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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Grounding for Lightening

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hhrock
Deckhand

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USA
18 Posts

Initially Posted - 05/21/2009 : 15:42:57

My husband and I just bought our first sailboat - a 1979 Catalina 25 TR FK. We are keeping it in a wet slip in an inland lake in North Carolina. This area can deliver some pretty nasty thunderstorms in the spring and early summer (some pretty suddenly), and I would like to know if anyone has ever investigated the grounding system. I have not been able to find anything about this in the owner's manual I downloaded from the internet, and my interest in more in our safety should we be on the boat in a lightening storm. (I was once caught in a very nasty squall on a Catalina 36 off the gulf coast of FL while hurricane Gustav was arriving.)

Our sailing instructor in the BVI suggested that for small sailboats, but a standard jumper cable and attach one end to the shrouds and drop the other in the water, but you'd think for a boat as popular as the C25, the grounding would be built into the design.

Anyone ever looked into this before?

Helen Rock
RockReation
79 C25 TR/FK #1207

Edited by - on

dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 05/21/2009 : 15:58:51

Welcome to the Catalina 25 "family" and to this forum. The C25 has a deck-stepped mast, so the mast itself is not grounded like a keel-stepped mast. I doubt that the shrouds could handle the charge from a lighning bolt. Best advice I could give if you were caught out in a thunderstorm is to stay away from any metal fittings and drive the boat to safety, hopefully to an area where someone else's mast it taller than yours!

There are several electrical engineer guys who read this forum, maybe they will chime in.

Edited by - dmpilc on 05/21/2009 15:59:41

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 05/21/2009 : 17:30:40

Helen, Welcome.

This has been discussed extensively on this forum. David's right, we have a few electricity gurus amongst us who will likely share some thoughts but in the meantime, here's a [url="http://www.catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=15855&SearchTerms=lightning"]link to a previous discussion [/url] on the topic. I think what you're going to discover is that the prevailing opinion is that a grounding system will protect you as much as not having one. At least, that's what I concluded when I read about this topic on the forum. I don't have one on Lake Erie. Lot's of midwest t-storms. Also, lots of taller masts in my marina

Edited by - John Russell on 05/21/2009 17:31:26

Voyager
Master Marine Consultant

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USA
5352 Posts

Response Posted - 05/21/2009 : 21:02:33

There are varying opinions on this point, even from the experts. Some say that intentionally grounding your mast "encourages" lightning to strike it. Here are a few points I can make, IMHO.

1. There is no doubt that our masts are already grounded. But they are not grounded well enough to protect us. The mast lighting cables and VHF antenna connect from the top of the mast to the electrical panel and the battery. The engine is also connected to the battery, and grounded to the water.

2. A properly grounded mast will protect us better than a poorly grounded one. In fact, this poor conduction path will encourage "step leaders", the precursor to a lightning strike. When the strike does take place, the bolt will follow your mast to its base, and jump through your hull to ground. This can also blow a hole in the hull.

3. A properly grounded mast will create a "cone of protection" around the boat. If you draw a triangle or cone from the top of your mast that has a 60 degree vertex at the top, everyone under the cone will be protected (but your electronics will all fry). Stay away from the bow and the stern during a storm.

4. To correctly ground a mast, you should connect a piece of #4 AWG cable to the bottom of your mast. Then attach a large copper grounding plate to the bottom of your hull, and connect the cable through the hull to the plate. For salt water, you need about 1 to 2 square feet of grounding.

Many engineers suggest you use a 3" wide strip x 60" long to distribute the electricity to more water.

For fresh water, they recommend 4 or more square feet of grounding.

I have connected the #4 wire to several of my keel bolts. They will carry much of the current into the lead keel. The keel has a thin laminate of fibreglass around it. I would rather burn this laminate than allow lightning to hole the boat.

You can also use the jumper cable (#6 wire) to go from the bottom of the mast to the keel bolts temporarily. You will be somewhat more protected than without the wire.

Edited by - on

hhrock
Deckhand

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USA
18 Posts

Response Posted - 05/22/2009 : 05:42:36

Wow!!!

This was my first posting to this forum, and you guys are wonderful!!! Thank you so much. We'll be down at the lake this weekend, and I will study the boat and see if I understand some of the suggestions. I may come back with more questions - but thank you everyone for the help/suggestions.

I do recall my friend's father (owner of the 36 Catalina) explaining his grounding system, and the 60 degree cone of protection, and he's a pretty brilliant guy. It's not a topic that really hits home until you are caught soaking wet in a storm where lightening is literally striking all around you (no space between it and the thunder). You sort of look up, and think - "crap" - what happens to me if...

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/22/2009 : 06:03:04

Welcome Helen! We have indeed discussed this periodically and at length here... You can try the "Search" function above, or the Google Search to the left to see lots of <i>opinions</i> (and few <i>facts</i>) on this.

I suspect the reason you don't see any system or mention of one from Catalina (or other builders) is that anything they do or so much as suggest will open them up to liability when it doesn't work as planned. (Perhaps that's good advice for us here.) Lightning is a fickle and powerful thing... The tallest mast in the marina or anchorage is rarely the one that gets hit. People in low, open powerboats are apparently at greater risk.

From what I've read and heard, jumper cables from the shrouds are not a good solution because stainless steel is a poor conductor--good enough to carry a leader, but not to handle a strike. The aluminum mast is much better, but it's almost 6' away from the water. You have a cast iron keel, not encapsulated lead like Bruce's, so the keel bolt idea might be worthwhile. There are articles about "air gap" devices that are supposed to prevent the leader from traveling upward through the system, but will allow a strike to go down...

Read everything you can, and then do what makes you feel better. It's all relative and somewhat random--there are no guaranteed solutions. (And most boats never get hit.)

Again, welcome to the community!

Edited by - Dave Bristle on 05/22/2009 06:06:31

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.