Well written! I have my Vega over 30 years and besides the zinks nothing ever corroded (galvanic action). There is one thing that kills boats: cheep battery chargers! If you're in a marina, ask the captain next (and next) to you what kind of battery charger he or she has. A good 75% of chargers sold as marine chargers are not really fit for boats- in goes AC, and out comes AC AND DC- and that will kill your boat! I've been told many times by boat owners that they're using a "good" charger. But when we checkt, out came AC and DC.
I rather get a boat owner angry at me than that charger damages my boat!
Wilhelm, V-257
Larry Bissell albinvega1493@... wrote: I don't want to beat a dead horse, but I am reading a lot of
misinformation on this site about sacrificial anodes. The idea I am
getting is that it is better to be safe than sorry, so wire the thru-
hulls all together in a daisy chain and protect them all.
I have done a lot of reading about sacrificial anodes, and it is my
understanding that any stand-alone bronze fittings do not need to be
wired together and connected to an anode. In fact many experts
recommend that stand-alone fittings be left exactly that, isolated
from any ground on the boat.
I quote John C. Payne in his book "Understanding boat Corrosion,
Lightning Protection and Interference" p. 11
"In reality, most modern fiberglass vessels don't need very much
protection. The general rule of bonding all electrically isolated
metal thru-hull fittings interconnected in a daisy-chain
arrangement, to keep then at the same potential, is flawed. It
probably causes far more harm than good. This may be at variance
with some recommendations. If all the underwater items are of the
same material, that is bronze, and are electrically isolated by
hoses that are rubber or PVC, there is no reason to protect them.
If there are no dissimilar metals there can be no corrosion cell
formation. If you bond everything and then connect into other
systems, you create a situation where outside influences, such as
stray current, can cause problems. Remember: you protect only those
items that are close to other items underwater of dissimilar metal.
This is usually in the stern, and covers propeller shafts, brackets,
rudder hangings, etc."
Probably the most dangerous item that can be damaged by galvanic
corrosion is the stern tube, due to the material it is made of
(bronze) and its proximity to the prop shaft (usually stainless).
You corrode a prop and it may even fall off, but the boat doesn't
sink. A stern tube corroding away could theoretically result in the
boat sinking. I wired my stern tube and bronze rudder fittings to
an anode just to the left of the stern tube fitting. The anode
showed significant loss of material after only 3 months in a slip.
(I was slipped right next to a live aboard using shore power 24/7).
The prop shaft anode collar also showed significant loss of
material. However, the anode I connected to the rudder heel
(electrically isolated from the rest of the fittings) showed zero
material loss. This supports the logic of Payne in his book.
In a 35+ year old boat, if the through hulls were never wired
together and they are still solid, I don't see any reason to do so
now. Prop, stern tubes etc. are another matter.
Larry Bissell
"Kemanalea"
Hull 1493
SF Bay Area