How to Choose a Fishfinder/Chartplotter Combo for Your Boat

Why a Combo Unit Makes Sense

A decade ago, fishfinders and chartplotters were separate devices. Today, combo units — a single screen that handles both sonar and GPS navigation — are the standard for most recreational and fishing boats. You get one display, one power connection, one NMEA network node, and a unified interface. The trade-off is that if the screen fails, you lose both functions — which is why many serious boaters keep a handheld GPS as backup.

This guide walks you through every major decision point so you can choose the right unit for your boat, fishing style, and budget.

Step 1: Decide on Screen Size

Screen size is the first filter. Bigger screens show more detail and are easier to read in bright sunlight, but they require more dash real estate and cost more.

5–7": Good for small boats, kayaks, and jon boats. Limited split-screen capability.
9–10": The sweet spot for most center consoles and bass boats. Enough screen for a useful sonar/chart split view.
12"+: Best for larger boats, offshore fishing, or anyone who wants to run multiple data overlays simultaneously. Often supports networking with a second display.

Measure your available dash space before buying — account for the bezel, not just the screen diagonal.

Step 2: Understand Sonar Technology

This is where most buyers get confused. Here's a plain-English breakdown of the main sonar types:

Traditional 2D Sonar

The classic cone-shaped beam that shows fish arches and bottom structure beneath the boat. Works at all depths. Every fishfinder has this as a baseline. Frequency choices:

50 kHz: Wide cone, better depth penetration (good for deep water, offshore)
200 kHz: Narrow cone, better detail in shallow water (good for bass fishing, inshore)

CHIRP Sonar

CHIRP (Compressed High-Intensity Radiated Pulse) sweeps through a range of frequencies in a single pulse rather than transmitting one fixed frequency. The result: dramatically better target separation (you can distinguish individual fish in a school) and cleaner bottom definition. CHIRP is now the baseline expectation on any mid-range or better unit — if a unit doesn't have CHIRP, it's entry-level.

DownScan / DownVü / DownImaging

Uses a very high frequency (455/800 kHz) thin-slice beam aimed straight down to produce a photo-like image of structure directly beneath the boat. Excellent for identifying dock pilings, brush piles, and rock formations. Not as useful for spotting fish in open water.

SideScan / SideVü / SideImaging

Fans out to both sides of the boat, covering a wide swath of bottom (up to 150'+ per side on some units). Exceptional for quickly locating structure, submerged timber, and drop-offs. A game-changer for tournament bass fishing and offshore wreck hunting.

LiveScope / LiveSight / ActiveTarget (Live Sonar)

The newest category: real-time, nearly live sonar that shows fish movement as it happens. You can watch a fish swim up to your lure. These systems require a separate transducer and are typically add-ons to compatible units. Premium price, but increasingly popular for serious anglers.

Step 3: Choose the Right Transducer

The transducer is the underwater sensor that sends and receives sonar pulses. The unit is only as good as the transducer paired with it. Key considerations:

Compatibility: Transducers are not universal. Match the transducer to your specific unit — check the manufacturer's compatibility list.
Mount style: Transom mount (most common for powerboats), thru-hull (best performance, requires drilling), trolling motor mount, or in-hull (shoot-through).
Frequency: Must match the sonar capabilities of your unit (CHIRP, DownScan, SideScan, etc.)
Depth rating: Make sure the transducer is rated for the depths you fish.

Browse our full Transducers collection to find compatible options for your unit.

Step 4: Evaluate Mapping and Chartplotter Features

The chartplotter side of the combo handles GPS navigation, waypoints, routes, and chart display. Key questions:

What charts are included?

Most units come with a base map. Premium cartography (Navionics, C-MAP, Garmin BlueChart) is either pre-loaded or available on a microSD card. If you fish inshore or navigate complex waterways, premium charts with depth contours and marina data are worth the investment.

Does it support custom depth maps?

Some units (Garmin Quickdraw, Humminbird AutoChart) let you create your own high-resolution depth maps as you fish. Invaluable for private lakes and unmarked structure.

GPS update rate

Look for at least 5Hz GPS update rate for accurate speed and position tracking at higher boat speeds.

Step 5: Check NMEA Connectivity

NMEA connectivity lets your fishfinder/chartplotter share data with other onboard electronics — VHF radio (for DSC position), autopilot, engine gauges, and more.

NMEA 0183: Older standard, serial connection, one-to-one wiring. Still common on VHF radios.
NMEA 2000: Modern network standard. Plug-and-play backbone that all compatible devices share. One cable run, multiple devices. Strongly preferred for new installations.

If you're building a new electronics suite, choose a unit with NMEA 2000 and build your network around it. Browse our NMEA Cables & Sensors collection for backbone components, T-connectors, and terminators.

Step 6: Consider Networking and Multi-Display Setups

Many mid-range and premium units support networking multiple displays so you can share sonar, charts, and waypoints between a helm unit and a bow-mount unit. If you fish from the bow frequently, this is a significant convenience feature. Check whether the units you're considering support the same proprietary network (e.g., Garmin Marine Network, Humminbird Ethernet, Lowrance Ethernet).

Quick Comparison: What to Expect at Each Price Point

Budget	What You Get
Under $300	Basic CHIRP 2D sonar, small screen (5–7"), basic GPS, no SideScan/DownScan
$300–$700	CHIRP + DownScan, 7–9" screen, NMEA 2000, decent cartography options
$700–$1,500	CHIRP + DownScan + SideScan, 9–12" screen, premium maps, networking capable
$1,500+	Full sonar suite, large touchscreen, live sonar ready, multi-display networking, premium charts included

Installation Tips

Run power directly from the battery (or fuse block) with an appropriately rated fuse — don't tap into an existing circuit
Keep the transducer cable away from other wiring to minimize interference on the sonar display
Mount the transducer at least 15" from the engine lower unit and away from any hull strakes that cause turbulence
Use a RAM mount or flush mount bracket rated for your unit's weight — vibration at speed will loosen undersized hardware
Connect to your NMEA 2000 network before final installation to verify data sharing with your VHF and other instruments

Shop Marine Navigation at Egret Marine

Browse our full Marine Navigation & Instruments collection, including transducers, NMEA cables, and accessories to complete your electronics installation.

Not sure which unit fits your boat and budget? Contact the Egret Marine team — we're happy to help you find the right setup.