# DIY Underwater Kayak Lights

Update: You can see the underwater lights in action in a clear freshwater lake here. The lights come on at about the 2:00 mark.

## Introduction

Many claim that bowfishing is strictly a nighttime activity. While I certainly don’t hold this belief, I still like to take a bow into the darkness from time to time in search of fish. That’s why I decided to build an underwater light setup for my kayak.

A lot of the information I needed was already out there on the web. Google “DIY flounder gigging light” and see for yourself. There are tons of articles and forum posts filled with gory details about how to build good, cheap, underwater lights.

I’ll still suggest a few pointers that helped me out in case you want to make your own underwater light rig.

## Design

There were a few specific requirements that I identified for my design. I wanted my setup to be:

1. Cheap (no car batteries)
2. Quiet and lightweight (no generators)
3. Long-lasting  (5+ hours per charge)
4. Removable

Points 1 – 3 required a delicate trade-off between a power supply that could last a long time and bulbs that got the most lumens out of the least amount of wattage. I decided to use MR16 LED bulbs, typically used for accent lighting in homes, as my light source. They output 350+ lumens at only 4W of power consumption each. With two bulbs mounted on both port and starboard, I estimated that I could power them for over six hours on a 9AH deer feeder battery. I used the following algorithm for this estimation:

$\text{watts} = \text{volts} \times \text{amps}$

The battery is 12V and has an estimated capacity of 9AH:

$\Rightarrow 12 \text{ volts} \times 9 \text{ amp-hours} = 108 \text{ watt-hours}$

Each of the four bulbs requires 4W of power:

$\Rightarrow 4 \text{ bulbs} \times 4 \text{ watts} = 16 \text{ watts}$

Divide the battery’s capacity by the power consumption:

$\Rightarrow \frac{108 \text{ watt-hours}}{16 \text{ watts}} = 6.75 \text{ hours}$

Points 4 – 5 were simpler to address. I built housings for the bulbs out of 3/4″ PVC, and mounted the housings to a scrap piece of lumber with conduit hangers. The conduit hangers could be loosened by hand to let me submerge the lights more or less depending on the depth of the water.

I have a NuCanoe Frontier 12 with six foot t-tracks running parallel to each other on port and starboard. I cut some scrap aluminum strips and hammered them into 90° angles to make brackets for mounting the scrap wood frame to the t-tracks.

After mounting the frame to the kayak, I wired the battery assembly together in an ammo box with an on/off switch and an in-line fuse box. I had to screw a frame together to wedge the battery into the ammo box so that it didn’t move around when the kayak was jostled. All electronic components besides the bulbs were purchased at AutoZone.

I think the pictures at the bottom of the post are more helpful than a detailed written description, but please let me know in the comments if you have any more specific questions.

## Results

Overall I consider this a solid first attempt. When I took the kayak out in a shallow saltwater marsh on a windless night I could easily see stingrays far enough away to set up a shot before I spooked them. The lights worked great under those conditions, as you can see in the second half of the video above.

However, I was disappointed with how limited the lights were when the water was even a little cloudy. When I took them out in freshwater I found myself relying solely on my headlamp to search in a large radius around me for gar on the surface. I barely even looked down in the two foot radius illuminated around my hull. Why use the light rig at all if a \$20 headlamp outperforms it?

Luckily the battery I bought greatly exceeded my expectations, powering the lights one night for almost seven hours straight! The battery actually outlasted me, and I paddled back to the launch before it died.

Given the poor illumination in cloudy water and surprisingly long battery life, the next iteration of my light setup will have more powerful LEDs. I may also add a third bulb to each side, and angle the bulbs away from each other for a wider field of view.

## 3 thoughts on “DIY Underwater Kayak Lights”

1. Felipe Dominguez |

Curious if you have played with different angles for the light. Do you fish deeper waters and therefor only shoot at the top? I plan on fishing in spring fed rivers that are about 3-4′ deep, was just wondering how deep the lights penetrated at that angle.

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• I built the mounting brackets with extra holes that I can use to adjust the angle but didn’t notice a difference when I tried it. The light scatters quite a bit in the murky waters I go to. In a spring fed river it might be worth it since I imagine the super clear water won’t scatter the light as much.

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