Omni sonar

Omni sonar is a full-circle scanning sonar. The technology has been around for more than 40 years, but its price and size kept it mostly on commercial fishing boats, where Furuno's FSV scanning sonars have long been a favorite.^1,2,5

Furuno was first into sport fishing with the CH250, or Searchlight, and most recently the CSH-8L MK-2, which Power & Motoryacht called the most popular model on sportfishers in 2021. Simrad and MAQ sell them too.^2,3

A searchlight sonar scans one sector of water at a time in a rotating pattern. An omni transducer is built of layered elements, each pointed a slightly different way, so it transmits all 360 degrees at once without turning. At a 1,000-foot range the CSH8LMK2 redraws the full circle every 0.54 seconds.^1,4

The transducer extends beneath the boat from a tube in the hull and retracts at running speed. A control pad tilts the beam. Target lock follows a fish and reports its depth and speed, gives a bearing to intercept it, and can engage the autopilot.^2,3

A sounder shows only what the boat has already passed over. With omni sonar a captain can keep bait on the inside of a turn and circle the spread around the mark, and in open water trade blind trolling for active hunting.⁴

Furuno rates the CSH8LMK2 to 5,000 feet, but the sweet spot is more like 1,000 to 1,500 feet. The units are most effective in the top 200 feet of water; captains speculate that fish deeper than that are traveling, not eating.^2,3

By 2024, Marlin reported omni sonars had become nearly standard on new sportfishing boats, and Viking said it fit them at the factory on nearly all its new builds 41 feet or longer.³

The hull unit needs roughly a square foot of hull space and six feet of vertical clearance, and the best picture comes from a transducer on the keel. Viking notched its forward engine room fuel tank to make room for the tube. In 2024 Marlin put the units at around $100,000 before installation, which an installer said typically runs $25,000 to $30,000.^2,3

The sonar is sensitive enough to pick up prop turbulence, and the picture gets noisy in shallow water or over hard bottom. Unlike a sounder it has to be run actively, and some boats bring in another person to man the controller. Crews retract it once a fish is hooked, so the line or leader cannot wrap the transducer.^2,3,4

Tournaments have split on it: some have separate categories for sonar and non-sonar boats, others prohibit it.³