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grounding question

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ronrryan
Admiral

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USA
561 Posts

Initially Posted - 04/27/2003 : 21:58:22

In the course of wiring dockside power into Orion, whilst hanging inverted in the traditional yachting "bat" position, I came across a rather moldy eight-gauge red wire, chopped off and coiled in the nether regions of the after bilge. Following this about, we pass under the picturesque (currently defunct) water tank, and emerge as a ground wire attached to the starboard chainplate. It appears I am ready for the lightning strike that will either seek out the cast iron keel with a large flash and hole in the bottom, or perhaps find another exit. Question: my previous boats have been grounded to an engine and shaft. In the case of an outboard hanging on the transom, where do you make a ground? I will NOT be hauling out for a while, so have no way to attach some sort of exterior ground. I am NOT knowledgeable about lightning, even tho I live in the lightning capital, Florida. Help, you knowledgeable electric folk, ron srsk #2343 Orion SW FL

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ssteakley
Captain

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USA
467 Posts

Response Posted - 04/27/2003 : 22:32:59

Good Luck,
Steve
Ps.
The previous post I have read referred to clamping jumper cables on your shrouds and hanging the free end in the water. All Kinds of ideas out there. The one thing to consider is that Lightening is upredictable...so go figure,
Steve

<img src="http://im1.shutterfly.com/procserv/47b3dc32b3127cce94d57c8cff3b0000001010" border=0> Moon Chaser #385WK <img src="http://www.catalina25-250.org/forum/forum1.gif" border=0>

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 04/28/2003 : 00:33:22

<center>My Catalina 25 has been struck by lightning.</center>

Did that get your attention?<img src=icon_smile.gif border=0 align=middle> It's true. This is the second time one of my sailboats has been hit by a lightning bolt of significant destructive force. On the C-25, the only damage seems to have been a vaporized windvane. When I say 'vaporized', I mean other equipment at the masthead looks like it was spattered with black paint overspray in a pattern radiating from the location of the former windvane.

Here's a description of the lightning grounding system on my C-25:

Tabernacle is thru-bolted at the deck. There's a #4 or heavier marine grade electrical cable from one of the thru-bolts which follows the compression post down to the area of the swing keel pivot. Both ends of the heavy cable have ring terminals which are fully tinned, crimped, and then soldered. The lower terminal goes around one of four 1/2" bronze bolts through the bottom of the boat in the area of the swing keel pivot. Those bolts are interconnected in pairs fore and aft with 3/4"x1-1/2"x18" bronze bars under the boat. The bronze bars are electrically connected athwartships by the keel pivot hardware.

Each bronze bar is protected from corrosion by two 3/4"x1-1/2"x3" sacrificial zinc anodes, one at each end of the bar. The zincs are thu-bolted, and connected to the 1/2" bronze bolts in the bilges with #10 fully tinned wire ending in tinned, crimped, and soldered ring terminals.

-- Leon Sisson -- also in the Lightning Capital State.

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 04/28/2003 : 17:58:23

Leon, just curious... were either of the two boats grounded when they were hit?

Arlyn C-250 W/B #224
<img src="http://www.stewartfam.net/arlyn/rr.jpg" border=0>
N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 04/28/2003 : 18:24:58

Arlyn,<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>... were either of the two boats grounded when they were hit?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>I assume you mean 'grounded' as in lightning protection system.

The Catalina 25 was protected at the time of the strike as described in my post above.

The other boat, a 19' wooden daysailor, had no lightning protection in place at the time of the strike. On that boat, the wooden mast was blasted into pieces, some large, most as small as toothpicks. The chainplate screws were blown out of the boat. It looked like it had been shot at. The metal masthead fitting showed considerable arc burns. That windvane also was nowhere to be found.

-- Leon Sisson

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Dave B
Admiral

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Mali
863 Posts

Response Posted - 04/28/2003 : 22:18:37

Boy, is this a controversial topic! There's some interesting reading at http://www.thomson.ece.ufl.edu/lightning/ and elsewhere. Lightning is somewhat less of a problem in CT than in FL, but a few friends here have had their boats hit.

From what I've read, I've concluded the following. (You should, however, draw your own conclusions).

1. Grounding systems slightly increase the likelihood of a strike, but good ones may reduce the damage when it occurs. A good system uses very heavy conductors that run in the straightest possible line from the base of the mast to a large conductive plate below the waterline on the outside of the hull.

2. A half-baked grounding system can increase the damage when lightening overwhelms it and ends up exiting the hull by blowing holes through it.

3. Stainless steel shrouds are very poor conductors compared to an aluminum mast. Lightning seeks the best, highest capacity path--the shrouds are very low capacity with high resistence, so the lightning will not likely follow them to jumper cables or whatever.

4. A deck-stepped mast leaves a considerable gap between the main conductor (the mast) and the water, with insulators in the form of the deck and the bottom of the boat. This may explain shorter masts being hit in very close proximity to taller ones. It also may explain direct strikes to the water within yards of a sailboat--more likely in salt water, since it is more attractive to lightning. And finally, it could mean more damage within the boat if nothing connects the base of the mast to a substantial ground.

5. No sailboat manufacturers that I know of install lightning protection systems, I suspect because no system is proven to be effective enough to protect the manufacturer from liability if it is deemed that the system itself is responsible for the damage from a strike.

6. Many "strikes" actually don't hit the boat, but damage its electronics and equipment due to the pulse that travels through the water as well as the shock wave in the air. Inboard engines and their connected electrical systems are especially vulnerable to a nearby strike in the water. Fresh water adds to this risk, since it does not conduct the charge to the ground as well as salt water does.

The net: Half-baked systems may be more risky than no system. If you are going to go for it, have it done professionally, or at least designed professionally. I'm not going to say what I did or didn't do, nor try to argue the merits of the decision. I will say that my first defense is to not be caught out in an electical storm--somewhat easier to accomplish here than in Florida.

Dave Bristle, 1985 C-25 #5032 "Passage" SR/FK/Dinette/Honda

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ronrryan
Admiral

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USA
561 Posts

Response Posted - 04/29/2003 : 22:05:35

Many thanks to all who responded. Leon, as usual you set the bar for proper repair at the highest level, as I have come to expect. For now, I guess i will have to hang something over the side as a ground from the shrouds, and when I haul will have to look at the prospect of grounding the mast to a plate or copper tubing/bars. Fair winds, ron-in-Venice

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