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Old 10-06-2017, 06:31 PM   #21
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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.
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Old 10-06-2017, 06:42 PM   #22
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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.
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.)
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Old 10-06-2017, 07:00 PM   #23
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Thanks Angus, I searched finding this:https://www.groco.net/products/valve...backing-blocks.
It looks like a better solution than a piece of square half inch teak.
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Old 10-06-2017, 07:53 PM   #24
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Thanks Angus, I searched finding this:https://www.groco.net/products/valve...backing-blocks.
It looks like a better solution than a piece of square half inch teak.
I must be more tired thanI realized, Bruce (cutting trees much of the day). I meant to send that link. They're solid products.
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Old 10-07-2017, 01:30 PM   #25
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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,
Cheers Steve
This is not quite correct. The acids and alkalinity created around a galvanic reaction do cause wood decay. See attached
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File Type: pdf Wood Decay Galvanic.pdf (419.4 KB, 8 views)
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Old 10-07-2017, 05:58 PM   #26
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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?
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Old 10-07-2017, 09:23 PM   #27
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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?
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.
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Old 10-08-2017, 01:06 AM   #28
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This is not quite correct. The acids and alkalinity created around a galvanic reaction do cause wood decay. See attached
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
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Old 10-08-2017, 07:54 AM   #29
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corrosion

Quote:
Originally Posted by CaptSteve53 View Post
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
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.
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Old 10-08-2017, 10:31 AM   #30
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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.
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
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Old 10-08-2017, 12:02 PM   #31
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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
No quarrel with the definition of "galvanic corrosion" however there are often more that one "metal" or metal contaminants within what would otherwise be a single metal. In fact most metals are made up of more than one base metal. These contaminants (other metals) can set up a galvanic cell within that single piece of metal as demonstrated by the Groco and many other instances of metals from that "other" country.

The well know "dezincification" of brass is due to this process i.e. a galvanic cell caused by different metallic componentsl within a single piece of metal.

PS. Recently retired Certified Corrosion Analyst.
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Old 10-08-2017, 06:17 PM   #32
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Old 10-18-2017, 10:58 PM   #33
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The skin fittings for the raw water intakes have been removed. Despite no bonding they show no sign of corrosion. So, perhaps the installing(former) shipwright got that right.
However, the fittings were easily, too easily, removed. Said shipwright used silicone, not Sikaflex, to install them.
Current shipwright proposes to dispense with backing plates due to the thickness of the hull, and to use Sikaflex. IGs have thick solid hulls, between 3/4-1". This is necessary to accommodate the osmosis which might otherwise penetrate the hull.
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Old 10-19-2017, 10:04 AM   #34
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Thruhulls are always easy to remove , on inspected boats they are pulled for inspection.

The challenge is the seacock where thru bolting thru the hull is the tried and true method.

Some folks want to glue a plate to the hull and simply bolt to it.

Works if it can take 500lbs of load, but is nowhere near as safe as 3/8 or better bronze bolts.
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