|Rapid Anode Consumption, Blistering Bottom Paint|
|Written by Ed Sherman|
|Monday, 22 October 2012 17:37|
Rapid Anode Consumption, Bottom Paint Blistering and More! Yikes!
This series of problems was brought to us from one of our readers last week. We need to share this one because there is a lot going on here, and power or sail, some of the tips here can help you along the way if some of these symptoms crop up. So here's the note from our reader:
"Hi Ed, I am ABYC-Marine Electrical certified and was recently asked to look at an '01 Sea Ray 28 w/ 2 Merc Alpha 1 Gen 2 stern drives in CT. Water is salt/brackish depending on the tide, anodes are all active aluminum and their mating surfaces are paint/oil free. Erosion of the anodes on both the drives and the trim tabs has been a tad excessive, 2 month replacement shows 75-90% wear.
Wow, what a bad string of events. OK, so here is what we know about some of these problems. First, the blistering bottom paint. We have known this to be a problem for some time now, especially with bottom paints that have a cuprious oxide content that is over about 55%. We have also noted that this seems to occur more frequently with black colored anti-foulant. Two things seem to work to mitigate this problem. One is to strip the bottom paint off the metalix fittings and re-paint them with some epoxy barrier coat. Then re-apply anti-foulant. Another cure we have seen work is to back off on the sacrificial anode voltage potential for the cathodic protection system. Get it down to about a maximum of -650 mV when tested in saltwater with a silver chloride reference electrode. In this case, our reader replaced all the fittings with Marelon through-hulls. OK, that will work as well. It also reduces the amount of metal that needs protection with anodes. All good on that count.
As for the seemingly rapid anode consumption, I think that our reader needs to double check that the galvanic isolator is truly OK and able to block galvanic currents. Otherwise the boat's anodes are indeed helping to protect all the boats on the same dock and will surely eat up any sacrifical anodes.
The battery issue is a mystery with the information provided. A new set of batteries and a new and programmable carger installed and they're still boiling over? Demons, it is near Haloween after all. More info needed on this one.