Marine Corrosion

 Are you concerned how marine corrosion affects your boat? 

If you are not sure what modifications have been made to your vessel, we recommend you conduct research to ensure your hull plates are being used as intended. Lightning strikes have heated up through hull fittings to the point where FBG can melt and leave one or more good size holes in the side of a vessel. Cathodic protection creates an alkaline state at cathodes; therefore, if you own a wooden vessel and have plans to bond through hull fittings be aware that a state of alkalinity is present in the seawater surrounding cathodes. This alkalinity can break down cellulose; therefore, if your hull is wood, problems can be created that break down the wood around through hull fittings to the point where you suddenly have a hole in the side of your vessel. Inform us if your hull is wood and you have a bonding system!

Although some vessels bonding systems are also utilized for lightening attenuation, and other grounding needs, systems usually work best when specifically used only as designed. If your hull plate designed for cathodic protection is also serving another purpose, it still needs to be changed out when depleted. Hull plates acting solely as grounding plates can be damaged by lightning strikes or other DC current and may need to be replaced as well. Some hull plates may require vessel to be pulled to install new plates!

If your vessel utilizes an impressed current cathodic protection system, we need to know about it prior to diving operations!

Our Views Your Plates

We frequently come across hull plates that can serve several purposes. Most commonly these are anodes and part of your vessels bonding system where through hull fittings are inner connected, in other words, bonded to this anode by electrical connection to prevent galvanic corrosion to your bronze through hull fittings. If this anode is depleted or its electrical connection deteriorates, the underwater metal it was meant to protect will corrode! 

In addition, to prevent galvanic corrosion, the following items may be connected to the primary bonding conductor: engine, fuel tanks, rudder (possibly for galvanic protection and/or because of its connection to the autonav system), bilge pump metal housing, and metal chassis of other equipment. All bonding conductors should be either bare wire, or colored green. The following things should all be connected together at one point only, referred to as the engine negative terminal: the primary bonding conductor, the engine block, and the negative terminals of all batteries.

The bonding system also sometimes gets connected to your green wire shore power lead. The grounding conductor of the 110v shore power system must not be connected to the bonding system unless a galvanic isolator or isolation transformer is in place. This galvanic isolator or isolation transformer prevents outside source DC current from attacking your vessel via the shore power green wire while still allowing your safety grounding circuit to work properly.  If DC current in your shore power supply is a problem (when any boat in your marina has a short) please purchase a galvanic isolator or isolation transformer. Do not ever break the grounding connection in your AC power circuit to prevent galvanic attacks of the low voltage DC bleed off from other vessels! This circuit is referred to as the safety grounding circuit for a good reason. It protects you and the diver under your boat from electrocution.

 The primary bonding conductor is usually a copper wire that runs from the stern to the bow along the bottom of the boat.

Some designs include a dedicated lightening protection system that utilize another type of hull plate referred to as a ground plate. This ground plate or grounding plate is normally not zinc but is monel, copper, or a type of metal not typically used for cathodic protection.

             To protect from lightening, all stanchions, shrouds, stays, pulpits, and the mast might be directly connected to the primary bonding conductor, preferably by very big wires. There may be a metal ground plate on the exterior of your boat's bottom that is also connected to the primary bonding conductor. Ideally, the electrical path between the mast and the ground plate should be short, through very heavy gauge wire, and should have no turns.

We sometimes come across hull plates designed for cathodic protection and made of zinc that are sometimes being utilized for grounding. These hull plates may be utilized for lightning protection or to provide a path for grounding any static electricity built up in fuel tank. When refueling we don’t want a static spark to ignite fuel vapors. Your hull plate might be used to ground the vessels radio system (loran) and/or a variety of other equipment.