How to choose a fish finder

Marine Werks buying guide · Updated November 2026

A fish finder sends sound down through the water from a transducer and draws what comes back. Four choices decide what you'll see.

1. Sonar type

• Traditional 2D or CHIRP sonar shows fish arches and depth under the boat. CHIRP sweeps a range of frequencies for sharper separation between fish and bottom.
• Down imaging draws a photo-like picture of structure directly below.
• Side imaging scans out to each side, which helps you search water quickly.
• Live sonar shows fish moving in real time. It costs the most and usually needs its own transducer.

2. Screen size

Bigger screens make split views (sonar plus map) usable. A 7-inch screen suits a kayak or small boat; 9 inches and up suits bass boats and console boats.

3. GPS and charts

A combo unit adds a chartplotter so you can mark spots and navigate. If you fish big water or unfamiliar lakes, get a combo.

4. Transducer mounting

Transom mounts are easiest to install. Trolling-motor mounts point where you're fishing. Through-hull mounts give the cleanest signal at speed but need a hull installation.