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Old 18-03-2009, 00:14   #61
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Chala: nice piece of kit, first time I see one! And I think I see a PSS dripless seal behind it and a dry bilge! ;-) We don't need that grounding thingy as we have a thrust-bearing with stationary part that provides a electric connection to the shaft.

Shack: Jedi's are always correct, they are noble knights, although I start to doubt that when I look at our ships cat Obi... ;-) I'm happy that a pilot joins this thread because I did know and notice the static dissipaters on planes but was not familiar enough with them to discuss it.

ciao!
Nick.
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Old 18-03-2009, 04:05   #62
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Quote:
Originally Posted by Shack View Post
The Jedi is correct. Dissipaters 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 dissipaters...
If you could sail your boat as fast as you fly your aircraft, the static wick would be similarly useful. Assuming you cannot, it’s not. Aircraft generate a frictional static charge* , which sailboats don’t.

* Lightning forms (in part) because of an accumulation of electrical charges inside a cloud (electrification) due to friction from rising & falling dust, ice, and water droplets (graupel) etc.

Excerpted from an earlier discussion on Lightning Protection at:
lightning strike prevention/protection against?

A “static wick” sheds (dissipates) static charges accumulated because of the aircraft’s high speed (not usually an issue /w sailboats – well perhaps some catamarans and Jeddi).

A static wick is a piece of metal connected electrically to the frame of the aircraft, usually with one or two spikes or needles on the end. It is housed in a fibreglass rod to insulate it from the airplane.

Because the spikes concentrate the electric charge around them, and they are connected to the airframe, they allow the airplane to dissipate any static charge it may build up* out into the air.

* Aircraft can pick up a static charge by flying through charged air. When they return to the ground, they can hold the charge for a considerable time, sitting on their rubber tires. A real danger exists if the charge sparks when refuelling.

Ie: 737
There are static dischargers (either wicks or rods) at the tips of the wings, stabiliser and fin. They encourage the static build-up on the airframe to bleed off which would otherwise accumulate and cause radio interference, particularly of ADF & HF.
Note that they are not for lightning protection.
Goto:
Static Discharge Wicks
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Old 18-03-2009, 05:19   #63
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If you could sail your boat as fast as you fly your aircraft, the static wick would be similarly useful.
Hey Gord, Jedi can! Those damn Dashew designs are FAST!
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Old 18-03-2009, 06:33   #64
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... A “static wick” sheds (dissipates) static charges accumulated because of the aircraft’s high speed (not usually an issue /w sailboats – well perhaps some catamarans and Jedi)...
So noted.
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Old 18-03-2009, 06:35   #65
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Quote:
Originally Posted by GordMay View Post
<snip>
A static wick is a piece of metal connected electrically to the frame of the aircraft, usually with one or two spikes or needles on the end. It is housed in a fibreglass rod to insulate it from the airplane.

Because the spikes concentrate the electric charge around them, and they are connected to the airframe, they allow the airplane to dissipate any static charge it may build up* out into the air.

* Aircraft can pick up a static charge by flying through charged air. When they return to the ground, they can hold the charge for a considerable time, sitting on their rubber tires. A real danger exists if the charge sparks when refuelling.
<snip>
Note that they are not for lightning protection.
Goto:
Static Discharge Wicks
Gord has beaten me to it . Do not confuse aircraft equipment with boat equipment, it may seem the same but it ain't.

Just to correct one minor point, the resistance from the bonding point of an aircraft staic wick to the discharge end is usually around 50 to 200 kilohms. (the bonding end to the airframe must be less 10 milliohms). If the resistance of the static wick is too low, the charge build up just arcs off the end of the wick giving the same problem as no static wick and if the resistance is too high, the charge arcs off the airframe itself.

To repeat in part what I previously posted the thread mentioned by Gord: "static wicks are solely provided to bleed off static build up on the airframe (especially precipitation static). If they weren't fitted, the charge on the airframe would build up until the charge is large enough to arc off to the surrrounding air (just like a mini lighting arc). .......Pull the static wicks off, fly through some wet cloud and the whole airframe becomes a mini platform of mini arcs and St Elmo's fire!"
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Old 18-03-2009, 10:40   #66
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See, now we get somewhere: static dissipaters do work, it's proven and planes don't (are not allowed to) fly without them: they effectively dissipate a static charge.

For planes: yes they build up the charge by going fast through air molecules or even wet cloud. But the static dissipaters do not need that airspeed to work, they work regardless of speed.

Many if not most of the readers in this thread don't believe the static dissipater can dissipate a static charge, so this is progress. Next thing to show to be true is the "opposite surface charge" that travels with storm-clouds and is responsible for forming leaders from the ground up. Anyone?

cheers,
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Old 18-03-2009, 14:32   #67
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Another thing we all agree on is that Jedi's boat is fast...
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Old 18-03-2009, 17:09   #68
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Hey, Jedi is the boat ;-) But really, all modern yachts with 64 foot waterlines are fast (12 kts hull speed); it's just that most have overhangs and are thus much longer than we are. The planing, retractable bowsprit and mizzen spinnakers are secret weapons but only work downwind.... and we mostly go the other way!

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Old 18-03-2009, 17:19   #69
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Quote:
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Chris
According to what I understood from that "grounding" article, you should not have your engine connected to the shaft.....
Now I'm confused. what would act as the boat ground?
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Old 18-03-2009, 19:02   #70
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Nick
"We don't need that grounding thingy as we have a thrust-bearing with stationary part that provides a electric connection to the shaft." 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.
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Old 18-03-2009, 19:31   #71
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Thumbs up We have a violent agreement!!

Excellent. We all at least can agree that the theory of dissipation of a static charge can be achieve by little wirey thingies. Whether the potential is casued from rapid air friction against the surface of an aircraft or from the slower air movement and resultant friction over massive square miles of earth surface is a moot point. A static build up of potentail remains as a build up of electical potential.

Now an analogy that a dumb pilot can understand. Compressed air also a form of store potential energy. The energy can be relieved through catastophic failure or through a slow leak. I like to think of dissipators like little relief valves in a compressed fluid system (hydraulic or pneumatic). They work, but only up to specified limits and their benefits can be exceeded with enough differenetial ...... we'll call it ... differntial "energy."

I feel like we should be sitting around a library with long white hair, wearing sweaters, and smoking pipes.

(If I had a hydraulic rupture because it exceeded the mechanical limits of the relief valve, I would be hard pressed to argue that relief valves are useless.) (Now I have to wait for some nut to tell me that hyd pumps don't fail by overpressure - do we have any airframers out there?)
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Old 18-03-2009, 20:25   #72
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Has the conductivity of the metal contained in some hoses been considered in bonding or lightning strikes? Jesse
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Old 18-03-2009, 22:06   #73
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So here's a wrench in the works...What about a deck stepped mast? If it's suggested taking a #6 wire or so straight down from the mast...how would that work? It would have to be concealed by making some turns and twists before arriving at the ground plate. Could you use a shroud and run a wire from it to the ground plane??? Inquiring minds want to know.
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Old 18-03-2009, 22:45   #74
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Whoa, not so fast

Quote:
Originally Posted by s/v Jedi View Post
See, now we get somewhere: static dissipaters do work, it's proven and planes don't (are not allowed to) fly without them: they effectively dissipate a static charge.

For planes: yes they build up the charge by going fast through air molecules or even wet cloud. But the static dissipaters do not need that airspeed to work, they work regardless of speed.
Sorry but this is not true. The aircraft static wick is not analogus to the brush thing on the mast head. Re-read my post regarding the resistance / conductivity of static wicks. The aircraft static wick doesn't EFFECTIVELY disspate the charge build up, it ALLOWS for the charge build up to be discharged in a SAFE way that prevents arcing. It can only do this because of its design and placement on the airframe. If this isn't the case, aircraft would simply have a SS brush thing hanging off its tail .


Quote:
Originally Posted by s/v Jedi View Post
Many if not most of the readers in this thread don't believe the static dissipater can dissipate a static charge, so this is progress. Next thing to show to be true is the "opposite surface charge" that travels with storm-clouds and is responsible for forming leaders from the ground up. Anyone?

cheers,
Nick.
I agree there has to be a opposite surface charge otherwise there would be no electrical potential differance (PD) for a discharge (lightning) to occur; however how and why it forms, I have no idea. As to the leaders, well this is getting into the realm of what really is current flow and how does ionization of a gas occur - again I bow out.

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Excellent. We all at least can agree that the theory of dissipation of a static charge can be achieve by little wirey thingies. Whether the potential is casued from rapid air friction against the surface of an aircraft or from the slower air movement and resultant friction over massive square miles of earth surface is a moot point. A static build up of potentail remains as a build up of electical potential.

<snip>
Again can't agree for reasons above. As for a metal brush sittting on a well grounded (to the seawater) mast, each tip of the brush will be at the potential charge as the surface of the water. Why would the pointy tip of each bit of wire dissipate a surface charge any better than the surface of the mast and rigging etc.

If the brush thingy was constructed in the same manner as a static wick, I MIGHT be willing to believe it or at least try it but we are talking of dissipating huge amounts of charge compared to the surface charge build up of an aircraft.

My 2 cents worth.
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Old 19-03-2009, 01:22   #75
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Sorry but this is not true. The aircraft static wick is not analogus to the brush thing on the mast head. Re-read my post regarding the resistance / conductivity of static wicks. The aircraft static wick doesn't EFFECTIVELY disspate the charge build up, it ALLOWS for the charge build up to be discharged in a SAFE way that prevents arcing.
According to Wikipedia, the version you describe is for small aircraft, while the bigger ones have just the pointy electrode. In short:

During adverse charging conditions (air friction), they limit the potential static buildup on the aircraft and control interference generated by static charge.

So... it does discharge at a level that can't yet ionize the air. If it would ionize, it would arc.

Quote:
It can only do this because of its design and placement on the airframe. If this isn't the case, aircraft would simply have a SS brush thing hanging off its tail .
I'm not saying it's the same thing, obviously, speed dictates other design considerations, but the speed of the aircraft isn't what makes the device work, the speed of the aircraft is what generates the static charge.
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. The field around a sharp point is much higher than around other objects.

Quote:
As for a metal brush sittting on a well grounded (to the seawater) mast, each tip of the brush will be at the potential charge as the surface of the water. Why would the pointy tip of each bit of wire dissipate a surface charge any better than the surface of the mast and rigging etc.
It was in fact Benjamin Franklin who noted the phenomena first:

Quote:
Franklin's electrical experiments led to his invention of the lightning rod. He noted that conductors with a sharp rather than a smooth point were capable of discharging silently, and at a far greater distance
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! ;-)

Quote:
If the brush thingy was constructed in the same manner as a static wick, I MIGHT be willing to believe it or at least try it but we are talking of dissipating huge amounts of charge compared to the surface charge build up of an aircraft.
It is using the same principles of operation but indeed the question is if it's discharge is enough camouflage so that the leader is formed from another object before it's formed off our boat. That mostly depends on availability of other objects.

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

This is about as far as we can go with the brush debate. The ground-charge under storm-clouds exists and a dissipater will dissipate a bit, hopefully giving another object the chance to win this nasty game. The question remains how much difference that brush makes on the massive scale of lightning strikes. 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.

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.
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