Establishing the method for simulation of electric potential in cooling water passages of outboard motors

Producing 3D models of cooling water passages of outboard motors, and calculating distribution of electric potential on the water passage surfaces using BEM, we have developed the new method for simulation of electric potential distribution. The outboard motor is a propulsion system attached to the transom of the boat with steering function. As the water around the boat is drawn in for cooling of the engine, the engine parts are susceptible to severe corrosion. As a means to help prevent corrosion, a part referred to as the anode metal, which has a lower natural potential, is provided. Such a method is called the sacrifice protection because the anode metal corrodes before the engine parts due to the difference of electric potential. Since anti-corrosion currents occur preferentially to areas close to the anode metal, the anode metal is required to be located at the most effective place for corrosion protection. However, there are certain restrictions in the layout of anode metal from the engine configuration and parts layout. In addition to it, the identification of potential distribution requires measurements from the actual outboard motor. That was why it was challenging to realize a design having an ideal potential distribution. To deal with the issue, we conducted simulation of secondary current distribution in order to help predict potential distribution at the design stage. Taking actual measurements of polarization curves of outboard motor parts in the environment that matched the actual water passages and where the flow velocity existed, the measured data was uploaded as the simulation parameter. The calculated data of the potential distribution simulation are very close to the actual measurement. With the potential distribution simulation method established, it is now possible to lay out necessary number of anode metals at appropriate locations for corrosion prevention.