Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 14-08-2010, 18:40   #16
Registered User

Join Date: Jul 2010
Posts: 7
I am so confused. If the electro-guard and other bonded controlled devices do not work why are they made?
I believe either the bronze fitting is eroded or the timber depending on how much zinc you have (in a non-bonded system) and you can never be sure if you have too much or too little. Now, surely the electro-guard system with bonded fittings where you can monitor and adjust the level with the control knob to a balance should be good and the way to go. Is this not so?
__________________

__________________
Marky is offline   Reply With Quote
Old 14-08-2010, 20:39   #17
Ike
Registered User
 
Ike's Avatar

Join Date: Oct 2008
Location: USA
Boat: FL12 12 ft rowboat
Posts: 184
Here is an excerpt from a page on corrosion on my web site 0n wood burning, This is also called cell corrosion, iron sickness and various other names. What it is, is corrosion of the metal fastener until it loses all of its strength. :

Quote:
Wood boats suffer from a special kind of corrosion called woodburning around metal fasteners. This type of corrosion is caused primarily by leaks and oxygen starvation around the fastener, and over protecting the boat with anodes. Yes, you can put too many anodes on the boat. The fasteners in wood boats are generally metal screws but boat nails, rivets, and bolts also suffer from this. In many old boats the screws are galvanized. At the point where the screw meets the wood and oxygen is excluded, sodium hydroxide forms, that eats away at the metal and destroys the wood immediately around the fastener. Sometimes this can be spotted in bare wood by a dark ring around the fastener.
But more often than not you cannot see any sign of this type of corrosion. Marine surveyors will often remove fasteners at random looking for this type of corrosion. Any that are corroded must be replaced. But, you cannot put a new fastener back in the samehole. The hole must be reamed out and plugged to get rid of the rot. Then a new hole must be drilled for the new fastener.


Another way to detect this is to spray white vinegar on the area around the fastener. If it foams sodium hydroxide is present. If the fastener is fairly new and there has not been much damage to the wood you can stop the process by spraying vinegar on it twice a day. Do this for several days until it no longer foams. But you also need to correct the cause.

Another variation on woodburning corrosion occurs in boats with wood hulls and metal interior structure. This used to be called composite construction, but today that term usually refers to fiberglass boats. Where the metal meets the wood, the metal will corrode. During yard periods when a boat is out of the water, a few planks should be pulled and the interior checked for this condition. If not, the framing and bulkheads can deteriorate until the hull fails.


The full page can be seen at http://newboatbuilders.com/docs/CorrosionOnBoats.pdf There are also a lot of links to other sites on corrosion on that page as well as discussion of all types of corrosion on boats. Each type of corrosion has a different cause and must be dealt with individually.

Also on my links page New Boatbuilders Home Page - Links -Ike's List are 10 reference links on corrosion several which deal with corrosion around fasteners in wood.

Most surveyors and builders, even the USCG, recommend you do not bond metal fittings on wood boats. This because it worsens the corrosion on metal fasteners. What you need to do is a lot of research on corrosion until you understand the problem.

Here is a quote from the USCG instruction on inspection of Wooden Vessels.
Quote:
On wooden boats, bonding systems can cause unexpected problems. First, by connecting
together a number of underwater fittings and fastenings, the bonding system may provide the
metallic links which turn otherwise isolated dissimilar metals into a galvanic cell. Second, the
bonding system often inadvertently supplies unneeded or unwanted cathodic protection to objects connected to the bonding system by connecting those objects to the propeller shaft's sacrificial zinc anode. This cathodic protection of underwater metal hull fittings often causes damaging alkali delignification of the surrounding wood.
This is on page 4-10

Here is the link to the instruction http://www.pacificmotorboat.com/down...e_nvic7-95.pdf By the way this is a great document on wooden boats and their problems. It is rather long but well worth it. It can also be found at http://www.uscg.mil/hq/cg5/nvic/pdf/1995/n7-95.pdf
__________________

__________________
Ike
"Dont tell me I can't, tell me how I can"
Ike is offline   Reply With Quote
Old 14-08-2010, 21:00   #18
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Thanks Ike, all good reading.

Marky, yes it is confusing until one gets ALL the knowledge pertaining to the subject; this is same with any complex issue. Also please don't take my posts as gospel, they only represent the level of knowledge that I know and I certainly don't everything about this subject but I have found that posting on CF is a great way of learning more about any subject.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 15-08-2010, 00:14   #19
Registered User

Join Date: Jul 2010
Posts: 7
Thanks Guys. I will read the information re the sites you have given me.
One question. When you speak of a bonded system do you mean the fittings bonded and connected to a zinc only. In some of the bonding systems (again I refer to electroguard) the bonding is connected to a meter with the ability to regulate the current. When this is set to 'safe' the corrosion problems are reduced/eleviated as the hull is not charged and hence the many fastenings (screws, rivets etc) throughout the hull are also not effected. Correct?
__________________
Marky is offline   Reply With Quote
Old 15-08-2010, 05:10   #20
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,336
Quote:
Originally Posted by Marky View Post
Thanks Guys. I will read the information re the sites you have given me.
One question. When you speak of a bonded system do you mean the fittings bonded and connected to a zinc only.
I don't know what others mean by bonding (on wooden hulls) but what I mean is that the underwater metal fittings are electrically connected together by a very low resistance path; usually copper strapping but sometimes stranded copper wire but not connected to any zincs..
My (limited) experience is that zincs are connected to steel hulls and also to shafts / props.

In other parts of the world it may have a different meaning .

Quote:
Originally Posted by Marky View Post
In some of the bonding systems (again I refer to electroguard) the bonding is connected to a meter with the ability to regulate the current. When this is set to 'safe' the corrosion problems are reduced/eleviated as the hull is not charged and hence the many fastenings (screws, rivets etc) throughout the hull are also not effected. Correct?
Hmm... No - I don't think this is correct. For starters I can't see how a wooden hull can be "charged" or "not charged". A metal hull can be but not a wooden (or fiberglass) hull. One of the problems with a wooden hull is that it usually has many metal fasteners throughout its structure and the wood itself will be slightly conductive thus one has many many galvanic cells throughout the structure. Each one of these will have its own potential and current flow slowly destroying the fastening and often the timber around the cathodic end of the cell.

Of course the best solution w.r.t. corrosion is to have no metal fasteners (i.e. wooden fastenings - trenails - trunnels). The next best is to have all the fastenings of the same material (say silicon bronze) and close to the noble end of the spectrum. Then check them every few years for deterioration.

The worst to to have a whole variety of fasteners say like copper, bronze, gal., stainless steel.

I think your electroguard is there to protect the throughhulls, shaft etc. basically whatever it is connected to rather than the fasteners.

To answer your original question, probably best to pull the fittings, repair the wood and refit the fittings with an electrical isolating medium between them and the wood; epoxy may be good start!
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 15-08-2010, 05:29   #21
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,596
Images: 240
Quote:
Originally Posted by Ike View Post
... Also on my links page ...

Thanks for sharing that information, and the MANY useful links.

I notice that this Forum never made the cut.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 15-08-2010, 11:56   #22
Ike
Registered User
 
Ike's Avatar

Join Date: Oct 2008
Location: USA
Boat: FL12 12 ft rowboat
Posts: 184
Well son of a gun, Gord, you're right. I'll have to fix that. Putting together a links list like that is difficult enough, but forgetting to add C & S forums is a gross mistake.

Wotname's answer is a good one. But I want to add, Marky is asking about two different systems. One is simple bonding. All metal fittings That Have Contact With The Water, are tied together usually with a green wire (that is why it gets confused with Grounding which is a whole different matter) to make them a have the same voltage potential relative to the earth, essentially zero. Normally no current will flow in the system which is what you are trying to achieve.

The other is Impressed systems such as Electroguard and the Mercruiser System. These supposedly measure any current in the bonding system and impose an equal but oppositely charged current that is supposed to bring it to zero. Impressed systems were originally designed to protect aluminum sterndrive units but have spread to other types of boats. Impressed systems IMHO should never be used on a wood boat.

Do either work? Yes they do. The system needs to be designed for the specific boat.

Normal bonding systems are probably not a good idea on a wooden boat either. Many knowledgeable people say don't use them on wooden boats. I would have to go with them on that.
__________________
Ike
"Dont tell me I can't, tell me how I can"
Ike is offline   Reply With Quote
Old 16-08-2010, 13:37   #23
S&S
Registered User
 
S&S's Avatar

Join Date: Jul 2009
Boat: 48' 1963 S&S yawl
Posts: 851
Images: 6
Quote:
Originally Posted by Wotname View Post
Why are zincs fitted to a wooden hull?
Assuming no zincs fitted then if you DON'T bond your below water through hulls etc on a wooden boat, you WILL have to electrically isolate them from the hull. But bonding them together (and keeping them well bonded) will achieve the same electrical effect.
Of course, if you have fitted zincs for some reason and attached them to some metal item below the waterline, the circuit changes and without working it all out, I would probably think that bonding might not be a good idea - however, electrically isolating them from the hull would become paramount IMO.
Usually the only thing with cathodic protection is the prop/shaft. It's when you drop the resistance with a bonding wire that the higher current creates problems. Damp wood is a still semi-conductive.

I agree, Isolation is a better bet than any type of cathodic protection with wood hull skin fittings.
__________________

__________________
S&S is offline   Reply With Quote
Reply

Tags
electrolysis

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electrolysis Bonding Question Beausoleil Electrical: Batteries, Generators & Solar 35 07-01-2011 06:41
Electrolysis biltong Electrical: Batteries, Generators & Solar 20 22-05-2010 10:23
Mast Electrolysis cvondo Deck hardware: Rigging, Sails & Hoisting 3 16-12-2009 18:45
Electrolysis bill good Electrical: Batteries, Generators & Solar 6 29-06-2009 06:32
Power Leaking and Electrolysis... svHyLyte Electrical: Batteries, Generators & Solar 33 27-04-2006 16:23



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 10:01.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.