Lightning and Surge Protection for Yachts

Lightning and Surge Protection for Yachts

Created by: Glen Zhu | Updated Date: December 23rd, 2023

Lightning Protection for Yachts, Sailboats and Marine

Have you ever wondered how to protect against lightning when sailing? Or is it unnecessary to take any precautions to prevent the lightning strikes?

Understanding the occurrence of lightning helps to answer the question. The lightning strike can be thought as a short circuit between the cloud and the earth. During a thunderstorm, positive charges accumulate at the top of the cloud and negative charge on water, when the electric field strength is sufficient, a stepped conductive channel forms within the cloud, ultimately resulting in lightning.

All current inside cloud flows through this channel and reach to water through the mast and boat body while damaging all sensors on mast; destroying antennas, radios and cables; damaging batteries inside and finally breaking down the engine and causing fire.

That is to say, a lightning strike is inevitable if an active thundercloud containing electrical charges passes overhead at a low enough altitude.

The lightning protection system actually function by acting as the “best” short circuit between the cloud and the water, designed to lead the lightning safely to the ground. As we know, lightning protection system offers a safe pathway to protect physical damage.

While modern yachts are built from electrical components installed between the water and the areas aloft, surge protection is required to protect electric equipment.

Rolling Sphere Concept and Protection Classes

The rolling sphere method is employed to ensure that the air terminals are strategically placed to intercept potential lightning strikes, thereby minimizing the risk of direct lightning hits to the structure.

By rolling a ball around an object or a group of objects and tracking where the ball stays in contact, the reaching points are the places where the lightning attachment would happen, and lightning protection system should be deployed.

Yachts often have mast-mounted equipment such as antennas and sensors. The rolling sphere method takes into account the risk of lightning strikes to these elevated components, providing a comprehensive protection strategy.

Figure 1 – Application of the rolling sphere method on the yacht

Rolling sphere radius depends on various factors, including the height and configuration of the structure being protected. The smaller sphere radius is, the higher protection level is.

Class III is typically used for yachts where lightning-related risks are very low, and the consequences are minimal. Large yachts may have different vulnerabilities compared to smaller ones. The shape and configuration of the yacht can influence the risk of lightning attachment.

The largest rolling sphere radius is 60m, however, side strikes could occur on structures that are higher than 60m, the probability of these side strikes is negligible on structures less than 60m in height.

Table 1 – Rolling sphere radius corresponding to the class of LPS

External Lightning Protection System

With the help of the rolling sphere method, the protection level for yachts is classified as LPS III. The mast of a yacht is the point where the lightning strike is easy to reach and lightning currents travel to the deck, then enter the inside of the ship through overall cables affecting the whole system of the yacht.

To install lightning protection system correctly, metal mast or not is the first thing to figure out.

For those with metal masts which themselves could act as natural lightning rods. No additional measures must be taken as everything is likely to be bonded with metal structures. Most lighting current is discharged via the mast and partial lightning currents are passed through the stays to the body and to the water.

Figure 2 – Lightning current distribution on a yacht following a lightning strike to the mast

Non-metal Yachts

The measures are different to yachts with wooden or GRP body. Unlike metal structures, non-mental yacht should consider how to build a direct path for lightning to pass. These materials are non-conductive but still have the potential to dissipate static charge. Air terminals, down conductors and ground terminals are installed to create a comprehensive lightning protection system.

If the mast is made of the wood, an air-termination rod with a thickness of at least 12mm must protrude at least 300mm from the mast. The distance between the mast and air terminals can ensure the lightning strikes on the air terminal first rather than the mast.

The down conductor should be made of copper and have a minimum cross-section of 70 mm2. It must be routed in the outdoor area of the yacht and connected to the copper-made or other saltwater-proof earth plate. A sufficient distance must be maintained between these earth plates to prevent flashover.

If lightning strikes the air-termination rod on the non-metal mast, the lightning currents must be discharged to the earth plate via the down conductor on the mast and via the shrouds, stays and chain plates.

There is also a mobile lightning protection system for easy implementation, but the effect is still to be confirmed as equipotential bonding and separation distance are ignored. A ball pin to the lower part of the aluminum mast serves as a down conductor with a lightning carrying terminal screwed on.

The terminal is connected to two others and two braided copper strips which extends at least 1.5 meters into the water. All components and connections must be capable of carrying lightning currents and be corrosion proof.

Figure 3 – Mobile lightning protection for a yacht

Equipotential Bonding

A complete lightning protection system addresses this issue through bonding or the interconnection of metallic building systems with the lightning system to create a common ground potential.

All protective conductors of the board electronics and all metal parts of yachts must be connected to the common equipotential bonding which prevents dangerous touch voltage/ sparking.

When grounded systems are bonded together there is no reason for the lightning to leave our designed current carrying path because the arbitrary arc over points don’t exist. The measure prevents electric shock and safe electrical environment.

Conductors should be anti-corrosive, and made from materials that can withstand the harsh marine environment. Anti-corrosive conductors are essential for maintaining the integrity and functionality of electrical systems on a yacht. The constant exposure to saltwater, humidity, and other corrosive elements can quickly deteriorate conventional materials, leading to a higher risk of electrical failure.

Surge Protection

Although external lightning protection has been offered the path for safely lead the lightning to the ground, dangerous voltage could be generated elsewhere, resulting in arcing and side flashes, threatening the boat and crew, and destroying electronic equipment.

Surge-induced damage to critical systems on a yacht, such as navigation or communication equipment, can compromise the safety of the vessel and its occupants. Surge protection contributes to the overall safety of the yacht.

Power Supply System

The surge protector, which is installed directly in the power supply system is one of the most important protection measures. The power source for yachts could be shoreside and offshore power supply.

When sailing on sea, yachts rely on internal or alternative power sources to generate the electrical power needed onboard. While connected to shoreside power, yachts have access to a stable and continuous power supply, allowing for the operation of various systems and appliances.

Lightning can induce transient over-voltages and electrical currents that may propagate through yacht’s electrical system. If the lightning strikes on the shoreside power supply, the breakdown of shoreside power supply is not directly affect the offshore power supply on a yacht, but maybe indirectly.

Install isolation transformers helps protect the yacht’s electrical system from shore power issue. An isolated transformer is designed to provide electrical isolation between its input and output circuits.

It can build an isolation between the yacht and the shore power supply, which prevents the transfer of stray currents, potential faults or voltage irregularities from the marina’s electrical system to the yacht. The defense maintains a consistent and reliable power source for the vessel’s electrical systems while allowing compatibility with different generators.

Figure 4 – Use of isolation transformer to prevent corrosion

For corrosion protection reasons, the protective conductor of the shoreside power supply system must not be connected to the earthed metal parts of the water vehicles.

The protective conductor of the shoreside power supply system is not required to protect persons on the yacht against electric shock since an isolation transformer on the yacht ensures protection against electric shock in connection with a residual current protective device.

Electronic Devices Protection

Figure 5 – Surge protection devices for a yacht

If lightning strikes the air-termination rod or the metal mast of the yacht at anchor which is supplied with electricity, the potential of this yacht is raised above the connection of the shoreside power supply system.

A part of the lightning current is passed to the water and flashover to the power supply system will occur depending on the conductivity of the water. This flashover can damage the cables/equipment on the yacht and cause fire.

However, it is even more likely that a yacht at anchor, which is supplied with electricity, is threatened by a shoreside lightning strike. In this case, the lightning current flows in the direction of the yacht and causes the damage above.

Additional surge protection is necessary, though surge protectors has installed in the power supply system. When installing a type 1 surge protector, precautions should be taken to prevent corrosion resulting from the connection between the earth-termination/equipotential bonding system of the yacht and the protective conductor of the shoreside power supply system.

Surge protective devices are designed to account for polarity changes typical in earthed socket outlets. In the event of lightning, such as hitting marine radio antennas or mast-installed wind sensors, there is a risk of damaging equipment and downstream devices, despite their location in a protected volume.

Figure 5 illustrates suitable surge protective devices for such scenarios. Additionally, attention must be given to induced surges and switching over-voltages from board generators and UPS systems, for which type 2 surge arresters in the distribution board are recommended.

VHF radio is crucial communication device for ship-to-ship and ship-to-shore communication aiding weather updates, navigational warnings and other emergencies. Wind sensors measure the speed of the wind and monitor the real-time wind conditions for safe operation of sails.

Both VHF radios and wind sensors works with the principle of electrical signals, additional surge protection is recommended to ensure their reliable operation.

Surge protective device for coaxial protection is installed for VHF radios to minimum contact erosion resulting from the large-area contact surface of the gas discharge tube.

RF Coaxial Surge Protector DS-UHF F/M

FRD4 series is featured with protecting four single lines sharing a common reference potential as well as unbalanced interfaces. FRD4-24 is installed to monitor the operation of wind sensors, ensuring the correct transmission of navigation instructions when sailing. The higher voltage surge protector, FRD4-30 protects the power supply system of the navigation system.


The solution for yachts and sailboats involves constructing an effective external lightning protection system to guard against direct lightning strikes and implementing surge protection for electric equipment.

Is that mean we could fully protect our yachts without lightning strikes?

There is no such thing as a lightning-prevented yachts, only a lightning-protected yacht. A lightning-protection system is not designed to prevent a lightning strike, but rather to provide a safe discharge path for the lightning, making it the most viable and effective solution.

The system can still be challenges when it is improperly or only partially installed. The antenna cable carries the lightning current if the air terminal is installed lower than an adjacent antenna.

Also, if the down conductor is linked to the bonding system instead of directly to a dedicated grounding terminal, the lightning strike may energize the entire bonding system before dissipating into the water.

Another common error is to secure the lightning down conductor to other wiring. The substantial current from a strike through the down conductor can induce voltage surges in these neighboring wires, causing additional damage to equipment that would otherwise remain unaffected by the lightning strike.

Combined with correct installation of each system, our yachts could get the best protection against the lightning. Necessary personal protection should be taken, not stay on deck since potential difference and keep away from rods or other metal objects.

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