Lightning Ground with an Encapsulated Keel

Ceasar Choppy · Post by **Ceasar Choppy** » Thu Dec 04, 2008 11:24 am

OK, so I could have done a search, but I think I would recall if something like this was discussed much in the last three years. Since I'm out of the water, now is the time to do this if I want... so here is my question:

My P-39, like make plastic classics, has no keel bolts. The lead is encapsulated in the FG around the keel (there is a centerboard in there too, but lets leave that out of this for purposes of this discussion). I have been trying to figure out a way to provide a ground for lightning AND a suitable ground for the DC that does not terminate at the engine.

The solution I've seen involves a copper strap bolted to the outside of the hull to which the standing rigging, mast, engine, and DC ground is connected on the inside. I'm hesitant to bolt on a hunk of metal like this, however, because I'm concerned about how it will affect performance of the boat. No, seriously. She's not a racer by any means, but she has a decent turn of speed and I don't want to bolt on a brake system. A tenth of a knot is no problem, but 1/2 a knot is.

So my question is, does anyone have any experience with a system like this and can you offer any advice?

Adam · Post by **Adam** » Thu Dec 04, 2008 12:10 pm

Grounding Plate....

http://www.jmsonline.net/LILLY-DLP-6-BR ... TE-6in.htm

David · Post by **David** » Thu Dec 04, 2008 12:51 pm

You should not combine a lightning ground with anything else; certainly not an electrical ground for you house system, an engine ground or your bonding system, if you have one. The lightning ground should be a heavy wire from your aluminum mast directly to an external ground plate, as direct a route with as little turns as possible. A Dynaplate can act as the external plate but I am personally not happy with the supposedly "gold plated" through bolts that are supplied. I think bronze of a larger diameter would be safer and longer lasting under water.

Chris Campbell · Post by **Chris Campbell** » Thu Dec 04, 2008 3:16 pm

I've read in a number of places that those dynaplates shouldn't be used as lightning grounds, and in at least one (two, now) that they should...

The figure I've read most often (including ABYC) is that you need a square foot plate. Don Casey recommends a one inch wide, 12 foot long plate, as it has less drag (thus the strips you've seen on hulls).

Here's some relevant links:
http://www.kp44.org/LightningProtection ... ndards.php
http://www.alohaowners.com/pages/projec ... htning.htm
http://www.sailmail.com/grounds.htm

I'm sure that a long strap could be faired in slightly - make the leading edge taper, grind a shallow trough to set it into...

Idon84 · Post by **Idon84** » Thu Dec 04, 2008 3:23 pm

OK... so I have to ask. How important is a grounding strap? I've never personally seen one being associated with so many racers. We get very little in the way of lightning around here. I'm thinking with my wooden (explosive nature) mast and dreams of travel I'm guessing it would be something I would want to do. I've read a couple of articles on the subject but am not familiar with the grounding system.

For instance some people (racers) have said just run a LARGE wire from an above mast arial all the way down one of your side stays (having external chainplates) so that you can connect a ground wire down to the water level when the need arises. I'm thinking that answer is more for the racing purist who needs every .25 knot of speed. Not only that but I think that would be ugly and foul things that float by.

That grounding plate linked above actually is through bolted through the hull? And then attached to the LARGE wire in the straightest fashion to the top of the mast? So instead of running the wire down the stays I can run an external wire down the side of the mast, through the deck and down to the grounding plate? After it comes through the cabin top it would need to be routed at a slight angle to miss the encapsulated keel? Am I grasping this concept ok? I feel dumb even after reading a lot about it.

Thanks,

David · Post by **David** » Thu Dec 04, 2008 3:33 pm

Bryon,

You got it. WIth a wooden mast you need an air conductor (lightning rod) at least 6 inches taller than the tallest thing above your masthead, connected to a big wire down the mast, etc. With an aluminum mast you can connected the rod at the top and the wire at the bottom of the mast and let the mast carry the current. Separately you would want to bond the chainplates to the same lightning ground point so that you don't energize your rigging and damage it (thats the current thinking anyway).

Ceasar Choppy · Post by **Ceasar Choppy** » Fri Dec 05, 2008 9:40 am

Thanks all for the suggestions.

Just for clarification:

1. I'm not interested in using sintered bronze plates (like the dynaplate) as a ground plate. They are heavy and there is the potential of explosion (perceived or real?) when the water between the sinters is heated up by lightning.

2. As I understand it, from reading Nigel Calder on this subject, the immersed ground plate IS the one place where everything is connected. By everything, I mean the DC negative main bus, and the non-current carrying main bus (including connections from the chainplates, mast, fuel tank, bonding system, zincs), and the main lightning conductor from the mast. A chart showing this is on p. 233 of Calder's Boatowner's Mechanical and Electrical Manual.

I'm envisioning something along the lines of the 1" x 12' strap mentioned above, except I have 7 feet to work with, so I guess it would be 2" x 7'? I'm not sure how thick... maybe 3/16"? And I'm thinking of using bronze carriage bolts through the hull.

From what I've read, the edges of this strap are important and must be exposed as this is where the lightning is dissipated... thus, fairing it into the hull a bit, does no good.

Ceasar Choppy · Post by **Ceasar Choppy** » Fri Dec 05, 2008 9:52 am

Idon84 wrote:OK... so I have to ask. How important is a grounding strap? I've never personally seen one being associated with so many racers. We get very little in the way of lightning around here. I'm thinking with my wooden (explosive nature) mast and dreams of travel I'm guessing it would be something I would want to do. I've read a couple of articles on the subject but am not familiar with the grounding system.

Lightning is a funny thing. I've seen more boats get hit at the dock than anywhere (although that is probably just because there are more boats there). I've sailed on long passages to Bermuda or transatlantic (in a 42' steel hull) where we were the biggest, tallest hunk of metal for miles around and lightning struck all around us, but never hit us. But all it takes is one bad hit. At least your mast isn't made of carbon fiber (explodes into many sharp tiny splinters when hit)!

Chris Campbell · Post by **Chris Campbell** » Fri Dec 05, 2008 9:57 am

Regarding grounding, I've always found this confusing since it seems to me that there are several conflicting opinions on how to go about it. The one source I've read that makes sense to me and doesn't seem to contradict other sources is in Don Casey's Complete Illustrated Sailboat Maintenance Manual in the chapter on electrical (which I believe is also available as a separate book). He discusses bonding and the reasons for it and against it, and then how to achieve the good and avoid the bad.

The bad is stray current corrosion, where you're near someone else's bad wiring job and the current flows through your boat's bonding system, destroying your underwater fittings. The best way to avoid it (according to Don) is to have a single underwater ground point for all systems (like Nigel says), and to keep all other underwater fittings isolated from this ground.

And here's something interesting about the size of the ground plate: "If your keel is encapsulated, a copper ground plate is needed. Lightning dissipates from the edge of the plate, so the perimeter of the plate should be at least 4 feet (1.2m) if you sail in salt water. If there is any chance that you might sail in freshwater, the ground plate should have at least 24 feet (7.3m) of sharp edge, usually accomplished by attaching a 12-foot (3.7m) length of 1-inch (2.5cm) copper strap fore and aft. Bronze bolts are preferred over stainless steel for bolting the plate to the hull and for cable attachment." So if you don't sail in freshwater and don't mind having reduced lightning protection should you sneak up a river in your travels, you can get by with a significantly smaller underwater plate.

If you don't have the Casey book and are interested I can type out more of it - I find it well written, easy to follow, and consistent.

David · Post by **David** » Fri Dec 05, 2008 10:49 am

I personally wouldn't just drink the Nigel Calder or Don Casey Kool-Aid. There are lots of opinions out there on how boats should be grounded and protected from all types of current. I would definitely suggest reading John Payne's books on the subjects of lightning, electronics and underwater corrosion. Also "Your Boat's Electrical System" by Conrad Miller is a bible for boat wiring. Also David Pascoe's website and books are a wealth of information. Ultimately we must each decide on a method of grounding and live with it (and sleep well at night).
Nothing is really predictible with lightning. I've been out hundreds of miles in the Gulf and had lightning hitting all around my boat--with no lightning dispersion system at all--and even close strkes that felt like cannon blasts did not seem to be interested in my 36' aluminum mast.

bcooke · Post by **bcooke** » Fri Dec 05, 2008 6:34 pm

The real story on lightning protection is that no one really knows.

There is no data to support or deny any theory and its just anyone's best guess as to what works.

There are many theories that seem right on paper but none of them have been shown to work with any hint of a scientific manner for the facts.

Idon84 · Post by **Idon84** » Fri Dec 05, 2008 7:32 pm

Britton,

I've heard that before too. I guess that is where my confusion comes in. So, what kind of tactics, if any, do all of you use?

I have read Casey, Calder, & Pascoe's (now going to find Payne & Miller) writings on the subject but because there are so many opinions I end up falling back to the original 1749 Franklin Rod which is where I have my base of understanding hence my prior post on this subject.

I typically stay away from wiring in general because I tend to let the smoke out of the wire. So the hole bonding/isolating/grounding gets me all confused.

bcooke · Post by **bcooke** » Fri Dec 05, 2008 10:28 pm

Since there are no clear benefits to 'protecting' a boat from lightning I don't do it. As soon as someone can show a method that works I will jump on it. I don't like the idea of being smoked by lightning either.

Ceasar Choppy · Post by **Ceasar Choppy** » Fri Dec 05, 2008 11:38 pm

bcooke wrote:Since there are no clear benefits to 'protecting' a boat from lightning I don't do it.

I think the one clear benefit of a ground pate is that you minimize the chance of lightning blowing a million holes in the FG. This, in the end, is all I'm trying to accomplish.

I've generally found Calder to be good on these things. Casey is OK too, but sometimes not so much. I've read some of the others too, but I sleep very well at night thankyouverymuch.

Oh, and I don't drink Kool-Aid.

David · Post by **David** » Sat Dec 06, 2008 9:39 am

I've only seen one boat hit by lightning. She was a Nonsuch cat boat in a marina in Titusville. The hit make a perfect two inch hole in the bottom and the boat sank in her slip. The hole was as symetrical as if it had been cut with a hole saw. The bolt apparently went straight down the mast and jumped off the maststep making the hole.

kendall · Post by **kendall** » Sat Dec 06, 2008 2:20 pm

over on the Ariel board there's a couple pics of an ensign that was lightning struck,
bottom of the page here:
http://www.pearsonariel.org/discussion/ ... 78&page=14

and top of page here:
http://www.pearsonariel.org/discussion/ ... 78&page=15

They got me wondering about what could be done.

I think the only thing certain about lightning is that nothing is certain.

I've had a car hit by lightning, while my antenna tower I was parked next to wasn't hit.
At my house in Dorr, there was a tree next to the garage that was hit a dozen times, even though it was one of the shortest trees.

The post for the ensign states that he was among taller boats when he was hit.

Did a lot of digging, and the only thing I could find is that there is no real consensus on grounding, and that lightning strikes are nowhere near as common as you'd think.

Ken.

Shark · Post by **Shark** » Sat Dec 06, 2008 5:15 pm

Protect your boat and yourself by providing lightning with a good path to ground.

Attract lightning to your boat by providing a good path to ground.

Beats me! If there is a definitive answer I'd like to know what it is.

I usually try to either stay off the water or get off it asap when lightning threatens, though this is not always possible.