Bonded vs Unbonded Boats

[Christian Van H]

Hi all! Any thoughts on bonding below waterline metals to decrease corrosion vs. leaving them isolated? Not to bring up a fight about lightning protection, which is a whole other subject, but I'm leaning toward leaving my thruhulls unbonded, and my shaft protected by zincs. I just dont see the advantage vs. the possible exposure to stay currents. I will be using a good galvanic isolator though... Thanks, Chris

[Rhosyn Mor]

Chris,
Am told by those who profess to know that unbonding creates less of a path for galvanic corrosion to occur, a good thing in other words, by the by it seems that only in the USA is there a preponderace of bonded boats, most EU boats are unbonded, for that very reason

[roverhi]

FWIW, I had one boat with everything bonded and it had terrible electrolysis problems. Would eat zincs and the center board cable in a couple of months. With that experience, did not bond our W32 when I built it. No problems. zincs lasted from haul out to haul out. Current boat is 40 years old, bonded and does okay though zincs need to be replaced at least annually. I'm not convinced bonding does any good but also not proven that it hurts.

[Christian Van H]

Thank you both for your replies! You both had similar experiences...and just what I expected. I can understand a ground plate for lighting protection, but I just see too many possibilities for making matters worse instead of better by bonding all underwater fittings. Mind you, we are all probably speaking of fiberglass boats here, or at least insulated thruhulls. Thanks again, Chris

[Cheechako]

unbonded. seen more problems on bonded boats than unbonded ones.

[Marinheiro]

Interesting article on bonding by Stan Honey
Grounding

[Orion Jim]

I have no scientific data, only practicle experience. My vessel has all through hulls bonded to a plate on the keel. As I enter my twenty-fifth season I have all the original seacocks, Sparten by the way, and they are in fine shape. I also have a propnut zinc which loses half its mass in seven months. There is also a dissipator at the masthead and this vessel has never been struck by lightning....yet.

[Christian Van H]

Marin, that IS a great article! I'm going to print that one! Thanks!

[s/v Jedi]

It is a mis-conception that bonding protects underwater metals from galvanic corrosion. Zincs give that protection. In theory, when you connect these metals by wiring (bonding) inside the boat, a zinc on one piece of underwater metal will also protect the other, connected parts. This is true but if the parts are different kind of metals, this bonding can actually create a circuit for the battery formed by the two different metals in salt water and that might do more damage than good.

I do longer posts on these subjects, so I continue ;-)

AC electrical ground is a good reason for bonding. A Dynaplate or similar is the path to ground (seawater, fresh isn't as good). This provides protection for your boat the same way a grounding rod or ground wire from power-plant does for a house. Machines with metal housings etc. are now connected to ground and if that housing shorts with the hot wire, the current will (mostly) follow the ground-path by the wiring instead of through your body (your body has a higher electrical resistance).

This is all that it does, but you do not get that safety from an isolation transformer. The transformer has no contact with the seawater I hope so it can't provide ground, period. It actually keeps ground from shorepower away by isolating you from it.

Next is the GFCI protection device, many outlets have it or you can have a centralized thingy for it. Many people think you need a ground wire for that but it is the exact opposite: it protects where you have NO ground wire or in case that ground-protection fails. This thingy just compares current running through hot wire with the return current running through the neutral wire. When they are not the same, it assumes the difference is a current running through your body and it interrupts the circuit. So if you have no bonding system: install GFCI/GFPD thingies in your boat! If you do have ground, install them anyway because they are cheap and provide extra safety.
You do not need to connect thru-hulls etc. to this bonding when you have a dynaplate.

Lightning protection: the bonding system can protect your boat, it will not prevent lightning strikes etc. When the mast/whatever is struck, a big current enters the boat and it wants to run to ground. Unfortunately, this means it needs to go through the hull in most cases. It can blast holes in the hull that way, unless one provides it with a better path, like a straight wire from the mast to a dynaplate under that mast. This wire can not make bends because the lightning might not want to take that bend and jump (called arcing) to something else or still go straight through the hull. Although this protection uses simple equipment, the implementation is tricky and must be done or checked by an expert. (And it's almost impossible on catamarans!!)

Lightning strike prevention devices. The brush on top of the mast. There are not many cruisers who understand this, most think it is some form of lightning rod.... it isn't. The info in the link posted by MarinHeiro is wrong. A lightning rod protects during a strike just like the previous part of this post describes: it provides a good path to ground. The brush thingy tries to prevent lightning from striking the boat and nothing more. It'll evaporate when struck. But that doesn't mean it's useless... it's not, when installed right. First of all, you need a grounding/bonding system with the mast electrically connected to the seawater or it won't work at all! I saw it on many boats that don't have that so it's useless for them. This brush is a static dissipater (not a lightning dissipater!!) and this technology is in use everywhere, from airplanes (just to get rid of static charge) to cellphone towers and it's method of operation is well known, documented and confirmed. There is no magic to it. What it does for the boat needs some understanding of lightning.

A storm cloud is electrically charged, everyone knows that. But totally invisible and little known is that it drags a charge of the opposite side with it along the earth surface. When the difference in potential (think voltage) between the two gets big enough, two things happen: from the cloud down, "stepped ladders" form (the charge is seeking it's opposite charge down below). From the surface, similar "leaders" form upwards. When these two connect, the air becomes ionized and changes from insulator to conductor and the strike occurs.
So what happens when that surface charge meets a house, tree or boat? It will actually travel up the structure to the highest point because that's closest to the opposite charge in the cloud. It can't travel up through the air yet (streamer) because it's to weak, but the object encountered is easy. At that highest point, it will do the same as on the surface: build up charge and hope it gets big enough to form a leader. The difference is that it's chance of success increased compared to the charge on the surface because the distance is smaller.... it found an easier path. In this stage you get that hair-on-arms-raising experiences and St Elmus fire in the rigging. If the leader forms, you will actually hear that happening.

Now the brush.... it actually helps the charge to "jump" in the air, like the airplane loosing it's static charge. This seems counter-productive and some people believe it will even attract lightning. But remember that the charge isn't build up enough yet to form a leader and the constant "bleeding" of ions off the brush counter-acts that building up the charge plan... it's loosing charge through the brush. If it does that well enough, another object might get an earlier chance to form the leader, or that leader goes up higher earlier and gets selected for the big prize. That is how the brush thingy works.

It can never be 100% safe. It has a maximum capacity for this bleeding ions thing and the surface charge reaching the boat can already be build up to a state that nothing matters anymore (well, maybe another hundred brushes or so but then still what they would dissipate might just be added to what comes off the masthead all at once. It's like the Dutch boy with his finger plugging the dike... works as long as the hole is small enough.

We have the brushes on both masts and I believed it saved us from at least one strike in Curacao. I even believe it saved the boats anchored next to us. We had the rigging arcing, heard the buildup, hair risen, felt like we were in a lift accelerating upwards at mach 10 and the strike was about 100 yards away in the water. The neighbors and I came out with white faces, we all had the same experience. My wife couldn't speak for minutes.

Another boat from friends was hit while he had the brush and it was grounded. After checking all burned out equipment, it was obvious that the lightning hit the insulated backstay, entering the SSB tuner first (was half gone). So, the brush might not have failed at all and the lesson is that all stays & antenna's must be grounded during lightning storms!

I also heard that insurance companies refuse to insure antenna installations (like cell towers) when static dissipaters are not installed. Insurance companies are good in statistics when it saves them paying out claims so that would mean something, but I never bothered to check that story.

I also just found a great web page from forespar on this: Forespar: Marine Products that Perform

cheers,
Nick.

[Christian Van H]

I get the whole "bottle brush" static discharge idea, but ofter wondered; isnt there a lot more area for static discharge throughout the surface area of the hundreds of feet of exposed rigging wire than on that minuscule brush? Well, I knew this thread would turn to lightning! Really though, as bonding thruhulls and prop shafts go, I'm not convinced...

[westsail42]

Originally Posted by Christian Van H

I get the whole "bottle brush" static discharge idea, but ofter wondered; isnt there a lot more area for static discharge throughout the surface area of the hundreds of feet of exposed rigging wire than on that minuscule brush? Well, I knew this thread would turn to lightning! Really though, as bonding thruhulls and prop shafts go, I'm not convinced...

I think the trick with the "bottle brush" and standard lightning rods is the "cone of silence" they produce. There is some theoretical angle from these devices that when placed atop the mast effectively envelopes the rigging below in the cone "protection area".

This cone is based on the natural limits of the angle of incidence of a lightning strike (under normal atmospheric conditions).

This is why the rigging will not "attract" the lightning with these devices properly installed at the very top of the mast.

That is what I understand. Someone here can probably correct me and/or fill in more details.

[Marinheiro]

Getting agrement on bonding is a bit like trying to get agreement from a bunch of economists. WRT Nicks comments
1. An isolation transformer is not supposed to eliminate the boat's electical ground, its function is to eliminate the link to other boats grounds via the shore power ground wire. The boat must still have all AC circuits bonded to a common ground
2. The bottle brush lightning dissapator - does anyone know if they really work, a bit like those sulphation eliminators for batteries? Lightning is so unpredicatable, like an experience I read where a power boat moored between 2 yachts was struck by lightning while the yachts were unharmed. It could be that in action the brush is not dissapating the charge but acting just like a conventional rod. If it is designed to self destruct at what point does this occur during the lightning strike? There are some interesting comments on these in Calder's Boatowners guide
3. From my experience in industrial installations (gas facilities, tall chimneys and steel structures in lightning prone Western Australia) the intallation always consists of a lightning conductor (a copper rod or a more fancy "collector') with a copper bar (not cable) following the straightest possible line to ground

[GordMay]

Originally Posted by Marinheiro

... 2. The bottle brush lightning dissapator - does anyone know if they really work, a bit like those sulphation eliminators for batteries? Lightning is so unpredicatable, like an experience I read where a power boat moored between 2 yachts was struck by lightning while the yachts were unharmed. It could be that in action the brush is not dissapating the charge but acting just like a conventional rod...

No - dissipators (charge transfer systems) aren't effective in preventing, nor reducing the risk of a lightning strike.

Pick your terms, and goto CruisersForum Google search at:
Cruisers & Sailing Forum

ie:

ightning strikes/ avoiding them? - Page 3 - Cruisers & Sailing Forums
If you had a ligtning rod (there's another name for it..dissapator?) Start with a dissapator (lightninig rod) at the tippy top of the mast. ...
www.cruisersforum.com/forums/f55/lightning-strikes-avoiding-them-3138-3.html

Lightning? - Page 2 - Cruisers & Sailing Forums
I have one of the little ionic dissapator gizmos at the top which apparently did little or nothing to ward off this strike. The electrical circuits in the ...
www.cruisersforum.com/forums/f122/lightning-6012-2.html

Struck by Lightning/seeking advice - Cruisers & Sailing Forums
The top of the mast has one of the little brushes at the top; a so-called ionic dissapator. I've heard those little gizmos are of questionable value also. ...
www.cruisersforum.com/forums/f80/struck-lightning-seeking-advice-5331.html

[s/v Jedi]

I think this thread is getting better all the time ;-)

There are things concerning lightning not fully grasped by science, which is the reason they still research the subject. (Did anyone see that documentary on Discovery Channel where they shoot these rockets up into the air during lightning storms?) But many aspects about it are understood: most questions in threads like this one (I read all Gord posted) are answered, so let's try to deal with those easy ones first:

A static dissipater is not a lightning rod. Repeat that ;-)

The lightning rod is designed to provide a better and safe(r) path to ground for the lightning strike than the object it is protecting. Think of a building protected by one. The rod is up on the roof and a very thick conductor connects it to a ground rod that is hammered into the ground 20 feet or so. They work and this is old technology. Many installations are done wrong however, like multiple rods interconnected with one wire down to ground: this means that the interconnecting wire has 90 degree or more bends in it: an invitation to arcing. Also, the idea of a lightning rod is to attract the lightning, making sure it doesn't hit something else nearby. This is why it should have a blunt end, not a pointy end. The blunt end makes it harder for ions to bleed of into the air, so that more charge is build up which increases the chance of forming a leader.

A mast-head makes a good lightning rod. That doesn't mean it's perfect: many boats get their direct hit in the rigging instead of the masthead. Jedi had two direct hits with the PO and both events led to fried electric wiring and most electronics. Also, everything at the mastheads was evaporated: VHF antenna had a 1" stub left, windex completely gone etc.
However, it was clear that the main discharge to ground followed the bonding system under each mast. The AWG-6 wires had their insulation burned off them and the bilge area around the ground plate under the mast was spotless. The outside of the hull has pockets under each mast in which the ground plates are fitted so that they are flush with the hull. The pockets are bigger than the plates so the sides are also in contact with the water. They are about 3/4" thick and look like cast from bronze. I can't say what would have happened if Jedi wouldn't have had these, but I can say that they guided the strike to ground nicely without damage to the hull.

I stick to my comments on the isolation transformer: it does NOT provide ground safety for your AC electrical system aboard: you need a grounding/bonding system with dynaplate or similar for that. It's as simple as that. The isolation transformer keeps the ground from the shorepower connection isolated from your boat, leaving you without ground connected to your outlets unless you have your independent ships ground with dynaplate.

All info above should not have any mysterious wizardry around it so if you think it has, you should read up on the subjects or ask here. But now we get to the brush thinghy;

The static dissipater is not designed to provide a path for the lightning strike. It is so fragile that it will evaporate when struck. It isn't designed for evaporating at all but that's just what happens when it gets struck. It has been demonstrated that the static dissipater will disperse ions very well and reduce the buildup of a static charge that way. The big question is if that is enough to prevent the leader from forming. But it can still help when it doesn't manage that: if it only reduces it somewhat, it also increases the chance that another object in the direct vicinity builds up a sufficient charge earlier and forms a leader earlier. Think of it like camouflage: if the other guy's camouflage isn't as good as yours, chances are he gets noticed first.

cheers,
Nick.

[s/v Jedi]

Originally Posted by GordMay

No - dissipators (charge transfer systems) aren't effective in preventing, nor reducing the risk of a lightning strike.

Gord,

I really value your opinion on all you write but I read all the links you provided for reference and didn't find any evidence supporting this statement of you. Pls. provide better links :-)

But, as I wrote before: many (if not most) boats using these brushes did not install them correctly in which case they are useless. Look at all the catamarans that have them: not a single one I asked had the mast grounded so it just will not work in that case (for many monohulls it's the same). Why didn't they read the installation instructions? When I ask that they reply: "our mast isn't grounded and I don't feel like tackling that job and decided the brush will still work without the mast grounded, maybe a little less effective but I don't mind that" or "you can't make a good ground for the mast on a cat so the brush will have to do it's job without the grounded mast". Both statements are understandable but show an utterly lack of comprehension of the issue.

Start counting the masthead-struck boats with static dissipaters and divide them into the two groups: with and without grounded mast. My list has zero examples in the group with grounded mast.

cheers,
Nick.