Tournament fleets bunch up. When several boats in the same patch of water are all running Furuno omni, captains sometimes see streaks or rings of noise that don't behave like fish. InTheBite's coverage of a dealer round table put it plainly: nearby boats with the same model and frequency sonar can create interference in the received images on both boats.
What it looks like
Interference tends to show as regular patterns, spokes, arcs or rings, that don't move with the water and don't respond to tilt the way a real target does. Step the tilt a few degrees: a fish brightens and fades as the beam passes its depth, interference usually doesn't.
What the CSH-10 gives you
- Selectable frequency. The CSH-10 transmits at 83.5 kHz but can be set anywhere from 81.5 to 85.5 kHz. Moving away from a neighbor on the same frequency is the first thing to try; agree channels with your fleet before the season if you fish together.
- Interference rejecter. A processing filter listed in the CSH-10 specification for exactly this kind of noise.
- Auto Filter and noise limiter. These clean background noise generally, at some cost in sensitivity to weak echoes.
On a CSH-8L MK2
The CSH-8L MK2 runs at 85 kHz. Use its interference and noise settings, and talk to your dealer about what can be adjusted on your unit.
If interference persists when no other omni is nearby, the source may be on your own boat. Other sonars, sounders and electrical noise can all show up. That's a job for your installer with the boat at the dock.
Published 2026-10-31. Sources: Furuno CSH-10 and CSH-8L MARK-2 brochures, Furuno USA product pages, InTheBite, Yachting and Power & Motoryacht.