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Old 19-03-2009, 01:39   #76
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Originally Posted by chala View Post
I too own a thrust-bearing (aquadrive 1400) but yours seems more sofisticated than mine. For me what transmits the thrust of the propeller to the boat is some nice little balls in the bearing. I would not like mine to be pitted by what I may call electrical erosion. So what I do is to provide an equipotential bonding to part of the vessel that I see vulnerable to an electrical current, but you know that.
Well, mine is the same: aquadrive ;-)

It's important to know that electrical erosion is the result of sparks. I am not too worried about electric erosion in the thrust bearing for two reasons:

1. low voltage. The voltage is very low so if sparks occur on the bearing balls, these sparks will be very small. Also, when the bearing isn't turning and you measure good conductance, it will not spark at all. Our bearing only turns when we use the engine, which is almost never.

2. Other path. A current will split with a ratio linear to the resistance of the multiple paths. The prop & shaft are automatically grounded by being under water. But we have a bonding and grounding system connected to both engine and thrust bearing, with big conductors and very low resistance. This means that any voltage potential on the engine block and thrust bearing will mostly flow to our ground plate under water instead of through the bearing.

So, if you don't have the bonding and grounding system like with a dynaplate, your solution will definitely make a difference, although I wouldn't know how much difference because of point 1 above.

But, we plan to replace the bearing in the coming years because of corrosion and I will definitely try to open it up and check it for electrical erosion.

cheers,
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Old 19-03-2009, 02:35   #77
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According to Wikipedia, the version you describe is for small aircraft, while the bigger ones have just the pointy electrode.
Yes, there are various types however they ALL have the same electrical porperties - namely between 50 Kilohms to 200 Kilohms resistance. Wikipedia is incorrect in so far as they state the wicks provide a continous LOW resistance discharge path (unless 50 Kilohms can be considered low). I check these things on a day to day basis, if they are measure below 50K's or above 200K's (depending of model), they are removed as unserviceable.

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In short:

During adverse charging conditions (air friction), they limit the potential static buildup on the aircraft and control interference generated by static charge.
The refernce goes on to say "Static dischargers are not lightning arrestors and do not reduce or increase the likelihood of an aircraft being struck by lightning." My emphasis.
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So... it does discharge at a level that can't yet ionize the air. If it would ionize, it would arc.
Agreed, that is their purpose. By definition, and arc (spark) occurs only when a gas is ionized.



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The principle of operation is exactly the same: a grounded conductor ending in a sharp point dissipates static charge well before the charge-level that would ionize the air and arc.
This is where we differ, I am saying they aren't electrically the same, they are VERY different electrically; therefore one can't argue that because a static wick will discharge a charge build up on a airframe into the surrounding air, a metal brush on a grounded mast will discharge the surface charge on the water safely into the air.

In fact I believe it probably won't work on a mast simply because if you put a electrically similar wick (i.e. a conductive wire with a sharp point) on an airframe, it won't discharge the airframe any better than leaving it off. This is why we check their resistance at every periodic inspection, they must NOT be low resistance OR open circuit.

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The field around a sharp point is much higher than around other objects.
Agreed, it also requires less voltage to ionize a gas around a sharp point.


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Originally Posted by s/v Jedi View Post
So, the brush starts discharge well before the level of charge buildup that would induce ionization and arcing. I have seen my rig discharging: St Elmo's fire. Before that happened, the brush was already discharging and later the first to arc (but I didn't see that, I was fleeing down inside! ;-)
I can understand the fleeing down inside bit .
How do you know the brush was discharging (by this I assume you mean the electrical charge was dissipating through the ends of the brush). Surely you could only observe it when there was ionization. St Elmo's fire is just proof that ionization is occurring. As I understand it (and I could be wrong ), the only difference between St Elmo's fire and arcing is the degree of charge being dissipated. Both require the ionization of the surrounding gas before anything happens. I would be thinking that the brush wasn't working as intended if I saw St Elmo's fire on the rig.

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To keep this thread going forward, I will show the existence of the ground-level charge under a storm cloud simply by pointing to the encyclopedia: Lightning - Wikipedia, the free encyclopedia
Agreed, in fact I once spent a very nervous 20 mins sailing in circles under a huge thunderstorm in Darwin harbour (another famous thunderstrm city) with almost zero visibility (due to the intensity of the rain) and with dozens of strikes to the water surface all around my wooden boat with an Al. mast (and many more cloud to cloud strikes just overhead).

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Originally Posted by s/v Jedi View Post
For that, we should gather statistics with some intelligence, like checking of the mast was grounded in case a dissipater didn't prevent a strike, or that a wooden mast had a conductor down to ground etc. On my list, a good installed dissipater wins hands down but it's a short list.
Can't argue with the gathering of good statistical data but I remain skeptical about the brush - BTW, I have a brush on my grounded mast but I reckon it is doing a better job just keeping the seagulls off the mast head .

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Another funny thing: resident of Florida often claim that they have lightning alley, with the most strikes in the world. That's funny because the top 3 is: Congo, Singapore and Brazil. Florida does up to 50 strikes per square mile per year... but Congo does 158, more than 3 times as much!

ciao!
Nick.
Those residents in Florida must be Americans
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Old 19-03-2009, 03:26   #78
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Wotname “I have a brush on my grounded mast but I reckon it is doing a better job just keeping the seagulls off the mast head”. I agree with you. A ball terminates modern lightning poles. It is interesting to recall that when B Franklin presented his “theory” of a ball be more efficient than a spear to the “British Academy of Science” who advocated the reverse, it was left to the King to decide. As England was at war with America the King decided that the spear was more efficient.
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Old 19-03-2009, 05:20   #79
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Evidence suggests that sharp-tipped lightning rods are not as effective as strike receptors, as are those with a more blunt geometry.

Goto: Lightning Rod Types

See the excellent “Lightning Rod Improvement Studies” by C. B. Moore, William Rison, James Mathis, and Graydon Aulich (Langmuir Laboratory for Atmospheric Research) as published in the American Meteorological Society’s “Journal of Applied Meteorology:
at:
http://ams.allenpress.com/archive/15...0-39-5-593.pdf

“... We conclude, from this analysis and from the results of the lightning strike competition, that moderately blunt Franklin rods with tip height–to–tip radius of curvature ratios of about 680:1 (i.e., with electric field enhancements of about 230 fold at their tips) are more likely to furnish return strokes and therefore to provide better protection against lightning than can either very blunt ones or the traditional, sharp rods...”

See also:
M. Bateman’s Atmospheric Electricity Bibliography:
http://ae.nsstc.uah.edu/
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Old 19-03-2009, 06:17   #80
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Gord's info re aircraft and electrical discharge is accurate.

In reporting on aircraft research on thunderstorms and participating in flight tests (I am a pilot) of airborne turbulence detection equipment, I can report that trailing edge dissipators did not prevent lightning strikes to aircraft. Aircraft were frequently struck by lightning, which generally exited the aircraft through tail/aft fuselage surfaces. Aside from pinhole burns in the aircraft surfaces from entering (but most often from exiting) the aircraft, I don't recall any damage to aircraft equipment. Nevertheless, ball lightning rolling from the radome and into the cockpit and down the aisle to exit the aircraft was a bit concerting, as well as static buildup that caused charts and paper to be instantly drawn to the windshield and every hair on our bodies to stand upright.

I should note that these tests were conducted with the intent to enter inside thunderstorms and if not actually inside the most intense cells (with a special armored/strengthened aircraft), then in close proximity to them.

My sailboat has been struck twice by lightning, which had no lightning grounding in the first strike, and a poor system in the second. The first exploded the masthead gear with no other damage; the second strike destroyed most of the electrical gear on the boat. In the second strike, side flashes also caused damage. My wife and I anticipated the second strike, as we watched a small cell break away from a major storm about 3-5 miles away. That cell, with lightning striking the water as it moved toward us, caused us a very helpless feeling aboard our anchored catamaran. We went below, quickly disconnected plugs and shut down all electric systems, and huddled in the middle of the boat, and waited for the cell to move above us. Intense static electricity was a prelude to the strike, which we saw as a blinding light and plasma discharged at the masthead, which was visible through the overhead hatches.

While few deaths have been reported from lightning strikes aboard boats, a lightning grounding system is aimed at protecting the vessel's passengers and crew. While providing a route to allow the energy to exit the boat, such a system may also reduce the damage to the vessel and its gear.

During the refit on our boat, we are installing a proper lightning ground.

Extensive testing by the U.S. government a few years ago demonstrated that excellent protection for communications equipment to survive a lightning discharge is accomplished by removing conducting wires that become "antennae," which collect RF energy. Disconnect HF antennas, remove battery connections, remove microphone cables, and other accessory cables. Vhf handhelds were found to be especially resistant to discharges, even with antennas attached. Following these suggestions resulted in near total survival of the equipment during testing.

One fact is clear, however: Lightning is what it is, and does what it does, without complete predictability.

Roger
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Old 19-03-2009, 06:26   #81
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Quote:
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Evidence suggests that sharp-tipped lightning rods are not as effective as strike receptors, as are those with a more blunt geometry.
Well, there you have it. The best lightning defense is to mount the sharpest tipped thingy you own at mast top. If I may be blunt, I think we may have strayed a little! As for the deck stepped mast question...the wire would run down the compression post or the bulkhead that supports the mast. If there is no support under the mast we are probably speaking of a daysailer.

JESSE asked about the wire encased in hoses for support. Under normal installation, the wire never touches the seacock, so I cant see it posing a bonding problem. With a lightning strike, I guess the helix could generate a current from the EMF pulse, but I cant see it reaching the point where it could do damage to the heavily constructed seacock.

Now, after looking at several different sources, it seems as though most experts agree that your engine AND its shaft and prop should ALL be electrically connected and GROUNDED to both AC and DC systems. Any comments from the exceedingly big brains following this thread?
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Old 19-03-2009, 23:11   #82
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“Now, after looking at several different sources, it seems as though most experts agree that your engine AND its shaft and prop should ALL be electrically connected and GROUNDED to both AC and DC systems. Any comments from the exceedingly big brains following this thread?”
Wrong.
My posts explained that for a few dollars I could minimise expensive damage to my gear train by connecting the shaft to the engine, and that by connecting the engine to the hull I could minimise current travelling through the control cables (Morse Teleflex). Obviously as DC is required to start the engine then the negative is effectively connected to the metal hull. No mention was made of connecting the AC to the engine or the hull.
In post 25 you write” since our engine block MUST be grounded to AC and DC ground systems”.
What is the reasoning behind the MUST?
If it is because the local regulations require it, then you must comply.
If not, then you have all options available to consider. For my-self I will consider a “double insulation” system protected by a RCD.

Lightning poles.
Here in OZ we must have a different technology. We even got the Franklin story the other way around. Must be because we are down under.
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Old 20-03-2009, 06:03   #83
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Chala, when I wrote about reviewing the work of several experts, I wasn't referring to you. Sorry, but I dont consider you an expert, yet. Also, as far as grounding the AC ground to the engine ground or buss, yes the ABYC does require it, if I'm reading the darn codes right. Dont forget that we are using isolation transformers or galvanic isolators here too. As far as metal boats go, there may be differences here. I'll look up what the Dashews say about them later. Add to that your strange problem of somehow allowing juice to flow through your morse cables, and you may be facing a somewhat uncommon problem...
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Old 20-03-2009, 07:15   #84
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... as far as grounding the AC ground to the engine ground or buss, yes the ABYC does require it, if I'm reading the darn codes right ...
Yes - you're reading it right.

Excerpted from AC Requirements per ABYC E-11:

11.5.3.3. The main AC system grounding bus shall be connected to
11.5.3.3.1. the engine negative terminal or the DC main negative bus on grounded DC systems,
or
11.5.3.3.2. the boat’s DC grounding bus in installations using ungrounded DC electrical systems.

(emphasis mine)
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Old 20-03-2009, 16:13   #85
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...Also, as far as grounding the AC ground to the engine ground or buss, yes the ABYC does require it, if I'm reading the darn codes right. Don't forget that we are using isolation transformers or galvanic isolators here too. As far as metal boats go, there may be differences here...
The ISO small craft standards are far more up to date on these things than ABYC is and are with the play with modern practices (specifically ISO13297 and ISO10133). Classification Society Rules are too.

ISO does not necessarily implicate the engine as far as grounding the ac and does not specifically require in all cases that the ac and dc negative be commoned. They also specifically address 2 wire isolated DC systems (aka isolated ground DC systems) and recognises that craft often have separate and normally isolated from each other engine and service DC systems and that many modern small craft engines are now 2 wire DC isolated ground (ie the block, etc is isolated from the cranking and service DC systems).

Another good thing exhibiting modern practice is they do not require fuses/breakers in the cranking battery to engine or service battery to DC panel circuits, instead giving the option of good installation practices instead. This is especially useful in boats with isolated ground DC ground systems as even in poor installations the opportunity for arcing accidents is greatly reduced so fusing is much less important for those conductors.

With respect to ISO standard boats with isolated ground DC systems the AC safety conductor must be grounded to the hull if the boat is metal, to the external ground (which does not have to be the engine), or to the lightning protection ground plate. Otherwise the AC protective conductor is to be connected to the DC negative ground as close to the battery as possible (but again the negative ground does not have to be the engine). But if an isolating transformer or RCD is fitted then the DC ground does not have to be connected to the shore ground (but may be).

That last paragraph above covers both metal and non metal boats but is a just very quick gloss over of the ISO requirement - as always one should read and follow the standards in detail if using them.
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Old 20-03-2009, 16:37   #86
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Thank you for watching my back, Gord! Midland, I would love to read the ISO standards...do you have to be a member of something to peruse a copy? Also, I think the ABYC just redid their codes recently, so ISO must be of similar age, but different thinking on some matters. You mentioned fuses in battery feeds...I have always wondered about fuses in starting circuits. I dont like the idea at all. However, house battery banks that feed the distribution...I foresee problems that could start fires here without fusing. Things like a 4 golfcart bank that shorts a cell heating between paralleling cables (I guess). My gut would be more wary of no fuse in the DC house feed. Anyway, I'd like to thank everyone who has posted on this thread. I have really learned alot here. I hope I can repay the favor someday!
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Old 20-03-2009, 17:14   #87
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If you do a google on the ISO numbers I quoted I think you will find pdf copies of them no problem .

Regarding the service battery to panel conductors with no fuses, while ISO is more expansive than this a simple way to look at it is that if they are physically isolated the only place they can ever contact each other is at the 2 pole isolating switch or where they are bought together again at the DC panel (and beyond which point each circuit is, of course, to be breakered/fused). Furthermore, if on an isolated DC ground boat there is nothing apart from each other against which they can arc as long as kept separated from the cables going to the various uses around the boat ex the DC panel - that latter separation would normally occur without even trying.

With respect to the engine cranking (where I have always been reluctant to fuse) a great protection is the use of isolated DC ground engines as if any conductor comes loose, chafes through on the engine, or alternator or starter chassis, etc they won't arc. This gets rid of one of the major causes of small boat DC arcing accidents. I get the impression that this is a very unfamiliar concept to US small boat owners even though the likes of Volvo-Penta's engine range is mostly (I have been told all by one of their distributors) isolated in this part of the world and in Europe. I have though, sourced DC isolated ground engines for big power boats from a US distributor but they were manufactured and delivered from Europe.

While the ISO standards are quite new the concepts they follow have been around for a long time as good practice but just been a slow drag getting those into standards. For example, my own boat which the builder's systems engineer and I specified the electrical for, complies with the new ISO standards even though it was built over 13 years ago (it is isolated ground). I have noticed that even with commercial vessels USA electrical practices are often quite dated - probably due to the protectionism of the Jones Act stifling the need to be innovative.
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Old 21-03-2009, 05:22   #88
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ISO Electrical Standards:

DC: http://www.sychut.com/nav/el/ISO10133.pdf

AC: http://www.sychut.com/nav/el/ISO13297.pdf


From ABYC Standards:

Dc Negative & Grounding Diagram
http://www.cruisersforum.com/gallery...r&imageuser=79

Overcurrent Protection for DC Circuits
http://www.cruisersforum.com/gallery...r&imageuser=79

DC Circuit Protection
(1)
http://www.cruisersforum.com/gallery...r&imageuser=79
(2)
http://www.cruisersforum.com/gallery...r&imageuser=79
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Old 21-03-2009, 10:30   #89
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Comments on the information in the attached link and its approach?

West Marine: West Advisor

Thanks,
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Old 21-03-2009, 11:30   #90
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Comments on the information in the attached link and its approach?

West Marine: West Advisor

Thanks,
Extemp.
A quick read gives me a positive feeling about it.

cheers,
Nick.
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