Lightning mitigation and galvanic protection system


On September 7th of 2013, Family Circus (at the time the boat was named On Delay) (along with five other boats) were struck by lightning in the Las Brisas anchorage off Panama City. Almost everything containing an electronic circuit was destroyed. While they were repairing and upgrading these systems, they also installed a lightning mitigation system to minimize damage from any future strike.

The plan was designed in consultation with Ewen Thomson Ph.D. of MarineLightning.com and implemented by Andromeda Yacht Services, Panama.

There are three parts to the plan:

  1. Lightning dissipation system
  2. Bonding of through-hulls to mitigate galvanic corrosion
  3. Surge suppression for electronics
1. Lightning dissipation system

Lightning wants to take the shortest path to the surface of the water.

The lightning dissipation system consists of the following components that allow the lightning to exit the boat in the easiest manner:

  • A 36-inch air-terminal attached and electrically bonded to the mast head and terminating above the VHF antenna.
  • The base of the mast is bonded to an electrode beneath the bridge-deck.
  • The bridge deck electrode is bonded to two Siedarc™ electrodes abeam of the mast.
  • The Siedarc™ electrodes are bonded to both the chain plates and the rudder post.
Lightning path

Lightning path

Siedarc™ lightning electrode

Siedarc™ lightning electrode

2. Bonding for galvanic corrosion

Galvanic corrosion is due to current flow between dissimilar metals and to stray currents from poorly grounded electrical systems in the vicinity of the boat.

To mitigate this there is i) a system of sacrificial zincs that are preferentially corroded by stray currents (factory installed), and ii) electrical bonding of below water-line through-hulls to the zincs. This was done using #6 AWG wire according to the design of Andromeda Yacht Services, Panama.

3. Surge suppression for electronics

During a lightning strike, electronic equipment is damaged by both direct voltage in wires connected to the site of the strike, as well as voltage induced by the EMP in unconnected wires.

While it is difficult to completely protect electronics from a strike, surge protection circuitry (as used to protect critical electronics in applications such as cell-phone towers), can decrease the extent and severity of damage.

Two approaches to surge protection have been taken on On Delay. One is installation of TVS diodes in parallel to the 12V power supply of equipment to be protected.  The other is the installation of grounded gas discharge tube containing circuitry in series with data carrying wires. In both cases (gas discharge tubes and TVS diodes), the component is an insulator during normal operation, but rapidly (pico – nano seconds) becomes a conductor during high voltage events, “clamping the voltage” and protecting the circuitry.

Ethernet surge protection box

Ethernet surge protection box