Hull Potential of Carbon Fiber Vessels

We recently fielded an inquiry from a customer looking to use our Corrosion Reference Electrode to establish his vessel's hull potential. That's an easy test with the CRE, but in this case, one very important detail - a carbon fiber hull - warranted an email.

The hull potential for a carbon fiber vessel is going to depend on which underwater metals are present (e.g., propellers, shafts, thruhulls, saildrives, etc.) and, importantly, whether they are bonded to the hull.

Carbon fiber is conductive, typically behaving like a noble metal.  Something like graphite, with a high positive potential.  Without proper electrical isolation, a carbon fiber vessel's potential may read as, say, +200mV.  With other metals bonded, the reading is going to be signficantly lower, likely negative.  Exactly how much depends on the usual variables in a potential test - metal type, surface area size, etc.  But that disparity in potential speaks to a pretty scary reality:

Carbon fiber can accelerate corrosion to your underwater metals if they're bonded together.  Sacrificial anodes would certainly help, but there's a very real risk here.

That's why, with a carbon fiber hull, the very best practice is very often electrical isolation.