How to Install a Fish Finder on a Kayak (Duct Seal Trick + Scotty Mount Guide)

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Picking a fish finder is the easy part. You read a few reviews, you land on the Garmin Striker Vivid 4cv, you click “buy.” Then the box arrives and you’re staring at a transducer cable, a bag of screws, and a RAM mount ball wondering how any of this is supposed to end up on your kayak. That’s where most people get stuck — not the unit itself, but the install.

There are really two paths here. The Scotty 141 side-arm mount screws a bracket onto the outside of your hull and clips the transducer into a swinging arm. It’s fast, it’s adjustable, and if you decide you want to move it, you’re only undoing a few screws. The in-hull duct seal method puts the transducer inside the hull with a $5 wad of plumber’s putty — no drilling into the bottom of your kayak, no external arm dragging on the water, no permanent modification. Both work. Your choice comes down to how you fish and how much you care about aesthetics.

If you’re new to this, start with the Scotty arm. If you’ve had a kayak for a season or two and you want a cleaner rig, read the duct seal section carefully — it’s the install method the r/kayakfishing community keeps coming back to, and for good reason.

Two Mounting Methods — Which One Is Right for You

Through-hull means you’re drilling a hole through the bottom of your kayak and epoxying a transducer housing in place. That’s a commitment. Unless you’re building a tournament rig, skip it.

Method 1 — Scotty 141 Side-Arm Mount (Step by Step)

The Scotty 141 is the community default for a reason. It’s twenty-five dollars, it ships fast, and the mount pattern is simple enough that you can do this in your driveway before you head to Lake Thunderbird on Saturday morning.

1. Choose your mounting location. The rear quarter of the kayak, just behind your seat, is standard. Port side (left) is the convention, but go with whichever side keeps the cable run shorter to your display. The transducer needs to hang below the waterline when deployed — hold the arm against the hull before you drill anything and confirm the depth.
2. Mark the screw holes. Use the Scotty base plate as a template. Hold it flat against the hull where you want it and mark the four holes with a pencil or a scribe. Keep the plate as close to vertical as you can so the arm swings cleanly.
3. Drill pilot holes. Use a #8 self-tapping screw as your size guide and drill slowly. Kayak plastic wants to crack if you rush it. Go slow, let the bit do the work, and don’t bear down hard on the final pass.
4. Apply marine sealant to each hole before screwing down. A dab of Loctite Marine Epoxy Sealant or basic 3M 5200 fast cure in each hole before the screw goes in. This is the step people skip. Don’t skip it. It’s what keeps water out of the hull foam.
5. Attach the arm and thread the transducer cable. Run the cable along the hull toward your display. Stay inside the cockpit rim where you can — the cable stays cleaner and doesn’t snag your paddle shaft.
6. Use cable clips or adhesive cable guides to keep the wire tidy. Self-adhesive cable clips spaced every 12 inches or so make a big difference. Loose cable flapping around is how connectors get damaged.
7. Swing the arm up when transporting. The Scotty arm folds up when you’re paddling to shore or loading the truck. It deploys in seconds once you’re on the water. You won’t drag it on the bottom, and it won’t snap off in the car rack.

Method 2 — In-Hull Mount with the Duct Seal Trick (Step by Step)

This is the one. If you spend any time on r/kayakfishing or the kayak fishing Facebook groups, you’ve seen this come up. Someone asks about in-hull transducer options, someone mentions duct seal, the post gets 200 upvotes, and the thread dies. It’s been that way for years because it actually works.

Duct seal is a gray putty that electricians use to seal conduit penetrations. It’s not the silver tape. It’s a heavy, pliable putty that you’ll find in the plumbing or electrical aisle at any hardware store — Home Depot, Lowe’s, Ace, all carry it. A block costs around $5.

1. Find your flat-bottom sweet spot inside the hull. Open the bow hatch or look through the cockpit. You’re looking for a section of flat or gently curved hull bottom, usually forward of center and well away from any scuppers. Avoid areas directly under a seat or where flex is obvious when you press down.
2. Fill a baseball-sized wad of duct seal putty. Pull enough putty to make a generous ball — think baseball, not golf ball. You want enough material to fully bed the transducer face and eliminate any air pockets underneath it.
3. Press the transducer puck face-down into the putty. The face of the transducer (the flat sensing surface) goes toward the hull. Work the putty up around the sides of the puck so it’s fully supported. No air gaps means a clean signal.
4. No drilling, no silicone, no permanent modification. The putty holds the transducer in place by friction and weight. It’s not going anywhere on the water, and it peels off clean if you want to move it.
5. Works with the Garmin Striker Vivid 4cv bundled transducer. The GT20-TM puck that ships with the Striker Vivid 4cv is exactly the right form factor for this method. Puck-style transducers seat in the putty cleanly. Long, narrow transducers are trickier.
6. Route the cable through an existing scupper or hatch. Fish the cable through your scupper plug hole or under a hatch rim — don’t drill a new hole for this. In most sit-on-top kayaks there’s a path from the hull interior to the cockpit area without any new penetrations.
7. Test it in a bucket of water first. Before you drive to Canton Lake or the North Canadian, drop the bow of the kayak in a big garbage can or livestock tank full of water, power the unit on, and confirm you get a depth reading through the hull. If you’re getting noise or no reading, recheck the putty — there’s an air gap somewhere. Re-seat the transducer and try again.

Mounting the Display

Your transducer can be perfect and your readings still useless if the display is mounted somewhere you can’t see it while you’re fishing. The industry standard is a RAM mount ball on a gear track or GearTrac rail — it’s flexible, you can adjust the angle on the fly, and the ball mount absorbs paddle bumps.

The community’s preferred display mount right now is the YakAttack Switchblade with CellBlok (~$70 together). It gives you a locking arm that integrates cleanly with YakAttack GearTrac, holds a heavy unit steady in chop, and the CellBlok doubles as a phone holder. A lot of people buy the Scotty display mount first and then upgrade to YakAttack — save yourself the step and start there if your kayak already has GearTrac installed.

Mount the display within easy line-of-sight but out of your casting stroke. Right-handed casters generally want the display forward and slightly to the port (left) side. Left-handed casters, reverse that. The RAM hardware or YakAttack ball adapter works with either setup — just make sure the ball size matches your mount arm.

Power — Battery and Wiring

The Garmin Striker Vivid 4cv runs on 10–20V DC. You have two real options: a 12V sealed lead-acid (SLA) battery or a LiFePO4 lithium battery. The SLA is cheap — a 7Ah SLA runs around $25 at any auto parts store, and it’ll run a Striker Vivid 4cv for well over a day of fishing before it needs a charge. The LiFePO4 is lighter by about 60%, charges faster, and lasts years longer. If you’re already hauling a heavy sit-on-top to the water, the weight difference is real. Worth the upgrade when you’re ready to spend ~$60–80 on a small lithium pack.

Run the power cable through a hatch or an existing access port. If your kayak has a stern hatch, the battery lives there in a small battery box and the cable runs under the seat. If you’re working with a bow hatch only, use a cable organizer to keep the run clean along the hull interior. Never drill new holes for wiring when an existing route exists — every penetration is a potential leak point, even when sealed.

A 10Ah battery runs the Striker Vivid 4cv for 20+ hours. You’re not going to run it dead in a day trip. Recharge it with a standard trickle charger between sessions. Store the battery in a dedicated battery box or rig a cord-loop sling inside the bow hatch so it doesn’t slide around in chop.

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