Electolysis and bonding

[pbbmorton]

Hi All, wanted get some input on bonding and electrolysis. First let me state that I am and electrical engineer and understand the process of electrolysis and the need for bonding.

Bonding is primarily for protection from electrocution if AC power is introduced into the DC circuit (also helps in lightning protection). Bonding’s attribute is to equalize the voltage across all components in touch with water. Very effective, however, in doing so it also creates a path for current flow. Current flow is the means by which electrolysis work. It allows ions from one metal to migrate to another … without a current path, electrolysis will not happen. Think a battery: one with nothing connected (no current flow) and one with both terminals connected (current flow).

So here is my question. Other than local zincs (e.g. prop shaft, iron keels, rudder hinges) and find very few sailboats with the bonding system connected to a zinc. Would appreciate informed opinions as to why and or what others do (if anything). E.g. using a zinc fish when docked at a marina

[smac999]

Every bonded boat needs zincs in the system or all the bronze etc will all corrode away naturally. At or away from the dock. You need a permimate one.

Most power boats have a large divers dream bolted to the stern and bonded. Not sure if many Sail boats do this or not. As it's easier with a flat stern

[fstbttms]

Originally Posted by pbbmorton

I am and electrical engineer and understand the process of electrolysis and the need for bonding.

Then you should know that it's not "electrolysis."

[Stu Jackson]

Marine Grounding Systems | West Marine

[pbbmorton]

Originally Posted by fstbttms

Then you should know that it's not "electrolysis."

Understood; galvanic corrosion is when two dissimilar metal come in contact. Electrolytic corrosion is created by coming in contact with AC ground from shore or from bad wiring in another boat. Both can cause considerable damage ... it is the electrolytic corrosion I am focused on.

[pbbmorton]

Originally Posted by Stu Jackson

Marine Grounding Systems | West Marine

Thanks Stu ... great article ... answered my question

[fstbttms]

Originally Posted by pbbmorton

Understood; galvanic corrosion is when two dissimilar metal come in contact. Electrolytic corrosion is created by coming in contact with AC ground from shore or from bad wiring in another boat. Both can cause considerable damage ... it is the electrolytic corrosion I am focused on.

No, no... I was only bustin' balls because electrolysis is a term that is constantly and improperly used by boaters. We are taking about electrolytic corrosion, not electrolysis, which is a different process and not one that affects a boat's underwater metal parts.

Just sort of a pet peeve of mine.

[jamhass]

I'll offer some anecdotal but real life experience.

We've run our boat for 8 years semi-bonded. That is, we have a galvanic isolator on the AC system and the boat has a hull zinc. Most, but not all thru-hulls are bonded to the hull zinc. The shaft (hence the prop) Is not bonded (shaft brush failed long ago), but there are of course zincs on both the shaft and prop. When in a marina, I generally hang a grounded (to the bonding system) zinc over the side.

To date, I see NO difference in corrosion between the bonded and unbonded thru-hulls. My prop and shaft are fine, and my zinc generally last several months.

The only time that I have problems have been in marinas and moored to a hot boat. In one instance I noticed that my hanging zinc nearly disappeared in less than a month. Problem went away when I moved slips. Shortly after, I added the galvanic isolator and have had no serious issues, but one other time, when near a suspect boat I did notice some additional loss of my hanging zinc.

Finally, I do make it a practice to disconnect from marina power supply when I do not need the power. I have sufficient solar to provide most of our needs when at a slip.

[boatpoker]

No qualified marine electrician uses the tern "electrolysis" as that is what happens to the electrolyte not the metals involved.
We should be talking about "galvanic" or "stray current" corrosion.
Bonding is another word often misused as people don't understand the references. Bonding against galvanic corrosion and bonding as a safety path are two different things i.e. two different bonds.

I once surveyed the sailboat of the electrical engineer who did the systems on "Maltese Falcon" .... I declared his electrical sytem a hazard. My slip neighbour just retired as President of IEEE and he readily admits to knowing nothing about electricity on boats although he does know what electrolysis is .

ABYC Certified Corrosion Analyst.

[pbbmorton]

Thanks all, and boatpoker you are right sometimes we trip all over our EE! I know enough to ask.