Could This be Repaired?

[Dave R]

:D

http://img.photobucket.com/albums/v506/weekender410/DSC00640.jpg

Removed this from my boat a couple of weeks ago after discovering a leak. Sometimes I wish I had my Weekender still. That boat never leaked a drop below the waterline.

[Jim Ledger]

Just replace it. They're not hard to get. It's not worth messing around with.

[Dave R]

Yeah, Jim, already done. ;)

[Jim Ledger]

:o Of course.

What happened to it?

[Dave R]

It's off a 1980 Catalina 27. I assume it is original. Looks like it corroded through. It's not very obvious in the picture but the threads have a distinct waviness in them in the area of the corrosion. I can't help but wonder if the thing was stressed a bit when it was orignally installed.

Fortunately it was found at launch time this spring and we were able to get it back on the cradle and replace it.

[kc8pql]

Humm... when bronze fittings corrode away I start getting worried. It may be worthwhile to check for stray current somewhere.

[Dave R]

Yeah, I thought of that. There's no metallic path from the fitting to the motor or anything else on the boat but I suppose the lake water could be conductive enough to carry some current. I think this took years to develop so I'm not too worried for the short run. Out of curiosity I'll take my DMM and see if I can measure a voltage potential between the fitting and the engine.

Maybe it was bronze-eating zebra mussels.

[SchoonerRat]

Yeah, I thought of that. There's no metallic path from the fitting to the motor or anything else on the boat but I suppose the lake water could be conductive enough to carry some current. I think this took years to develop so I'm not too worried for the short run. Out of curiosity I'll take my DMM and see if I can measure a voltage potential between the fitting and the engine.

Maybe it was bronze-eating zebra mussels.
No metallic path to anything. That's why the bronze corroded. Any piece of metal that comes into contact with water needs to be part of the bonding system. Otherwise the dissimilar metals create a battery. Bronze is an alloy-I think copper and zinc. Your thruhull is acting as a positive battery pole and the zinc is leeching out leaving weakened porous copper. Look closely at the fitting. It probably shows a distinct pink discoloration. This is a sure sign electrolosis.

[Dave R]

Yeah, I understand that. The new thru-hull has a bonding screw which could have a wire on it to ground on the motor.

[SchoonerRat]

Although salt water makes a much better electrolyte than fresh, use that bonding screw. Unless you sail in distilled water, there are enough impurities present to create a battery. It'll take longer for the physics to work, but eventually.........well---you've seen the results. A few feet of 8 or 10 gauge wire is cheap.

[Bob Cleek]

"No metallic path to anything. That's why the bronze corroded. Any piece of metal that comes into contact with water needs to be part of the bonding system. Otherwise the dissimilar metals create a battery. Bronze is an alloy-I think copper and zinc. Your thruhull is acting as a positive battery pole and the zinc is leeching out leaving weakened porous copper. Look closely at the fitting. It probably shows a distinct pink discoloration. This is a sure sign electrolosis."

I must humbly beg to differ...

Bronze is an alloy of copper and TIN, not zinc. Copper and zinc makes BRASS. That through hull fitting is BRONZE, so there's no zinc in it to leach out.

If the damage was caused by electrolytic corrosion, it should not be localized as it appears to be, but rather, would affect the entire fitting, which is one solid conductive mass. Generally, electrolytic damage in yellow metals presents itself as a general weakening of the entire fitting, not as a corroded "cavity." On the other hand, if this fitting were "bonded," and there was stray current induced in the bonding system, causing it to "ground out" at the point where the fitting met the water, that could do it!

"Bonding" through hull fittings to the engine is a rather thoroughly discredited practice that went out with the dinosaurs. In fact, wiring that through hull fitting to the engine does indeed make it a much larger "positive battery pole." If it is insulated from the other bits and pieces of metal in the water, it is not likely that anything will bother it.

[Dave R]

I'm thankful for your input Mr. Cleek. That thru-hull was not bonded to anything and there's no apparent corrosion elsewhere on the part. It is indeed localized to the place where you can see light coming through. (Thanks to a handy trach light.)

If I read you correctly, there's no need to do anything to the new one as far as bonding it.

[SchoonerRat]

Sorry bout the zinc-tin thing.

Could you please cite some sources for the discrediting of bonding. I still see new sources calling for bonding. This has always been a "must do" for me. If I've been inadvertently destroying the boats I've been trying to protect, I'd like to know. I've installed both active and passive corrosion systems, and all seem to start with a boat that is already bonded. I never even thought to question this practice, because it seems so logical to eliminate differences in electrical potential by connecting all grounds and thus giving them all the same potential.

[John B]

It almost looks like its been hit with a grinder or even RO, and then they've given up. Was the inside hull all freshly sanded/ painted or worked on around the fitting?

[prestonbriggs]

Bronze is an alloy of copper and TIN, not zinc. Copper and zinc makes BRASS. That through hull fitting is BRONZE, so there's no zinc in it to leach out.

Well...
There are many different bronze alloys.
Copper alloyed with tin is phosphor bronze,
copper alloyed with silicon is silicon bronze,
etc.

Nevertheless, your points about zinc, brass, etc. all still stand.

Preston

[BETTY-B]

Well...
There are many different bronze alloys.
Copper alloyed with tin is phosphor bronze,
copper alloyed with silicon is silicon bronze,
etc.

Nevertheless, your points about zinc, brass, etc. all still stand.

Preston

And copper with zinc is monel. Pardon me, I just learned that the other day. And had to share... Ooops. I mean nickel and copper...

DAN

[Dave R]

It almost looks like its been hit with a grinder or even RO, and then they've given up. Was the inside hull all freshly sanded/ painted or worked on around the fitting?

No, the inisde of the hull should probably be hit with something like dynamite but it wasn't hit with anything. All of the corrosion is on the part of the threads below the nut that was on there. So it's the threads that were buried in the caulk between the inside and outside of the boat.

Actually, above the bottom of the nut and the inside of the strainer actually look pretty good considering the boat is 28 years old. The outside of the strainer is covered with bottom paint so I don't know what it looks like.

[John B]

Oh, so its definitely corrosion or electrolysis then. strange the way its not all around.

A bit different, but I saw a pretty bad case of crevise corrosion in some stainless chainplate bolts last week. These were plates bolted through a bulkhead with about 4 bolts each ( 1980's glass boat, 28 ft fractional rigged). The boat dropped its rig due to one whole chainplate just pulling right out of the deck. The bolt the guy showed me was one of the 'good ' ones from the side that didn't go.

[PeterSibley]

If you ever feel like a bit of entertainment , search around in the mud at your favourite slip for discarded 316 bolts .They will frighten you ! They tend to look like very brightly sandblasted ,very badly corroded mild steel .Actually sometimes mild would last better .

[Gary E]

Many insist on BONDING... here is why..
http://www.practical-sailor.com/newspics/charts/9010corrosion.pdf

and this from another fellow....



Robert Kocher of

National Fisherman,

does not believe in bonding. In

the September 1979 issue he said:
“Bonding as a tradition arose before
knowledge of metal chemistry, or it
wouldn’t have arisen.” However, he
does recommend the use of zincs to
protect engines and other iron parts.
“Zinc collars on bronze or Monel
shafts will aid in protecting the engine,
which must necessarily be attached


to those shafts.”



Ok... so you can put zinc's on shafts and rudders....
How are you going to attach a zinc to each or the many through hull fittings?


Here is the article..... with the above quote..


http://www.practical-sailor.com/newspics/charts/883marinecorrosion.pdf



And From David Pascoe....
http://www.yachtsurvey.com/corrosion.htm


He likes bonding...




The vast majority of inboard powered and sail boats don't even need zincs. We put a few on as a precautionary measure, and to serve as a telltale should a problem develop. Why? Because on most boats everything is in balance without a lot of dissimilar metals creating electrical current. Do you need to put a zinc on every piece of underwater metal? No, you don't if your bonding system is in good condition. That means that the wire connections are still making a good electrical connection. If your boat is 10 years old and you have never serviced the wire connections, then rest assured that your bonding system is now useless. The wire ends to components like sea cocks, rudders, struts, etceteras, should be serviced every few years. If you have wire splicing tools, it will take you about an hour to redo your entire system.





Bonding Systems The purpose of a bonding system is to equalize the electric potential of dissimilar underwater metals by tying them all together with wire or copper straps. The benefits of a bonding system are wide ranging but little perceived. One is that it serves to dissipate stray current leaks. 12 volts of current focused on a small piece of metal will result in rapid destruction. But that same 12 volts spread over a much larger surfaces, causes less damage in proportion to the size of the water exposed surfaces of the metal. Bonding systems can reduce the corrosion potential of metals inside and on the bottom of the boat. Boat which have all the hardware bonded, such as the railings, will suffer much less corrosion.
As mentioned above, bonding systems are not maintenance free. The wire connections corrode too, and need to be reestablished periodically. This is done by cutting off the old terminal or connection, and then establishing a new one. It's as easy as standing on your head in the bilge ;-)

[Bob Adams]

I've seen bonding systems destroy wood boats. I removed Enterprise's the first season I owned her. No problems 15 years later.

[SchoonerRat]

I've seen wooden boats destroyed by galvonic or electrolytic corrosion that were not bonded. I need to see some science before I'll give up a practice that has been drilled into my head since childhood, and at least so far, seems to be supported by science.

[paladin]

Monel is 67% nickle, and the balance copper and iron.....

[Bob Adams]

I've seen wooden boats destroyed by galvonic or electrolytic corrosion that were not bonded. I need to see some science before I'll give up a practice that has been drilled into my head since childhood, and at least so far, seems to be supported by science.

Do a search of our host, they did an extensive article on the subject a few years back. Personally, I've seen alot of punky wood around the fittings of bonded boats.For what it's worth, bonding being the way to go has been driven into my head since I was a kid also.

[S B]

Copper alloyed with tin is phosphor bronze
copper, tin and a small percentage of phosphorus is phosphor bronze. It wasprobably a porous casting, it isn't the sort of thing that would be tested for. I wouldn't get allarmed unless everything else in the boat was headed the same way.

[SchoonerRat]

Do a search of our host, they did an extensive article on the subject a few years back. Personally, I've seen alot of punky wood around the fittings of bonded boats.For what it's worth, bonding being the way to go has been driven into my head since I was a kid also.
The WBM search function is woefully inadequate, so off to Google. After dozens of sites that say "bond your boat" with no reservations, I was ready to give up. I finally came upon this site.


http://www.answers.com/topic/electrical-bonding?cat=technology


The "Reader's Digest" condensed version.


Bonding CAN cause problems in the presence of stray currents UNLESS the bonding system includes a sacrificial zinc (use of zincs was also drilled into my head from puppyhood). Bonding also can protect one from shock due to a faulty appliance (much like the green ground on land side electrical systems), reduce radio interference and it provides an easy path to ground for a lightning strike. I will continue to bond and zinc my boats, and recommend to others that they do the same.

In my experience, it is also possible to over zinc your boat, and cause the very problem you are trying to protect yourself from. Monitor your zincs, if they last forever, you may be over zinced. If they disappear faster than you can replace them, you have a problem. Your boat may not be the source of the problem, but things need to be checked out.