SUPPLIED BY PETER :
the Capac meter is just a voltage meter that measures the DC voltage created by the “battery effect” of dissimilar metals reacting in an electrolyte bath. As the meter states, our aluminum is protected from corrosion if the voltage is between .90 and 1.05 volts
Your probe is the reference electrode (positive) leading to the meter. The other wire on the back of the meter is grounded to the hull. The reference electrode is made of silver (a stable bio-unfriendly metal like copper) which is then electroplated with a silver chloride coating for even more corrosion protection. Even without it's silver chloride coating (amonium will dilute it), the electrode will still work. But if it's painted over, it will be insulated and won't work. Those few barnacles should not prevent your probe from working.
If you want to test it
while on the hard, use a 1.5 volt flashlight battery (D, C or AA it doesn't matter)
Connect the negative end of the battery with a wire to the aluminum hull, and touch the positive end of the battery to the reference electrode while a friend pushes the button on the meter. If it reads close to 1.5 volts, the probe is working. If it doesn't, it might be a bad meter or bad connections at the terminals, the splice in the wire from the probe, or a bad ground wire to the hull.
Capac Detector on the hull: The center 2" disk is the reference electrode. The larger 10" disk is just a plastic insulator. The outer area may be painted.. not the center disk.
If your anodes are working properly, they will generate a slight electrical charge as they corrode and sacrifice themselves.
Ions from the zinc or magnesium anode will travel to the positive terminal, which is any metal that is more noble.
Aluminum is more noble than magnesium and zinc, so anodes made of those 2 metals will protect our aluminum hulls as long as the potential (voltage) is within a certain range. Below that range and the aluminum is not fully protected. The aluminum starts to act as a sacrificial anode "protecting" other more noble metals like stainless shafts, brass or bronze, by corroding and shedding aluminum ions. This is what happens if a brass cutlass bearing is installed by the boatyard instead of a phenolic or non-metalic bearing.
Look at the pictures of Jeff's hull.
If the potential is above the safe range you are creating a "battery" that is too big. You have too much anode surface area or you are using magnesium anodes in salt water. That causes the current to pull too many ions from the anode and push them to the aluminum hull. The hull and anodes are no longer polarized (electrically ballanced) and you have begun to electroplate the aluminum with magnesium or zinc.
Treat the center disc very, very gently. No scraping or sanding. But, sandblasted, barnacled and painted-over Capac reference electrodes can be salvaged as long as the silver disk or screen is still there, according to one of our members. Once you remove the barnacles or paint and get down to the silver, you can use ordinary salt to deposite the chloride back on the silver. (
More info on that process needed here)
Here's a diagram of the electrode. File Attachment(s):
http://marinetteboat.com...rum/resource.ashx?a=897
Joel Albert, Potomac MD
"Charlie B" - 1988 32' FBS
Twin 318's/FWC/16x15 nibral props
docked Deale, MD
