Canals can be a special challenge for a boat’s hull, because narrowboats and widebeams tend to have metallic hulls, and are often connected to shore electric supplies either permanently, or for long periods of time. Much of that time they are unattended, so your Galvanic Isolator needs to be unquestionably reliable.
Whether your vessel has a metal, GRP or wooden hull, it needs protection from galvanic currents, which corrode steel and aluminium hulls, outboards, outdrives, propellers, and other underwater fittings. Galvanic Corrosion can be worse on rivers, because of the water flow, & the fact that the water can more conductive high mineral concentration.
Galvanic protection is crucial for sea going vessels, as they float in highly conductive water. When docked, outdrives, propellers etc are extremely vulnerable to Galvanic Corrosion. Anodes on sterngear, being small, corrode rapidly, leaving the boat’s metalwork at risk. Additionally, much modern “Tech” equipment causes earth leakage, which is even more dangerous than Galvanic Currents.