Invisible killer: Electrocution while swimming in your boat slip

May 1, 2016 by Scott McDowell

People die each year in the U.S. while swimming in fresh water around boats and piers with alternating current (AC) shore power; seven persons in 2012 alone. Electric Shock Drowning (ESD) is called the “Invisible Killer” and there needs to be more publicity and boater education about this deadly process that causes immediate muscular paralysis and subsequent drowning.

With the proliferation of electric boat lifts and underwater lighting of slips, ESD events are growing rapidly at the expense of unsuspecting swimmers.

No wise person would step into a swimming pool if he or she saw an energized electrical cord submerged in the water – we all know better. Why then, are people so comfortable entering the water around boats in a marina? Boats and piers have the potential to kill swimmers by leakage from AC power cords or from metal components on a boat’s submerged hull.

Electrical facts for boaters

Saltwater is 500 times more conductive than fresh water and stray electrical current can easily find a ground for dissipation – a safe situation. However, when AC current is discharged into fresh water, a nearby swimmer’s body becomes the equivalent of a sponge for the stray electrical charge.

Stray DC current from boats does not kill swimmers.

Small boats typically have 30-Amp AC service from a shore-power source but only 0.1 Amp discharged into a nearby swimmer can cause death in a few seconds. This is equal to one-third of the current needed to illuminate a 40-watt light bulb.

ESD is normally caused by an electrical fault or grounding problem in a shore-power cable or aboard the vessel and these problems can easily be detected by a trained boater. Another common source of AC ground-faults aboard boats are onboard water heaters that have electrical leakage from their heating elements.

Marina managers should conduct annual checks for electrical faults around their piers. Additionally, boaters should have a trained marine electrician conduct tests if a problem is suspected. Take responsibility for electrical testing to save lives – maybe your own.

Lifesaving of ESD victims

If you’re swimming and feel tingling or electrical shocks, shout to people about your problem and get out of the water, preferably far from boats and the pier that provides AC power. Warn people not to jump in to save you as they could die also.

If you witness a person experiencing ESD, do not enter the water. Get them out in some other manner and have the AC power shut off at its source.

ESD victims often respond to Cardiopulmonary Resuscitation (CPR) so administer this lifesaving procedure as soon as possible, on dry land.

For prevention of ESD casualties, do not let swimmers come within 100 yards of a boat or pier that has active AC shore power.

All boaters should be aware of ESD dangers and educate others. Whenever boating in freshwater and docking at piers with AC shore power, consider the water is ‘hot’ from stray electrical current until you have proven otherwise. Freshwater conditions conducive to ESD are found in lakes and rivers but don’t overlook riverine areas, estuaries and marinas where freshwater may reside above saltwater due to natural density differences. Imagine the thousands of boats berthed in the Miami River and Fort Lauderdale’s New River that reside in fresh water during rainy periods. Divers beware!

If you are a saltwater boater, remember ESD when you visit friends who are inland boaters.

For the latest information on ESD, visit the Electric Shock Drowning Prevention Association (


Scott E. McDowell has a doctorate degree in ocean physics, is a licensed captain and author of Marinas: a Complete Guide available at Contact him at [email protected].