Courtesy CMP The solar-powered SMartyr SCP anode is an impressed current cathodic protection system that saves underwater marine hardware from galvanic corrosion.
At IBEX 2024, CMP Group won an Innovation award for a wireless, impressed current sacrificial anode whose power source is a small embedded solar panel. It would have been easy to dismiss the SMartyr SCP System as just another fringe idea we see at one IBEX and find it gone at the next, but I was intrigued that it had enough technical credibility to satisfy the judges who granted it an innovation award (and a DAME award at Metstrade in November).
Then I discovered Scott McMillan, the owner of Electric Yacht and a brilliant engineer I have known for many years, was a key developer. For this project he had worked with CMP, the world’s largest producer of sacrificial anodes for recreational boats with manufacturing plants in four countries on three continents. More inquiry revealed the technology behind the new device was created by Silvestro Scotto, a 30-year veteran in the sacrificial anode industry and the founder of another of the top sacrificial anode companies in the world. I was satisfied this is not some kitchen-table invention.
The Claims
The SMartyr SCP online literature is light on technical details and heavy on performance and benefits claims:
- Innovative Technology: An internationally patented device that captures underwater solar energy to power an impressed current cathodic protection system (ICCP), safeguarding metal components from galvanic corrosion.
- Eco-Friendly: Free from harmful elements like cadmium, mercury, indium, and copper, ensuring no deposits are left on the seabed, and marine ecosystems remain protected.
- Smart Device: Automatically detects and adjusts to the level of corrosion protection required for all water salinity types, ensuring optimal performance in any environment.
- Simplification: A single device replaces the need for various sizes, shapes, and alloy types of traditional anodes.
- Longevity: Equipped with high-efficiency solar panels and large-capacity lithium-ion batteries, the SMartyr SCP System has a lifespan of at least 2-3 years, reducing maintenance costs.
- Ease of Installation: Quick and secure attachment with no drilling or wiring required.
Questions
Knowing CMP Group would have a stand at Metstrade (Amsterdam), I prepared a series of highly skeptical questions for company President, Don Hambly. I learned from his responses that the application is considerably more restricted than the literature suggests, but if you accept these constraints, the SMartyr SCP lives up to the hype.
Question 1:
If no wiring is required, how is the electrical circuit completed from the device through the water to the protected metal and back to the device?
In conventional systems, this connection is either via direct attachment to the metal being protected or via a bonding circuit inside the boat. It turns out the primary market for the device at present is for protection of metal trim tabs—significantly more limited than the literature implies. In this application the device is bolted to the trim tab or other flat metal surface (some drilling may be required). It has metal-to-metal contact on its backside at the base of the bolt hole, establishing the necessary electrical connection. Hambly told me it can protect up to 3 sq ft (0.3 m2) of bare stainless steel.
Question 2:
How does the device automatically adjust to the “level of protection required for all salinity types”? Does this mean the current output is based on salinity rather than the 200mV shift recommended in ABYC standards? If so, how do you determine protection levels from salinity?
This is where McMillan’s contribution to the technology comes in. The device includes a tiny zinc reference electrode. When the anode is first immersed, it starts out in a passive mode while it “learns” the “natural voltage” of the metal being protected. It then switches to an active mode set to achieve a 300mV shift. The impressed current, supplied by the internal lithium-ion batteries, is distributed via titanium screens in the sides of the device. The 300mV shift is programmable.
It’s important to note that the device will get confused if conventional anodes are also present. It remains to be seen how long the zinc reference anode will hold up over time.
Courtesy CMP Submersible, super-efficient monocrystalline solar cells charge the unit’s lithium-ion battery. Titanium screens on the side expose the calibrated impressed current to the surrounding water.
Question 3:
What is meant by “underwater solar energy?” Is the device using conventional solar cells for power? If so, how important is water clarity, depth of immersion, and angle relative to the sun? What testing has been done?
The system is powered by conventional, high-efficiency solar cells. These have a monocrystalline structure with a published efficiency of 25%—very much at the top end of commercially available technology. Turbidity, depth, and angle are all issues, but not as much as might be expected. Hambly’s explanation is that water diffuses light and solar energy in ways that make the angle to the sun less significant than in above-water applications. Indeed, in clear water, solar energy is available to depths of up to 50′ (15.2 m), but this range reduces significantly with turbidity.
Mounting the anodes on trim tabs keeps the devices at an acceptable angle and close to the surface. The SMartyr illustrations also include rudder and other vertical applications that will be substantially shaded by a boat’s hull. I find it difficult to imagine there will be sufficient diffused sunlight to reliably power these applications. Time and experience will tell.
Courtesy CMP When mounting the anode, it’s important to maximize possible exposure to sunlight and direct contact to underwater metal components such as trim tabs.
Question 4:
What happens in those cases of severe shading or other obstructions to sunlight that block the supply of solar energy? How long can the device maintain protection levels of impressed current?
When first immersed, higher levels of energy are required to polarize the metal than are required to subsequently maintain protection levels. If the device is properly matched to the metal being protected, Hambly says the lithium-ion batteries can maintain protection levels through, “30 days of darkness.” What I neglected to ask is what happens if the lithium-ion batteries are totally discharged? Is there an internal battery management system (BMS) that shuts them down? Are there conditions where they can be driven into thermal runaway with a risk of catching fire (of course, a fire, if it is possible, will be rapidly quenched through the immersion)? What kind of testing has been done?
Question 5:
Given the extended use-life of solar cells and lithium-ion batteries, why does the device not have a life expectancy longer than 2-3 years?
It may. These are early days. The first devices used lower grade Chinese lithium-ion batteries, which have been replaced with high-end Japanese cells (two of the popular 18650-sized cylindrical cells).
Conclusions
For boat builders, service technicians, and owners, this is an intriguing technology with much potential in specific applications. Perhaps not as wide a set of uses as the promotional literature implies, but nevertheless there are many tens of thousands of boats with metal trim tabs and similar underwater appendages for which this promises to be a useful piece of protective equipment. It will be interesting to see how it performs in the field over the next couple of years.
