Grounding my smallish cat electrically

Hunky

Member
56
5
NW Alaska
I have a 30' cat with outboards, so wondering if/how to ground for lightning. Been reading a few links and some suggest a copper rod on top of mast and the aluminum mast grounded to a copper plate outside the hull. I understand this may or may not work. But also some of my electrical panels have the yellow wire for battery negative, but also the yellow/green wire for "earth" which I assume I would hook to that copper plate outside as well. No thru-hulls as of yet.

A builder of a same-design cat used copper plates like this. I think he did on both hulls - the image with the red arrow points at one of these plates. And the other image is how he hooked 'em up. I'm wondering about peoples' thoughts on this - size of copper plate, is it even necessary?, both hulls or would just one work?  Be good if I ever used a SSB or Ham radio (no current plans!)?

thx, JD

grounding.jpg

plate.jpg

 

Zonker

Super Anarchist
9,657
5,616
Canada
We had a 40' cat. For grounding it against lightning strikes I had AWG #4 cable at the base of the mast clamped to a copper pipe. In lightning storms you could lower the pipe right into the water where the cable suspended it.

Lightning likes a straight easy path. Asking it to make a few 90 degree turns means it may head off in other directions.

A lightning ground doesn't HAVE to be hooked up to your boat's electrical system. It can be it's own thing.

A copper plate on the outside of the hull will work. If you went that route I'd use bronze bolts and nuts, not s.s.  A long skinny plate has more "edge" length than a more square plate for lightning to arc away and may work better. I think the one shown should be 3 or 4x longer.

 

Hunky

Member
56
5
NW Alaska
We had a 40' cat. For grounding it against lightning strikes I had AWG #4 cable at the base of the mast clamped to a copper pipe. In lightning storms you could lower the pipe right into the water where the cable suspended it.

Lightning likes a straight easy path. Asking it to make a few 90 degree turns means it may head off in other directions.

A lightning ground doesn't HAVE to be hooked up to your boat's electrical system. It can be it's own thing.

A copper plate on the outside of the hull will work. If you went that route I'd use bronze bolts and nuts, not s.s.  A long skinny plate has more "edge" length than a more square plate for lightning to arc away and may work better. I think the one shown should be 3 or 4x longer.
Thanks for that Zonker. I had planned on maybe just clamping chain or something to a shroud and tossing the other end in the water, but now I may go synthetic rigging so that wouldn't work. Your method sounds similar and I may try that rather than routing more copper wire through the deck.

From what I've read - it seems if I understand it - you should have an "earth" connection, perhaps separate from the battery negative.. such as what someone might ordinarily hook to a saildrive or something permanently in the water. To ground metal cases, panels, etc. Only option for me if that is the case would be mounting something (copper plate) outside the hull under the waterline. So if I did as you with tossing a pipe in the water grounded to the mast, the copper plate wouldn't need to be so big (I just priced 1/4" plate and started wondering about alternatives) and I maybe wouldn't need one on each hull. Or spend the bucks and have double the protection (in mind, at least, if not in actuality).

Was planning bronze bolts.

 

Upp3

Anarchist
718
260
A builder of a same-design cat used copper plates like this. I think he did on both hulls - the image with the red arrow points at one of these plates. And the other image is how he hooked 'em up. I'm wondering about peoples' thoughts on this - size of copper plate, is it even necessary?, both hulls or would just one work?  Be good if I ever used a SSB or Ham radio (no current plans!)?

thx, JD

View attachment 433898

View attachment 433900
Those seem tiny compared to one pictured in this article: https://www.yachtingworld.com/special-reports/yacht-lightning-strikes-damage-protection-127469

 

Zonker

Super Anarchist
9,657
5,616
Canada
Electrically speaking, you can think of 3 grounds:

- ship's DC electrical system ground. This can float and not need any connection to the water

- bonding ground. You connect all big bits of metal, inside and out, to a bonding system and one or more external anodes connected to the wires of the bonding system inside the boat. This is common US practice but not done in most of the rest of the world. I prefer to avoid any bonding system. For underwater items like thru hulls you can use a corrosion resistant metal like bronze or glass reinforced plastic (Marelon). For shafts and saildrives you can use zinc anodes on the piece of equipment.
 

- a lightning grounding system. This does need a connection to the water. Ideally you ground the mast and shrouds all together to a big underwater metal object. This is easy for monohulls with external ballast keels and very tricky for cats because forestay and mast are in awkward locations.

Best article on grounding is Stan Honey's http://honeynav.com/grounding-on-sailboats/

Those seem tiny compared to one pictured in this article:
Yes, I agree the original picture showing little grounding plates was too small for lightning protection.

In that article they reference a fancy lightning protection system that claims to reduce the chance of a strike by 99%. However strangely their brochure does not say how they make such a claim, nor do they offer any sort of guarantee. There's a LOT of snake oil in lightning protection.

 

Trovão

Super Anarchist
Electrically speaking, you can think of 3 grounds:

- ship's DC electrical system ground. This can float and not need any connection to the water

- bonding ground. You connect all big bits of metal, inside and out, to a bonding system and one or more external anodes connected to the wires of the bonding system inside the boat. This is common US practice but not done in most of the rest of the world. I prefer to avoid any bonding system. For underwater items like thru hulls you can use a corrosion resistant metal like bronze or glass reinforced plastic (Marelon). For shafts and saildrives you can use zinc anodes on the piece of equipment.
 

- a lightning grounding system. This does need a connection to the water. Ideally you ground the mast and shrouds all together to a big underwater metal object. This is easy for monohulls with external ballast keels and very tricky for cats because forestay and mast are in awkward locations.

Best article on grounding is Stan Honey's http://honeynav.com/grounding-on-sailboats/

Yes, I agree the original picture showing little grounding plates was too small for lightning protection.

In that article they reference a fancy lightning protection system that claims to reduce the chance of a strike by 99%. However strangely their brochure does not say how they make such a claim, nor do they offer any sort of guarantee. There's a LOT of snake oil in lightning protection.
lightning protection is a mix of dark arts and (some) science, with emphasis in the former...

 

MRS OCTOPUS

Anarchist
699
237
AUSTRALIA
lightning protection is a mix of dark arts and (some) science, with emphasis in the former...
Exactly. Funny (Not) how the facts have been buried by the spin doctors and the ignorant on any google search.

Just coz it’s on the Internet doesn’t make it true. :)

 
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Hunky

Member
56
5
NW Alaska
Electrically speaking, you can think of 3 grounds:

- ship's DC electrical system ground. This can float and not need any connection to the water

- bonding ground. You connect all big bits of metal, inside and out, to a bonding system and one or more external anodes connected to the wires of the bonding system inside the boat. This is common US practice but not done in most of the rest of the world. I prefer to avoid any bonding system. For underwater items like thru hulls you can use a corrosion resistant metal like bronze or glass reinforced plastic (Marelon). For shafts and saildrives you can use zinc anodes on the piece of equipment.
 

- a lightning grounding system. This does need a connection to the water. Ideally you ground the mast and shrouds all together to a big underwater metal object. This is easy for monohulls with external ballast keels and very tricky for cats because forestay and mast are in awkward locations.

Best article on grounding is Stan Honey's http://honeynav.com/grounding-on-sailboats/

Yes, I agree the original picture showing little grounding plates was too small for lightning protection.

In that article they reference a fancy lightning protection system that claims to reduce the chance of a strike by 99%. However strangely their brochure does not say how they make such a claim, nor do they offer any sort of guarantee. There's a LOT of snake oil in lightning protection.
I don't want to unnecessarily complicate things. I was thinking of the bonding ground as "earth", I suppose. Very happy to know this is not required. I'll assume the ship's DC system ground is just a return to the battery negative. Unless persuaded otherwise, I'll not do a copper plate on the hull, but use your method instead - perhaps keeping it neatly coiled and lashed to the tramp as I don't have any lockers up front.

I don't really need to worry too much about lightning up here - it is pretty rare and mostly occurs inland when it does happen, starting fires on the tundra. Scares the bejesus out of the children because it is so rare. But it does happen. I was looking at this (as well as a few other links): https://www.pbo.co.uk/expert-advice/expert-answers/make-a-grounding-system-to-protect-your-boat-from-lightning-strikes-67072

 

stief

Super Anarchist
8,118
2,440
Sask Canada
FWIW, the "cone of protection" is probably larger than shown. Or irrelevant.

Lost my first keelboat (Martin 242, similar to this) to a lightning strike. Out for a Sunday sail, a few of us saw the clouds building, so headed back to harbour. We were between two bands of clouds, with clear sky above. I was at the mast flaking the main; wife was at the boom end. Mother on the tiller. 2 yr old son sleeping wrapped around the mast down below with 7 yr old daughter and guest.

Thunder boom, thought it was close, but wife saw Windex went flying and yelled we had been hit. Guest called up about fire below. Fiberglas was punched up and smouldering under the cockpit (port side), but easily snuffed with the spinnaker bag (area about the size of my fist) Discovered the area leaking water, so we pulled the boat.

All were safe. Wife and I, in contact with the mast/boom felt nothing. Mother thought she felt a tingle on the tiller extension, but that was it.

Adjusters totalled the boat: the hull was compromised, with about a dozen crazy patterns like gunshot-in-glass around the keel and port stern quarter.

Here's one pic of the pattern.

1990560056_Aug904997-005.jpg

Obviously inside the "cone of protection."

We were using VC-17 for anti-fouling, so the whole hull was thinly, veeeery thinly, copper-plated.

Our guest's answer is probably just as valid: he would laugh over the story and take credit for our safety (he was a Catholic priest).

 

Hunky

Member
56
5
NW Alaska
FWIW, the "cone of protection" is probably larger than shown. Or irrelevant.

Lost my first keelboat (Martin 242, similar to this) to a lightning strike. Out for a Sunday sail, a few of us saw the clouds building, so headed back to harbour. We were between two bands of clouds, with clear sky above. I was at the mast flaking the main; wife was at the boom end. Mother on the tiller. 2 yr old son sleeping wrapped around the mast down below with 7 yr old daughter and guest.

Thunder boom, thought it was close, but wife saw Windex went flying and yelled we had been hit. Guest called up about fire below. Fiberglas was punched up and smouldering under the cockpit (port side), but easily snuffed with the spinnaker bag (area about the size of my fist) Discovered the area leaking water, so we pulled the boat.

All were safe. Wife and I, in contact with the mast/boom felt nothing. Mother thought she felt a tingle on the tiller extension, but that was it.

Adjusters totalled the boat: the hull was compromised, with about a dozen crazy patterns like gunshot-in-glass around the keel and port stern quarter.
Yikes! Good you all were ok. Anyone ever rehab the hull or did it end up scrapped?

I was hiking on a mountain top and clouds came in - way back in the day when backpacks had metal strap buckles and things. Our hair on our heads and arms started standing up, and I was getting shocks from the metal buckles. We beat feet pretty quick off the mountain. Another time as a child we were in the front yard in a rural area watching a lightning storm sitting on inner tubes (to keep us from being grounded - yeah right!). A real bright flash and immediate thunder - it ended burning off the hair on a friend's arm up the road, killed a couple cows across the road in a pasture, and blasted a hole through a house roof right over a couch with a man taking a nap on it - but he was ok. Must be scary on a boat.

 

stief

Super Anarchist
8,118
2,440
Sask Canada
Anyone ever rehab the hull or did it end up scrapped?
Rumour has it someone bought it as salvage. Heard a year or so later that it fell off the trailer going down a hill, then someone else bought it (story goes they tried to inject some bonding between the delaminated hull), then a few years later someone else swam ashore after a sinking. Story goes the RCMP found a 4" hole drilled in the bottom, so the sinking was fraud. 

As with your memories, worst part is not knowing what can be done for protection.  I keep watching the round-the-world racers of their stories in the doldrums. Carbon masts on carbon boats sitting in the brine, but so far no reports of damage or what they do for prevention. Shrug. Guess they, like us, won't let the fears stop them sailing ;)  

 

Sarimanok

New member
39
8
Is there anything that can be done to protect a cat with carbon mast and synthetic rigging against damage from lightning ?

 

Zonker

Super Anarchist
9,657
5,616
Canada
So you really need a bag of rock salt. If a lightning storm threatens, quickly dissolve around the boat to make the water more conductive.

 

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