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Old 07-07-2019, 23:36   #1
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Lightning Protection, pros and cons

After possibly being struck or at least very nearby by lightning a couple weeks ago, I read up a fair bit on the subject of lightning protection/mitigation. Some use it, some thinks it attracts more. Some throw jumper cables off the shrouds into the water to prevent leaders from forming...... Is there any consensus at all regarding strategies to prevent strikes?
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Old 07-07-2019, 23:47   #2
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Re: Lightning Protection, pros and cons

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Some throw jumper cables off the shrouds into the water to prevent leaders from forming.
I've never heard of any consensus.

But I do have two sets of cable plus copper pipe that I can attach to shrouds and drop into the drink.

Not in the hope of preventing a leader from forming, but in the hope that it might persuade electrons to travel along the cable and pipe to or from the drink instead of burning holes through the GRP.
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Old 08-07-2019, 00:08   #3
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Re: Lightning Protection, pros and cons

The science behind marine lightning protection is reasonably clear cut.

Correctly installed protection will decrease the damage associated with a strike. This is especially true of the most severe strikes which can cause catastrophic damage by, for example, blowing out seacocks and sinking the boat. On the other hand, minor damage, especially to electronics is likely to be only slightly reduced.

It is commonly feared that lightning protection will attract a strike. This is not the case. By dissipating the static charge at the mast head the evidence is that the risk of a strike is very slightly reduced, but the effect is minor.

Overall marine lightening protection is designed to mitigate damage and not to reduce the chance of being hit.
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Old 08-07-2019, 00:34   #4
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Re: Lightning Protection, pros and cons

So the idea above of some cables clipped to shrouds and dragged in the water during lightning storms is sound policy to mitigate catastrophic blowout damage?
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Old 08-07-2019, 00:49   #5
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Re: Lightning Protection, pros and cons

Anyone know what would happen to a carbon mast if hit. Looking at yesterdays strike in Boston, this stuff scares the crap out of me. Would love to see what solutions there are.

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Old 08-07-2019, 01:30   #6
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Re: Lightning Protection, pros and cons

Best practice is heavy duty wire from the masthead with a reasonably direct path to a large underwater metal structure. The keel can be suitable in some boats and others require a plate similar to a SSB grounding plate.

The idea of battery cables, or chain, clipped to the shrouds or the base of the mast and dangled in the water is a common, low cost, and easy solution used by many cruisers. It is difficult to gauge the effectiveness. It certainly never does any harm, but often it is not a very direct path (lightening likes to travel in straight lines) and the idea is not always well implemented with high resistance at the connection points.
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Old 08-07-2019, 01:53   #7
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Re: Lightning Protection, pros and cons

So an ssb plate is good? I have one, and a keel cooler, both grounded/bonded well. I was worried that that's exactly what would blow out in a strike, hence the cables in the water...
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Old 08-07-2019, 02:18   #8
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Re: Lightning Protection, pros and cons

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Anyone know what would happen to a carbon mast if hit.
Carbon masts do not fare well. The combination of higher resistance and lower heat tolerance means they are easily destroyed, often in a spectacular fashion.

However, while many lightning strikes are relatively mild damaging mainly electronics, severe strikes can do enormous damage such as melting the area around chainplates in fibreglass boats (so the mast falls down anyway), or worse still blow holes at the underwater exit point (often a seacock). The resultant hole may be large enough to sink the boat very quickly, before any practical steps can be taken by the crew.

The risk of a sailboat boat being hit by lightning is around 0.5-1% per year. So the risk is not high, but it cannot be ignored completely. Fortunately, severe strikes are less common, but they are one of the few risks that can rapidly sink a seaworthy, well maintained vessel, with a competent crew that have not made any fundamental mistakes.
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Old 08-07-2019, 04:58   #9
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Re: Lightning Protection, pros and cons

0.5% to 1% seems high. Can you put up a link to this information?

I find it hard to believe that 1 out of every 200 boats gets hit by lightning every year.

If this were true, I'd imagine cruisers would be at significantly higher risk, than those at marinas. Being the only boat in an area, must increase the risk. Whereas those at marinas, especially the smaller boats, have the benefit of being within the cone of protection, of the larger boats.

We were hit, off bermuda, in 2006.
Minor electrical damage. Non-grounded mast.

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Old 08-07-2019, 05:04   #10
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Re: Lightning Protection, pros and cons

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0.5% to 1% seems high. Can you put up a link to this information?

I find it hard to believe that 1 out of every 200 boats gets hit by lightning every year.

If this were true, I'd imagine cruisers would be at significantly higher risk, than those at marinas. Being the only boat in an area, must increase the risk. Whereas those at marinas, especially the smaller boats, have the benefit of being within the cone of protection, of the larger boats.

We were hit, off bermuda, in 2006.
Minor electrical damage. Non-grounded mast.

Cheers.
Paul.

This report shows a different number.

Striking Lightning Facts - Seaworthy Magazine - BoatUS
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Old 08-07-2019, 05:47   #11
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Re: Lightning Protection, pros and cons

Because lightning is a static electrical charge, the composition of the mast and its grounding make little difference to whether or not a strike occurs. The fact of masts being the tallest sharpest items around make them objects of charge concentration, and likely to be hit, given the immediate options for dissapating a charge.

When the charge does go to ground the conductive property of the route to ground makes a lot of difference. Hitting a tree, for example, results in conduction through wood, with lots of resistance, ergo heat, ergo steam, and flying wood/bark. If another more conductive route is available, such as you standing under the tree (you're a saline conductive capsule) the route may veer to incorporate you.

Transfer that understanding to your boat. You can't do much about your boat's mast, but you can supply good routes to the ground that don't involve you, your electronics, or blasting fiberglass. Don't think "wire," because you are dealing with a huge current, well beyond anything we think of as electrical conduction. Think grounding stays, mast, prop shaft, through hulls, rudder shaft, etc. with the biggest conductors available.
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Old 08-07-2019, 05:58   #12
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Re: Lightning Protection, pros and cons

Lightning does respect conductors all that much. Remember that it just hopped across a thousand feet or more of air which is generally considered pretty nonconductive. Concepts that make sense for 12 or 240 volts break down when the voltage is in the billion range. My boat has a grounding system as well as a lightning rod at the masthead, but I don't count on it to do much. The overpriced brush style dissipators are worthless. NASA says a rod with a 3/16" rounded tip is most effective and they have a bunch of really smart people protecting a lot of really expensive really tall toys in a really high risk area.
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Old 08-07-2019, 06:13   #13
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Re: Lightning Protection, pros and cons

We were hit by lightning on a previous vessel.
We had boats near us with taller masts.
We had earth (electric start outboard) in the water

Damage was everything electric over $20 toast
Everything else good

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Old 08-07-2019, 06:24   #14
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Re: Lightning Protection, pros and cons

Considering an aluminium mast is just standing there on a Fibreglass boat and is not connected to ground or earthed out in any way,
Why would it attract a lightning strike, ???????????
On anchor with a chain out, Yes then your earthed out,
Very small gap between your anchor chain and the front Guy wire for your mast,

Would it not be the same as an aircraft getting hit by lightning,
Its a large aluminium structure flying through the air and not earthed or grounded out,
They seem to be uneffected by lightning strikes,
Their electronics and wiring dont short out or melt when hit by lightning,

Its a totally different story if your mast is connected to the water in some way, Welding wires over the side into the water attached to the mast,
Then the mast is and will be grounded out,
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Old 08-07-2019, 06:43   #15
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Re: Lightning Protection, pros and cons

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.....
Would it not be the same as an aircraft getting hit by lightning,
Its a large aluminium structure flying through the air and not earthed or grounded out,
They seem to be uneffected by lightning strikes,
Their electronics and wiring dont short out or melt when hit by lightning,
..........
Ahh, no... Aircraft are very affected by lightning. Bits and pieces of the fuselage go missing after been struck and a full inspection has to be carried out - it was part of my previous occupation to do such inspections. It is true their electronics are rarely affected but this is due to the design and installation methods that are employed.

Normally a definite entry and exit point can be identified!
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