Sizing Zincs.

[StanleyMarcus]

I have a 37 foot Pacific Trawler. I am planning on installing a stern thruster on it this fall. To do this I will need to relocte the center stern zinc which is about 5 by 6 inches. I'am considering installing two plate zincs this size, one on each side of the thruster. The two would be about three to four feet apart. Is it posible to have too much zinc on the transom?
Any help would be appreciated.

 

[Marin]

(Stanley-- Sent you a Private Message re your question.)

 

[Larry M]

Have a corrosion survey done or talk to a ABYC Marine Corrosion Technician. You can find one in your are via this link.

American Boat and Yacht Council (ABYC): Education and Certification - Certified Technician Search

We had a corrosion survey done this past July and it was well worth the $65 we paid for one hour. We've put Hobo in a marina, that's up a river, in brackish water and the summer rains hadn't really started yet. We wanted to see if our bonding system was in good order and that we didn't have any stray current in AC or DC systems.

The results showed that the bonding system and AC/DC systems were fine and we were within the recommended range of -550 to -1100 millivolt. We tested -635 millivolts. The technician suggested that even adding more zincs may not get us more negative because of the freshwater content potently increasing so he suggested that we switch to aluminum anodes. A week later after changing from zinc to aluminum anodes he retested. The reading was -1028. We changed out a 6" x12" x 1/2" plate, prop and rudder zinc all to aluminum. The change-over was ~$10 more.

 

[psneeld]

usually on a glass boat no...can't have too much zinc...but some boats for what I have never heard as a definitive cause will burn off some types of copper bottom paints...it is usually when they add or increase the size of their transom zincs.

with that in mind.....the recommended method is to do a zinc survey of your underwater metals with the proper gear...if you are a handyman...you can but the setup for a little over a $100 if memory serves me correctly...lot's less if you own a good multimeter.

 

[Larry M]

I looked at buying a reference electrode but I also wanted the shore power and Hobo's AC/DC system checked for stray current. The technician, with our help, checked every circuit (AC and DC) on the boat plus the shore power. Since we've owned Hobo, we had practically rewired the entire DC and most of the AC system so it was good to get another set of eyes (plus a report).

A silver/silver-chloride (Ag/AgCl) reference electrode can be had for ~$125 plus you still need a digital millimeter.

 

[psneeld]

I looked at buying a reference electrode but I also wanted the shore power and Hobo's AC/DC system checked for stray current. The technician, with our help, checked every circuit (AC and DC) on the boat plus the shore power. Since we've owned Hobo, we had practically rewired the entire DC and most of the AC system so it was good to get another set of eyes (plus a report).

A silver/silver-chloride (Ag/AgCl) reference electrode can be had for ~$125 plus you still need a digital millimeter.

wow they have gone up...had mine for about $35 years ago....