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 ;-)
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
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