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Old 10-02-2017, 10:08 PM   #1
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S/Steel Thru Hull Bonding

Should a stainless steel thru hull be electrically bonded, the same as a bronze one?
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Old 10-02-2017, 11:09 PM   #2
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Many experts would tell you that bonding is not necessary. Beneteau, the largest boat builder in the world does not bond. As a former sailboater, and Beneteau owner, i have never heard of problems associated with bonding or lack there if.

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Old 10-03-2017, 12:24 AM   #3
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I come from the old school. By not bonding, any metal not included in the bonding chain needs zinc protection. If everything is bonded all the zincs share the load. No metal is attacked except zinc. Depending on what other metal is in the water, the stainless could be the least noble.
Except in a metal hull where the hull becomes the bonding path, I run a heavy solid copper wire to all thru hulls and other metal. I run brass brushes on the shafts to tie to the bonding.
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Old 10-03-2017, 01:22 AM   #4
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Exactly. We all run shaft zincs, how are through-hulls different?
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Old 10-03-2017, 03:34 AM   #5
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Aisi true hull bigest problem is Crevice corrosion if your boat is salt water area. Watch your thru Hull every yars, if it starts to look like this

and more time you have risk sinking be cose stanles stell have crevide corrosion







http://sCorrosion in Through-Hull Fittings and seacock valves in ...

and US guru Steve http://stevedmarineconsulting.com/st...miracle-metal/
NBs
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Old 10-03-2017, 03:40 AM   #6
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So is bronze a better option? I have several plastic sink/AC/Bilge pump drains at or near the water and was going to replace them next time the boat is out. I already had one AC outlet crack.
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Old 10-03-2017, 06:14 AM   #7
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SS thru hulls are used above the WL as there safe in that use, and bonding is not necessary.
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Old 10-03-2017, 07:48 AM   #8
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My SS plates and bolts used to secure struts are bonded to the vessel grounding system. Wire size is important. ABYC guidelines are your friend.

As to no bonding system on an electrified FRP vessel I'd raise the question - is this a wise thing? How are 110 and higher voltage systems then grounded? Does not swimmer safety, new GFIC 3 ma dock codes or certification come into play?
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Old 10-04-2017, 06:55 AM   #9
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"My SS plates and bolts used to secure struts"

Its not the dock or boat electric that causes SS to depart, its being deprived of oxygen.

Why not pull one of the underwater SS bolts on the next haul and see how it fairs?
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Old 10-05-2017, 02:02 AM   #10
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There are a lot of half truths being tossed out in this thread.

Stainless steel must have a sacrificial anode attached to it. I would never use a s steel thru hull fitting below the water line, only bronze.

In a glass boat all my bronze would be bonded to a sacrificial anode. With wood boats bronze fittings should only be bonded to impressed current devices. Over protection of bronze fittings in wood boats causes an acid that eats the wood.

If stainless steel is deprived of oxygen it will deteriorate even if bonded. Stainless steel is more noble than bronze and can become an anode itís self if a more noble alloy is not present.

This is just scratching the surface of galvanic corrosion and electrolysis.

Bonding systems are not ground systems, electrical system should be kept separate from bonding systems.
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Old 10-05-2017, 02:47 AM   #11
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My ss. seacocks and their elaborate strainers were installed in 2010 by an old shipwright firm in Drummoyne in Sydney, when I was even more ignorant than now.
In a recent survey, both the use of ss and the lack of bonding came in for adverse comment, though there was no suggestion the ss itself had degraded. The bonding is there, right next to the seacocks, not connected. The teak pads under the seacocks, in at least one instance, are degrading, the surveyor says that is due to the lack of bonding. I don`t know, but I`m hauling the boat as soon as I can. Being Spring here, that`s 2 weeks away.(I won`t even redo the antifoul, the Jotun Seaguardian is amazingly good after nearly 11 months.)
Perhaps I should put in bronze, that means replacing the strainers too.I gave the current shipwright, who I trust completely and is located 2 Marinas away, a work list today and I will get his advice.
Meantime, I greatly appreciate the input.If the seacocks look fine, I might go with refitting and bonding,after 7 years any problems should be obvious. They have to come off to replace the pads, facilitating proper inspection.
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Old 10-05-2017, 03:33 AM   #12
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Years ago I welded a stainless steel nipple to the hull for an engine water intake and have yet to see any change in it. Will be inspecting it again tomorrow and if it looks OK will make another one for the head outlet.
I know the elephant brain surgeons will throw up their hands in horror, but it seems to have stood the test of time.
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Old 10-05-2017, 07:52 AM   #13
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Some clarification passed to me by a marine engineer....

"Bronze fittings on wood boats don't produce acid due to electrolysis, they make an alkaline product, sodium hydroxide. Vinegar, an acid, is used to remove and neutralize the alkaline crystals that form and destroy the lignin in the wood (delignification) that makes wood fuzzy around the fittings and through hulls.

http://www.mcclavemarine.com/
in Training bar....then under....Corrosion.and.Corrosion.Protection.Wooden .Boats.pdf Page 23

"Stainless steel is more noble than bronze..."

Passivated stainless steel, such as 316 which is the most commonly used stainless alloy in marine applications, is more noble than bronze but the "general purpose" less expensive (Chinese) version that usually shows rust spots is almost certainly not passivated and is less noble than bronze. Passivated 316 would require something like graphite or titanium to share the electrolyte before it would become an anode.

http://www.kastenmarine.com/_drawing...c_series_2.png
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Old 10-05-2017, 10:25 AM   #14
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Should a stainless steel thru hull be electrically bonded, the same as a bronze one?
Many theories here to be sure, how ever one or two things to note,

1) If you connect (electrically bonded) your SS thru hull to other non SS (such as BRONZE then you have connected two different metals with differing values on the Galvanic scale and with the Bronze being less noble it could behave like a sacrificial anode (in the right circumstance's) meaning the Bronze will react prior to the SS (that is if the SS is a marine grade such as 316 or 316L and has been "passivized"(which means usually dipped in a mild nitric acid solution to remove any surface free iron and or other impurities that can interfere with SS ability to resist corrosion, So IMHO you are best not to connect to other thru hulls if a different metal.

2) Where you have these two materials together(and electrically bonded) such as your SS prop shaft and Bronze prop you ALWAYS use a zinc anode (Right!) Dont think I will get to many arguments there? so using that very same theory bonding the thru hulls in different materials with out zinc protection will be a possible issue sooner or later,

Cheers Steve
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Old 10-05-2017, 11:15 AM   #15
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Many theories here to be sure, how ever one or two things to note,

1) If you connect (electrically bonded) your SS thru hull to other non SS (such as BRONZE then you have connected two different metals with differing values on the Galvanic scale and with the Bronze being less noble it could behave like a sacrificial anode (in the right circumstance's) meaning the Bronze will react prior to the SS (that is if the SS is a marine grade such as 316 or 316L and has been "passivized"(which means usually dipped in a mild nitric acid solution to remove any surface free iron and or other impurities that can interfere with SS ability to resist corrosion, So IMHO you are best not to connect to other thru hulls if a different metal.

2) Where you have these two materials together(and electrically bonded) such as your SS prop shaft and Bronze prop you ALWAYS use a zinc anode (Right!) Dont think I will get to many arguments there? so using that very same theory bonding the thru hulls in different materials with out zinc protection will be a possible issue sooner or later,

Cheers Steve
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Your number 1 is nicely dealt with by having a zinc plate in the water with the boats bonding system tied to it. Without the zinc plate (Al too in some cases) it is not a bonding system in the realm of our small boats.

So your answer to the OP should be no problem maybe?
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Old 10-05-2017, 10:31 PM   #16
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Your number 1 is nicely dealt with by having a zinc plate in the water with the boats bonding system tied to it. Without the zinc plate (Al too in some cases) it is not a bonding system in the realm of our small boats.

So your answer to the OP should be no problem maybe?
Tom, I see that too, but if we read 2, it suggests that without bonding, where there are dissimilar metals there will be a problem.
I`m fairly confident the ss fittings will be 316, but passivated? No idea and no way of finding out 7 years on.
My current shipwright frankly admits it`s not his area and suggests getting the local sparkie(Aussie for electrician)to take a look.
Not hard to bond them if we decide to, the unconnected strip is right there.
Are there downsides to bonding? Using that timeworn phrase "What could possibly go wrong?"
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Old 10-05-2017, 11:45 PM   #17
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Tom, I see that too, but if we read 2, it suggests that without bonding, where there are dissimilar metals there will be a problem.
I`m fairly confident the ss fittings will be 316, but passivated? No idea and no way of finding out 7 years on.
My current shipwright frankly admits it`s not his area and suggests getting the local sparkie(Aussie for electrician)to take a look.
Not hard to bond them if we decide to, the unconnected strip is right there.
Are there downsides to bonding? Using that timeworn phrase "What could possibly go wrong?"
Bruce,

In answer i would say there's not usually an issue as long as the dissimilar metals are not touching each other (electrically bonded), as most SS used below the water line is 316 or 316 L it is more noble (less reactive) than just about any thing else under the water line, if they are seven years on with no issues I would not change what ever system you are using,

The question remains is: Are all your thru hulls SS OR is there a mixture?

If all the same material IMHO then you could bond them together, if dissimilar materials then for me I wouldn't(unless using zinc anode protection), The comment on using a zinc plate in the water (same deal as a prop shaft anode) obviously would/does work and in fact protects a dissimilar metal combination in all cases and in a correctly set up vessel this is the norm.

Cheers Steve
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Old 10-06-2017, 12:24 AM   #18
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Steve, Of 5 thru hulls, 2 serve the main engines, one the genset, one the head, and one the(240v) salt water washdown pump. All but the last were renewed in 2010 and look similar type. Of the 4, all but the head have large ss strainers with locking caps which can be rotated off the strainer tube for access to the finger biting strainer inside.
I`m coming to the view that if the through hulls, which have come off the hull to replace the pads, check out ok, I won`t be bonding. Some violence may occur to the thru hulls in the process, then I`ll be considering whether to replace with ss or bronze, but one step at a time.
I come back to the degrading wood pads under the seacocks inside the hull, which the Surveyor thought results from no bonding. Would anyone like to comment on the validity of that?
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Old 10-06-2017, 02:24 AM   #19
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Bruce,

I dont see any connection with wood backing plates and being bonded or not, galvanic corrosion is caused by two (or more) dissimilar metals, wood however (although commonly used) is not the best material to use as it does suffer from swelling/compressing/degradation over time which can lead to issues with the thru hull , preferably today backing plates are made from easily available epoxy sheet G9/G10 material such as found
here:G9 G10 FR4 Glass Epoxy Sheet,

Strangely Australia it seems uses more SS thru hulls than i have come across else where, certainly in the larger sizes and commercial applications it abounds, some time ago we did a re-power ( C-18 ,875 Hp Cats) in Dongara WA, and all of the thru hulls where replaced with SS 316 (and yes "passivized") is the norm and highly polished, these all were installed with "Teflon type" isolating/locating washers so they had no contact with the Aluminium hull (No contact = No galvanic corrosion)

Cheers Steve
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Old 10-06-2017, 02:35 AM   #20
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Bruce,

Forgot to say there is one possible influence with say wet wood and SS and that is Micro-biologically Influenced Corrosion, but that normally effects the SS steel not the other way around, it's a fairly involved theory which is a bit like rocket scientist stuff!!

Cheers Steve
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