Preventing Hull Corrosion with ICCP Systems

Although modern hull coatings can provide some protection against corrosion, they seldom offer a complete solution. For this reason, most operators choose to protect their vessels with a purpose-designed impressed current cathodic protection system (ICCP).

Using an arrangement of hull mounted anodes and reference cells connected to a control panel, the ICCP system produces a powerful impressed external current to suppress the natural electrochemical activity on the wetted surface of the hull. This eliminates the formation of aggressive corrosion cells on the surface of plates and avoids the problems, which can exist where dissimilar metals are introduced through welding or brought into proximity by other components such as propellers.

An essential feature of Impressed Current Cathodic Protection (ICCP) systems is that they constantly monitor the electrical potential at the seawater-hull interface and carefully adjust the output to the anodes. Therefore, the system is much more effective and reliable than sacrificial anode systems, where the level of protection is unknown and uncontrollable.

By installing an ICCP system, operators can make significant cost savings in hull maintenance and achieve reductions in fuel costs by having a smooth hull surface. Furthermore, the system will safeguard the owner's investment and ensure greater safety through stronger hull integrity.

Cathelco Ltd. has developed ICCP systems for vessels of every type:

• ICCP for container, cruise, tankers, and other ocean-going ships.
• ICCP for steel-hulled supply, crew, ferries, tugs, yachts, work, fishing, and other commercial vessels.
• ICCP for aluminum-hulled supply, crew, ferries, tugs, yachts work, fishing, and other commercial vessels.
• ICCP for military vessels.
• ICCP for water-jet propulsion systems.

Ships such as container vessels, VLCCs and bulk carriers are usually protected by forward and aft systems.

Forward system. To provide a smooth hull profile, the forward system normally uses circular or elliptical anodes of approximately 100 amps mounted port and starboard. Power can be supplied from a modular or thyristor (SCR) control panel.

Aft system. Linear loop anodes are ideal for installation on large commercial vessels as they provide a high output from a relatively small surface area. Because of their powerful output, one 300 amp anode fitted on each side of the hull gives effective protection. Alternatively, linear anodes can be fitted. Generally, thyristor control panels are used for aft systems on larger vessels, as they are economical and incorporate comprehensive information systems.

The Cathelco Ltd. Minitek System uses the latest technology to protect steel-hulled craft against corrosion. This is achieved by using a compact control panel and an arrangement of anodes and reference cells which are flush mounted on the hull – so there is nothing to interrupt the smooth profile or cause additional drag.

The current to the anodes is constantly monitored and adjusted to provide the "optimum" level of protection at all times. This is far superior to the performance of sacrificial anodes where the amount of protection cannot be easily verified and may be insufficient to prevent corrosion.

• Anode life 15 years - unlike sacrificial anodes.
• Reduced weight in comparison with sacrificial anodes.
• Flush-mounted anodes to ensure smooth hull profile.
• No maintenance required.
• Self-diagnostic system.
• Operates from 230V or 115V AC. electrical supply.
• Control panel only measures 500 x 390 x 210 mm for systems up to 40 amps.
• Lower yard installation costs than recessed sacrificial anodes.

Aluminum is generally regarded as a stable material which does not corrode easily. However, when used in conjunction with other metals such as bronze propellers and steel components, serious problems of hull corrosion can arise.

The Cathelco Ltd. Alutek System uses the latest technology to eliminate corrosion on aluminum hulls. Unlike traditional sacrificial anode systems, it uses flush mounted, lightweight anodes and advanced monitoring systems to provide the optimum level of protection. So there is nothing to detract from the smooth lines of your craft or reduce its speed.

• Flush mounted anodes keep the hull streamlined.
• Reduced weight in comparison with sacrificial anodes.
• Automatic system - constantly monitors and adjusts output.
• Operates from 230V or 115V AC. electrical supply.
• Monitoring electrodes - measure the electrical potential near the dielectric shield
• Controlling anodes - measure the electrical potential at a remote point on the hull.
• Shield sensors - detect changes in resistance at the coated aluminum/seawater interface.
• Lower yard installation costs than recessed sacrificial anodes.

The Cathelco Ltd. Corrintec Division is a technological leader in the design and manufacture of ICCP systems for naval vessels. Their equipment has been supplied to 22 navies around the world for frigates, guided missile destroyers, fast patrol craft, submarines and fleet auxiliaries.

In addition to a long association with the British Royal Navy, Cathelco Ltd. has supplied equipment to the new generation of high-speed vessels including the U.S. Navy's "X" Craft.

I-Shield and Patroltek by Cathelco Ltd. represent the latest systems in a continuing technological evolution based on the highest levels of product integrity, reliability and performance.

Cathelco Ltd. now protects the USS Missouri. For the full article reprint, please see Cathelco Ltd. Protects Historic Naval Vessel.

The Cathelco Ltd. Jettek ICCP system provides a unique and highly effective corrosion protection for fast craft. Its reliability has been proved on fast ferries and military high-speed craft around the world, superseding systems solely based on "isolation" methods.

The Problem: Water jet tunnels are particularly vulnerable to corrosion because they are constructed from dissimilar metals, typically aluminum and stainless steel, or high tensile steel and stainless steel. Problems can arise at the interface of these materials resulting in rapid corrosion, which can put the safety and structural integrity of the vessel at risk.

Most high-speed craft are fitted with "isolation" systems to prevent corrosive activity between the dissimilar metals. However, many have a history of repeated failure, indicating that "isolation"’ is not a particularly efficient or successful method of preventing galvanic corrosion.