Author Topic: Lightning Issues  (Read 1708 times)

Soggy Paws

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Lightning Issues
« on: August 01, 2009, 12:05:03 am »
All,

Here is a bit of interesting info on lightning, its cause, prevention and cure from a discussion on an SSCA forum at this link:
http://ssca.org/phpBB3/viewtopic.php?f=14&t=8016 .

"Actually, lightning is very well understood in the scientific community. How it forms and how it reacts is also understood. The University of Illinois and others have many detailed scientific papers available on the subject. Exactly where and when lightning will strike is a variable as it is part of Mother Nature and there is a reason she is called "Mother Nature" and not "Father Nature."
As to lightning and boats, the issue comes in two parts - 1. Prior to the strike; and 2. During the strike.

Part 1. concerns how to reduce the probabilities of a lightning strike. Lightning is a two part event. The ionized "leader" sweeps an area below the generating cloud and an opposite "leader" sweeps back and forth up from the surface of the earth. When they connect a pathway is opened and the energy is discharged. To a boat the ground/earth "leader" is of most interest. As this "leader" oscillates around it reaches up "x" distance into the atmosphere. Whenever this leader encounters a vertical object like a tree, house, telephone/power pole, or the mast of a boat it can reach further up into the atmosphere and has a better chance of making a "connection." [same thing as tall men in a bar full of good looking women].
So reducing the "electrical" apparent height of your boat is good. This can be done with static dissipators such as the Forespar Lightning Master. (Which is a copy of the static wick principle used on airplanes and airliners). The sharp small "spikes" of the device "bleeds" off ions as they build up and electrically reduces your mast height to equal that of the ocean. However, to do this it must have a "significant" and good ground to the ocean. That translates to 4 square feet of flat plate copper in contact with the ocean and 2/0 welding cable between the mast and the plates submerged in the ocean. A static dissipator will not dissipate if it is not connected with the ocean.

So the result of part 1. is to electrically make your boat height equal to the ocean. If you are anchored close to shore or in the close vicinity of other "unprotected" masts/boats your probability of being hit is significantly lower than theirs. If you are out in the middle of no-where/ocean by yourself you are now "even-steven" with the ocean as to getting a hit.

Part 2. is what can you do to prevent/minimize damage to the boat and its contents during a strike. Again, the 4 sq ft. of copper joined with significant sized welding cable to the mast(s) will provide a highly desirable pathway for the lightning's energy to get directly to its only objective - earth ground. If the mast(s) are not sufficiently well-grounded then the lightning energy will try to find an alternate path to the ocean. If the mast is not available to the lightning, then it will travel down the shrouds/stays to the bonding system and set up a "field" inside the boat that will "fry" most electronics and has been known to heat metal thru-hulls sufficiently enough to melt them out of the hull and you are left with 1.5" holes for the ocean to enter. Lack of any grounding to the ocean and you can end up with holes blown through the hull.

Side note: while your boat is floating in the water it is grounded. When you boat is "on the hard" (out of the water) it is not grounded and any lightning strike to your boat or to a neighbors boat will fry your electronics or other fine metal objects or more serious damage. It is advisable if you are going to leave your boat on the hard, in an area with probable lightning, to drive a copper or steel grounding stake into the ground beneath your boat and hook up a significant sized wire from it to your masts or boat grounding system.

There are many other esoteric factors available to folks wanting to get the "whole story" such as positive versus negative forms of lightning, high frequency vs low frequency lightning, etc. but for the boater I think the primary interest is minimizing damage to the boat, contents, and not curling the crew's hair. This is done by dealing with the before and during aspects of protecting/guarding your boat from the energy in lightning.

Exactly where and when a strike will occurs is not determinable - the same as the actual path of a hurricane or tropical storm is not totally predicable as there are too many variables in nature for even the powerful human built computer to input and resolve. So you can only do what you think is cost-effective to "lower the odds" that you will
CSY 44 Walkthru #35, Soggy Paws
Soggy Paws the CSY has been SOLD
http://svsoggypaws.com/CSY/For_Sale.htm

Warren Daniels

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Lightning Issues
« Reply #1 on: August 01, 2009, 06:33:21 pm »
Dave,
Excellent information!!

Soggy Paws

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Lightning Issues
« Reply #2 on: August 02, 2009, 11:10:41 am »
Warren,

The idea for the copper bar lightning ground came from the ABYC rules for boat lightning protection.
CSY 44 Walkthru #35, Soggy Paws
Soggy Paws the CSY has been SOLD
http://svsoggypaws.com/CSY/For_Sale.htm

Soggy Paws

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Lightning Issues
« Reply #3 on: August 05, 2009, 09:00:56 pm »
Warren,

The copper lightning bar pics are up at this link for anyone interested:

http://svsoggypaws.com/hull.htm
 
We currently have the bar off while the hull is stripped down to bare fiberglass and drying out. After we have added multiple layers of epoxy barrier coat and antifoul, I will take a couple of better pics and add them to the article.

Re your Dynaplate, it provides a very effective connection to sea water for your HF radio ground plane.
CSY 44 Walkthru #35, Soggy Paws
Soggy Paws the CSY has been SOLD
http://svsoggypaws.com/CSY/For_Sale.htm