Electroshock Drowning in Freshwater Marinas

Electroshock Drowning  is a topic in which myself and many others have been very vocal about these past few years and I have written about it many times in my magazine articles. It is a phenomenon which has been occurring in fresh water marinas, cottage docks and anywhere boats are moored and plugged into shore supplied AC (alternating) electrical current. It occurs when AC current, by way of faulty electrical wiring or appliances either on board the boat or on the dock leak current into the water and if persons or animals (yes pets and wildlife are susceptible to this too) are in the water nearby, the current travels through their bodies causing paralysis and even death.

Here is the equation: AC electrical power is supplied to boat shore power systems typically in the range of 15-30 amps   ……   .6 of an amp of electrical current is enough to stop your heart almost instantly if it travels through your body in an effort to reach ground.

How does this occur: It occurs when, through a wiring fault or a fault with an AC appliance allows stray current to  travel through the boats DC ground circuits which include underwater metallic components such as the prop shaft or stern drive. Think of your boat when plugged into shore power as similar to a hair dryer plugged in and floating in the bathtub. This in effect electrifies the water in the immediate vicinity of the affected boat. Anyone swimming nearby can be affected by this as the electrical current moves from the charged water to ground. If you remember your basic electrical theory electricity always moves from the source to ground and if your body gets in the way it will pass right through you and your heart.

Another point that you need to be aware of is that this occurs mostly in fresh water situations, much more so than in salt water. This is because salt water is a better conductor than fresh water and any current dissipates rapidly after it enters the water. In fresh water it remains at a concentrated level in the immediate area surrounding the boat. And when you take into consideration that the high salinity levels of the human body actually make it a better conductor than the water itself, just by being in the water we actually provide the best path for the current to move to ground.

This is a very brief overview on how this can occur and is occurring. I will have much more to say in future posts. For more on this I invite you to visit a couple of websites dedicated to this phenomenon.  I will add them to my links page as well.

http://www.electricshockdrowning.org/    This site is operated by Kevin Ritz who has a very deep connection to this issue.

http://www.boatus.com/seaworthy/magazine/2013/july/electric-shock-drowning-explained.asp       A very good article by Boat US which offers a very good description on how to inspect for electrical leakage aboard boats.

http://www.boatingmag.com/how-to/electric-shock-drowning-prevention      More good information.

Capacity Calculation for a Marine Starting Battery

I was asked how to determine the battery size (capacity) for a typical engine starting battery. To that end I have come up with some information on how to do just that.

Starting Battery Ratings: Marine Cranking Amps (MCA) or Cold Cranking Amps (CCA). 1 CCA = 1.3 MCA. The ratings are calculated by the same process just at different ambient temperatures.

Minimum Size for Starting Battery: Engine Displacement (in cubic inches) X 2 (Cranking Requirements) X4 (Reserve Capacity) = Required Battery Size (CCA)

I should note that this calculation will give you the minimum size requirement for a starting battery and I sure won’t hurt to increase the size somewhat. I an also a fan of using a deep cycle rated battery as your starting / reserve.

Marine Battery Basics

Your batteries are the heart of your boat’s electrical system. They supply power for engine cranking and all of your on-board electrical accessories. Treat them well and they will reward you with a long service life but abuse them and they will fail in very short order.

All marine batteries are a variation of he flooded cell lead acid battery originally invented in France in the late 1850’s. They’re big, heavy and can be the source of some very bad odors if not properly maintained. They produce electrical current by the immersion of two dissimilar metals (plates) in a liquid that conducts electricity (electrolyte). It is the reaction of the metals in the electrolyte that produces the electrical current. With one metal being more noble (the metals resistance to erosion) than the other it will erode at a different rate and produce an electrical current (potential difference) between the two. It is this continual erosion of the plates that determines the batteries life span and is the principal reason why no battery will last forever.

Marine batteries generally fall into two classifications, starting batteries and deep cycle batteries. Starting batteries are similar to what you would find under the hood of your car or truck. They have a large number of thin plates and produce a large amount of electrical current for short periods of time, just what you need for engine cranking applications. Starting batteries do have one disadvantage when used solely for marine applications (especially in sailboats), they will not tolerate repeated deep discharges. Using them in this way will reduce their lifespan greatly.

Deep cycle batteries on the other hand have fewer, thicker plates and while they may not produce as much peak current as a starting battery they will produce a smaller amount of current for a longer period of time and they can withstand repeated deep discharges. This is especially important in sailboat applications because engines are usually run for short durations (providing limited charging time) and batteries are called upon to power radios and instruments for long durations while under sail. It is for this reason that the best sailboat systems will usually feature a combination of both types of battery, a starting or reserve battery dedicated to engine cranking and deep cycle house batteries providing power for the on-board systems. In recent years it has become common practice to equip sailboats with only deep cycle batteries. This has proven to work quite well and is a practice that I employ on my own boat.

Fortunately maintaining your batteries is a relatively easy task. The electrolyte level should be kept above the plates and topped up with distilled water as necessary. The positive and negative terminals should be kept clean and as should the exterior of the battery case itself. Clean terminals ensure low resistance and proper current flow to the vessel’s electrical system and if the battery case is allowed to accumulate dirt this can provide a current flow between the terminal posts causing discharge.

Dirty Battery

The batteries pictured above are a good example of a poor maintenance, showing dirty cable clamps, residue forming on the case and sloppy wiring.

Monitor your vessel’s charging system with a voltmeter. If you don’t have one hard wired to your electrical system they are relatively inexpensive and easy to install. Charging voltages (with the engine running) will fluctuate according to load but should be within 13.25 to 14.25 volts, with all accessories turned off and providing batteries are in good condition. Voltages may intermittently fluctuate outside this range on a fully functional system but if they remain either higher or lower this may be an indication of trouble. Lower voltage levels may indicate a problem with the vessel’s charging system leading to dead batteries and higher voltage levels may indicate overcharging which will shorten battery life drastically. Overcharging may also be accompanied by a bad smell from the batteries themselves. If either of these conditions are encountered it is probably best to have your vessel’s charging system serviced by a professional.

A proper battery installation is also essential to ensure safe and reliable system operation. Batteries should be installed in approved acid resistant containers which will prevent spillage should a leak in the battery case occur. Also the batteries should be secured to prevent movement less than one inch in any direction and the area should be vented to allow for the discharge of gas produced by batteries as they charge.

Covered Batteries

The picture above shows batteries secure and in approved containers.

Recently two somewhat different types of batteries are gaining popularity with boaters and while they aren’t exactly new designs, both being used by the automotive and aircraft industries for some time now, they are referred to as Gel cel and AGM (absorbed glass mat) batteries. Both are a variation of the flooded cel design. The Gel cel uses an electrolyte which is thickened with a silica compound resulting in a cel with a thickness similar to petroleum jelly. The AGM battery uses an internal glass mat which reduces the internal movement of the electrolyte. Both types offer advantages such as reduced maintenance and quick re-charge rates but at this time they are considerably more expensive than their flooded cel counterparts. At this time the AGM appears to be the popularity winner an almost all applications.

With any type of battery proper maintenance of both the battery and the vessel’s charging system is the key to a reliable and long service life.

Wiring Suggestions for the Master Battery Switch and Multiple Battery Banks

I have never been happy with the way that my own boat’s battery switch is wired and went looking for ideas and suggestions on alternate methods. I stumbled across a couple of interesting Ideas and I thought that I’d share them here. These methods may not be new to some of us but both are somewhat different from the way that most boats are wired at the factory. Here they are.

Battery Switch Metod 1

The above shows Method #1. The 1-2-Both battery switch is at the top center and for clarity I have just shown the 1,2 and Common terminals. Wiring your switch in this manner has the following advantages:

You would likely run with the battery switch in position 1(connecting the house bank to the common terminal on the switch) for most situations. The house bank is shown as two 6 volt batteries wired in series but the configuration doesn’t matter. 

1-With the alternator wired directly to the house battery bank it allows the house batteries to be charged separately from the reserve (or starting battery). If it ever became necessary to charge the reserve battery off of the engine the switch could be moved to position 2 which combines both battery banks and the common terminal.

2-While at the dock the shore power charger would automatically charge both banks regardless of the battery switch position.

3-The shore power charger will keep the reserve battery fully charged and maintained eliminating the need (in most situations) to utilize the engine alternator.

The only option that this configuration doesn’t cover is that it won’t completely isolate the house bank from the rest of the system but if you feel that its necessary adding a switch to the negative side of the house batteries will accomplish this.


This is similar to Method #1 except that the engine starter is switched and connected to the reserve battery only. This allows the high engine starting loads of the starter to be isolated from on board electronics which some feel that is a good idea. Hide the starter switch and it becomes an effective anti-theft devise.

Batt Sw

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