"Bonding" Thru Hull Fittings

[Sea Hunt]

I was watching "Ship Shape TV" this evening. They had an interesting segment on "bonding" metals on a boat to a sacrificial metal - usually zinc in salt water (I think aluminum in fresh water). I think I learned some useful information, including the use of green wiring for bonding important metals to the sacrificial zinc.

There is also a company called "Ancor" which seems to have quality boat wiring, electrical parts, etc.

If I understood the "bonding" segment correctly, it stated that ALL thru hull fittings, in addition to normal things like the engine, alternator, prop shaft, prop, etc., must be connected and bonded to a sacrificial metal (zinc). This was puzzling to me.

As we all know, I have looked at more than a few Cape Dory sailboats and I cannot recall seeing where all of the thru hulls were "bonded". For example, in the CD 25D, there are at least two thru hulls for the marine head (salt water flush in and waste discharge overboard). I have not observed any green wires running from these thru hulls to an area in the bilge which is then connected to the sacrificial "zinc plate" which I think is located on the hull outboard from the bilge on the starboard side.

On the CD Typhoon Weekenders I have looked at, there are two thru hulls for the cockpit drains. Again, I have not observed any green wiring from these thru hulls to a sacrificial zinc plate.

I tried researching this issue on the board’s search function. I could not find any specific discussion of this issue although several years ago a few folks posted comments suggesting that thru hulls were not "bonded" on their Cape Dory sailboats but no discussion of why not.

I also tried doing a Google search and read Don Casey's discussion of sacrificial zincs. However, unless I missed it he did not discuss thru hull fittings.

My question is: Are all thru hulls supposed to be "bonded" to a sacrificial zinc If not, why not If they are supposed to be "bonded", where would one look for the wiring on a CD 25D marine head thru hulls and/or a Typhoon Weekender cockpit thru hulls

Is it possible that because the thru hull fittings I have looked at on Cape Dory sailboats are made of only one metal (bronze) that there is no galvanic corrosion and thus no need for zinc:?: However, if this is so, what about all of the stray electrical current in the water, especially at mooring fields Would not that stray current degrade the bronze thru hull fittings

I would be grateful for any explanations, etc. Please remember in submitting your response(s) that you are dealing with a dummy and try to use simple words. Sort of like the program "Are You Smarter Than A Fifth Grader?"

Thanks in advance for the education.

[Oswego John]

Hi Robert,

A person could write for hours on metallic bonding and not cover very much of what is entailed. For that reason, I will only speak in headlines and avoid the fine print.

There are different reasons of bonding and different methods for each.

One of the reasons is to prevent the destruction of metal via the short circuiting of unwelcome stray currents between DIFFERENT metals. A smaller shunt wire can be used for this purpose.

Another reason for bonding (grounding) all metal on a boat is for lightning discharge. This bonding/grounding generally terminates on a sinterred Dynaplate attached to the outside of the hull beneath the waterline. A much heavier gauge wire is used for this purpose.

One source of interesting reading on the subject is:

http://www.thomson.ece.ufl.edu/lightning/title.html
Click on "Sea Grant Pamphlet".

Another good read is:
http://www.yachtsurvey.com/corrosion_in_marinas.htm


ANCOR is one of the better manufacturers of marine grade wire and cable, as well as electrical fittings.

http://www.boatelectric.com/ancor.htm

Good luck,
O J

[bottomscraper]

For what it's worth, on Mahalo all thru hulls are bonded using thick uninsulated solid copper wire, All are connected to a grounding plate. (see pictures below) The only zinc is on the nut for the prop. The ground plate is not zinc but rather sintered bronze (I think). I'm not sure if is is made by Guest or Newmar. I believe the plate is designed mostly for lightning protection and improved radio performance (and probably Loran when it was installed).

Newmar:


Guest:

[Oswego John]

Rich, Robert, All

Rich: You are correct on all counts The sintered ground plate is made of bronze. Dynaplate is a trade name of the Guest Mfg Co.

The Dynaplate and other similar grounding plates actually do help prevent electrolytic destruction. I'm not sure if bronze is the next, or close to being the next metal to zinc on the galvanic scale. It does make for an excellent counterpoise for shipboard electronics

Because of the many peaks and valleys on its porous surface, the sintered bronze provides much more contact area for a given dimension than does a smooth surface.

For some brief info, go to:

http://www.pyacht.net/cgi-local/SoftCar ... ?E+scstore

Think spring,
O J

[Sea Hunt]

According to Boatowner's Mechanical and Electrical Manual (@1996) by Nigel Calder, at page 133, zinc is almost at the top of the "anodic" scale. Bronze is somewhat near the bottom, close to stainless steel, lead and nickel.

If possible, back to my basic question.

Are ALL thru hull fittings on Cape Dory sailboats "bonded" For example, the two thru hulls from the two cockpit drains on your CD Ty Weekender OJ - are they bonded to a sacrificial zinc:?: If yes, where and how If not, why not For those of you who own CD 25Ds, are the thru hulls for the marine head bonded

I am continuing to research and read but so far cannot find any answer to the question of whether ALL thru hulls should/must be bonded to a sacrificial zinc. OJ, the articles you referenced in your first post are excellent, particularly the UF article on lightening strikes. For someone who lives in "the lightening capital of America", it was educational and scary.

[Oswego John]

Hi Robert,

As far as having any metalurgical smarts, I don't even know how to properly spell the word metalurgy. I haven't the faintest clue where zinc and bronze are on the galvanic scale, much less which weighs more on the scales. Jes kiddin'.

[quote Guest Mfg. Co.]
The bronze Dynaplate material also serves as the next sacrificial metal on the galvanic scale after your zincs, providing another buffer against corrosion of stainless steel parts.[end quote]

So it looks to me as if the Guest Co. scientists and Nigel Calder will have to slug this one out between themselves. I only know what I read.

Now, let's get back to your basic question.

[quote Sea Hunt]
If possible, back to my basic question.

Are ALL thru hull fittings on Cape Dory sailboats "bonded" For example, the two thru hulls from the two cockpit drains on your CD Ty Weekender OJ - are they bonded to a sacrificial zinc:?: If yes, where and how If not, why not

Robert, the two through hulls from the two cockpit drains on my CD Ty Weekender are not bonded to a sacrificial zinc.

The reason that they aren't bonded to a zinc is because they don't exist. The soles of the earlier years Tys are below the waterline and therefore aren't self bailing.

My Ty has no metallic through hull penetrations. The one through hull I made was for a plastic type speedo. I have a porta-potti. I have an outboard motor that swings up when sailing or tied up at the slip.. No engine cooling or exhaust. No shaft, prop or stuffing box. My running lights are battery powered. I have no dockside provision for AC power. I keep it as simple as possible.

Hopefully, others will fill you in as to how their hulls are, or aren't bonded. Sorry that my situation hasn't much bearing on what you are trying to find out.

Good luck,
O J

[Boyd]

Hi All:

I cant speak for other CD boats, but on mine all of the underwater metal fittings are connected by a large (#8) solid bare wire to the sintered ground plate on the side of the keel. This plate is also connected to the engine block by a #4 stranded black wire. This spider web of connections will by default tie all underground metals to the zinc which is attached to the prop shaft.

In addition the mast, shrouds, lifeline stanchions, and edson pedestal are tied to the same sintered bronze ground plate.

The cockpit drains and the above waterline metal thru hulls (bilge pump discharge, engine exhaust, etc.) are not bonded.

The boat came that way and as far as I can tell it meets AYBC standards.

This system of wires provides both a modicum of lightening protection to the occupants and galvanic protection to the underwater metals.

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

[sgbernd]

It is my understanding that 2 methodologies are at work with different outcomes.

1) Bronze is relatively saltwater stable, shows <200mV diferential from salt water, and does not need to be protected with zinc if left by itself (that is unconnected to a dissimilar metal). For evidence, I have inspected an old wooden wreck on the beach that was fastened with bronze bolts, which after 50+ years still look in serviceable condition. Or even more extreme, I've seen photos of some bronze Greek statue and other boat bits pulled out of some Mediteranean wreck from 2000 years ago.

2) Lightning strikes which pass thru a thru-hull can sink the boat. Thus everything is shunted to the dynaplate so the current will hopefully exit there as it has much larger surface area and less resistance. However, by connecting the thru-hulls to the ground (and consequently the cast iron engine block), you risk corroding the engine block because bronze is more noble than cast iron. (The voltage differential between Bronze and cast iron is about 350mV). If your zinc falls off or is not maintained, the engine block becomes the sacrifical anode trying to protect the bronze.

If I recall, Don Casey recommends disconnecting the thru-hulls to reduce galvanic corrosion potential, while the ABYC standard requires grounding for lighting protection. I've tried both, and never noticed a problem either way, but then I've kept up the zincs religiously.

Since you can make a good case for either approach, my recommendation is to consider the threat of lightning, and if that is not particularly high, keep what you got, maintain your zincs, and go sailing.

[Gary H]

OJ,
Would you mind telling me more about your battery powered running lights? I would like to install such on my Ty. What components do you use and where do you buy them?
Thanks,
Gary

[Oswego John]

Hi Gary,

Like I said in an earlier post, my lighting system is Spartanly simple. I don't make a practice of sailing after sundown. For the few rare times that I get caught short and require navigation lights, I get by with the bare essentials.

My Ty is a weekender. It had lights on it when I bought it in the mid eighties. There is a red and green bullseye lamp on either side of the cuddy. They have a chrome partial deflector to shield the angle of view. There is a lamp post socket on the stern deck, into which a 24" chrome post with a white fresnel type 360° lamp can be inserted. I also have one interior cabin light with its own built in switch.

I power this setup with a garden tractor type 12 volt battery. Simplicity personified. This has proved to be ample power for my modest requirements. I don't have electric start on my smaller size ouboard engine. I have been halfheartedly toying with the idea of switching over to LED lamps. Why? I haven't a clue. The thought is still in its incubation stage. So far, it has been a 12 year gestation period, and holding.

If I remember correctly, I have seen various types of nav lights, such as these, featured in marine catalogues such as BoatUS (West Marine).

The above info is off the top of my head. I could go outside and refresh my memory by lifting the boat cover and looking at what I have. But I won't, and there is a darn good reason why not.

Last night and all day today we got hammered with lake effect in addition to a general, run of the mill snow storm. We got off easy. We only received a little more than three and a half feet of snow. The village a few miles from here got over four feet. They predict another 8" to 12" tonight. The city of Oz-wego is totally shut down. The wind off the lake is averaging 50 MPH. That makes for king sized snow drifts. -12° wind chill factor. The saddest news is when older homes and barns roofs collapse under the abnormal snow loads.

Maybe tomorrow, I'll take a better look at my Ty (If I can find it)

I think winter is about here.

Stay warm. Think spring.
O J

[Sea Hunt]

Hello "sgbernd":

Thank you very much for your post. It really makes a lot of sense - even to a dummy like me. I now think I understand why the TV show "Ship Shape TV" insisted that all thru hulls be bonded/grounded - they are following the ABYC standards and protecting themselves from lawsuits while guys like Don Casey and others on this board are perhaps suggesting not to bond/ground all bronze thru hulls - and protect the cast iron engine, etc., again depending upon where you live, etc.
I have gone back through my photos and inspection notes and cannot find any photos suggesting the thru hulls on any of the CDs I have looked at were bonded/grounded.

However, the CD Manual (found on this website ) at page 28, Section 3.17 Bonding System, states: "All thru hulls and seacocks below the waterline, including the stern tube, are connected to one
another, to the engine block and to the external ground plate with a continuous loop of 18 copper wire."

In future inspections (hopefully not too many more ) I will look for this copper wiring.

Because I live in South Florida, apparently "the lightening capital of the world", when I finally buy my CD I will probably make sure all of the thru hulls (at least all that are below water) are bonded/grounded and, as you suggested "sgbernd", I will be sure to be diligent in checking and replacing zinc anodes.

[John Vigor]

I have gone back through my photos and inspection notes and cannot find any photos suggesting the thru hulls on any of the CDs I have looked at were bonded/grounded.

However, the CD Manual (found on this website ) at page 28, Section 3.17 Bonding System, states: "All thru hulls and seacocks below the waterline, including the stern tube, are connected to one
another, to the engine block and to the external ground plate with a continuous loop of 18 copper wire."

On my 1983 CD27, all the through-hull fittings are bonded in exactly this way. All the wire rigging, pushpit, and pulpit, too. Everything is joined to the engine block and to the sintered bronze plate on the outside of the hull.

John Vigor

[Gregg]

As with others in reply, all of my through hole fittings are bonded to the plate and the engine. In addition, the previous owner set up a set of large zincs to hang (when at the marina where stray current is problematic) over the side. One is wired to the engine (common DC ground) and the other to the stern tube. I will admit that I am not as religious as I should be on rehanging after every sail but the zincs are sacrificing. Perhaps the one to the stern tube should contact the shaft as will since the maxprop zincs must be replaced every 3-6 months.

[JBA]

I find the discussion on bonding to be quite interesting. I have a 1978 Typhoon with the standard (for 1978) cockpit drain thru hull fittings. My Mercury 4 has a zink on it, but it is out of the water most of the time. So....how do you bond without putting in a zink plate somewhere?

Thanks, jba

[Oswego John]

jba,

Good question. Gives a person something to think about. The first thing that comes to my mind will probably generate some flack, but what the hey.

If you will scroll up to sgbernd's previous post, you will read some facts about the nobility of bronze compared to other metals. Bronze, especially tobin bronze, is very compatible to immersion in salt water.

The prime use of sacrificial zincs is to deter and reduce electrolytic destruction of different types of metal in water, that are in close proximity to each other. The key thing to concentrate on is "different types of metal".

Unless there has been changes made in newer models of the Ty, your boat's underwater metal is all bronze. Other than your outboard motor which has its own protective zinc, the rudder post, its shoe fitting below at the rear of the keel and the through hull fittings are the only metal objects that are exposed to water.

I won't come out and say it, but it is a thought running through my mind that in a situation such as this, is it a dogmatic necessity to have to bond the through hull fittings? And as you ask, to what?

While we are on the subject, let me stick my head a little farther into the noose. I read that the CD manual states that all through hulls, sea cocks, stern tube, engine block, etc shall be connected together in a loop of #18 copper wire. Do you realize how small #18 wire is. Probably no bigger than the wire size that feeds your printer or scanner. Kind of small and chintzy. Not much mechanical strength to it. Ampacity wise, it is big enough. It is a common neutralizer.

The #18 copper loop is generally called a bond. It is not to be confused with a "ground". The bond makes all the metal common with each other, shunted together, short circuited out. When this bond is created, no current can flow. When there is no current flow, there is no electrolysis between the metals. Any stray current will be disposed of through the sacrificial zinc. Without a common bond, two different metals, immersed in a electrolytic, creates a battery which, unhampered, causes destructive current flow.

Please don't anyone think for one minute that this tiny #18 wire will create lightning protection. If lightning hits an unprotected boat, it will only produce 10,000 or more copper buck shot strafing the area. As previously mentioned, #8s and #4 awg stranded copper, minimum, is necessary for lightning protection. This grid is connected to an underwater, external discharge plate. This ground wire, or bonding for that matter doesn't have to have a green coating. A large part of bonding and most grounding uses bare copper.

Think spring,
O J