Fresh electric shock danger

Oct 21, 2011

On Aug. 15, an 18-year-old boy died in a marina in Traverse City, Mich. The cause of the drowning was from an electrical fault in dock wiring at the city-owned facility. A friend of the victim who swam at the marina luckily escaped injury. The case highlights the dangers of waterborne stray current and its potential to cause fatal accidents. Since 1986 more than 50 people have been killed in stray current incidents. The biggest lesson from these accidents is a simple one: don’t swim in marinas. A lesser-known aspect to these tragedies is the difference between fresh water and salt water as they relate to stray current.

Since salt water is a good conductor of electricity, one might assume that the danger from stray currents in salt water would be greater than that of fresh water, which, lacking dissolved salts, does not conduct electricity as well. Yet, the opposite is true: one is far more likely to be injured by stray current in a body of fresh water.  

Capt. David Rifkin of Quality Marine Services in Jacksonville, Fla., (qualitymarineservices.net), co-authored, with James Shafer, a 2008 report for the Coast Guard and the American Boat and Yacht Council titled “In-Water Shock Hazard Mitigation Strategies.” According to Rifkin, the danger of electric shock is much greater in fresh water because the human body provides a more convenient electrical path than in salt water. Rifkin wrote in an e-mail. “In freshwater the human body is a much better conductor of electricity and therefore competes very well for current flow. In salt water, the water is far more conductive than the body (skin resistances wet are in the 1,000-Ohm range) so the body doesn’t see much of the current in the water. More of the current takes the lesser resistive path of the water in getting back to its source.”

Rifkin notes, “it takes about 2v/ft to cause paralysis and drowning. It would take a tremendous amount of current to get up to a gradient that high in salt water.” The reason this is unlikely is that by the time that powerful an electrical field built up, the circuit breaker on shore would likely have tripped, cutting off current to the faulty circuit supplying the stray current. As Rifkin further notes, “in a salt water situation, the greater danger is fire from local heating at the point of the electrical fault.”

Rifkin maintains a database of stray current accidents and he notes, “We don’t have a single instance of a fatality in salt water environments. Sure, people get shocked in salt water, but it usually involves actually touching a ‘hot’ fitting while in the water.”

So for voyagers in salt water, there is less danger. For those who sail in the Great Lakes or other bodies of fresh water or who are visiting those areas, the danger of electrocution does exist should you find yourself in a marina with faulty wiring. The best policy for all types of water is to observe posted signs and don’t swim in marinas.
Munching muskrats

When you think of hazards that can sink your boat, muskrats probably aren’t high on the list. But for boat owners in the Pacific Northwest, especially power voyagers who own trawler-type yachts, muskrats are a hazard to contend with. According to marine surveyor Jane Christen of Michel & Christen Marine Surveyors (www.michel-christen.com) in Shelton, Wash., muskrats can climb up into a boat’s exhaust discharge pipe and chew through the black plastic exhaust tubing. Christen writes on her website: “Any boat that has a wet exhaust with a discharge opening of about three inches or larger is at risk. A critter can and will swim up the exhaust hose and then chew through the hose to the inside of the boat.”

Our own Susan Hadlock was recently visiting the Seattle Yacht Club and snapped a picture of a sign warning of the dangers of the dreaded muskrat: “Check your exhaust, muskrats can sink your boat.” One wonders if Herman Melville were alive today, would he write about whalers and the pursuit of a ship-killing white whale, or would he focus on the vessel-sinking activities of the muskrat?

Luckily, there are solutions to muskrat attacks. One way to thwart them is to install an adjustable fitting inside the discharge pipe. This unit is held in place by friction. The threaded bars are turned which extends the fitting to fit the internal diameter of the discharge pipe.

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