What We Found During the Dry-Docking of a Coastal Vessel<\/h2>\n
In a recent technical survey, we observed the docking of a coastal vessel whose ICCP we had been inspecting for several years. With the vessel in dry dock, the hull showed: <\/p>\n
- \n
- Extensive areas of coating loss<\/strong> at the bow and midship, primarily on the bottom plate and at the transition between the bottom and the side, with exposed steel and active corrosion;<\/li>\n
- Pitting corrosion<\/strong> at localized points;<\/li>\n
- Wear was concentrated<\/strong> in the areas farthest from the ICCP anodes, which on this ship were located only at the stern.<\/li>\n<\/ul>\n
The first instinct is to look for “the culprit”: the painting or the ICCP. The analysis showed that there is no single cause. <\/p>\n
![\"Pitting](\"https:\/\/mcpmarine.com.br\/wp-content\/uploads\/2026\/10\/corrosao-pite-casco-docagem.webp\")
<\/figure>\nWhy Corrosion Occurs: A Combination of Factors<\/h2>\n
1. Paint loss increases current demand.<\/strong> Each area of exposed steel is an additional surface that the ICCP must polarize. The larger the exposed area, the greater the current required. When coating loss is concentrated in certain areas, the current demand is also concentrated. <\/p>\n
![\"Coating](\"https:\/\/mcpmarine.com.br\/wp-content\/uploads\/2026\/10\/perda-revestimento-fundo-casco.webp\")
<\/figure>\n2. The current must reach the areas where the steel is exposed.<\/strong> Most ships have ICCP at the bow and stern, precisely to distribute the current throughout the entire hull. In this case, the anodes were located only at the stern, and the bow and midship were dozens of meters away from them. When the paint degrades precisely in these distant areas, it is not enough for the rectifier to supply more current\u2014the current must reach those areas. <\/p>\n
3. The system’s margin decreases.<\/strong> An ICCP system sized for a well-painted hull may not have sufficient margin when large areas of steel are exposed at the same time. This often happens without triggering any alarms on the control panel, and it only becomes apparent in the trend data or during docking. <\/p>\n
Where River Navigation Comes In<\/h2>\n
On ships that travel both at sea and on rivers, each of these factors carries greater weight:<\/p>\n
- \n
- Abrasion:<\/strong> With the river at low water and the channels silted up, the water carries more suspended sand and silt, which wear down the hull\u2019s paint, especially on the bottom and the bow.<\/li>\n
- Freshwater conducts electricity much less efficiently:<\/strong> the ICCP requires a higher voltage to deliver the same current, and the current travels shorter distances. Areas already far from the anodes, such as the bow, become even more vulnerable. <\/li>\n
- Changing salinity:<\/strong> near the mouth of the river, saltwater flows upstream when the flow rate drops. The ship can transition from freshwater to brackish water in a single day, and the system must adapt quickly. <\/li>\n
- Electrode readings:<\/strong> Zinc reference electrodes, used in most systems, measure the hull potential so the controller can adjust the current. In fresh or brackish water, the readings change, and the operating point for the river section must be evaluated by a technician. <\/li>\n<\/ul>\n
In fresh water, aluminum sacrificial anodes also lose their effectiveness, which underscores the importance of a properly sized ICCP system. We explain this difference in the section on ICCP versus sacrificial anodes<\/a>. <\/p>\n
What We Recommended in This Case<\/h2>\n
- \n
- Fully restore the ICCP to operational condition<\/strong>, with commissioning upon completion of the services.<\/li>\n
- Restore the hull coating.<\/strong><\/li>\n
- Reevaluate the sizing and distribution of the ICCP<\/strong>, taking into account the ship’s length, the position of the anodes, and realistic scenarios for paint degradation.<\/li>\n
- Increase the<\/strong> radius of the<\/strong> anodes’ dielectric shields<\/strong> from approximately 1 m to 2 m.<\/li>\n
- Evaluate the addition of an ICCP at the bow<\/strong> to provide a current source near the areas that are currently furthest from the stern anodes.<\/li>\n
- Check the supplementary galvanic protection.<\/strong><\/li>\n
- Monitor the continuity and grounding<\/strong> of the mobile structures and propulsion systems, recording the values as a reference for future inspections.<\/li>\n<\/ol>\n
What to Check on Your Ship Before Dry-Docking<\/h2>\n
![\"ICCP](\"https:\/\/mcpmarine.com.br\/wp-content\/uploads\/2025\/06\/servicos-c.webp\")
<\/figure>\nWhile the ship is in operation, dielectric shields and anodes cannot be fully inspected visually. Therefore, the system readings serve as the best warning: <\/p>\n
- \n
- Monitor the rectifier’s performance\u2014<\/strong> output current and voltage\u2014at least once a week. A steadily rising current indicates lost paint; maximum voltage with low current indicates high-resistivity water or a faulty anode. <\/li>\n
- Compare the fixed electrodes with a calibrated portable electrode<\/strong>, taking measurements near the bow as well. Large differences indicate an incorrect reading from one of the electrodes or protection that does not cover the entire hull. <\/li>\n
- Schedule underwater inspections:<\/strong> these allow you to check the external condition of the system and the paint without docking. See the ICCP repair and anode replacement performed underwater<\/a>. <\/li>\n
- Check the operating point<\/strong> when switching between sea and river, with technical support.<\/li>\n
- Bring the data to the dry dock:<\/strong> the ICCP history helps plan paint repairs, component replacements, and any system upgrades. Learn about our dry dock services<\/a> and the annual inspection of the ICCP and MGPS<\/a>. <\/li>\n<\/ol>\n
- Compare the fixed electrodes with a calibrated portable electrode<\/strong>, taking measurements near the bow as well. Large differences indicate an incorrect reading from one of the electrodes or protection that does not cover the entire hull. <\/li>\n
- Restore the hull coating.<\/strong><\/li>\n
- Freshwater conducts electricity much less efficiently:<\/strong> the ICCP requires a higher voltage to deliver the same current, and the current travels shorter distances. Areas already far from the anodes, such as the bow, become even more vulnerable. <\/li>\n
- Pitting corrosion<\/strong> at localized points;<\/li>\n