Boat cleaning fatality - Fort Myers, Florida

[fstbttms]

Perhaps fstbttms can answer that (though I think he works only in salt water where it's less of an issue).

It's not "less of an issue", it is actually not an issue. I have been working in saltwater marinas in the Bay Area for over 21 years. In that time, well over 1,000,000 in-water hull cleaning events have occurred here (the number is probably more like 1.8 million) and to my certain knowledge, not one of those events has resulted in the injury or death of a hull cleaner due to ESD. The reality is that you are in greater danger driving to the saltwater marina than you are diving in it.

That said- why be stupid? Unplug any boat you are working on, saltwater or fresh.

 

[2airishuman]

For context, I think that this is best understood as an electrical accident that occurred while diving.

Stray voltage electrical accidents are rare in the U.S., but they do take place even on land. I've read the accident reports, and it's hard to characterize a single cause. From memory, some examples were: a bridge railing, a light fixture at the top of a metal warehouse rack, a garbage disposal in a food service establishment. These are all essentially identical accidents, electrically, involving the combination of an open equipment grounding conductor and a short to ground of one of the current carrying wires.

Properly wired docks and boats don't pose a hazard. There are various safety devices that reduce the risk in the event of a wiring fault.

Very scary. Seems impossible to notice before too late, as well as nearly impossible to save anyone stricken.

If I were to witness such an accident taking place, I would disconnect power from likely sources.

 

[2airishuman]

I've been thinking about this and realize that there are some unique things about this situation that amplify the hazards.

It's not unusual for owners of ocean-going yachts to deliberately cut the equipment ground wire in the shore power line. It's a dangerous practice, but it reduces the problems with galvanic corrosion on metal parts of the boat that are continuously immersed, particularly the lower unit(s) (on stern drives) or the prop shafts (on inboards). Stern drives are particularly subject to galvanic corrosion due to their aluminum construction. The corrosion results from dissimilar metals being immersed in seawater while electrically connected, and can be made worse by some kinds of DC wiring faults. Connecting the equipment ground makes this problem worse because it connects the boat electrically to all the other boats and equipment in the marina.

Galvanic corrosion is much less of a problem in fresh water, and so the practice of deliberately cutting the equipment ground wire is less common on inland lakes and rivers.

The fact that the accident took place in a freshwater marina that is connected to the ocean leads me to wonder about the history of the boat. Perhaps its home mooring was previously in salt water, leading its owner at the time to cut the equipment ground.

There are various means of preventing galvanic corrosion without creating a hazard, but they are expensive. Perhaps the most effective (and most expensive) means of doing this is through installation of an isolation transformer, either on board or at the pedestal. This leads to a separately derived service and the equipment ground can safely be cut. There are also means of coupling the equipment ground that block low DC voltages typical of those that cause galvanic corrosion, but allow AC to flow in the event of a fault.

Finally there are GFCI-like devices that can be installed at the pedestal that will prevent an accident like this even if there are wiring faults (including an open equipment ground, deliberate or otherwise) in the boat. It would seem to me that such devices would be of particular importance in brackish water where boat owners may be tempted to follow the dodgy grounding practices common in marine environments despite the water having low enough salinity -- even if only some of the time -- for the hazard to be comparable to a freshwater harbor.

 

[CuzzA]

This is a good resource for learning some boat basics from a retired Marine Surveyor.

Maintenance and Troubleshooting : Tips on Electrical System Use and

 

[Wookie]

You don't cut he ground wire because you are trying to disable the safety features of the equipment, you cut the ground wire because the boat is an ungrounded system, and a grounded piece of non-marine equipment shows up as a ground on the ground detect circuit. Modern electronics want a ground. Large vessels have ungrounded systems. Dryers, ranges, fridges, etc. use electronics to control the unit, and if plugged into an ungrounded system, the electronics mess with the ground detect circuit something fierce. When that happens, real grounds (refrigeration or air conditioning compressor insulation breakdown, or, God forbid, an actual short or ground) will go unnoticed causing an real dangerous situation. The 2 solutions are to buy marine UL listed equipment (not possible, they don't make Marine UL listed dryers), or install a lighting transformer to "fool" the system into thinking there is a ground in the system. I personally route all ground plugs back to the generator neutral, but that isn't right either, however, the electronic devices accept it as it should be.

Not hooking the ground wire up in the shore power cable is right and proper, by the way. You do not want the ground wire connecting the boat to earth.

 

[JohnN]

I've been thinking about this and realize that there are some unique things about this situation that amplify the hazards.

It's not unusual for owners of ocean-going yachts to deliberately cut the equipment ground wire in the shore power line. It's a dangerous practice, but it reduces the problems with galvanic corrosion on metal parts of the boat that are continuously immersed, particularly the lower unit(s) (on stern drives) or the prop shafts (on inboards). Stern drives are particularly subject to galvanic corrosion due to their aluminum construction. The corrosion results from dissimilar metals being immersed in seawater while electrically connected, and can be made worse by some kinds of DC wiring faults. Connecting the equipment ground makes this problem worse because it connects the boat electrically to all the other boats and equipment in the marina.

Galvanic corrosion is much less of a problem in fresh water, and so the practice of deliberately cutting the equipment ground wire is less common on inland lakes and rivers.

The fact that the accident took place in a freshwater marina that is connected to the ocean leads me to wonder about the history of the boat. Perhaps its home mooring was previously in salt water, leading its owner at the time to cut the equipment ground.

There are various means of preventing galvanic corrosion without creating a hazard, but they are expensive. Perhaps the most effective (and most expensive) means of doing this is through installation of an isolation transformer, either on board or at the pedestal. This leads to a separately derived service and the equipment ground can safely be cut. There are also means of coupling the equipment ground that block low DC voltages typical of those that cause galvanic corrosion, but allow AC to flow in the event of a fault.

Finally there are GFCI-like devices that can be installed at the pedestal that will prevent an accident like this even if there are wiring faults (including an open equipment ground, deliberate or otherwise) in the boat. It would seem to me that such devices would be of particular importance in brackish water where boat owners may be tempted to follow the dodgy grounding practices common in marine environments despite the water having low enough salinity -- even if only some of the time -- for the hazard to be comparable to a freshwater harbor.

Thanks, very informative post. I'm a bit confused why a standard GFCI (and disconnecting the common ground) wouldn't be sufficient to solve problems like this.

 

[FinnMom]

How salty does water need to be for this to not be a risk? Seas around Finland are only 0.7- 0.8 % salt.

 

[fstbttms]

How salty does water need to be for this to not be a risk? Seas around Finland are only 0.7- 0.8 % salt.

Unless the marina in question is located on a river, freshwater lake or is otherwise likely to experience large freshwater infusions, it should be OK to dive in.

 

[seeker242]

Thanks, very informative post. I'm a bit confused why a standard GFCI

Similar devices are sufficient to prevent this problem. They are called ELCIs (Equipment Leakage Circuit Interrupter). They work on the same principal as GFCI but they cut power to the whole boat. Which is why ABYC standards made them mandatory in the 2009 code revision.

 

[2airishuman]

Thanks, very informative post. I'm a bit confused why a standard GFCI (and disconnecting the common ground) wouldn't be sufficient to solve problems like this.

GFCIs and other devices of the same ilk (ELCIs, etc) do solve the safety problem.

They are prone to nuisance trips in a marine environment and so haven't seen widespread adoption. Much of the problem is that they trip when the wiring on boat has excessive leakage, which is common, and hard for the average yacht owner (or marina electrician, or most electricians for that matter) to fix. Truly capable electricians who can find and fix grounded neutrals and leakage problems are few and far between, and most of them have well-paying cushy industrial jobs that don't require them to try to fix wiring in some tiny little odoriferous forward compartment on the bottom deck.