7 Answers About Boats & Being Grounded (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 incredibly important to make sure 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, as well as the boats that need them, too.

Here are 7 answers about boats and grounding:

1. Should You Ground a Boat?

Grounding, in regards to a boat, 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 engine terminals.

Grounding is absolutely required in order 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 or heating up to dangerous levels.



If you are confused about grounding, rewiring, or upgrading and how to properly do it, 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.

These are different categories of electrical equipment and the processes with which to properly ground 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 in 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.

This means that they use a “neutral source” or “current carrying conductor” in order 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 “bond” 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: nothing should ever be grounded to the bonding system!

If you have an AC grounding system, you will notice a green wire onboard your vessel. If you see it, make sure that it is not being corroded or uncovered, and be sure to leave it alone.

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

DC (Direct Current) Grounding System:

A DC grounding system operates 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.

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

Furthermore, it is traditionally said that DC grounding requires that the electrical system should 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 it isn’t crucial that you know what a bus, terminal block, or other jargon are at this point in time, you do need to know what kind of grounding system your boat has.

Once you do, either educate yourself on how to properly care for it or get it regularly maintenance 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 primarily 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, which helps a wayward electrical current becomes neutralized in the event of a short circuit.

Batteries have a “floating ground,” which means that it doesn’t require an earth ground in order 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 add the battery to your boats electrical circuitry, make sure that you are confident you know how to properly attach it to the system – especially if you have a 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 hotbed for electrical injuries and can even heat up 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.

Make sure 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 mechanic who works specifically on boats – NOT cars.

You need someone who understands the intricacies of boating circuitry, 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 labor, which adds another few hundred dollars on top of that.

A quick check on your boat would be cheaper, just to make sure everything is okay, but if you run into problems or want to upgrade or amplify your boat 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 properly ground your boat can result in electrical shocks, heating of the boat metal, 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 to properly maintain that system and get it checked often.

If not, you could go to touch your metal 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 a rare occurrence, it is still very important 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 is basically like the disintegration of boat metals on board and the heating up of your materials.

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

Using Your Grounding System for a Lightning Strike:

You can use your grounding system to lessen the effect of a lightning strike.

However, the use of grounding to dissipate a lightning strike requires upgrading the wiring in your system.

It is recommended that you upgrade your system to a minimum of 6 American Wire Gauge (AWG) for your secondary conductors. Then you will need to add a minimum of 4 AWG or a “down conductor.”

All in all, once you’ve added the proper upgrades, you should have a grounding system that can take the excess charge of a lightning strike and send it safely through the current system to prevent shocking you or harming anyone on board during the time of the strike.

Remember: preparing for lightning strikes is mostly dependant upon the type of boat that you have, so make sure that you know what upgrades or tweaks 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

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