Humminbird HELIX 15 CHIRP MEGA SI+ GPS G4N CHO (Head Only)

The Humminbird HELIX 15 G4N MSI+ CHO is the big-screen MSI HELIX you buy when you want both Side Imaging and Down Imaging on a 15-inch display, but you already have sonar coming from somewhere else. The 15.4-inch 1280 by 800 LCD is the largest in the HELIX lineup, with the proven keypad-driven menu system that long-time HELIX owners know cold. The CHO designation means Control Head Only. There's no transducer in the box. The MSI+ in the model name means the unit has both Side Imaging and Down Imaging engines built in, ready to drive a compatible MEGA Imaging+ transducer that you provide separately.

The CHO model exists for three real use cases. First, owners running a network-capable trolling motor with built-in MEGA imaging in the head can feed sonar straight to the HELIX over the included sonar port without buying a redundant transom transducer. Second, anglers who already run a HELIX or APEX network on the boat can pull sonar from another unit over Ethernet and put the HELIX 15 at a second station. Third, builders who plan to add MEGA 360 Imaging or another accessory transducer separately don't need to throw away the standard transducer that would have come bundled. You build the system you actually want.

The 15.4-inch display is the headline. On a center console where the helm has the real estate to support it, a 15-inch HELIX is genuinely transformative compared to a 9 or 10. You can split-screen MEGA Side Imaging, MEGA Down Imaging, CHIRP sonar, and the basemap chart at the same time without any of the four panels feeling cramped. Resolution is 1280 by 800, which is sharp enough to make MEGA imagery look like the photo-style returns it's marketed as. Sunlight readability is good, the keypad is the proven HELIX layout, and the unit is sealed for marine use.

MEGA Side Imaging+ is the imaging tech that pulls this unit ahead of the DI-only sister model. It scans 200 feet on each side of the boat at 1075 to 1150 kHz, giving you photo-quality bottom imagery laterally that 2D and Down Imaging can't show. You see brush piles, dock pilings, fish schools, weedline edges, structure transitions, and downed timber lying on the bottom out to either side, not just directly below. For finding fish in big water (large reservoirs, coastal flats, big lakes), MEGA Side Imaging is the feature that matters most.

MEGA Down Imaging+ is in there too. Same 1100 to 1200 kHz frequency range as Side Imaging, but pointed straight down for ultra-detailed bottom and water-column imagery. Maximum depth on MEGA DI+ is 200 feet, with 455 kHz fallback giving you 400 feet of penetration when you need to go deeper.

Dual Spectrum CHIRP is Humminbird's working CHIRP sonar across the HELIX line. Two ranges, wide mode (140 to 200 kHz) for maximum scan area when you're searching, and narrow mode (180 to 240 kHz) for the highest detail when you've found a piece of structure. Switch between them on the fly with a button press. Target separation gets down to 2.5 inches at the right range.

Internal GPS plus Humminbird Basemap means you can navigate out of the box. The basemap covers more than 10,000 inland lakes plus the continental U.S. coastal waters with depth contours, hazards, marina locations, and points of interest. Add a premium chart card on the dual SD slots if you want LakeMaster, CoastMaster, SmartStrike, or compatible third-party charts on top of the basemap. Storage handles 2,750 waypoints, 47 routes, and 50 tracks with 20,000 track points.

AutoChart Live is the HELIX feature that turns the unit into a personal cartographer. As you idle around a piece of water, the sonar feeds depth, bottom hardness, and vegetation data to the unit, which builds a custom contour map in real time. Eight hours of recording sit in the unit by default, expandable indefinitely with an AutoChart Zero Line SD card.

Connectivity is the HELIX G4N strong suit. Ethernet for sharing sonar, charts, and waypoints across multiple units. Bluetooth for wireless control of compatible shallow water anchors and downriggers in the One-Boat Network ecosystem. WiFi for software updates and chart downloads via the FishSmart mobile app. NMEA 2000 for engine data, fluid levels, autopilot, and other vessel data. The 5-port Ethernet switch is supported for larger multi-unit installs. Optional radar dome integration is built in.

Power. The unit runs on 12V DC. Use a dedicated power run from the battery, fused appropriately, with marine-grade tinned wire sized for the run length. Don't share the power feed with bilge pumps or noisy accessories or you'll see interference patterns on the sonar imagery. The compass safe distance is short enough that the HELIX 15 fits comfortably in most helm electronics packages.

What's in the box. Control head, gimbal mounting bracket, power cable, and the install hardware. No transducer. No sun cover (sold separately). No charts beyond the preloaded basemap.

Two-year limited warranty. Same-day shipping before 3 PM ET on in-stock units. We can help you spec the right MEGA Imaging+ transducer for your boat if you're not sure which way to go.