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Old 22-02-2011, 06:02   #1
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Thumbs up Lightning Protection for a Cat

I am sailing into Indonesia and concerned about lightning strikes.
Can anyone give me information how to protect the catamaran if a lightning event is likely ? Are there any simple ideas like heavy duty battery cables clipped to mast and dropped into the seawater either side...will this work ??
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Old 22-02-2011, 06:09   #2
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Re: LIGHTNING PROTECTION FOR A CAT

Boat type, mast type, rigging type etc would be useful maybe some pictures.
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Old 22-02-2011, 06:40   #3
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Re: LIGHTNING PROTECTION FOR A CAT

I see a lot of folks using a chain strapped to their stays, dangling in the water, this is really of no use! The contact area between the links is minimal!(galvanizing and contact area) If you are going this way, use a cable, not a chain.
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Old 22-02-2011, 06:47   #4
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Re: LIGHTNING PROTECTION FOR A CAT

Greetings and welcome aboard the CF, Yandanooka-t.
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Old 22-02-2011, 06:51   #5
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Re: LIGHTNING PROTECTION FOR A CAT

Considerations really no different that those for a monohull which has been discussed in great detail on this forum. Below are links to just a few of the previous lightning discussions.


Don't Want to Be BBQed by Lightning

Lightning Protection

Lightning Safety

Question for All You Lightning Rods

Best Lightning Insulator?
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Old 22-02-2011, 07:04   #6
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Re: LIGHTNING PROTECTION FOR A CAT

I was an ABYC member when I put the Lightning Protection system in our tri, and followed their standards.

First I put a pointy "lightning rod" on top of the mast. I chose the expensive "bottle brush" type, but their advantage is not proven. Either type will work...

We have the advantage of having a hull under the base of the mast, with the mini keel's ground plate (2 sq ft min), only 2' below it. An "00" size wire from mast base to the plate below, (with corrosion proof connections), gives me a good STRAIGHT path to ground.

I then tied in all of the rig through the interior end of the chainplate bolts. This is using #6 wire in as direct a path as possible with gentle sweeping bends.

This is mostly to prevent side flashes, as lightning likes to seek ground in a HURRY, without making two 90 degree turns.

This is a disadvantage of cats... Nevertheless, I would put in a long rectangular copper plate, (like shown), on the bottom of each hull, or side of their keels. These need to each be a min of 2 sq ft. Then, using #6 wire, tie in ALL of the rig. The port side to the port plate, and starboard side to the starboard plate. Then tie in the mast base as well. It would be to impractical (heavy & expensive), to use an appropriate "00" size wire for this long run. Lightning is not likely to make these two 90% bends anyway... We're just talking about doing the best that one can here.

A final step that is worth considering, if you are cruising in REALLY lightning prone areas like I have, might be this...

From the base of the mast, go straight through the wing with the above BIG wire, attached with a 1/2" min bronze bolt, (I used 3/4") and corrosion proof connections.

On the underwing I would attach to the bronze bolt a very long strap of woven tinned copper, like used to be common on battery posts. It would be best if its at least 2" wide. I would make this strap the length from the bolt to the aft edge of the wing. Then solder / press on a grommet to the end of the strap. This gives you a way to sail with it tied up tight up against the wing out of the way. When in a storm, or when ever you're not under way, you can lower this into the water by its long piece of 1/8" parachute cord. It might hang 5' or more in the water. This cord is kept cleated on its bitter end for retrieval later. (keep the cord away from the props!)

This idea isn't very elegant, but like I said, lightning likes to go in STRAIGHT LINES, and the rest of the system, while being worth the effort, is more than likely "wishful thinking".

A large copper plate dangling from a large wire connected to the bronze bolt, would be better ground, but too likely to spin, flop, or hit the hulls. Chains, or battery cables clipped to the rigging, like some folks do, can't hurt, but probably have such poor connection and surface area, as to be useless.

You are correct to take action now. All we can do is improve our odds, and the above system will do that. The boats around me have been hit on several occasions. It happens all the time!

If you want to know how I make 20 year, "100% corrosion proof" connections, I can give the routine, but that is another post.

Mark

PS. Do NOT use a Dynaplate for lightning ground! They will explode...
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Old 27-02-2011, 02:21   #7
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Re: Lightning Protection for a Cat

Thanks to everyone who posted a response. First time I've used this forum.....took me a while to figure out how to get back to message etc!. I've read thru all the posts and web connections, and now have a good idea how to do the best lightning protection 'value for money and effort', so again thanks very much. North Australia and Indonesia are expected to be hot-spots for electrical activity, so I think I'll now be prepared (whether my system works or not, well, maybe one day I'll post another message)
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Old 27-02-2011, 09:03   #8
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Re: LIGHTNING PROTECTION FOR A CAT

[QUOTE=Mark Johnson;625359]

From the base of the mast, go straight through the wing with the above BIG wire, attached with a 1/2" min bronze bolt, (I used 3/4") and corrosion proof connections.

On the underwing I would attach to the bronze bolt a very long strap of woven tinned copper, like used to be common on battery posts. It would be best if its at least 2" wide.



I like that.
But the tinned wire I've seen in contact with salt water doesn't stay tinned long, and then turns black.
Do they make such a strap of woven bronze?
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Old 27-02-2011, 09:58   #9
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Re: LIGHTNING PROTECTION FOR A CAT

Quote:
Originally Posted by Mark Johnson View Post
snip
PS. Do NOT use a Dynaplate for lightning ground! They will explode...
Mark that is urban myth (busted). The prior owner of my boat put in a Dynaplate bonded directly to the mast base and the boat was struck (see image showing melted stainless VHF whip with connector blown off) without damage to Dynaplate. Carbon-fiber mast, too which survived without damage (another urban myth busted). Most of the electronics were fried and had to be replaced, windex blew up, diodes in engine panel were blown, various bulbs blew. Boat was hauled and surveyed, including thorough rigging inspection. No damage to hulls or rig, except what looks like a small weld mark on the stainless mast base (cosmetic).

Having said that, I agree that a plain copper strip or plate is a better choice. Also, I would go with #4 wire if space allows, rather than #6.

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Old 08-03-2011, 08:03   #10
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Re: LIGHTNING PROTECTION FOR A CAT

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Originally Posted by SailFastTri View Post
Mark that is urban myth (busted). The prior owner of my boat put in a Dynaplate bonded directly to the mast base and the boat was struck (see image showing melted stainless VHF whip with connector blown off) without damage to Dynaplate. Carbon-fiber mast, too which survived without damage (another urban myth busted). Most of the electronics were fried and had to be replaced, windex blew up, diodes in engine panel were blown, various bulbs blew. Boat was hauled and surveyed, including thorough rigging inspection. No damage to hulls or rig, except what looks like a small weld mark on the stainless mast base (cosmetic).

Having said that, I agree that a plain copper strip or plate is a better choice. Also, I would go with #4 wire if space allows, rather than #6.

I hate to disagree... but for over 20 years, during my boatbuilding projects, I got about 20 monthly periodicals and have read countless thousands of articles on these subjects, It kept my energy level up to the 70 + hours a week, 365 days a year...

Dynaplates can explode on a lightning strike. I have read of it happening on more than just a theoretical basis. NOTHING regarding lightning, "always happens", however! It is too variable and fickle a phenomenon. Sorry if I implied otherwise.

The point was not what the likelihood of a Dynaplate exploding is. That would be something above "possible", on up to "who really knows"???

They make a poor lightning ground because for one thing, the interior is clogged with growth 99% of the time. Also, they are two small, and the wrong shape.

They need to be a MINIMUM of 2 square feet, and as long and rectangular as is practical. It is not thickness, but "linear inches of exposed EDGE" that matters most.

What I did on my minikeel, was "practical", but would've been even better, if it was a 1" wide strip, the entire length of the boat. (Not practical)

Dynaplates aren't that good as radio grounds either, unless one removes them at every haul out, and lets them soak overnight in acid, then reinstall. I have NEVER known anyone who does this necessary maintenance. Not that they wont still work, just that they don't have the surface area claimed without the above regular maintenance.

Mark
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Old 08-03-2011, 08:18   #11
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pirate Re: Lightning Protection for a Cat

I've never heard of an Iroquois Cat being stuck by lightning....
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Old 08-03-2011, 08:21   #12
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Re: LIGHTNING PROTECTION FOR A CAT

[QUOTE=ggray;629854]
Quote:
Originally Posted by Mark Johnson View Post

From the base of the mast, go straight through the wing with the above BIG wire, attached with a 1/2" min bronze bolt, (I used 3/4") and corrosion proof connections.

On the underwing I would attach to the bronze bolt a very long strap of woven tinned copper, like used to be common on battery posts. It would be best if its at least 2" wide.



I like that.
But the tinned wire I've seen in contact with salt water doesn't stay tinned long, and then turns black.
Do they make such a strap of woven bronze?
You are exactly right about that. I don't know of a source of bronze strap, but it would also corrode.

In the case of lightning however, it is like hand grenades: "Close is good enough". It WILL go to ground! Right through a hull if necessary...

The best grounded boats, BAR NONE, are properly lightning grounded metal hulls. They generally have waterproof epoxy barrier coats, (or the like), below the waterline, and on a strike, the charge is dissipated right through the coating! Yes, It might ruin it, but that's a small price to pay.

If you have 6' of 2" wide woven strap in the water, directly below the mast, I would imagine that this being the path of least resistance, trumps the fact that it's corroded on the surface.

We're only trying to improve our odds here, as none of "lightning protection" comes with absolutes. Too damn fickle!

Mark
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Old 08-03-2011, 08:25   #13
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Re: Lightning Protection for a Cat

Of the things I have learned about lightning is that it likes "points and sharp edges". To that end we always made lightning plates with sharp 90 angles, stood off the hull by at least 1/4".

The "bottle brush" gizmos often seen are in fact ion dissipators which are NOT lightning rods, but "lightning preventers".... Theory being that the ion path that lightning follows is dissipated, thus forcing the bolt to another point. If you want to conduct a strike to ground, you need a SINGLE point rod on your mast AND extreme forward and aft metallics (rails).

The best way to conduct the energy is by a non-insulated braided copper conductor from the lightning rod(s) to a ground plate in contact with seawater. I have seen some route the conductor to one of the bolts that holds the copper plate, and others bring the conductor through the hull above the waterline and than down to the plate. The later's school of thought is that IF water were to intrude into the hull matrix around the bolt and a strike were conducted through, a steam flash opening a hole in the hull below the waterline was a possibility.
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Old 08-03-2011, 10:11   #14
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Re: Lightning Protection for a Cat

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Of the things I have learned about lightning is that it likes "points and sharp edges". To that end we always made lightning plates with sharp 90 angles, stood off the hull by at least 1/4".

The "bottle brush" gizmos often seen are in fact ion dissipators which are NOT lightning rods, but "lightning preventers".... Theory being that the ion path that lightning follows is dissipated, thus forcing the bolt to another point. If you want to conduct a strike to ground, you need a SINGLE point rod on your mast AND extreme forward and aft metallics (rails).

The best way to conduct the energy is by a non-insulated braided copper conductor from the lightning rod(s) to a ground plate in contact with seawater. I have seen some route the conductor to one of the bolts that holds the copper plate, and others bring the conductor through the hull above the waterline and than down to the plate. The later's school of thought is that IF water were to intrude into the hull matrix around the bolt and a strike were conducted through, a steam flash opening a hole in the hull below the waterline was a possibility.
Our "lightning rod / ion dissipater" is both. It has thousands of short horizontal bristles, and a bare cone ended rod that is the core, and extends several inches above this.

It may actually work! The boats, water, or ground next to us have taken a hit about a dozen times over 15 years. (So far so good) If the "dissipater" didn't get rid of those pesky ions, and I took a hit, I suspect it would hit the rod anyway, with it being tallest. (Who really knows?)

The ground connection is indeed important. Ours is "00" wire, 2' long, straight down to the plates 5/8" silicon bronze bolt. Should the worst happen, I want it to be a case of: "Don't mind me, jus passin through".

By far, our best safety feature is to keep a live owl at the top of the mast.
I have NEVER heard of a boat so equipped bing hit!

Mark
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