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Old 16-03-2009, 11:22   #46
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Originally Posted by s/v Jedi View Post
... A good thick (AWG 6 or bigger) conductor connected to the mast base, going straight (no bends) down to earth will always be the path selected when a lightning strike travels down the mast, making you the one who decides the route.
cheers,
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I’m afraid lightning is nowhere nearly as rational as Nick (Nick is a very knowlegable & intelligent fellow), and is, in fact, quite capricious. "Always" is a poor choice of words, when describing any aspect of lightning, including it’s path to ground.

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Old 16-03-2009, 11:32   #47
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For any normal charge that travels solely through wiring, that is true. But lightning doesn't play to those rules.
Yeah, I've read some of that as well.

With all due respect. How many times have you been hit by lightning?
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Old 16-03-2009, 12:21   #48
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"Always" is a poor choice of words, when describing any aspect of lightning, including it’s path to ground.
I agree, however, I used the word in combination with the "if" like in "if it travels down the mast". This doesn't mean that the lightning will always select the mast... it might choose the pullpit instead, or whatever.

But, IF it strikes the (conducting) mast, the main body of the strike will go through a correctly installed grounding wire/plate under the mast. There's no question or magic to it. All the shore-side lightning protection systems do that every day. In more technical terms: once the charge of a lightning strike is traveling vertically down to ground through a conductor that is connected to ground, it will not leave (arc jump from) that conductor if: 1) the conductor makes no bend or turn, ie. keeps going straight and vertical down to ground and 2) the conductor stays intact, ie. doesn't burn out/evaporate.

Quote:
Yeah, I've read some of that as well.
With all due respect. How many times have you been hit by lightning?
Tropic: what's not to believe about that? You can see lightning traveling through air in the sky, why don't you believe that? Or do you think that once the lightning enters a conductor, that it will stay in there without jumping out into ionized air or jumping over through ionized air into another conductor? All that is documented science, no "brush-magic" there.

Lightning will jump from a conductor, unlike a smaller electrical charge. But the same goes for any man-made high voltage, that's why you see those tall (up to several yards) insulators holding wires at power-plants. Electric engineers have died by accidently moving in between two high voltage, high power conductors (like hot and neutral) because their body lowered the air-insulation between the two conductors enough for arcing.

Jedi has had 2 full hits in the city-marina in Naples, Florida, with much damage to electronics but exited her through the grounding systems under the masts. Later, we had a near-strike, about 50 yards to our starboard side while at anchor, with sparking rigging and everything but no damage whatsoever.

cheers,
Nick.
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Old 16-03-2009, 12:27   #49
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You did not indicate if you were on board or not. Crew safety is paramount.

Other than that omission, your experience mirrors mine. Fried electronics, no hull damage. Your boat has a 'grounding system', mine does not. My boat merely has inboard diesels which channeled the charge to ground.

My point is.... And the advantage of a lightning protection system is...????????
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Old 17-03-2009, 02:10   #50
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Lightning (but not bonding) !

While I tend to agree with most of the posts so far, I must add the following points:
  • Lightning flow DOES follow all electrical principles, the problem that most (all?) of us don't understand ALL the principles of extremely high voltage (static) circuits.
  • Lightning current will flow in ALL paths inversely proportional to the resistance. This is often forgotten, we say put a large conductor in and the current will flow through that and all will be good. When you have tens of thousands of amps available before the charge is fully dissipated, even the high resistance paths can have hundreds of amps flowing in them. Each circuit will be dissipating power and even a thousandth of say 1000 kilowatts is a lot of power (read heat, destruction etc).
  • While air is poor conductor, once ionized, it becomes a very good conductor. The trick is to provide sufficient low resistance high capacity paths so that the voltages (PD) at any points inside (around) the vessel remain too low for ionization to occur. Air will only be ionized once the voltages available are high enough. I am not talking here of the initial charge that has ionized the air above the point of entry, rather the voltages that are produced once the current is flowing throught the various paths in the vessel to the "ground"; more technically the area of opposite potential - the seawater. If these can be kept low (say a few thousand volts), ionization cannot occur. The only way to keep them low is to have enough low resistance conductors available that can handle the current flow (and therefore the power).
  • However once ionized, the air path (spark) is a good conductor and handle a lot of current. The problem being the unpredicability of the entry / exit points of the ionized air path.
However, this is unrelated to the question of bonding IMO (or have I missed something)
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Old 17-03-2009, 06:06   #51
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However, this is unrelated to the question of bonding IMO (or have I missed something)
Nope, you are on the ball! As I said in the original post, you cant post about bonding without the thread eventually devolving into a lightning discussion. IMHO, bonding has nothing to do with lightning protection, with the possible exception of the knot log and sounder transducer. Both of those can sink the boat with the right (wrong) strike.

So, do I ground the prop shaft and prop to the engine, or leave it isolated and zinc protected?
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Old 17-03-2009, 07:05   #52
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According to what I understood from that "grounding" article, you should not have your engine connected to the shaft....I'm actually considering not bonding after reading this thread.
During my refit I have had to disconnect all that bonding...would be great if I didn’t have to re-install it all.
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Old 17-03-2009, 07:27   #53
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I just cant see an advantage to bonding, James. I am going to run lightning grounds to cap shroud chainplates, the forestay and the mast base down to a bronze underwater plate though. No AC or DC grounds to that system though...
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Old 17-03-2009, 08:19   #54
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I have been watching this thread with interest and as usual there are some gems and a lot of myths. I have taken courses on these topics with three of the leading people in the industry (Ed Sherman, Ben Craig, these two are responsible for most of the ABYC stuff on these topics and Dave Rifkin who has a terrific web site ( http://qualitymarineservices.net/ )and is a consultant to the USN on these isssues) I will never know as much as these three guys but I can tell you that they disagree on almost as much as they agree on so the chances of you guys coming to a consnsus is a bit thin..
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Old 17-03-2009, 09:14   #55
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Originally Posted by Christian Van H View Post
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

LOL well so much for not wanting to get into the lightning bruhaha
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Old 17-03-2009, 09:30   #56
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knot log and sounder transducer. Both of those can sink the boat with the right (wrong) strike.
Why not build a sea-chest-like box around those with those pressure-gasket thingies for the cabling?

Quote:
So, do I ground the prop shaft and prop to the engine, or leave it isolated and zinc protected?
I'm stupid with engines... is the shaft electrically connected to the gearbox/engine? Anyway, the prop and shaft are always grounded as they are in the water, no way around that. They either have to be 100% isolated from the engine, or 100% bonded using low-resistance wiring to the common ground point on the engine. We have a thrust-bearing and it is bonded.

Those flexible coupling things will probably isolate electrically? The question is if the flexible material it's made off is a good isolator or not.

In both cases, prop and shaft should have zincs. If isolated, they are the only protection and if bonded to other zincs, you still put zincs there because it's too expensive to take a risk (like resistance in bonding-wire like corrosion at which time you loose protection). This is all galvanic corrosion protection. I actually also have a zinc on the shaft inside the boat.... to prevent it from sliding out when something breaks!

cheers,
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Old 17-03-2009, 15:20   #57
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I will never know as much as these three guys but I can tell you that they disagree on almost as much as they agree on so the chances of you guys coming to a consnsus is a bit thin..
Oh, I think we will come to consensus...it just might be wrong!

So Boatpoker, whats YOUR opinion on bonding?

Jedi, that whole seachest thing bothers me...I think its the seals. As for the coupler, yup its urethane I believe...no conduction. I think I'm gonna keep it that way.Your zinc on the inside idea is perfect. I have a similar hose clamp. A friend had a new shaft seal installed by the yard. Halfway across Chesapeake bay the prop and shaft slipped right out the back of the boat. He had to run her aground to keep from sinking. He said the boat filled up scary fast, even with both pumps running.
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Old 17-03-2009, 15:27   #58
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If you do have a probelm adress one issue at a time and wait to see what happens before moving on to the next step. Regardless of all the very bright people studying these issues we seem to be dealing with theories rather than absolutes.
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Old 17-03-2009, 20:47   #59
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Bonding.
After finding out that my supposedly isolated main engine was in fact connected to the vessel through its control cables (Morse Teleflex) and not wanting to have an electrical path from engine to gearbox (pinions, bearings) to propeller shaft, I decided to bond the engine and propeller shaft to a common point on the steel hull, in doing so bypassing the gearbox.

Lightning.
Living in a town renown for its electrical storms, I have seen a coconut tree split in half, a tree pulverized and a reinforced concrete wall at the top of building with lighting protection damaged by a direct hit, but I have never seen or heard of a ship in the harbor getting a direct hit. This does not mean that ships should not be equipped with lightning protection, the tallest the greater is the need. Buildings with lightning protection are normally equipped with a meter that records hits. In over 25 years some buildings have never recorded a hit when others 100 meters away will record many hits in one year.

Static.
When in an electrical storm I disconnect my aerial. I have witnessed sparks as long as 75mm coming out of the aerial cable and jumping to the steel structure. For this reason I keep the extremity of the aerial cable pointing downward and more than 1 meter away from other electronic equipment. In the thread “speed transducer, post 41 (There's 5 wires including the shield drain wire)”, I would not be surprised if in a metal casing the shield drain wire was connected to the casing and in this case a metal transducer will work like a “mini Dynaplate” which could be expensive. I only own plastic transducers but if I had metal ones I would disconnect the transducers cables at the terminals and keep the cables far away from other electronic equipment, not an easy task if flush mounted.
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Old 17-03-2009, 21:36   #60
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Shocking!!!

The Jedi is correct. Dissipators work, but they are not a pancea to bad weather.

I love these discussions, too. I've have a lot more experience flying airplanes around thunderstorms than sailing near them. So let me state that if we don't have static dissipators (or static wicks as we call them) on our aircraft, it gets recorded as downing discrepancy and the plane stays on ground until fixed. We expect to take a hit without them.

Next time you're out on a flight line, take a look at the trailing edge of all the wing surfaces you see and count how many little wires you find protruding from the back of the wings or stabilizers. Those aren't left over strings of wire we forgot to cut off when making the plane. They are static dissipators. We had a large plan take a hit (while flying). Wouldn't you know, it was the one plan on the line that was missing a few static wicks.

OTOH- we also had a big plane take a very expensive hit while sitting on the ground minding its own business (it was grounded by the way).

I figure most lighting protection can be similar to how umbrellas keep you dry. An umbrella will keep you dry, but under the right set of natural circumstances, they can also be useless. People still use umbrellas. (I don't because I was raised that umbrellas are for women ... and I wear a hat.)
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