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A propeller and prop guard in one unit

RingProp’s aluminum ring is attached to the prop blades so it won’t cause repeated slashings

RingProp’s aluminum ring is attached to the prop blades so it won’t cause repeated slashings

British manufacturer RingProp PLC is bringing its ringed propeller to the U.S. market in response to concerns about the slashing injuries that open-blade props cause to people and wildlife, manatees especially.

RingProp’s aluminum ring and blades are an integral unit — that is, the ring is attached to the outer edge of the blades so the whole unit rotates, setting RingProp apart from prop guards with fixed rings that are detached from the blades, says RingProp director Mark Chappel.

Fifteen years in development, RingProp has been “exhaustively” tested. Chappel says the ring doesn’t significantly degrade performance and can actually improve boat handling. Going into a sharp turn, he says the ring directs water flow over the blade tips and prevents them from losing their grip in the churned-up water. Chappel says it also eliminates torque steer, the tendency of a boat to steer in the direction of prop rotation. “You actually get better maneuvering,” he says.

Acceleration and thrust with a RingProp are “very good,” and top speed is only marginally affected, says Chappel. “Maybe a knot or two,” he says.

The striking surface of the RingProp is slightly less than that of an open-blade propeller and significantly less than the striking surface of a prop with a detached ring with space between the outer edge of the blades and the ring, according to Chappel. The unit still can cause significant blunt-impact injury at high speeds, but at slower speeds it won’t cause the repeated slashing that an open blade will, he says.

“If it can reduce injury, mitigate injury, prevent death or paralysis — take away the worst — it’s something that ought to be done,” he says.

He says the ring offers other benefits. It strengthens the blades, protects them from floating debris, and works as an anti-fouling device. RingProps will be available in various sizes for outboards from 9.9 hp to 250 hp, and carry a universal hub for easy installation. Chappel expects the first RingProps to become available through West Marine by January.

The feasibility and effectiveness of prop guards to prevent disfiguring or incapacitating injury are matters of ongoing litigation. In a December 2002 decision, the U.S. Supreme Court ruled that the fact that the Coast Guard has found that no single prop guard is uniformly safe and effective in preventing injury in all small boats doesn’t prevent victims of prop injuries or their families from suing engine manufacturers for not putting guards on their engines. That case continues.

Florida has been tussling for a decade or more with strategies to protect the endangered manatee from lethal or mutilating propeller strikes across their backs. The strategies range from slowing boats down to keeping them out of manatee habitats to putting high-frequency underwater transmitters on boats to alert manatees that they are coming. Prop guards also have been considered.

The Coast Guard announced Oct. 6 a grant to survey propeller injury protection technologies on the market, assess each method, and summarize the options, and the advantages and disadvantages of each in various boating activities. Applications are due Jan.18.