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Old 10-11-2009, 05:08   #1
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Junk Rig and Lightning Strikes

I am looking at a junk rigged boat design and I've never owned one before - all my sailing has been Bermuda rigs: Making the vessel stayed is not really an option.

I currently live in South East Asia and we have a very significant thunderstorm problem - both frequent and extremely violent: In Cambodia (my base), there are several hundred deaths every year from lightning strikes (including one death in the city near my house, a man sitting under his metal-roofed veranda). So we have good reason to respect thunderstorms.

On a stayed mast, it is possible to bolt chain to the beam stays and take any strike over the side into the water. Nav electronics might get fried but at least, the charge is unlikely to travel down the mast cables and out through the hull via the depth gauge (which has happened, blowing a sizable hole in the hull and sinking the unmanned anchored boat).

But an un-stayed junk rig mast is stepped into the keel, with any nav-light cables and masthead electronics fed out at deck or below deck levels.

So my question is how do you earth a un-stayed mast. For me it's a real issue ... be it at anchor or underway, a 30' metal mast poking sky-ways in an otherwise flat sea presents a when not if likelihood of getting hit.

Rhoel
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Old 10-11-2009, 06:29   #2
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Bond the Mast to an immersed Grounding Electrode (Strip, Plate, or Keel) with #4 AWG (or larger) Cable.

See ABYC E-4, Lightning Protection (ABYC Standards may be available at your local BoatU.S. store), and see:

http://www.marinelightning.com/EXCHANGEOct2007Final.pdf

Lightning Protection - ABYC Recommendations
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Old 10-11-2009, 07:35   #3
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Quote:
Originally Posted by GordMay View Post
Bond the Mast to an immersed Grounding Electrode (Strip, Plate, or Keel) with #4 AWG (or larger) Cable.

See ABYC E-4, Lightning Protection (ABYC Standards may be available at your local BoatU.S. store), and see:

http://www.marinelightning.com/EXCHANGEOct2007Final.pdf

Lightning Protection - ABYC Recommendations
Many thanks for your fast and informative response - I'll read up on the ABYC guidance - not sure I have a Boat US store anywhere near us but the online information will be an ideal starting point.

Rhoel
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