To bond or not?

[exposure]

I am in the middle of several projects on the boat. I'll post some photos in the future.

As I am running wires around the boat I am wondering if I should bond my through hulls?

I have an aluminum saildrive on my Prout, and it is bonded direct to a zinc mounted on the hull. The engine is also wired to this zinc. The through hulls are not. The through hulls are all bronze, All except one has a threaded on ball valve with a hose barb and rubber hoses attached. The other is a seacock with mounting bolts. There are a total five thorugh hulls below the waterline in two locations on the boat.

There is a large dyna plate on the boat that is wired to copper foil as part of the SSB ground plane. There are two small dynaplates that are wired to the shrouds as lightening ground protection. BTW, for those not familiar, Dynaplates are a porous bronze plate that bolts on the outside of the hull, below the waterline. Wires can be attached on the inside of the hull via the through bolts that hold them on.

It seems that every time I try to understand bonding I get confused, often by conflicting information. I think bonding the saildrive is important, but is it wise to bond all of the through hulls? I would have to attach the wires using hose clamps.

Woody

[Alan Wheeler]

Yes, Bond them all. Use good size wire and good connections and get it all to a good common earthing point.

[Alan Wheeler]

Actually, let me explain in a little more detail. Place two different metal types together in an electrolyte and you will have electrons flow from one to the other. In basic theory, you now have a battery. Along with those electrons is carried the metal of the "lesser" element on the Periodic scale of the two.
So in the case of boats, the metals can be aluminium and Brass for instance. The electrolyte is the salt water. The Zinc anode is very far down on the periodic scale and tends to errode away before most other metals. It's not the lowest, but it is one of the ceapest and hence why it is used. So we use Zinc as a sacrificial metal. By boning all the metals together, we stop that flow of electrons from one to the other through the water. However, there is always something else out there that the metals can all flow to. Another vessel or even the treated timber in the amrina has enough arsnic (metal) in it to cause a problem. So the Zinc desolves away first. Once the Zinc has gone, the next metal on the scale goes and so on untill either you reach a metal that is the same as the one nearby, or all the metals on your boat have gone. Of course, you boat more than likely won't be on top of the electrolyte at that stage and yoiur suspicions would be that maybe something is amiss.

[exposure]

From West MArine Advisor...

http://www.westmarine.com/webapp/wcs...ingsystems.htm

Zincs and Protection from Galvanic Corrosion

Use zincs to protect against the galvanic currents that are set up by dissimilar metals on your boat that are immersed and that are in electric contact with one another. The best example is your bronze propeller on a stainless shaft. The best protection is to put a zinc right on the shaft next to the propeller, or a zinc on the propeller nut. An isolated bronze thru-hull doesn't need protection because it is not in electrical contact with another immersed dissimilar metal. If electrically isolated, high quality marine bronze, is electrochemically stable in seawater; nothing good can come from connecting wires to it.

[Talbot]

My through hulls are of bronze and are electrically isolated from the rest of the boat. The only item that is heavily anoded is the outboard, as the original anodes were insuffient.

[GordMay]

EXPOSURE cites Stan Honey’s excellent article, which recommends NOT connecting ISOLATED Thru-Hulls to the boat’s Bonding System. TALBOT doesn’t bond his “Isolated” Thru-Hulls. In fact, most experts don't recommend the bonding of electrically isolated metal thru-hulls and seacocks.

WHEELS, however, recommends bonding all Thru-Hulls.

This is a complex, and sometimes contentious issue - To Bond or Not to Bond (isolate)!

Are your Bronze Seacocks, in fact, Isolated?

Metal valves and plumbing systems connected by hoses to any water source (including bilge pumps & raw-water-cooled exhaust systems) may NOT be Electrically Isolated. The water within the non-conductive Hose may provide an electrical path between the otherwise (assumed to be) Isolated components.

BTW: Forespare DOES recommend Bonding Marelon (Non-Metalic) Seacock Fittings. “Properly bond or ground the bronze thru-hull. It is still subject to electrolysis and corrosion, even with the Marelon® valve installed.”
http://www.forespar.com

ABYC doesn’t dictate a method for addressing galvanic corrosion. They do provide guidelines for a particular method if chosen to be used. "Where metallic thru-hull fittings and drain plugs are installed below the normal accumulation of bilge water, consideration shall be given to the installation of a bonding system. See ABYC E-11, and ABYC E-2.

Aluminum Outdrives:
A fiberglass boat with an aluminum stern drive is kept in a marina and is supplied with AC electrical power from the dock. A boat nearby on the same dock is also built of fiberglass, but its propulsion system uses a standard inboard engine driving through a stainless propeller shaft and a bronze propeller. This boat also is supplied with AC power from the dock. Both boats, either purposefully or inadvertently, have electrical continuity between their on board AC safety ground systems and their underwater metal structures. Since both boats also have continuity between their AC safety ground systems and the dock safety ground system, there is electrical continuity between their underwater metal structures. Because the aluminum stern drive is more reactive than the bronze and stainless drive hardware, the stern drive will corrode, acting as a sacrificial anode, and will deliver galvanic electrical current to the other boat's propeller and shaft via the AC safety ground system.

AC BONDING & ISOLATION:

There should be no direct (low resistance) connection between any of the AC shoreline conductors and a vessel's underwater metal structures.

There are several solutions to the problem of exposure of a boat's underwater metals to influence by electrical currents passing through the AC shoreline distribution system. The most effective (and expensive) is the installation of a properly sized AC ISOLATION TRANSFORMER aboard the vessel. This transformer should be installed as the first device downstream of the AC shoreline receptacle, ahead of the ship to shore switch and the electrical distribution (circuit breaker) panel. The transformer should be installed on an electrically isolated mounting with the AC shoreline safety ground conductor connected to the metal housing of the transformer. The shoreline safety ground conductor should not be connected to any on board AC device that is being supplied power from the secondary side of the transformer and/or to the under water metal structures of the vessel. Use of a properly designed and installed isolation transformer electronically isolates the electrical power being used aboard the boat from that supplied by the shoreline. This will effectively prevent corrosion currents from using the shoreline as a conductive pathway between the boat with the device and any other vessel using the same dock power system.

Another solution, though not quite as effective as a transformer, is to install a GALVANIC ISOLATOR in the AC shoreline ground conductor between the boat's receptacle and the first AC device, such as a ship to shore switch or distribution panel. This device allows AC current to pass unimpeded, while blocking low level (galvanic) DC currents. A galvanic isolator will block approximately eighty-five percent of the potential problems that occur due to safety ground interconnection between boats.

I look forward to further stimulating & (perhaps) controversial discussion.

Gord

SOME ON-LINE REFERENCES:

“Corrosion, Zincs, & Bonding” - By Micheal Kasten (Metal Boat Qurterly)
http://www.kastenmarine.com/mbqCref.pdf

Marine Electrical Check List - by Robb Zuk
http://www.islandnet.com/robb/marine.html

[delmarrey]

Might I also mention that most marine hoses have a steel reinforcement wire that runs through them and once clamped down to a thruhull fitting the continuity runs through the wire, as well the water.

If you ever cut an old marine hose apart, you'll find the wire to be erroded into several pieces, one main reason for their failure............_/)

[Wahoo Sails]

OK Gordy,
Ya got me to bite. All of this talk about galvanic corrosion is well & good ... to bond or not to bond? Figure I would be in the "not to bond" category ... however ... why no mention of lightning dissipation? We had 15 boats struck by lightning in this marina in a single storm! Those with a bonded ground system faired somewhat better than those without ... though all suffered some damage. Yes ... my single bronze through hull is now bonded ... for what it's worth ... ABYC recommends AWG 6 as a minimum ... and for those of us that may have to work on the boat at some time in the future ... "green" please

L S/V Eva luna

Bob

[Alan Wheeler]

Yes I know this is a very contensouse issue. Many experts and yes they really are Experts are for the argument of not bonding. Many experts and just as expert as the above, are for bonding. I see each ones point of view.
My argument is the same as already now stated. Salt water is that electrical link between differing Metals. Infact, in wooden hulls, the wood itself absorbs something like 13% of it's total weight in water. There is enough moisture to conduct. Even though it is small, it does conduct and especially if two skin fittings are close enough to one another and are of differing materials. Although small, there are evne differences in the same metals. Depends on who cast the metal and where. Especially if you have castings from say Asia and say the UK or US.
OK, so to add just a little more to my original post. If you bond all metal, it is effectivily a dead short within the boats system. A dead short means no flow of electrons. If you don't have that dead short, a very simple law of physics takes place. It is called Ohms law. The Salt water has a resistance. The dissimilar metals have a voltage potential between them.
V/R = I. The voltage divided by the resistance equals a current. Thus a current flows from one metal to the next. The wire between those metals effectivily short circuits that circuit. If V=2 and R=0, then the current is 0.
But a current can flow from one to another boat. In the event of poor electrical systems in marinas, it can even flow to the mud and rock on the bottom. I have actually seen in a land based situation, Glav water pipes that have electroplated themselvs to the surrounding stones. But that's another story.
So my take is, yes Bond all metals and have a sacrificial anode, By the way, with lightening strike, if you can get the energy to the water, it will do no damage. The problem is, you have to have a damn good grounding rod that can take the flow of energy and that would most likely be impracticle on a boat. But a cable all the way from the top of the mast to the water and one that has a good surface area and good conductive properties is best. Maybe it isn't too silly to have something you can hoist to the top of the mast when in a bad storm in a Marina. The lightening strike is a large flow of extremely high current and voltage. The reason why it tends to bounce around everything inside a boat, is that it can't flow fast enough to earth. If you can provide a good path to earth, it will always prefer to take that path first. The Surface area of a cable is because the voltage tends to flow on the outside of the wire. No not because it is high frequency,( if I haven't just become to nerdy for most), but because the voltage is of such high pressure, it leaps around in and out and back to the conducting material.

[GordMay]

Thanks for the good input, all !!!

As has been pointed out - there are several considerations involved in Bonding:
Safety:
~ Corrosion
~ Lightning amelioration
~ RF Counterpoise
... among others

Unfortunately, not many experts tie it all together (pun intended). Neither will (can) I.

Here’s a few quick points - specific to our discussion (to date) - my OPINION only:

Lightning Protection:
The “sintered porous bronze” construction of the “Dynaplate” may not be the best choice for dissipating (ground plate) the huge energies developed in a lightning strike..
It’s been suggested that hey could literally explode when the water they contain (w/in their “pores”) is heated up and turns into steam. The same might be said for Thru-Hull Fittings.
ISOLATE your RF Ground (counterpoise) and Thru-Hulls (if bonded) from your Lightning (dissipation) Ground Plate.

BTW: A lightning strike IS more than merely a very large DC (or AC) event, and includes an important RF component.

Aluminum Outdrives:
Aluminum is VERY susceptible to galvanic corrosion, and must be passively protected by bonding to a sacrificial anode (zinc), or actively protected with an “Impressed Current” device (Mercury’s “Mercathode” etc.).

Thru-Hulls
Bronze Thru-Hulls that service Engines, Metallic-bodied Pumps etc should be Bonded. It is virtually impossible to Isolate them.
Non-Metalic (Marelon) Thru-Hulls and those not connected to metallic equipment (cockpit drains, etc.) may be Isolated and left un-bonded.
Bonding conductors are subject to corrosion, and must be inspected & maintained regularly.

Some further reading:

Grounding and Bonding on Boats - By Kevin Hughes
http://www.oceanpix.co.uk/sailing-groundingbonding.htm

Understanding Galvanic Corrosion - By Kevin Hughes
http://www.oceanpix.co.uk/sailing-galvaniccorrosion.htm

Understanding Electrolysis - by Kevin Hughes
http://www.sailnet.com/collections/a...eid=hughes0004

Lightning & Sailboats (SGEB-17 ) - by Ewan M. Thomson
http://www.thomson.ece.ufl.edu/lightning/SGEB17.html

From a “Station Grounding Website”: http://members.cox.net/pc-usa/station/grounding.htm
This website outlays the basic knowledge, safe design and installed equipment that are employed in the lightning protection system of a US Coast Guard Auxiliary Radio Facility - including:
Lightning Misconceptions
http://members.cox.net/pc-usa/station/ground2.htm
Lightning Basics
http://members.cox.net/pc-usa/station/basics.htm
ASPECTS, COMPONENTS, AND DAMAGES FROM LIGHTNING
http://members.cox.net/pc-usa/station/aspects.htm
Common Bonding: Rule #1 for successful grounding
http://members.cox.net/pc-usa/station/ground3.htm
External grounds: a better place for lightning!
http://members.cox.net/pc-usa/station/ground4.htm
Inductance - Why grounding is never enough
http://members.cox.net/pc-usa/station/inductance.htm
Conclusions, sample equipment, links, and credits
http://members.cox.net/pc-usa/station/ground5.htm

Lightning strikes at Sea ! – Lightning Strike! - By Kathy Baron
http://www.oceanpix.co.uk/sailing-lightning.htm

Lightning at Sea 2 - Understanding Lightning, Part Two - By Kevin Hughes
http://www.oceanpix.co.uk/sailing-lightningatsea2.htm

Grounding considerations to ponder for Lightning Protection - from “Strikeshield”
http://www.strikeshield.com/lightningground.html

RF Grounding for Marine Vessels - By Dr. John Gregory (CruiseEmail)
http://www.cruiseemail.com/rf_grounding.htm

Grounding & Antenna Considerations - from the Icom Manual
http://www.icomcanada.com/techbullet..._grounding.pdf

[Wahoo Sails]

In Nigel Calders book on boat wiring (sorry ... don't remember the exact title) he discusses the 2 most common forms of lightning protection, grounding systems and those designed to dissipate static build up ... as a final caveat, he say's that lightning appears to have a mind of it's own, and often does unexpected things. I got to see that first hand, New Years eve 2 years ago. Among the 15 boats struck was a hapless old wooden Chris Craft ... nestled between two 35'+ sailboats ... wouldn't you have thought lightning would have preferred their masts? Neither of those were damaged ... blew the screen out of the guys radar, and when I got there ... the VHF was still a glowing lump of orange! Further down the sea wall, a fellow's masthead light was completely vaporized (as in GONE ) .... the rest of the boat was undamaged. Of course it's only right and proper to take all prudent actions to prevent damage ... but when it comes to lightning strikes ... well? Don't count on it necessarily working. By the way, lightning doesn't have to strike the vessel to do damage either ... EMP can take out a GPS antenna 500' away!

L S/V Eva Luna
Bob

[Alan Wheeler]

Correct. Lightning doesn't go for the highest point, the most metalic object or many other things that science would most presume. It has totally bamboosaled scientists for sometime now. Just when somebody say's ArrrrHaaa, Eureka, I've found how it works, a lightning strike goes and does something that totally blows the theory out of the water.
Something I saw from a direct hit once, when I was a kid. The strike hit the power lines outside my home. The Telephone was blown off the wall. The house shook and the bang was deafening. The power was triped by the Pole fuses being vapourised. But the truuely amazing part was, a bolt of flame jumped a good foot out of each side of a light bulb that was pluged in at the time. Yet the bulb remained intacked and still worked when the power was restored. Go figure.

[tenknots]

Don't bond.

Install a GFCI at the entrance of the shorepower and separate the AC and DC ground.

Whatever you do about lightning will not work. Or it will.

[exposure]

Thanks everyone for the words of wisdom.

After considerable study, I think I will leave my boat as is. That's with all of the bronze through hulls with bronze valves ungrounded. None of them are in a wet bilge. I'll leave the shrouds attached to their grounding plates and leave the saildrive and engine bonded to their zinc. I'll probably add one of those removable fish zincs for extra protection at the marina.

If nothing else, it's the easiest thing to do and I have more tasks to complete than time to complete them.

Thanks, Woody