Yes replace them. Firstly, normal service
is to replace them one per year at every haul out
. They are Zinc by the way.
Now to your two anodes. They should not have the white powder (Zinc oxide) on them. This can be caused by several factors. Poor Zinc quality is the least usuall, but possible. The more probable are, poor anode connection to the hull
leaving the anode not working. Or more commonly is over Zinc'd. That is having too much Zinc to do the work. All situations are bad and need solving. Firstly you need to ensure the anodes are bonded to the metal.
When you place the boat
back in the water
, you need to do some testing. Get a Marine
sparky to take alook. He needs to test the current
flow for protection. That flow needs to be within a specific range for adiquate protection. Too much or not enough will both cause damage. You need to then add or subtract anodes to get the current
in the right range.