S/Steel Thru Hull Bonding

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
BruceK

BruceK

Moderator Emeritus
Joined
Oct 31, 2011
Messages
13,347
Vessel Name
Sojourn
Vessel Make
Integrity 386
Should a stainless steel thru hull be electrically bonded, the same as a bronze one?
 
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.

Gordon
 
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.
 
Exactly. We all run shaft zincs, how are through-hulls different?
 
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
th

and more time you have risk sinking be cose stanles stell have crevide corrosion
crevice-corrosion-example.jpg







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

and US guru Steve http://stevedmarineconsulting.com/stainless-steel-miracle-metal/
NBs
 
Last edited:
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.
 
SS thru hulls are used above the WL as there safe in that use, and bonding is not necessary.
 
Bruce
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?
 
Last edited:
"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?
 
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 it’s 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.
 
Last edited:
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.
 
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.
 
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/_drawings/galvanic_series_2.png
 
Last edited:
BruceK said:
Should a stainless steel thru hull be electrically bonded, the same as a bronze one?
Click to expand...

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
 
CaptSteve53 said:
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
Click to expand...

CS
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?
 
sunchaser said:
CS
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?
Click to expand...
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?"
 
BruceK said:
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?"
Click to expand...

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
 
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?
 
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
 
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
 
Steve, I considered starboard as a pad material for its non degradable non compressible properties, but as I doubt anything adheres to it, it becomes difficult securing the thru hulls using it.
 
BruceK said:
Steve, I considered starboard as a pad material for its non degradable non compressible properties, but as I doubt anything adheres to it, it becomes difficult securing the thru hulls using it.
Click to expand...

Bruce, I used these Groco composite backing plates throughout my boat (along with the flanged adapters). They don't absorb water and make a very strong base when epoxied in place. (Not sure what brand your through hulls are or if you're keeping them/buying new.)
 
CaptSteve53 said:
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,
Cheers Steve
Click to expand...

This is not quite correct. The acids and alkalinity created around a galvanic reaction do cause wood decay. See attached
 

Attachments

  • Wood Decay Galvanic.pdf
    419.4 KB · Views: 21
Thanks Boatpoker. That accords with comments by the hull surveyor.
The article suggests wood degradation occurs in the presence of corrosion. That being so, should I expect to see corrosion when we pull the s/s thru hulls? And if so, replace with bronze?
 
BruceK said:
Thanks Boatpoker. That accords with comments by the hull surveyor.
The article suggests wood degradation occurs in the presence of corrosion. That being so, should I expect to see corrosion when we pull the s/s thru hulls? And if so, replace with bronze?
Click to expand...

Not a fan of ss below the waterline ( tho' we're pretty much stuck with it for shafts) I've seen far too much crevice corrosion in ss below the water line. I'd stick with silicon bronze or Marelon as a second choice.
 
boatpoker said:
This is not quite correct. The acids and alkalinity created around a galvanic reaction do cause wood decay. See attached
Click to expand...

Just to note here it's not really comparing Apples with Apples how ever as the article uploaded is basically comparing wood with STEEL and IRON (NOT 316 SS or 316L). Both Steel and Iron and even Bronze have decades of recorded reactions with damp wood and yes wet wood will provide the catalyst/fluid to complete the cycle required for Galvanic issues to take place but again for a TRUE Galvanic reaction you require the THREE elements (two dissimilar metalsand the electrolyte where as in this specific case being discussed does not apply, as you have only one metal being SS,can damp or wet wood cause all sorts of misunderstood issues YES, thats why we now go with G9/G10 or similar material (and no wood/not even epoxy soaked wood).

As earlier stated corrosion/erosion/Galvanic or other wise is a highly controversial issue,

Finally the change to Bronze (check if Silicon Bronze or Manganese Bronze) could be worse in this case(if not changing the wood backing plates) as Both Bronzes are less noble than (316-316 L -Passivized)meaning in a Galvanic series situation Bronze will react sooner than (316/316 L passivized.

I do agree with the use of synthetic thru hulls and NZ has a fairly new range called TRUDESIGN which have impressive testing and even fire ratings and varying government approvals including the well respected Bureau Veritas Marine Division Approval.along with 9093-2 classisications

I have fitted numerous TRUDESIGN thru hulls both on commercial type craft and pleasure vessels in the past 3-4 years in our yard and can applaud there design both in strength and easy to use condition, found Here:Seacocks And Through Hull Fittings | TRUDESIGN.

Also to note today there are many more shafting materials available better than SS 316/316 L both in corrosion and strength,

Just Saying!

Cheers Steve
 
corrosion

CaptSteve53 said:
Just to note here it's not really comparing Apples with Apples how ever as the article uploaded is basically comparing wood with STEEL and IRON (NOT 316 SS or 316L). Both Steel and Iron and even Bronze have decades of recorded reactions with damp wood and yes wet wood will provide the catalyst/fluid to complete the cycle required for Galvanic issues to take place but again for a TRUE Galvanic reaction you require the THREE elements (two dissimilar metalsand the electrolyte where as in this specific case being discussed does not apply, as you have only one metal being SS,can damp or wet wood cause all sorts of misunderstood issues YES, thats why we now go with G9/G10 or similar material (and no wood/not even epoxy soaked wood).

As earlier stated corrosion/erosion/Galvanic or other wise is a highly controversial issue,

Finally the change to Bronze (check if Silicon Bronze or Manganese Bronze) could be worse in this case(if not changing the wood backing plates) as Both Bronzes are less noble than (316-316 L -Passivized)meaning in a Galvanic series situation Bronze will react sooner than (316/316 L passivized.

I do agree with the use of synthetic thru hulls and NZ has a fairly new range called TRUDESIGN which have impressive testing and even fire ratings and varying government approvals including the well respected Bureau Veritas Marine Division Approval.along with 9093-2 classisications

I have fitted numerous TRUDESIGN thru hulls both on commercial type craft and pleasure vessels in the past 3-4 years in our yard and can applaud there design both in strength and easy to use condition, found Here:Seacocks And Through Hull Fittings | TRUDESIGN.

Also to note today there are many more shafting materials available better than SS 316/316 L both in corrosion and strength,

Just Saying!

Cheers Steve
Click to expand...

Manganese bronze was not even mentioned as it is actually in the "brass" class due to it's high zinc content.

There is no confusion or controversy regarding galvanic corrosion among the educated. It is the most straight forward of all the corrosion processes.

Like steel and iron, "stainless steel" is a ferrous metal and suffers from many of the same maladies to differing degrees.

A galvanic cell can develop within within in single piece of metal due to impurities as has been shown by the well known issues of metals imported from a certain country.e.g. Groco recall.

Yes, there are many other materials for shafts however 98% (my guess) of the pleasure craft market uses ss.
 
boatpoker said:
Manganese bronze was not even mentioned as it is actually in the "brass" class due to it's high zinc content.

There is no confusion or controversy regarding galvanic corrosion among the educated. It is the most straight forward of all the corrosion processes.

Like steel and iron, "stainless steel" is a ferrous metal and suffers from many of the same maladies to differing degrees.

A galvanic cell can develop within within in single piece of metal due to impurities as has been shown by the well known issues of metals imported from a certain country.e.g. Groco recall.

Yes, there are many other materials for shafts however 98% (my guess) of the pleasure craft market uses ss.
Click to expand...

Well, therefore i stand corrected as what I have commonly seen in these forums is a high degree of confusion then regarding Galvanic corrosion issues (normally called in the boating public Electrolysis -which is wrong),as there are/have been so many posts on these issues

Now when you consider even Groco valves (not there Tru Flanged Sea cocks) but what you see very commonly used as thru hull fittings the threaded type are in fact Manganese bronze of the C-86300 class (very clearly stated) but not clearly stated is that contains 22-28% zinc (as you well point out), if your not one of the informed then it's very easy to make this mistake (hence my above reference re Silicon and Manganese) I was under the impression it would be good to provide clarifications perhaps for the not so well formed(my apologies again),

You are correct again in the statement re ferrous metal: the only real thing the same between 316/316 L SS and mild steel is infact, is that is a ferrous metal after that there is basically no common reference at all typical SS composition:Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S
and what the article principally referred to mild steel /iron typically contains no chromium/no nickle/no moly/ with only trace elements as follows: copper/carbon/manganese/silicon with the rest as 98% iron, Ferrous YES the same NO!

Just for clarification here's the definition of Galvanic corrosion from the dictionary(Yes cut and pasted): Quote :Galvanic corrosion (also called bimetallic corrosion) is an electro-chemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. End Quote

Just saying !

Cheers Steve:hide:
 
You must log in or register to reply here.

Similar threads

S
For Sale: bronze thru hulls and fittings
Replies
0
Views
409
SIBERNUT
S
N
Bronze vs Stainless steel aesthetics
Replies
18
Views
1K
Juggerknot
J
PhilPB
Scoop thru-hull
Replies
7
Views
435
rslifkin
R
S
Ground Bonding Wire - Steel Hull
Replies
5
Views
480
CharlieJ
C
S
Thoughts on pipework for bilge thru hulls
2
Replies
49
Views
3K
sndog
S

Latest posts

Back
Top Bottom