If I'm reading things correctly it was Coppercoat antifouling. Not a great testament!

Apparently these type of barnacles thrive on oxygen created by turbulence hence the fact that the boat was continually moving was detrimental rather than advantageous (contrary to the requirements for ablative antifouling to work). Think barnacle encrusted rocks that are continually pounded by frothy oxygenated water in between the high and low tide marks.