The unforgiving saltwater environment poses a constant threat to your vessels. Marine corrosion, the deterioration of metals by seawater and its elements, can significantly affect a boat's performance, safety, and lifespan. This handbook equips you, the marine professionals, with the knowledge to identify, understand, and prevent this costly problem.

What is Marine Corrosion?

Marine corrosion refers to the deterioration of metals exposed to seawater and its elements. It's an electrochemical process where saltwater acts as an electrolyte, facilitating the flow of charged ions between the metal and the environment. This flow of electrons breaks down the metal, causing it to weaken, rust, and eventually fail.

Types of Marine Corrosion

 

Galvanic Corrosion

Galvanic corrosion occurs when two dissimilar metals are in electrical contact with seawater, which acts as a conductive electrolyte. Here's why it happens:

• Metal Voltage Potential: Each metal has a natural electrical potential. This potential determines how readily a metal releases electrons (tendency to corrode).
• Electron Flow: When these dissimilar metals are connected by an electrolyte (saltwater), a chemical reaction occurs similar to a battery. The metal with the more negative potential (anode) has a higher tendency to release electrons and become oxidized (corroded). These electrons flow through the conductor (seawater) to the metal with the more positive potential (cathode), which attracts them.
• Sacrificial Corrosion: As electrons flow from the anode to the cathode, the anode material gradually corrodes at a faster rate. In essence, the more reactive metal (anode) sacrifices itself to protect the more noble metal (cathode) from corrosion.

Common examples of galvanic corrosion include bronze fittings on aluminium hulls or stainless steel fasteners on mild steel. In these cases, the aluminium or mild steel (more negative potential) corrodes faster to protect the bronze or stainless steel (more positive potential).

Stray Current Corrosion

Stray current corrosion (Electrolysis) occurs when stray electrical currents from external sources (e.g., faulty wiring, malfunctioning electrical equipment onboard, lightning strikes) come in contact with the water. The water provides a path to ground through any exposed metals in the water, such as an outdrive, propeller, engine mounting bolt, or the aluminium hull itself. As it's always the negatively charged metal (anode) that corrodes, the poor electrical connection causing the fault that's touching the water will cause the more expensive hull or outdrive to rapidly corrode away.

External Sources of Stray Current

While faulty wiring and onboard equipment are common culprits, stray current can also originate from other boats in the marina. Here's how it happens:

• Faulty Wiring in Neighbouring Boats: Poor electrical connections or grounding issues on nearby vessels can introduce stray current into the water.
• Marina Electrical System: Problems within the marina's electrical system, like malfunctioning grounding points, can also contribute to stray current issues.

Impact of Shore Power

If you're connected to shore power, your boat can become part of the stray current path. Here's the risk:

Return Path to Ground: Seawater acts as a conductor, and your boat's underwater metals can unintentionally provide a path for stray current to return to the source (e.g., another boat or the marina's grounding system) via the shore power's grounding cable. This can accelerate corrosion on your boat's hull, propellers, and other submerged metals.

Mitigating Stray Current

The good news is that you can significantly reduce the risk of stray current corrosion by using a shore power galvanic isolator. This device blocks stray DC currents while allowing the safe passage of AC current for powering your boat.

Corrosion Protection

1. Sacrificial Anodes (Passive Protection)

This is the most common and simpler method for preventing galvanic corrosion. Sacrificial anodes are electrically conductive components strategically installed on or bonded to your boat's underwater metallic components. They work by creating a small electrical current in the surrounding water.

• More Reactive Metal: These anodes are made from a metal even more reactive (more negative potential) than the metals you want to protect. Common choices include zinc (saltwater), aluminium (saltwater and brackish water), and magnesium (freshwater).
• Effective Protection: For effective protection, a sacrificial anode needs to shift the underwater voltage potential of the protected components by at least 200 millivolts (mV) in the more negative direction. This essentially forces the anode to corrode preferentially, taking the brunt of the electrochemical attack and protecting the boat's underwater metals (cathode).
• Limitations: Sacrificial anodes require regular inspection and replacement as they wear down. Additionally, their effectiveness can be limited for larger vessels or those operating in highly corrosive environments.

2. Impressed Current Cathodic Protection (ICCP) (Active Protection)

ICCP is a more sophisticated approach used for larger boats or those in particularly harsh conditions. Here is how it works:

• External Power Source: Unlike sacrificial anodes, ICCP systems use an external power source (battery or shore power) to generate a controlled direct current (DC).
• Insoluble Anodes: The ICCP system employs specially designed anodes made from inert materials like platinum or mixed metal oxides. These anodes don't corrode themselves but efficiently distribute the impressed current.
• Controlled Protection: The system carefully controls the amount of current delivered, ensuring optimal protection for the boat's underwater metals without wasting energy or causing excessive corrosion on nearby structures.

Example: Mercury Mercathode System
The Mercury Mercathode system is a good example of ICCP in action. It utilizes an external power source and strategically placed platinum anodes to deliver a controlled current, effectively protecting your boat's underwater metals from galvanic corrosion.

3. Galvanic Isolators: Shielding Your Boat from Electrical Invaders

While sacrificial anodes and ICCP systems directly combat corrosion on your boat's underwater metals, a galvanic isolator takes a preventative approach. It acts as a guardian against a specific threat: stray electrical currents.

• The Culprit: Stray currents are unwanted electrical currents that originate from external sources and can enter your boat through the water. These currents can come from:

  • Faulty Wiring or Equipment: Poor electrical connections or malfunctioning equipment on nearby vessels in the marina can introduce stray current into the water.

  • Marina Electrical System Issues: Problems within the marina's electrical system, like grounding faults, can also contribute to stray current issues.

• The Impact: When stray current enters your boat's underwater metals, it can accelerate corrosion at the point where it exits the vessel. This can be particularly damaging if the stray current is strong or persistent.

• The Solution: A galvanic isolator is an electronic device installed inline with your boat's shore power connection. It acts like a sophisticated gatekeeper, strategically interrupting these unwanted electrical currents:

  • AC Current for Power: The isolator allows the safe passage of the Alternating Current (AC) used to power your boat's electrical systems. AC constantly reverses direction, so the isolator doesn't impede its flow.

  • DC Current Blockade: However, the isolator effectively blocks the small Direct Current (DC) components of stray current. These DC currents tend to flow in one direction and are the primary culprits behind stray current corrosion.

Protection Benefits

By interrupting the DC path of stray currents, a galvanic isolator helps safeguard your boat's underwater metals from corrosion caused by:

• Neighbouring Boats: Stray DC currents originating from faulty wiring or equipment on nearby vessels in the marina.
• AC Leakage: Minor leakage of AC current from the shore power system that can be rectified (converted) into DC current within your boat's grounding system.

Important Note: While galvanic isolators are very effective against stray current DC issues, they don't directly address galvanic corrosion caused by the natural potential difference between underwater metals on your boat. Sacrificial anodes or ICCP systems may still be necessary for comprehensive protection.

Testing Corrosion Protection

Ensuring the effectiveness of your boat's corrosion protection system is crucial. Here's a key point to remember:

Precision Testing: For high-precision testing of your boat's corrosion protection system, a Silver/Silver Chloride reference electrode is recommended. This specialized tool provides accurate measurements to assess the effectiveness of your sacrificial anodes or ICCP system.

Testing Hull Potential

Measuring your vessel's "hull potential" is a straightforward process with significant implications. Avoid water disturbance to ensure precise readings while measurements are taken:

1. Deactivate all AC and DC circuit breakers onboard.
2. Disconnect all shore-based electrical connections, including AC power cables and cable TV.
3. Attach the electrode's cable connector to the negative terminal of a digital multi-meter.
4. Set the meter to DC Volts; mV or 2V scale.
5. The sensor end of the cell is protected by a “screw storage cap.” Prior to use, unscrew the cap and retain it for future use.
6. Submerge the Corrosion Reference Electrode to the required depth (approx. 30cm) as close as possible to the vessel.
7. Connect the positive test lead of the meter securely to a clean metal connection on the equipment you are testing.
8. For fiberglass and wood hulls, connect the meter’s positive terminal to the vessel's main engine block or DC power ground. For metal hulls, connect to a suitable spot above the waterline.
9. Note the voltage reading. This reading represents the vessel's hull potential.

Hull Potential: A Window into Corrosion Protection

Hull potential, measured in millivolts (mV), is a crucial indicator of how well your boat's underwater metals are protected against corrosion. By understanding the recommended hull potential ranges for different hull types and taking corrective actions when readings fall outside these ranges, you can significantly extend the lifespan of your boat's underwater components.

Recommended Hull Potential Ranges

The table summarizes the recommended hull potential ranges for various hull materials:

Metal	Minimum Voltage
Aluminum (e.g., outdrives, outboards, hulls)	-950 mV
Mild Steel (e.g., hulls, rudders)	-850 mV
Stainless Steel (e.g., propeller shafts, rudder posts, trim tabs, high-performance propellers)	-750 mV
Bronze (e.g., propellers, thru-hulls, seacocks, struts, rudders)	-550 mV

Interpreting Your Readings:

Within the Range:

If your hull potential reading falls within the recommended range for your boat's hull material, it's a positive sign! This indicates your corrosion protection system (sacrificial anodes or ICCP) is functioning effectively, and your underwater metals are well-protected.

Below the Range:

If your hull potential reading falls below the recommended range (more positive voltage), it signifies insufficient protection for your boat's underwater metals. This can lead to corrosion. Here's what you can do:

Investigate the Cause:

Several factors can contribute to insufficient protection. Here are some key areas to inspect:

• Sacrificial Anodes: These are the first line of defence. Check if they are:
  • Worn Out: As sacrificial anodes corrode, they shrink in size. If they are significantly reduced in size or appear crumbly, they need replacement.
  • Properly Connected: Ensure the anodes are securely connected to the boat's electrical system.
• Bonding System: This system ensures all underwater metals are electrically connected. Inspect for:
  • Corrosion: Corroded connections can impede electrical flow, reducing the effectiveness of the corrosion protection system.
  • Wire Gauge: The bonding system wires should be of adequate size to handle the required current. Undersized wires can create resistance and hinder proper current flow.
  • Misuse: Ensure no accessory circuits are using the bonding system as a ground. This can interfere with its functionality.
• ICCP System (if applicable): If your boat uses an Impressed Current Cathodic Protection (ICCP) system, check its functionality according to the manufacturer's recommendations.

Above the Range (Excessive Protection):

Readings that exceed the recommended range (more negative voltage) might seem ideal at first glance. However, excessive protection can also be detrimental. Here's why:

Vessels that are over-protected can lead to adverse effects on underwater hull coatings (anti-foul), aluminium alloy metals, and wooden hulls.

• Steel and Fiberglass Hulls: In saltwater environments, an excessively negative potential below -1100 mV can diminish the efficacy of anti-fouling paints and barrier coatings.
• Aluminium Hulls and Outdrives: In saltwater, aluminium is highly vulnerable to alkali corrosion and hydrogen gas blistering of paint coatings if the potential goes beyond -1200 mV.
• Wooden Hulls: In saltwater, potentials more negative than -650 mV can cause the destruction of wood fibres around metal fittings, resulting in "fuzzy wood" or alkali delignification.

Over-protection usually stems from using incorrect anode types, such as employing magnesium anodes on aluminium metal in saltwater, or directly attaching zinc anodes to underwater metals on a wooden hull.

Note: While magnesium anodes might yield "overprotection" readings, this isn't problematic in freshwater due to its lower conductivity.

The Importance of the 200 mV Shift:

The explanation about voltages below the recommended range emphasizes the need for a negative voltage shift of at least 200 mV for effective corrosion protection. This essentially means that a well-functioning corrosion protection system should be able to shift the underwater metal's voltage in a more negative direction by at least 200 mV compared to its natural tendency to corrode (galvanic voltage). This shift provides the necessary protection against galvanic corrosion.

High-Precision Silver/Silver Chloride Reference Electrodes: WE50 Series

Protecting Underwater Metals: Verify Voltage with Silver/Silver Chloride Electrodes

Defending submerged metal surfaces against relentless corrosion is paramount. To ensure the effectiveness of your anode protection systems, we introduce the WE50 Series - featuring precision-engineered Silver/Silver Chloride Reference Electrodes. These tools enable straightforward and accurate measurement of your boat's anode protection systems, offering a shield against nature's corrosive forces.

Anodes play a pivotal role in guarding boats against corrosion in diverse water conditions. When different metals interact underwater, corrosion takes hold. In the realm of boats, anodes act as sacrificial metals, corroding in place of vital components like sterndrives and propeller shafts. Click here to learn more about anodes.

Selecting the appropriate anode hinges on your boat's metal surfaces and the water type you navigate. For instance, saltwater necessitates zinc or aluminum anodes, while freshwater requires magnesium anodes. Routine anode inspection and replacement are crucial, determined by material, water type, and usage duration. As a general guideline, replace anodes once they corrode by 50%.

The WE50 series reference electrodes empower you to scrutinize your protection system's efficiency by gauging the voltage in your vessel's vicinity. This measurement accurately assesses your vessel's bonding systems, confirms proper anode functionality, and bolsters overall corrosion prevention for your boat.

Designed specifically for saltwater and brackish water conditions, the WE50-Salt reference electrode combines advanced materials and expert craftsmanship to deliver unrivaled accuracy and durability. Each WE50-Salt reference electrode undergoes rigorous testing and meticulous calibration during the manufacturing process, ensuring optimum performance and peace of mind.

Each WE50 series high precision Ag/AgCl reference electrode comes with 10m of 2.5mm insulated flexible cable and a 4mm banana plug compatible with most digital  volt-meters, ensuring simple and accurate measurements of cathodic protection systems, also known as anodes.

 

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Designed specifically for freshwater, the WE50-Fresh reference electrode showcases precision engineering at its finest. Impeccable design and robust materials ensure your assets remain shielded against corrosion, while exhaustive testing and calibration procedures guarantee consistent and reliable results in every application.

Each WE50 series high precision Ag/AgCl reference electrode comes with 10m of 2.5mm insulated flexible cable and a 4mm banana plug compatible with most digital  volt-meters, ensuring simple and accurate measurements of cathodic protection systems, also known as anodes.

 

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PROMT Parts is proud to announce its collaboration with esteemed global leaders in the cathodic protection industry, Silvian. Together, we have brought forth a line of portable Silver/Silver Chloride Reference Electrodes that combine exceptional quality with affordability. Founded in 1984 by Dr. S Pathmanaban, a highly seasoned electrochemist and corrosion scientist holding a Ph.D. from the University of Manchester, Silvian has established itself as a pivotal player in this field. Dr. Pathmanaban's academic background served as the cornerstone for the establishment and growth of Silvian, focusing on the development and production of 'Silvion' reference electrodes meticulously designed for application in Cathodic Protection (CP) systems.

Benefits of the WE50 Portable Silver/Silver Chloride Reference Electrodes:

High-Precision Engineering: The WE50 Series is a testament to precision engineering, crafted to exacting standards to provide accurate and dependable measurements in diverse water conditions.

Tailored to Environments: Whether you navigate saltwater or freshwater, our electrodes are optimized to excel in their designated environments, offering superior protection against corrosion.

Rigorous Testing and Calibration: Each WE50 electrode undergoes a comprehensive testing and calibration process during manufacturing, guaranteeing optimal performance and adherence to the highest quality standards.

Longevity and Reliability: With robust construction and meticulous attention to detail, the WE50 Series is built to withstand the rigors of waterborne corrosion, extending the lifespan of your assets.

Easy Integration: Effortless integration into existing corrosion management systems ensures a seamless and effective corrosion protection strategy.

Testing your anodes and protection systems is an important part of boat maintenance. It can help you to identify any potential problems early on, before they cause damage to your boat.

Our WE50 Series high precision reference electrodes are scientifically engineered for accuracy in Salt, Brackish and Fresh Water environments.

To test your anodes and protection systems with a silver/silver chloride reference electrode, you will need to:

• Attach the electrode to your bonding system of your vessel.
• Connect the electrode to a voltmeter.
• Hang the electrode into the water about 30cm below the surface.
• Measure the voltage at all of the components that come in contact with the water, like propeller shafts, rudders and sea cocks.

The voltage should be between 0.8 and 1.2 volts. If the voltage is below 0.8 volts, it means that the anodes are not working properly and that your boat is not protected from corrosion. If the voltage is above 1.2 volts, it means that the anodes are corroding too quickly and that they need to be replaced.

Testing your anodes and protection systems regularly is an important part of boat maintenance. It can help you to identify any potential problems early on, before they cause damage to your boat.

There are several benefits to testing your anodes and protection systems with a Silver/Silver Chloride Reference Electrode:

• Know exactly where you stand: By measuring the voltage potential of your vessel, you know that your anodes are installed correctly.
• Early detection of problems: Testing your anodes and protection systems can help you to identify any potential problems early on, before they cause damage to your boat.
• Prevention of corrosion: By ensuring that your anodes are working properly, you can help to prevent corrosion from occurring on your boat's metal components.
• Peace of mind: Knowing that your boat is properly protected from corrosion can give you peace of mind when you are out on the water.

If you are a boat owner, it is important to test, or have your anodes and protection systems tested regularly. This is an easy way to help protect your boat from corrosion and keep it in good condition for years to come.

The battle against corrosion requires a proactive and precise approach. The WE50 Series offers not just electrodes, but a comprehensive solution for corrosion management. With a choice between WE50-Salt and WE50-Fresh, you gain access to high-precision tools meticulously tailored to your specific needs. Invest in the WE50 Series today and secure a future free from the relentless grip of corrosion.

 

WE50 Series: Your Precision Defense Against Corrosion

 

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