zinc adnodes on AIs

The salt water and friction of the kayak moving through the water will generate some small electrical currents that can cause electrolysis. 

Powder coating, thick paint, nail polish, dielectric grease,  marine grease, etc... individually and together can slow down this process.   Also coating bolt/nut threads with Corrosion-X, and or Permatex anti seize compound can also reduce corrosion.