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An important barrier in the fight against biofouling, corrosion and drag that impact fuel efficiency is the Marine Growth Prevention System (MGPS) which can be used by vessel operators and superintendents. It's not enough to install an MGPS. The only way to know if it is working properly is by regular checkups, where it can continue to keep your boat safe. SME Group has been developing monitoring protocols to distinguish the real from the virtual for over 20 years. To monitor effectively the MGPS is more than just looking at a control panel display, we have a practical framework based on our experience in working on over 500 annual retrofit and maintenance projects.
The goal is to learn about the Core Parameters
The first step in a successful MGPS monitoring program is to identify what variables are indicators of system health. As soon as you start thinking, you think of anode current, anode voltage, but there are more terms. In most systems the electrical readings will be acceptable even if the surface of the anode is passivated or heavily coated, reducing the release of protective ions. For this reason, SME recommends keeping track of the current density per surface area of the anode (per unit of surface area) rather than the total current that is drawn. A sudden decrease in current density (even if the voltage is stable) is indicative of the need to clean or replace the anode.
Another parameter that is sometimes neglected is the flow rate of water over the anodes. When the flow is less than the designed rate, the flow of the water is uneven and causes dead water areas in the sea chest or piping where fouling can occur. Our regular service visits always involve verifying the flow reading with the vessel's operating profile, using the SME technicians' expertise. This is especially important for boats that tie up for long periods, or operate at low speeds when navigating, where the natural flow is low.
Establishing a Baseline and Trend Analysis
A common mistake we see is taking an absolute value of MGPS reading rather than a relative trend. The same voltage may be an indicator of degradation a month later if the water temperature, salinity or anode surface area has changed. At SME we ask our customers to take at least three measurements each week (current, voltage and reference cell potential) and plot the values on a simple trend chart. This level will be lowered gradually with the years until a failure occurs.
Our mechanical and electrical technicians have been trained to search for rate-of-change alarms. No matter if the reduction in the current of the anode is within the “green zone” of the manufacturer or not, we investigate it straight away if it is reduced by 15% from one week to the next. This is a proactive approach which has enabled many of our international partners to reduce their emergency callouts. So much so that our 12-month project services warranty is based on this concept: We don't wait for the system to fail before we do something about it!
This is the critical role of Reference Electrodes and Hull Potential.
A typical well-functioning MGPS will keep the hull potential in the protected range of -800 mV to -1050 mV vs. Ag/AgCl. Direct monitoring of this potential gives information regarding the activity of the impressed current protecting the steel or just passing current through the water. We take calibrated portable reference electrodes with us on every site visit as a service to SME's as we have experienced built in panel meters can drift or may be affected by ground loop.
When the hull potential is falling less fast (from -950 to -850 mV), but there is no change in system current, it is most likely that the coating has deteriorated or there is a stray current on board from another equipment. A general survey of electrical bonding and survey of the paint condition of the vessel is needed in these cases and will not be sufficient to alleviate the issue if only changing the MGPS output. Here's where an integrated electrical, mechanical and technical engineering methodology used by SME's proves to be more valuable than siloed maintenance activities.
Physical Inspection: Visual and Ultrasonic Checks
Nothing can replace actual physical examination of the MGPS parts with electronic data. SME recommends that the anodes should be removed for visual inspection at least at the time of dry-docking or at the end of a 12 month period. Look for wear and tear, cracks or chalk on the anode surface. These deposits can be calcium or magnesium precipitates which prevent the ions from leaving the anode and can still occur with an apparently normal electrical supply. The ultrasonic thickness testing of the anode stub and the mounting bracket can be performed by our Nantong workshop, this method can detect the hidden corrosion of the anode assembly, and prevent possible catastrophic failure.
In a similar manner, the reference electrode should be removed and cleaned, and re-calibrated in a known seawater standard. Numerous instances have been reported where a moving or floating reference electrode has led to much faster (or slower) flows of current through the anode, leading to increased coating damage or to recurring incidences of biofouling. If the inspection is conducted in an orderly fashion, all such problems can be avoided.
When it's time to seek help
If detailed monitoring is in place, there are situations which mandates outside expertise. If systems are running at full capacity and still producing low readings on the hull or if readings are low in specific areas while systems are reading normally, then it's time for a specialist team. SME is active in all around the world shipyards, especially with a strong presence in mainland China, enabling us to send technicians quickly. A comprehensive stock of replacement anodes, reference electrodes and control boards is in store allowing us to get the system back up and running, often in one port call.
Keep in mind that monitoring isn't just about numbers, it's about making sure that the MGPS is working to maintain your vessel's efficiency and structural soundness. At SME, we go the extra mile, committed to not only inspecting but also offering actionable insights and lasting solutions. Let us help you use your MGPS data to create a dependable maintenance plan—after all, if your system performs, your vessel performs.