Bonding

[Gordon J]

Food for thought: the largest boat manufacturer in the world, Beneteau, does not bond. I owned one for ten years. I lost one through Hull, that was nestled between two others that were unaffected. I am thinking it was cheap Chinese bronze. All other metals good after ten years.

 

[Gordon J]

I seem to go through trim tab zincs at a fairly rapid clip. The trim tabs are not bonded and I don’t see a way to bond them. The tab hinge is screwed directly into the hull and the Bennett hydraulic rams are made of plastic. Anyone else have this issue?

 

[Comodave]

If you want to bond them you could replace one of the screws with a through bolt and then bond the inside part of the bolt. But I would still keep the individual anodes on the tab since the hinge may not be the best conductor.

 

[Gordon J]

Wish it were that simple

If you want to bond them you could replace one of the screws with a through bolt and then bond the inside part of the bolt. But I would still keep the individual anodes on the tab since the hinge may not be the best conductor.

Thanks Dave. The screws go into the bottom of the hull. I am guessing the glass is 2 or more inches thick. So I can not replace with bolts.

 

[SteveK]

Thanks Dave. The screws go into the bottom of the hull. I am guessing the glass is 2 or more inches thick. So I can not replace with bolts.

A thought, are the zincs eroded by cavitation on the underside. Been a while since I had tabs but I think the zinc was on top side.

 

[Gordon J]

Not quite

A thought, are the zincs eroded by cavitation on the underside. Been a while since I had tabs but I think the zinc was on top side.

The trim tabs are sandwiched between to zincs, top and bottom.

 

[SteveK]

The trim tabs are sandwiched between to zincs, top and bottom.

Is there any difference in wear bottom to top half? If yes, mount on top only.

 

[Comodave]

Thanks Dave. The screws go into the bottom of the hull. I am guessing the glass is 2 or more inches thick. So I can not replace with bolts.

They make 3” long bolts...

 

[SteveK]

They make 3” long bolts...

It sounded like lag bolts that end in the hull bottom, so no nuts. But one can be added higher and bonded outside to the tabs, inside to the transom zinc (if there is one). My guess is the zinc on bottom is worn by water/air and debris.

 

[Comodave]

Our anodes are mounted through the tabs with one on top and one on bottom. We don’t see any difference in wear between the top and bottom.

 

[CharlieJ]

@Gordon_J
Trim tabs are typically not bonded and are therefore not protected by the hull anode (if fitted.). The trim tabs are meant to be protected by the anodes that are attached to them. To gain more life on your anodes, recommend you switch to aluminum alloy anodes. They have about 50% more Ahr than a similarly sized zinc anode, have about 50mVDC more potential and do not have the heavy metal cadmium that sloughs off and comes up the food chain.
They cost the same or a bit less than zinc, are available at West Marine and Performance Metals.https://performancemetals.com/

 

[Choices]

A question regarding the wood vs fiberglass hulls....

I completely understand what you said, but had never considered it.

Is there any data regarding different types of wood? Oak versus mahogany, etc.?

Is there any data regarding different frp? Foam, epoxy, carbon, Kevlar?



This just got quite interesting.

 

[boatpoker]

A question regarding the wood vs fiberglass hulls....

I completely understand what you said, but had never considered it.

Is there any data regarding different types of wood? Oak versus mahogany, etc.?

Is there any data regarding different frp? Foam, epoxy, carbon, Kevlar?



This just got quite interesting.

My Marine Corrosion Certification expired last year but I do not know of any studies covering delignification of different woods. As to composite construction, the only outlier is carbon fiber which is conductive and should in my opinion be treated like a metal hull.

 

[CharlieJ]

@Choices
I agree with Boatpoker; I know of no study on high hull potential and its effects on different species of wood.

To clarify: Cathodic protection is considered to be adequate to prevent galvanic corrosion when the potential (measured against a silver/silver chloride reference cell) of a submerged metal has been shifted at least -200mVDC from its "freely corroding" potential. The freely corroding potentials are represented in the Galvanic Series.

The construction of a fiberglass boat, whether cored, solid, polyester, vinylester, etc. makes no difference but represents a class of boats where cathodic protection cannot harm the base structure. Wooden boats, aluminum boats and boats with aluminum underwater components do have limitations on cathodic protection current as indicated by the hull potential because excessive hull potential will damage these materials.

 

[Gordon J]

Mix zinc and alu?

@Gordon_J
Trim tabs are typically not bonded and are therefore not protected by the hull anode (if fitted.). The trim tabs are meant to be protected by the anodes that are attached to them. To gain more life on your anodes, recommend you switch to aluminum alloy anodes. They have about 50% more Ahr than a similarly sized zinc anode, have about 50mVDC more potential and do not have the heavy metal cadmium that sloughs off and comes up the food chain.
They cost the same or a bit less than zinc, are available at West Marine and Performance Metals.https://performancemetals.com/

Charlie, thanks for the response. Using aluminum on trim tabs won't cause a problem?. I have two hull zincs about two feet away.

Thanks
Gordon

 

[CharlieJ]

No they will not cause issues as they are two independent cathodic protection systems.

 

[Comodave]

Why not just go to all aluminum anodes including the hull anodes?

 

[Art]

Dear Charlie Johnson - BYC Master Technician

I am pleased to see a person with your qualification in his discussion.

Having been a boater since mid 20th Century I learned to follow these rules to keep each boat free from metal corrosions. Some people tell me I'm incorrect. Would like to learn your input regarding my methods... to help keep boat metals free from galvanic and corrosive dilapidations.

1. Do not leave boat plugged into shore power for long durations, especially when not aboard. I have never been a full timer liveaboard.

2. Tie off the boat into as close as possible to center of slip as possible.

3. Make sure when leaving boat for any duration to have a master switch turned to off... that completely isolates the battery bank.

4. Have applicable material anodes [depending on salt, fresh or brackish water] in correct placement positions and in good/operable conditions.

Also - Dock in fresh water if possible... due to its reduced transmission of electric currents that may be emanating from other sources.

Having followed those rules I've never had severe galvanic corrosion nor electrolysis problems. Usually "0" trouble.

Your thoughts appreciated.

Thanks!

Art

 

[SteveK]

Why not just go to all aluminum anodes including the hull anodes?

My thought as well.
Especially if they last longer and are better for environment.

 

[Comodave]

Yup, also easier to order all aluminum than a mix.

 

[CharlieJ]

@Comodave

Why not just go to all aluminum anodes including the hull anodes?

Absolutely! They are superior in all aspects.

@Art

1. Do not leave boat plugged into shore power for long durations, especially when not aboard. I have never been a full timer liveaboard.

A well found boat with a functioning galvanic isolator or, better yet, an isolation transformer, can stay plugged in to shore power indefinitely with no adverse effects.

2. Tie off the boat into as close as possible to center of slip as possible.

Location of the boat within the slip has no relationship with the possibility of corrosion on your boat

3. Make sure when leaving boat for any duration to have a master switch turned to off... that completely isolates the battery bank.

Not a bad idea overall but this does not buy you any protection from galvanic corrosion. It may, under some very unique and arcane circumstances, protect you from stray current created on your boat.

4. Have applicable material anodes [depending on salt, fresh or brackish water] in correct placement positions and in good/operable conditions.

Good. And ensure that the diver reports to you whenever he performs hull husbandry tasks. BTW, aluminum alloy anodes can be used in all three types of water.

Also - Dock in fresh water if possible... due to its reduced transmission of electric currents that may be emanating from other sources.

True, but fresh water is much more dangerous from an electric shock drowning perspective.

 

[IntoTheBlue]

I happen to agree not to bond thru hulls, no need, bonding just creates a current flow. Shaft is bonded to a stern zinc, but rudders are not, they do have their own zinc attached. dissimilar metal currents to protect the stainless but not to be a source for stray current flow. Self contained circle.
Shaft protectors isolate the shaft from the engine/tranny.
But each to their own thoughts.

See attached article.
View attachment 109991

I've never really thought about it, but you bring up an interesting point. The green wire bonding on my Mainship Pilot 43 is wired to the aft zinc. This large zinc deteriorates in a rather short period of time, being changed twice a season. I've always though that was due to conditions in the canal where the boat is docked. Any concern here?

 

[backinblue]

People here are confusing some issues which is common when talking about bonding. The reason that the thru-hulls are disconnected is to prevent an electrical path for stray currents from passing thru your bonding system. For instance, coming in to a thru hull, passing thru your bonding wires, and exiting from the rudder. This article below recommends not adding thru-hulls to your bonding system. I am dealing with a similar issue on my Mainship and am considering disconnecting the wires. They are commonly bonded in the US but not in Europe. It's a shame this is such a mysterious subject and not one proven scientific method that is universally accepted. Consult with a good marine electrician before you change anything.

https://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems

 

[CharlieJ]

@IntoTheBlue
The transom anode is doing exactly what it is designed to do. If you want to extend the duration between anode replacements, change to aluminum anodes as I described upthread.

 

[backinblue]

I've never really thought about it, but you bring up an interesting point. The green wire bonding on my Mainship Pilot 43 is wired to the aft zinc. This large zinc deteriorates in a rather short period of time, being changed twice a season. I've always though that was due to conditions in the canal where the boat is docked. Any concern here?

There is a difference between electrolysis bonding of your vessel and stray currents in the water where you are docked. If your thru hulls are bonded and there are stray currents in the water, they will find an easier path by going into your thru-hulls and out your transom zinc than in the surrounding water. This could cause a more rapid deterioration of your zinc.

 

[CharlieJ]

@backinblue
First off, "electrolysis" is the dissociation of water into hydrogen and oxygen molecules or it is what beauty salons do to remove unwanted hair.

That said, you do bring up a good academic point. However; it has been my experience, as I said upthread, that the vast majority of DC stray current (also called electrolytic) corrosion is caused by the boat suffering the damage. What you describe can certainly happen, but it is a vanishingly rare occurrence.

 

[Art]

@Comodave

Absolutely! They are superior in all aspects.

@Art

A well found boat with a functioning galvanic isolator or, better yet, an isolation transformer, can stay plugged in to shore power indefinitely with no adverse effects.


Location of the boat within the slip has no relationship with the possibility of corrosion on your boat


Not a bad idea overall but this does not buy you any protection from galvanic corrosion. It may, under some very unique and arcane circumstances, protect you from stray current created on your boat.


Good. And ensure that the diver reports to you whenever he performs hull husbandry tasks. BTW, aluminum alloy anodes can be used in all three types of water.


True, but fresh water is much more dangerous from an electric shock drowning perspective.

The way I see it...

"A well found boat with a functioning galvanic isolator or, better yet, an isolation transformer, can stay plugged in to shore power indefinitely with no adverse effects."

That mean that in lieu of having a functioning galvanic isolator or an isolation transformer that my way of unplugging boat from shore power does help stop the wasting-away of metal parts?

"Location of the boat within the slip has no relationship with the possibility of corrosion on your boat"

Seems to me that the further away from another boat [e.g. boat in adjoining slip that may be leaking electric current into water] the less chance of electric effect on your boat's metals.

 

[Comodave]

We dock at our house so it is the only boat there. We use aluminum anodes except for the heat exchanger on the main engines and there we use magnesium since we can find the correct size and that is a different body of water. We changed the anodes 2 years ago so I ordered all new ones this fall. While I was fiberglassing some unused thru hulls closed on the bottom, I asked my wife to replace some of the trim tabs anodes. After a while she asked why we were replacing them, I replied they should be replaced when they are half way wasted away. She said they were not half gone. So we will wait another year.

 

[Steve DAntonio]

@Soo-Valley
In my experience, most stray current corrosion cases are self-inflicted. In other words, the victim boat is causing the stray current that is causing the corrosion on the victim boat. There are cases of stray current migrating from another boat but they are exceedingly rare.

So, if all of the metal underwater bits are bonded together with a bonding system where each connection is < 1 ohm, no daisy chains, etc. all of the underwater metal is at the same potential. With no voltage difference between the underwater metal components, current cannot flow should a B+ connection be made to an underwater metal component. No current flow, no stray current corrosion.

Note that a bonding system is, well, another system. And like every system on a boat, there is maintenance required to keep the system functioning properly.

100% correct. Bonding is optional as far as ABYC Standards are concerned. I wouldn't be without one.
More on bonding systems here https://stevedmarineconsulting.com/wp-content/uploads/2014/03/BondingSystems138_05.pdf

 

[SteveK]

I've never really thought about it, but you bring up an interesting point. The green wire bonding on my Mainship Pilot 43 is wired to the aft zinc. This large zinc deteriorates in a rather short period of time, being changed twice a season. I've always though that was due to conditions in the canal where the boat is docked. Any concern here?

@IntoTheBlue
The transom anode is doing exactly what it is designed to do. If you want to extend the duration between anode replacements, change to aluminum anodes as I described upthread.

Charlie, not exactly the answer I expected from you after the other posts. Really, the transom zinc is doing the job. Of course it is, but the underlying condition has not been identified why it has to be replaced twice a season instead of once every two years.
I would have concerns if I had to replace a transom zinc once every year.