GPS Chartplotter and Fishfinder Combo Buying Guide: Screen, Sonar and Charts

By Boat Supplies Direct·Updated Oct 18, 2026·5 min read

Center console helm with a chartplotter showing a chart and sonar split screen

Quick answer: Buy the biggest screen your helm can fit (about 7 inches for small boats, 9 to 10 inches for most center consoles and bay boats, 12 to 16 inches for larger boats), make sure it includes the sonar views you will actually use (CHIRP, down imaging and side imaging), and check that it comes with charts for your waters and a transducer that fits your hull. If you plan to add radar, autopilot or engine data later, choose a unit with NMEA 2000 networking.

A chartplotter/fishfinder combo is the center of most boats' helms: GPS navigation, charts, depth and fish finding on one screen. The options get confusing fast, with screen sizes, sonar acronyms, chart brands and transducer types all mixed together. This guide breaks it down into the decisions that actually matter so you can buy once.

Step 1: Pick the screen size

Screen size	Best for
5 to 7 in	Kayaks, jon boats, small skiffs, budget installs
9 to 10 in	Most bass boats, bay boats and center consoles up to about 25 ft
12 in	Larger center consoles, split-screen users
16 in and up	Offshore boats and glass helms

Bigger screens make split views (chart plus sonar) usable. Measure your dash space and check whether the unit is bail mounted or flush mounted.

Step 2: Understand the sonar options

Traditional CHIRP sonar: shows fish arches and bottom depth. Standard on almost every unit.
Down imaging: a detailed, photo-like view of structure directly below the boat.
Side imaging: scans out to each side to find structure, ledges and bait over a wide area. Ideal for searching new water.
Live (forward-facing) sonar: real-time view of fish and lures. A separate, higher-cost add-on with its own transducer.

Model names usually hint at sonar features. For example, Garmin units ending in "sv" include both down imaging and side imaging.

Step 3: Check the charts

Most combos come with built-in maps, but coverage varies. Look for detailed coastal charts if you run saltwater, or lake maps with contour detail for freshwater. Popular options include Garmin Navionics+, C-MAP and Humminbird's own chart systems. Some units support chart subscriptions with regular updates.

Step 4: Match the transducer to your boat

Mount	Best for	Notes
Transom mount	Most outboard boats	Included with most combos, easy to install
Trolling motor mount	Bass and freshwater fishing	Sonar follows where the trolling motor points
Thru-hull	Inboards and offshore boats	Best performance at speed, professional install

Check that the included transducer supports every sonar view you are paying for.

Step 5: Plan for the future

NMEA 2000 lets the unit share data with engines, autopilots, radar and other displays.
Wi-Fi and app support make updates and chart downloads easier.
Touchscreen vs. buttons: touchscreens are fast in calm water, buttons are easier in rough conditions. Many units offer both.

Step 6: Install it right

Use a dedicated, fused power supply to the battery or a fused panel circuit, keep transducer cables away from engine and VHF cables to reduce interference, and mount the transducer per the manufacturer's height and angle guidance. A clean install makes a big difference in sonar picture quality.

Common mistakes to avoid

Buying too small a screen. Split screens on a small display are hard to read. Most owners wish they had gone bigger.
Mounting the transducer in turbulent water. Bubbles from strakes, rivets or the hull cause a poor picture at speed. Follow the manufacturer's placement guide.
Sharing power with noisy circuits. Interference from bilge pumps or other electronics shows up as noise on the sonar screen.
Skipping software and chart updates. Updates fix bugs, add features and improve chart accuracy.
Not learning the settings. Sensitivity, range and frequency settings make a huge difference in what you see. Spend time on the water learning them.

Our picks by boat and budget

All in stock at Boat Supplies Direct.

Frequently Asked Questions

What size fishfinder should I get for my boat?

Go as big as your helm allows. About 7 inches suits small boats, 9 to 10 inches suits most bay boats and center consoles, and 12 inches or more works well on larger boats and for split-screen use.

Do I need side imaging?

If you fish structure or search new water, side imaging helps you find ledges, brush and bait quickly. For simple depth and fish arches, traditional CHIRP and down imaging are enough.

What is the difference between a chartplotter and a fishfinder?

A chartplotter shows your GPS position on charts. A fishfinder uses sonar to show depth, bottom and fish. A combo does both on one screen.

Which transducer do I need?

Most outboard boats use a transom mount transducer, which is usually included. Inboards and offshore boats often use thru-hull transducers. Make sure the transducer supports all the sonar views your unit offers.

Are remanufactured chartplotters worth it?

They can be a good value. Remanufactured units are restored by the manufacturer and are typically sold with a warranty. Check the warranty terms before you buy.

Do I need NMEA 2000?

Only if you plan to connect other devices like engines, autopilot, radar or a second display. If you might expand later, choose a unit that supports it.

This guide is general information. Features vary by model, so check each manufacturer's specifications. Chartplotters are an aid to navigation and should not be your only source.