayak
By Trevor Bellrichard
Resident Fishing Expert/Voyager/Explorer/Pisces/Some Guy/Miles Paddler since 2017

Do you have a kayak? Me too, weird! Do you like to go fishing? Samesies! I can tell we’re going to be friends. As friends, I’m going to share the tips and tricks, successes and failures that I’ve encountered while modifying my sit-in kayak for fishing. Shelling out $2000 for a fishing-specific kayak is simply not in the cards during this lean time. Also, it’s much easier to drill holes in a $400 Facebook Marketplace purchase. So without further ado, here’s a simple-ish DIY modification to a sit-in kayak to improve your fishing experience.

Let’s start with the most daunting task – a depth finder. Don’t worry, after some trial and error, this project ended up being relatively cheap and pretty easy. I made a few mistakes you won’t have to. I chose to install the transducer inside my kayak. Sit-in kayaks do not have scupper holes and many companies make transducers that fit inside sit-on kayak scupper holes. An alternative option for the sit-in kayak owner would be mounting the transducer on an arm that you can attach to the side of your kayak. I chose not to do this as the arm and transducer would decrease my maneuverability and tracking. Now, let’s begin and get down to brass tacks.

Equipment and Cost

Installing a depth finder on a kayak
Lowrance Hook2 4x: $106
This is the simplest depth finder that Lowrance makes. Shooting the sonar signal through the hull means no side-imaging and a greatly reduced signal if you try to use down-imaging. I chose basic sonar, no GPS.

12v Battery: $22
This battery is small and weighs around 4lbs. You don’t need a massive battery to run a fish-finder only. I should get 10 hours+ of run time before requiring a recharge from this unit.

Large Watertight Box: $15
Your battery will fit inside this, on its side. I picked this up at a Farm & Fleet while there for another item. It’s also on Amazon for a similar price.

Duct Seal: $9
This is for sticking your transducer to the bottom of your kayak. This stuff never gets hard and you can remove it at any time. Even still, I’ve been confident with this holding while in transit; as have many others on kayaking forums. This can be found much cheaper locally than on Amazon.

Velcro: $20
I have Velcro in many spots around my boat. You can add a lot of storage sticking odds and ends against the interior walls. In my case, I use kinda-sorta waterproof bags, see below.

Kinda-sorta Waterproof Bags: $12
I use all sizes of bags all over my boat. I have a large one under the bow, medium-sized ones on either side of the seat, and for the purposes of this project, one medium bag behind the seat to manage cords. The material is waterproof, but the closure method (a regular zipper) is not.

Odds and Ends: $34 Maximum
These are things that you can probably find around your house, junk drawer, or the bottom of your tool bag. Most of these items could be found in singles and cheaper at your local hardware store too. You’ll need two female connectors ($12 for an assortment that should cover most situations if you don’t already have some) to link your depth finder wires to your battery. You’ll also need one wire cap ($8 for a mess of them) and electrical tape ($4). Finally, I used three hooks ($10) to keep the depth finder wires high and dry under my gunnels.

Total Cost: $78.00 in materials, $106 for depth finder, or $184.00 all in (assuming you already have the odds and ends).

Connecting the Battery
First things first, open your depth finder box, make sure all of the parts that should be there are and start day-dreaming about all the walleye you’re going to catch. Day-dream over, let’s connect to the battery and make sure this thing turns on. Take your two female connectors and crimp them down on the exposed wires of your depth finder. You’ll have two bare wire ends sticking out of your main depth finder cord bundle as well as an inline fuse box and wire. On the black negative wire, crimp a female end directly onto the bare wire, wrap in electrical tape.

Now the tricky part, put another female connecter on one end of your wire with the inline fuse and wrap in electrical tape. Then, cap together the red wire still sticking out of your main cord bundle and the other end of the inline fuse wire. (A guy at True Value checked this to make sure I did it right, ask someone if you are unsure).

Installing a depth finder on a kayakOk, that done, hook up to your battery and turn that baby on! Familiarize yourself with the functions of your unit. The systems, especially on basic models, are very intuitive. Push all the buttons, find out what they do, no judgement here.

Waterproof Box
Preventing the battery from getting wet is electronics on the water 101. I thought a lot about the easiest way to achieve that and came up with the following.

Open your waterproof box, place  the battery inside on its side, make sure it fits with the wires attached. Assuming it does, decide where your battery box will be in your boat. I placed mine as far into the bow as I can reach while in the kayak seat. It’s out of the way of my feet, but still accessible in an emergency. Cut three strips of Velcro. With two of the strips, stick one side to your waterproof box bottom and the other side to the bottom of your boat where the battery box will reside. Give those a couple of minutes to properly adhere and test it out. Use the last strip to secure your battery in one spot, in the box. This will hold your battery in place should things get a little western while on the water.

Next you’ll be making your waterproof box… less waterproof. The only way to get the wires into the box without crimping them is to drill a hole. Open the lid, you’ll be putting a hole in the box itself. Get a largish drill bit and drill a ¾” hole into the center of the box when looking at it length-wise.

Installing a depth finder on a kayakInstalling a depth finder on a kayak

Now, give yourself plenty of slack and place your connections and extra wire in the box with the main line sitting in the hole you just drilled. Make sure the lid still closes properly. If it doesn’t, enlarge your hole to adequately accommodate the wire.

Installing a depth finder on a kayak

If it seems counter-intuitive to drill holes in a waterproof box, it is. My feelings are, if your battery is in danger of getting wet using this system, you also have 3” of standing water in your boat and your problems are far more dire than a battery getting wet. Being under the deck, in a waterproof box, and well forward of “the splash zone” is plenty of protection.

Place the box with wires and battery inside into its home location and make sure you like it.

The Screen
The placement of my depth finder screen was a no-brainer. I already have a hole in my cockpit deck that serves as a very poor drink holder. I think the previous owner may have put it there. The wire connection for my screen comes up through that. My screen is mounted very close to that, on top of the deck and a little to the right. The install of the mounting bracket is very easy, using only four screws.

Installing a depth finder on a kayak

Think long and hard about where the screen will serve you best. You’re putting four holes wherever you choose, so choose wisely. My kayak has a ridge in the absolute middle of the deck that wouldn’t allow for a center placement of the screen, which is also why I put mine slightly to the right of that ridge.

Installing a depth finder on a kayak

Make sure to place your battery box in its final location, wires inside, before attaching the screen bracket. You need to make sure the wires will reach, wherever you decide.

My Failure
Skip this section if you are all business and want to get your boat in the water. This how-to is kind of long already. If you have time and want to smile quietly to yourself, thinking about my screw up, read on.

This most important part of this project is ensuring that your transducer has adequate contact with the bottom of your boat and is sending/receiving a signal well. I read many, many, MANY forums and decided that I was going use marine glue to stick the transducer to the bottom of my boat. I was very nervous and rightfully so, it turned out. Your transducer will not function if there is any air between it and the bottom of your boat. That air could be as simple as tiny bubbles in the glue you use or the smallest deviations of angle between your transducer and the hull. The process seemed pretty simple, cut the end off of a tube of silicon sealant, put a big ol’ glob on the bottom of your boat, shove the transducer down into it and let it dry. I followed those steps and headed toward Lake Waubesa for a test run.

Installing a depth finder on a kayak

At the boat launch, someone was asking me about my kayak set-up and the depth finder specifically. Thinking I was hot sh*%, I told him all about it and the simplicity of my system. Feeling pretty good about myself, I shoved off onto the lake. Immediate failure.

Installing a depth finder on a kayak

It’s amazing, how quickly the universe can humble you. I thought something like this may happen and had brought extra glue and duct tape along. All that resulted in was wasted tape and wet marine glue all over myself and my boat. I wiped my hands the best I could and drove my sticky boat and SUV home. Had it not been the morning, a few drinks would have been consumed.

The Transducer
After some trial and error, I settled on mounting my transducer to the hull of my boat using duct seal. As you learned in the description above, duct seal is 100% pliable all the time and not permanent. Should you decide you don’t like your transducer’s location, you can change it. With that said, it is also very sticky and gives you great peace of mind while travelling and on the water that your transducer will not move in a significant way. I don’t know what this stuff is made of, but it’s amazing. Better living through Chemistry.

Decide where your transducer will be mounted. Mine is directly behind my seat. The way my boat is designed, that area is wasted space. Choose a spot where your transducer can sit, unmolested, the majority of the time. Its chosen location must also be flat which may limit your options.

Make sure the transducer wire will reach the spot where you want it with your battery and screen in place and connected. Once you decide, roll a large chunk of duct seal into a snake long enough to go all the way around your transducer without touching.

Installing a depth finder on a kayak

Now, smush the inside and outside of that snake down onto the hull of your kayak, still making sure that the transducer won’t be touching on any side. You need a water tight seal, make sure that you go all the way around your circle.

Installing a depth finder on a kayak

Pour water into the bowl you have created and check for leaks.

Installing a depth finder on a kayak

Put your transducer back into your bowl and work the duct seal around the back of the unit, where the wire comes in. If you need more material to make this happen, use it. One brick of duct seal is more than enough for this project.

Installing a depth finder on a kayak

Get more duct seal material and form a sheet/lid to your bowl that will cover ¾ of it. Place it onto of the transducer bowl and begin to join the two pieces of duct seal. This is your last chance to ensure that the transducer is making good contact with the hull and doesn’t have any material below it which would impede the signal. Check carefully. If you are happy with the placement, finish joining your lid and bowl together, creating one piece that is water tight. Use as much material as is necessary to ensure your transducer will not move and that your bowl will hold water.

Installing a depth finder on a kayak

Why is there water in your duct seal bowl you may ask? Good question. While you made sure that your transducer was making excellent contact with your hull, there is a chance that it is angled up or down, left or right, the tiniest amount. Enter the water. Water works into all of the nooks and crannies you may have left, filling them completely. Air between your transducer and the hull will limit sonar performance or stop it from working all together. The water ensures a solid sonar return. I usually just scoop a few handfuls of water at the boat ramp into my transducer bowl.

Cord Management
This is the home stretch, if you followed along this far, I commend you on a job well done. With my transducer in the back of my boat and my screen/battery system in the front, I have a lot of wiring on the floor of my boat. You’ll have a ton of left over wire on the transducer end as well. Here is where the hooks mentioned above come in. I screwed three of these hooks, equally spaced, along the inside of my cockpit, under the gunnel. This gets the wire up and off of the floor.

Installing a depth finder on a kayak

Behind my seat, on the same side as the hooks, I attach a medium zip bag to the wall of the kayak with Velcro. Inside, I can wrap all of my slack cord up and zip the bag mostly closed, keeping everything neat and tidy. Choose a bag that is large enough to hold the battery connection wire and screen wire as well. When your boat is in storage or when you are on a trip that doesn’t require sonar, your wiring is out of way and completely contained, waiting for the day that you decide to go out and fill the freezer.

Installing a depth finder on a kayak

While the duct seal isn’t permanent and can be removed at any time, you will not want to be recreating the bowl and cover, making sure your transducer is in the right spot every time you hit the water. Managing the cord and keeping it in the boat at all times is much easier and more effective. The bag achieves that.

Sweet, Sweet Victory
Pick your favorite body of water and give your system a test run. If you are not getting a good signal from your system, press your transducer down into the bottom of your boat, it may have been jostled during transport. To date, I have not had any problems other than that. Get out there and get some fish!

Installing a depth finder on a kayak Installing a depth finder on a kayak

Yes, this is only a white bass, but it christened my system.

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