Here we go again
- The dissipators do not prevent lightning strikes: true and proven beyond doubt.
- The dissipator is a bad lightning rod: not just true because you should never use a dissipator in the role of a lighting rod. For sailboats, the mast itself works as a lightning rod.
- The dissipator does not dissipate: not true but like everything, they must be installed correctly (which is bonded to ground)
Below is Wotname's post and he accurately describes how the static wick works on an aircraft. A correctly installed dissipator works in the exact same way. Boats build up the static charge due to both the wind
molecules and weather
systems just like on airplanes. This means you also get uncontrolled arcs if left unaided: we call this St Elmo's fire dancing in the rigging and it has done so for ages, here is a nice drawing from Wikipedia:
So the use of the dissipator is to dissipate the static charge. This will not prevent a lightning strike but it may prevent or at least delay a leader forming (before the lightning strike, a leader forms as a possible path for the strike) which may land the strike elsewhere. This is key: the strike still occurs but may hit something else. The dissipator acts like a camouflage.
Before investing in a dissipator, one should invest in a bonding system that has a bronze plate under the hull right next to the mast, with a big cable connecting it to the mast. This cable should be short and straight, no bends because lightning wants to go straight and will blow holes in fiberglass
if left unaided. Also, all the chainplates should be connected to the bronze plate. I have a ketch
and was hit in the mizzen with the main mast untouched. It means a ketch
needs two bronze plates.
Last but not least, the dissipator only works when it too is bonded to the plate. You can use the aluminium mast as conductor but a wooden mast needs a cable or stay for this.
Another important thing is the SSB antenna
. If you use an isolated backstay then you must have a jumper or switch to ground it and disconnect it from the tuner. I have seen lightning hits on the insulated backstay so this is not theoretical.
Originally Posted by Wotname
Always good to see an old thread resurrected
I'm pretty sure but can't prove that these dissipators don't dissipate any static electric field.
I do know they are no way similar aircraft static wicks and any argument that they work in a similar fashion is false.
Let me explain why aircraft are fitted with static wicks and how they work and you will be able to see why the argument is erroneous.
The aircraft skin builds up a static electric field during flight, especially when travelling though moist air. This charge migrates to the pointy parts
of the trailing edges and will build up to tens and tens of thousands of volts. Left unaided, it will finally arc off in big sparks. Just like a small lightning flash really. The corresponding RF noise
emitted during the discharge can be strong enough to shut down legacy nav aids (ADF) and VHF
coms (remembering the coms are AM, not FM). Also causes errosion of the aircraft skin - not good.
The static wick is well bonded to the aircraft skin at one end and the other end has a couple of fine sharp metal points. In between is a high resistance path, some hundreds of thousands of ohms.
The static field still builds up and still arcs off but now it arcs off at the ends of the sharp points. The sharp point also allows the voltage to arc off at a longer valve than just the aircraft skin however it is still many thousands of volts. The real difference is the high resistance path the discharge occurs though. This limits the discharge current dramatically and thus limits the amount of RF interference as the size of the RF interference is proportional to the current flow. The actual circuit is high volts
on skin, high value resistance in the static wick and low resistance of ionized air (ie spark path).
This in no way resembles what one is trying to do on a boat with a dissipator