To protect the boat from galvanic currents, two systems are used:
The sacrificial zinc anode, and active protection.
The sacrificial anode(typically zinc for sea water, and magnesium for soft water) a panel of soft metal electrically connected to the metal surface it is required to protect.
Being the less resistant material, it is consumed first, preserving the materials that comprise theengine or transmission to which it has been applied .
When the soft material is depleted, the corrosion of the materials previously protected by the sacrificial anode begins.
Active protection consists of a system that corrects the voltage potential to cancelout the currents that generate galvanic corrosion.
This system is fed from on-board batteries and must be complementary to the protection with asacrificial anode, it cannot replace it entirely.
The duration of the zinc is not possible to predict.Unfortunately, it depends on multiple factors:
These are just some of the factors that influence the zinc's lifetime.
Our advice is to inspect itswear at least every 4-6 months.
For monitoring, it is necessary to check the wear, replacing the anode when it has reached 50% of its original volume.
Before assessing the wear, the anodes are brushed to remove the oxide and salt that is deposited on the surfaces in contact with thewater.
The oxide and salt make the zinc appear larger and reduce its electrical conductivity and functionality.
Galvanic corrosion is an often unpredictable and very dangerous phenomenon. It is a direct result of electric currents that are develop in two or more metals, more or less close to each other in the galvanic scale, electrically connected to each other, and also immersed in a saline solution. Under these conditions, any metal assumes an electrical potential. If the metals concerned by this phenomenon are different, either directly, or through the saline solution in which they are immersed, they will cause a natural flow of electrons, as in any electrical circuit when, for any reason, two points of differing electric potential are in contact. Naturally the intensity of this flow of electrons will be increase as the difference in electric potential between the metals object of the phenomenon increases. This movement of electrons represents a true electrical current, known in this case as a galvanic current. The galvanic current immediately triggers a corrosion process that involves all the metals involved in the electrical flow. As the intrinsic nature of the very different metals, the corrosion to which they are subjected sometimes varies greatly. The corrosion will be greater in the baser metals. (E.g. Aluminium corrodes more rapidly than steel). Galvanic currents normally arise completely spontaneously, but under the conditions mentioned above, they do so quite unpredictably. It has, however, been noted that there are almost always external influences that contribute to triggering the electrochemical process, which then continues by itself. One of the major external causes to be found are the electrical potentials that occur with the connection of the on-board 12 or 24 Volt systems to the 220 Volt electric distribution systems. These electrical potentials, which are different from those in the immersed metals of a boat, can often assume even considerable values in relation to the earth's surface and with respect to other immersed structures in the vicinity. As already stated, all the metal structures in contact with salt water are expected to undergo damage when they are affected by electric currents of any nature or origin. All metals are therefore affected by this corrosion effect. Statistical experience has shown that the mechanical components most subjected to severe damage by these electrical currents are usually the base of the transmission, immediately followed by the axles and their related propellers. For all boats, then, the rudders and their axles, despite being ranked lower statistically, are not exempt and must be inspected. To a lesser extent, the sea anchors may also be affected, so it is best not to forget about them and include them in the check-list.
There are many reasons. For your information, we list some of them here.
We must also point out that your boat's engines are generally positioned
out of sight and difficult to access.
Thisis normal, and ensures as much space as possible is available tothe crew.
It is often not possible to access all sides of the engines without first removing panels, furniture, carpets, floor boards, tenders, and/or other accessories.
For this reason, it is important that at least once a year, qualified personnel can access the engine room to inspect
the engines and check for any anomalies.
During these inspections, consumables are also replaced as needed.
Checks are made forwear, and any worn components replaced.
Our engineers are also able to check for theneed for other work related allengine plant, allowing us to
anticipate potential disruptions.
The regular replacement of consumables will lengthen the life of the engines, reduces the possibility of sudden breakdowns and maintains
the value of your boat.
Our INBOARD, IPS and SAIL DRIVE transmissions are immersed in water almost the whole yearround.
They are thus subject to galvanic corrosion, ordinary corrosion, to mechanical wear of the deposits on the
rubber components, and tocontamination of the liquid lubricant.
It would be madness not to check theintegrity of the rubber parts, the quality of theoil, and thewear on the sacrificial anodes.
Also, stern drives must be stripped down at least once a year, otherwise all the components to be removed
for disassembly and maintenance will be blocked.