Lightning Protection and Corrosion Protection
Lightning is one of nature’s most awe inspiring wonderful sights. I am forever in awe and can recall some spectacular shows, such places like the Caribbean and the Mona Passage spring to mind. Florida is probably the capital of the world for this so if sailing down to Key West your risks will be higher.
On an average year Florida experiences greater then ten deaths and more than thirty injuries. What is also important to note is that some 50% of those deaths and injuries happen to people doing recreational activities, and of that some 40% are water-related, which includes boating, sailing, fishing, swimming etc. On a recent summer offshore passage I was unfortunately hit by a rather unpleasant weather front, accompanied by a great deal of activity all around, and it had me looking at the whole subject again.
This has long been a problem for mariners. As far back as the early 1800's on old sailing ships, the boat builders were installing protection systems to minimise the catastrophic effects of strikes. These methods were essentially based upon the grounding of spars and rigging. More than one vessel lost mizzens and masts along with subsequent electromagnetic pulse related compass problems as a result. Protection systems were also evolved as a response to dissipation of strike energy. In the early 21st century, nearly 200 years on, the same measures are still valid, even though the subject seems frequently awash in controversy.
It is a simple fact that virtually all marine classification societies and national marine authorities lay down recommendations for protection of vessels from strikes (one good example is The National Fire Protection Association) but relative few yachts owners adhere to the them. This causes along with death and injury an enormous amount of damage in shore installations, in particular in the telecommunications and electrical power distribution industries.
More than a 1000 people are killed worldwide annually by strikes. In the USA transient damage exceeds 1 billion dollars. For these simple economic cost considerations many measures are taken to design systems that minimize the effects of strikes. The main effects are high energy, high voltage transients that result in flashovers and damage. They can be either resulting from direct strikes or induction into power or signal cables, or induced, either through capacitive or inductive coupling. Lightning Protection Part 1 All about boat and yacht lightning protection, what causes it and the effects. Protection Part 2 All about boat and yacht lightning protection systems and grounding. Protection Part 3 All about boat and yacht lightning protection system grounding, bonding, surges and protection devices. Protection Part 4 All about boat and yacht lightning safety for you and your crew.
WHAT CAUSES LIGHTNING? THE PHYSICS
A quick refresher course is in order. Within the cloud formation, strong updrafts and downdrafts generate high electrical charges. When the voltage reaches a sufficiently high level both cloud to cloud and ground discharges occur. Strikes occur when the ground is at positive polarity and the cloud negative region attempts to equalise with ground. Alternatively strikes can occur when the positively charged cloud top equalises with the negative ground, or when the positive charged ground equalises with the negative charge cloud or the negatively charged ground equalises with the positive charged cloud top.
A strike consists of a number of components which form a multidirectional flow of charges. Peak currents can exceed 200,000 amperes (200kA) at over 30,000°C for a matter of milliseconds (25-100 mS). The positively charged ions rise to the cloud top, and the negative ions migrate to the cloud base. Regions of positive charged ions also form at the cloud base. Eventually the cloud charge levels have sufficient potential difference between ground or another cloud to discharge.
WHAT IS A PROTECTION SYSTEM?
There is some confusion as what protection can be installed. This can never be an achieved using a single method, and a number of measures should be used to minimize the risks and best security involves a holistic and overall systems approach. The main objectives of any protection systems are as follows, and while not being ever a 100% given the power of lightning adoption of measures at least will minimise the effects:
1. The capture of the strike at a nominated point, i.e. the mast head.
2. The conduction of the strike current to ground safely using a well installed down conductor that reduces side flashes.
3. The dissipation of the strike energy to ground, through a low impedance ground system so that rises in ground potential are minimized
4. The equipotential ground bonding of all relevant systems and components
5. The protection of power supplies from high voltage transients and surges that may damage equipment
6. The protection of conductors both power and signal from induced surges that may damage equipment
Boat corrosion is a very controversial subject, whether it's galvanic or electrolytic corrosion, there are many who suffer it.
Corrosion can be reduced and eliminated, and the first step is to understand the basics so that protective measures can be implemented
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