Lightning protection

What are the latest ideas and products to deal with lightning on large sailboats?

 

Try these sites and keep on searching:

http://www.thomson.ece.ufl.edu/lightning/
http://www.boatsafe.com/nauticalknowhow/lightning.htm
http://www.marinelightning.com/science.htm
http://www.yachtgard.com/surge.html
http://www.building.org/profiles/93640.html

 

Depends on the materials used in the vessels constructionm metal boats can get by with a spike atop the main mast, composite,wooden and ferro vessels should have an earth plate anode, or exposed keel bolt connected to a low resistance large conductor that is in turn connected to the mast. Correct Installation is critical.
On non conducting hulls even when fitted with a lightening conduction system, the massive current transient can cause an EMP effect in other wiring that often takes out all the existing electronics. This should be considered in the design and routing of the conductors. Metal hulls act as a faraday cage.

 

You are familar with the "cone of protection" idea? That thought is that the shrouds and the metal mast make a zone where the lightning will probably stay on them and there will be less chance of high current in us. There will always be a giant EM voltage field radiated, so transistors are vulnerable, although less so if they are in a faraday shield, and even then, who knows. The electrons are repulsive to them selves (sound familar?) and so are constantly changing their path, so you can't say "never".

The sail club in NM had a Dr Partridge, who told me his job at Los Alamos was to keep the A- bomb from going off due to lightning. He said if you do a FFT of the charateristic frequency of the lightning pulse it was only at 20K, which is fairly low, so although you can't do anything about a near strike, the impressed voltage surge of a distant strike can be frequency suppressed.

If I had a big boat, I think I would have a straight (plump) path ( large diameter copper pipe?) from the mast base to a large plate below the hull, but I would reserve the keel bolts for other uses than passing juice, if I possibly could.

Dan

 

Its not so much what gets used rather than the fact that it is taken seriously and connected to something that gives a decent discharge path.
Most people seem to trust in luck when it comes to lightening and I have a battle getting people to fit anything, let alone an ideal system.

A lot of people cary a length of chain which they attach to a shroud and dangle in the water when they see lightening . This doesn't work very well at the best of times let alone when a strike on your boat is the first sign !

A lot of people are killed each year worldwide by lightening strikes on boats, and many boats are sunk each year from the same. A couple of years ago several glass yachts without protection sank in a Capetown marina from one strike. Your mast is the highest thing around at sea and the likelihood of a strike is very high in an electrical storm.

 

"Its not so much what gets used rather than the fact that it is taken seriously and connected to something that gives a decent discharge path."

IMO, there are two things going on. One is avoiding a buildup of charge, which is the possible utility of a sharp burr at the top of the mast and the shroud connection for the chain over the side. If there is not a buildup of charge, an initial discharge path may be less likely to establish itself there. On the other hand, that lightning has the force to breakdown 2 or 4 miles of one of the best insulators there is, air, so it really doesn't get that much steerage by a mast sticking up 35 feet. Rubber golf shoes don't help. I have had a 1 cm spark discharge sustained between the metal trim ring joining the top and bottom halves of a fiberglass boat, discharging into the motor while I was motoring out for a race, one inclement day. I thought it was the outboard plug and shut it off and the charge remained.
This "shunt off any initial charge so I look like the rest of the water" strategy also provides a short to earth for any antennae effect of buildup in the mast from nearby strikes, which radiate out a field.

The other strategy is to give a preferential path for the discharge if there is a direct strike. The 1/4" copper wire one sees in barn anti lightning systems does this. If there were a direct strike, no wire gauge will carry it, it will ionize the air, no doubt. The goal is to give an initial path with lower impedance to ionize than our electrolyte-rich liquid bodies.

Dan

 

Yes if the wire vaporises the path remains but thats not a good system when you have subsequent strikes and your ion path has dispersed.

A decent copper strap will survive the hit conduct the main surge and be there to take subsequent strikes afterwards. Lightening conductors on church towers are a good study. Some will take two or three hits in one electrical storm and still look none the worse for wear.

 

I am not suggesting the shroud/chain overboard business is a solution for a strike but rather it is a means of dissapating charge which marginaly may decrease chance of a strike.

Dan