Capt VR here again,
It does amaze me that we get so many answers to some of the simplest questions.
Most of them being wrong! To this day I wonder why ABYC does not make an owners
manual to basic questions and safety
. I know my Surveyors manual is 5" thick.
Owners really could use professional guidance from ABYC.
1. Most used bronze in the marine trade
is silicon bronze with a 12-13% tin, not zinc.
Trace amount of zinc, usually less than 3%
2. Boats don't get electrolysis
, unless you have hairs on your boat growing where you
don't want them to grow.
3. The term, "electrolysis" is wrongly applied to stray current
4. For those of you that think I'm wrong, look up the different type of corrosion
will not find electrolysis
. Look up ABYC or any qualified industry standard, you will
not find electrolysis in there for a corrosion
5. Most degradation is stray current
corrosion, this is what most people use the term
"electrolysis" Most stray current comes from dockside power. A boat 2-3 boats down
from you has a grounding problem, closing the circuit on his boat causes a slight
positive charge to go down his green earth ground on his 110v system, comes aboard
your boat on your 110v green wire earth connection and mingles amongst your green
bond/ground wires that should not be connected.
Then goes out to your under water hardware
. This eats up your zinc's and causes the
degradation to your props, rudders, shafts and struts. After surveying for a number of
decades, I'v found most boats with eaten away bronze is from a surrounding boat, not
from the boat with the damage. That's when you change slips that you've had or get
a new neighbor within 50' or so, you should have your boat checked by a shop with a
galvanometer to check polarities and for stray current.
6. Breaking a liquid into component or removing hair is electrolysis, not corrosion.
7. Zinc's - You all should have an 8-10 ga green bond wire going to all your underwater
, this is your bonding system. All should be tied in together. You should
never tie this bonding system to the green ground on the 110v system. Reason one,
this opens the path for a bad neutral to ground 110v to your bonding system which
could kill someone.
8. The man with the broken strut never mentioned his bonding system. A lot of people
do not have a zinc on their struts. But one of those bolts are tagged into the bonding
system inside the hull
and get protection from other zincs in the system. This bolt
should be pulled and cleaned to insure good contact with the strut at least yearly, I
tag to two bolts should I loose continuity to one of the bolts. I personally on all my
boats have installed a 4X8 zinc for a master zinc in addition to all the individual zinc's
in the bonding system.
Take it to the bank, SILICON BRONZE is the most used alloy for underwater hardware on a boat. Highly corrosion resistant and almost as strong as steel
Capt. Vince Rakstis, Ret. MS St.Petersburg, Fl. "Old School