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**Boracay** · 05-12-2006, 21:20

So this means my steel boat is perfectly safe?

**Alan Wheeler** · 05-12-2006, 21:39

From everything bar rust!

NoTies · 07-12-2006, 20:40

I had a suggestion from a Ham operator that the mast should not be directly grounded but a heavy gauge conductor should be placed about 1/2" away from the mast then attached to the keel. Idea was to provide a spark gap to absorb a lot of the energy.
Anyone heard of this?

**Alan Wheeler** · 07-12-2006, 22:00

No a spark gap will not absorb any energy. The Electron pressure increases till a point where it will cross a gap and then hopefully disipate to Earth, thus lowering the electron pressure till it can no longer jump the gap. However, the ionised air in that gap also crates a path the a much lower Elctron pressure can continue to flow, and thus a current can remain flowing when the pressure has dropped to well below what was originaly required to jump the gap in the first place. Eventually the current stops flowing across the gap. But no, the gap will not "use" energy apart from the small amount of energy being dissappated ionising the air and heating it. Although in reality it is a lot of energy being expended to heat and ionise, in the bigger scheme of things, the lightening dicharge is so imense, that spark is taking rather a minute amount of energy form it. If I say this in another way that may make more sense. The lightnign bolt has just traveled maybe ten miles or more through open air. A half inch gap is not really much to it eh.

44'cruisingcat · 07-12-2006, 22:29

The gap would probably make matters worse - the arcing would cause extremely high temperatures and most likely blow a hole in the mast.

yotphix · 07-12-2006, 22:57

Chris,
Being in a steel boat does not strictly mean that you are safe. You can still be hit and it can still fry your electronics. I was on a steel square rigger that was hit and it blew half the wood yardarm off and fried the LoranC (yep, it was that long ago!)

**GordMay** · 08-12-2006, 00:43

Spark Gap (surge or transient protectors) are most often utilized in an attempt to provide an AC, RF, and/or Lightning ground connection; whilst maintaining Galvanic (DC) Isolation (to prevent electrolytic corrosion of immersed metals) in bonding conductors. Often the Spark Gap is bridged with ceramic capacitors.

Many “home-made” Spark Gap devices are probably ineffective, and potentially dangerous.
The main downconductor (mast to water) is probably the last place I would install a spark gap.

Metal boats are frequently struck (by lightning), but the high conductivity of the large quantities of metal, with hundreds of square feet of hull in direct contact with the water, causes rapid dissipation of the electrical charge. - so significant damage or personal injury are relatively rare.

44'cruisingcat · 08-12-2006, 13:43

Gord, my metal boat doesn't have hundreds of square feet of hull in direct contact with the water - or at least I sure hope it doesn't! I spent hundreds of dollars and nearly as many hours sandblasting and epoxying it to make sure it wasn't!

Which raises a question - would a lightning strike on a steel boat be likely to damage the paint below the waterline?

**Alan Wheeler** · 08-12-2006, 14:13

Yes it would damage it. Once again, the few microns of paint are nothing to a voltage pressure that just jumped many miles through "non-conducting" air. The paint can literally be blown off the hull. Especially for any layers that may have moisture under them. The moisture will boil instantly.
However, if that is all that happens, you got off lightly.