GRP and wooden craft have hulls that are not affected by galvanic corrosion. But their stern gear, (outdrives, outboard motors, propellers etc.) are.  When moored, and connected to  a shore supply, galvanic & stray currents can have a destructive effect on these vulnerable parts of your boat. This is made worse by the fact that many of the parts that make up stern gear are made of “soft” metals. By soft, we refer to metals that are quite “anodic”, that’s to say that they are easily etched away by galvanic and stray currents. That’s why the parts of the stern gear that are under water always seem more “weathered” than the dry parts. Added to this, the fact that  a flowing body of water is naturally quite abrasive, and quickly erodes any protective coating that might be in place. Even without a protective coating to the underwater parts, a galvanic isolator can prevent galvanic AND stray DC currents from flowing, potentially adding years to the life of a boat’s underwater metal equipment.