Understanding Fishfinder Technology

This overview explains the features of fishfinders to help you choose the right one for your needs.

Fishfinders provide anglers with a graphic representation of what lies beneath their boats, allowing them to identify fish. When selecting a fishfinder, consider factors such as the unit type—whether it includes GPS and is part of a boat-wide network—the size of the fishfinder's footprint, the display resolution, the necessary transmitting power, and the frequencies best suited for inland, coastal, or deep-water environments. Here are some key features to consider:

• Standalone, Combo, or Network Fishfinder 
• Display Specifications
• Screen Size
• Transmit Power and Frequency
• CHIRP or Broadband Fishfinders
• Side View, Straight Down, or All-Around
• Transducer Style and Shape

Standalone, Combo, or Network Fishfinder

Choose a fishfinder that offers a clear view of fish arcs, bottom structures, and underwater landscapes. There are three main types of fishfinders:

1. Standalone Fishfinder: If your primary goal is simply to see what's below, dedicated standalone units provide the largest display and best performance at a lower cost. These are ideal for small boats used on inland lakes or for those on a limited budget. If you have space for multiple displays or recently purchased a GPS, a larger standalone fishfinder may be a wise investment. Many of these units can be upgraded with a GPS sensor later, converting them into combo units.

2. Combination Fishfinder/Chartplotter:Combo units are a popular choice for mid-sized boat owners. They allow you to use GPS for navigation while simultaneously viewing fishfinder data on a split screen, or displaying only the fishfinder information. “Black box” sounder modules can convert many chartplotters into combo units by adding a transducer.

Display Specifications

LCD displays consist of a grid of “picture elements,” commonly called “pixels.” Each pixel darkens when electrical current is applied. Higher vertical pixel counts lead to improved depth resolution since each pixel represents a smaller depth increment. The number of horizontal pixels affects how long objects remain visible on-screen, which is especially important for split-screen displays that show narrow columns of information.

A higher pixel density provides better detail of underwater structures and improves the overall representation of what lies beneath your boat. This allows you to see the air bladders of smaller fish, distinguish closely spaced targets, and identify fish around “bait balls.” Keep in mind that the display's contrast must also be sharp to maximize the benefits of higher resolution. As with most features, better display resolution typically comes at a higher price.

Screen Size

Screen sizes are usually quoted in inches, measuring the diagonal distance across the display. Widescreen options allow you to view more information simultaneously when using a split-screen display for different types of data, such as GPS charts, radar images, or readings from multiple transducers.

Transmit Power (Watts) and Frequencies

The transmitting power of a fishfinder is measured in watts RMS (root mean squared), indicating the strength of the “ping.” Higher power is essential for viewing in murky water, detecting deeper targets, and distinguishing separate objects and bottom structures. A fishfinder with 500 watts RMS should suffice for most coastal applications, while serious bluewater anglers should seek units with 1,000 watts or more. For inland fishing in shallow waters, 200 watts is often adequate.

Transducer Frequency

Fishfinders operate using single-frequency transducers, dual frequencies, multiple frequencies, or broadband CHIRP systems. Generally, higher frequencies provide finer detail and less background noise, making them ideal for fast-moving boats, but they do not penetrate as deeply as lower frequencies. For shallow inland waters, frequencies of 200 kHz, 400 kHz, or 800 kHz are commonly used. For greater depths, lower frequencies like 80 kHz or 50 kHz are recommended. We suggest using 200 kHz or higher (up to 800 kHz) for water depths up to 200 feet, and 80 kHz or 50 kHz for deeper waters.

CHIRP or Broadband Fishfinders

The latest broadband fishfinders, known as CHIRP (Compressed High-Intensity Radar Pulse), transmit across multiple frequencies rather than just one or two. Instead of a single frequency (e.g., 200 kHz or 50 kHz), CHIRPing devices send out signals that sweep linearly across a range (e.g., from 40 to 75 kHz or 130 to 210 kHz).

Although CHIRP fishfinders transmit less peak power than traditional units, their wide-band, frequency-modulated pulses can be much longer in duration, allowing them to deliver 10 to 50 times more energy into the water. This capability enhances their effectiveness in identifying fish and structures beneath the surface.