7 Answers About Boats Electrical Grounding Systems (Earthing)

Grounding is a term that discusses the process of preventing electrical shocks or electrocution in a home, in an RV, or on a boat.

It is essential to ensure that your boat has been grounded before you end up injured or shocked while on the water.

Grounding systems have particular requirements, which we will discuss how they should be installed on boats.

Here are 7 answers about boats and grounding:

1. Should You Ground a Boat?

In regards to a boat, grounding is about bringing your electrical systems to a “zero voltage potential.” In Europe and other parts of the world, this is called earthing, or earth ground.

Grounding is a process that can be done on land or through the use of special circuitry, wires, and connections to the metal parts of the boat, including the engine.

Grounding is absolutely required to have safe boating experiences, but most boat users don’t know a lot about it.

Grounding not only prevents shocks and injury, but it also can protect the metals and wiring on your boat from corroding and reduces the chance of unintentionally draining the batteries.  

If you are confused about grounding, rewiring, or upgrading and how to do it properly, consider getting it done by a professional first before attempting to do it yourself.

2. How Do you Ground a Boat?

Grounding has two separate systems, often referred to as AC and DC grounding systems.  Besides, many boats, especially sailboats, have bonding systems that connect the metal rigging and major hardware to the metal through-hull fittings. 

These are different electrical equipment types and the processes that each needs to be properly grounded on your boat to keep it as safe as possible.

Often it is advised that boaters do not hook up their own electrical wiring for grounding, especially if they aren’t well-versed in boating-specific electrical components or don’t know the differences between grounding and electrical wiring.

If this is you, please seek professional help with your boat first!

Now, the basic premise for how to ground your boat is this:

AC (Alternating Current) Grounding System:

An AC grounding system is often referred to as a “free-floating” system. This means that they do not ground the boat directly to the vessel itself.  If you plug your boat into dockside electricity, the boat should have a galvanic isolator system.  These may not have been installed on older boats, so they should be added, probably by a professional.

This means that AC systems use a “neutral source” or “current-carrying conductor” to ground the boat and get it to zero voltage potential – basically to prevent it from shocking you or causing serious damage.

More specifically, the AC grounding system uses a dedicated ground or “green wire,” which is intended to channel a current safely in the event of a short circuit, therefore protecting anyone on board who might be touching metal at the time from getting a shock.

Note: the AC system should never be grounded to the bonding system!

If you have an AC grounding system, major connections will use green wires onboard your vessel. If you see them, make sure they are not corroded or uncovered, and be sure to leave them alone.

That green wire will redirect the current and send it back to its source, turning the power off if a short circuit occurs.

DC (Direct Current) Grounding System:

A DC grounding system originates at the battery.

It is also a free-floating system because it is never grounded to a metallic part of the boat. It is especially not grounded in the bonding system.

Instead, the DC grounding system works with negative potential rather than a neutral source like the AC grounding system. The battery provides that negative potential.

Furthermore, it is traditional for the DC system to be connected to seawater ground at one point ONLY on the boat – usually through its negative terminal or its “bus bar.”

A bus bar brings studs or terminals together in one “bus,” which becomes the electrical connection between one source to many other branch circuits.

Overall Grounding Information:

While you don’t need to know what a bus, terminal block, or other jargon is at this point, you do need to know what kind of grounding system your boat has.

Once you do, educate yourself on how to properly care for it or get it regularly maintained by a professional who can walk you through the process or do it for you at a reasonable price.

3. Do Boat Batteries Need to be Grounded?

Boat batteries are the primary connection used in a DC grounding system on your vessel.

The battery negative is connected to the engine negative terminal or bus in a DC grounding system, containing all electrical currents to the DC wiring. 

Batteries have a “floating ground,” which means that it doesn’t require an earth ground to work. The battery itself doesn’t have to be grounded before you touch it, and it most likely wouldn’t shock you with a wayward circuit.

However, if you are going to modify your battery connections on your boat’s electrical circuitry, make sure that you are confident you know how to properly attach it to the system – especially with the DC grounding system.

4. Should Aluminum Boats be Grounded?

Aluminum boats should be grounded like any other boat, but NOT to the hull of the boat.

An aluminum boat is a potential hotbed for electrical injuries and can be quickly be corroded drastically if it is exposed to electrical currents for too long.

All engine chassis should be insulated from the hull using spacer plates and insulating sleeves, and the propeller shaft should be insulated from the engine as well.

Ensure that you contact your mechanic or a professional who understands this process and can help or walk you through proper grounding.

5. How Much Does it Cost to Ground a Boat?

If you need your boat rewired, checked, maintained, or grounded in any fashion, you are most likely going to hire a professional.

Most boat owners don’t know how to wire their own boat, and they shouldn’t have to. Furthermore, doing it yourself could be incredibly dangerous!

Therefore it is important to seek out a marine technician who works specifically on boats – NOT cars.

It would help if you had someone who understands boating circuitry’s intricacies and who can do it right the first time.

That being said, this isn’t a cheap cost.

Most rewiring at a shop could cost you between $90-$120 an hour, not to mention parts, which adds another few hundred dollars on top of that.

A quick check on your boat would be cheaper to make sure everything is okay, but if you run into problems or want to upgrade or improve your boat’s electrical systems in any way, this will cost you far more in both time and money.

6. What Happens if you Don’t Ground a Boat?

Neglecting to ground your boat properly can result in electrical shocks, corrosion of the boat metals, or other injuries and damage to yourself and those on board.

It is crucial to know what kind of grounding system your boat has and properly maintain that system and check it often.

If not, you could go to touch metal parts or equipment on your boat one day and receive a terrible shock or even be fully electrocuted.

You could also cause extreme electrolytic corrosion, which eats away at your boat metals and disintegrates them very quickly.

While this is rare, it is still essential to stay on the safe side and prevent any potential injuries.

7. What if the Lightning Strikes on a Boat That is Not Grounded?

Your boat should absolutely be grounded no matter what.  Without grounding, you could be injured, shocked, or even corrode your boat and engine.

Electrolytic corrosion can cause the disintegration of boat metals on board.  This is prevented by the galvanic isolator on your AC system and by the galvanic anodes on the other major metals that are immersed in the water, such as the propeller and shaft.   

Galvanic corrosion can even completely corrode your boat propeller and motor in a matter of weeks if you aren’t careful.

Using Your Grounding System for a Lightning Strike:

Although your grounding system may lessen the effect of a lightning strike, the bonding system is designed to handle higher accidental currents, such as a lightning strike. 

There is much debate about how this works, but the bonding system is designed to maintain the same neutral voltage potential of the water around your boat, reducing the chance for a lightning strike.

If you want to add a bonding system to reduce the lightning strike’s potential damage, it requires adding to the wiring in your boat’s electrical systems.

It is recommended that your system uses a minimum of 6 American Wire Gauge (AWG) for your bonding conductors. Then you will need to use a minimum of 4 AWG or a “down conductor” for the wires at the metal through-hull fittings.

All in all, once you’ve added the proper upgrades, you should have a grounding system that can reduce the chance of a lightning strike and send it safely through the bonding system to prevent shocking you or harming anyone on board if a strike happens.

Remember: preparing for lightning strikes depends on the type of boat you have, so make sure that you know what upgrades to your system that your boat requires to do this properly.

References:

Why does a Circuit Always Have to Have Ground?

Marine Grounding Systems

Tips on Electrical System Use and Maintenance

Grounding Inverter/Chargers on Boats