Before and after Sonihull’s Ultrasonic anti-fouling system

To cure a recurring problem of marine bio-fouling, a Nordhavn 55 owner from Maine, USA has fitted a Sonihull ultrasonic anti-fouling system to the internal pipework that feeds his vessel’s Fernstrum keel cooler.

Previously, the underwater heat exchanger was prone to heavy fouling by weeds, barnacles and mussels. This would impede water flow around the keel cooler and reduce the effectiveness of the cooling system, putting extra strain on the engines and adding to the annual lift-out and service costs.

“The photos speak for themselves,” says Dominic Findlow, Technical Director of Sonihull. “The owner took them in the same boat-lift after voyaging nearly 5,000 miles each year over the same waters, including six-month periods of stationary mooring in Maine waters.”

By fitting the Sonihull system to the metal pipe fittings inside the hull, the system can transmit strong ultrasonic pulses throughout the heat exchanger, protecting any surface that is in contact with raw seawater. The pulses create a microscopic layer of micro-cavitation which disrupts the first stages of the food chain and prevents further colonisation and attachment of weeds, barnacles and mussels.

Because the only mounting surface available was a short section of threaded bronze inlet pipe, a novel solution was employed. “One Sonihull transducer was bonded to a stainless-steel plate which was welded to a threaded collar.

“As there was no space to screw the assembly into position, the collar was machine split and then secured to the threaded pipe by two locking bolts,” explains Findlow. “A second Sonihull transducer was bonded to the inside of the hull, directly aft of the keel cooler.”

Sonihull is said to be a zero-harm solution. There are no poisons, or biocides leached into the marine environment, no microplastics are shed from ablative coatings and no toxic metallic ions are left in wakes.