Grounding Plate / Bonding

[sfreihofer]

My CD25 is not bonded and has no grounding plate. I'm considering adding this, but first I'd like to make sure I understand the theory and application.

Bonding is joining, by heavy copper wire loop, all major metal components like rails, mast, rigging, engine, etc. This is grounded to a submerged grounding plate. The system allows all connected metal parts to maintain zero electrical potential (?) and protects the metal from stray voltage electrolysis (?)

It also protects from lightening strikes by keeping metal parts (i.e. masthead) at the same potential as the water around the boat. Thus, the masthead cannot build up an electrical charge to attract lightening (?)

What are the pros and cons of adding a grounding plate and bonding wire? Please enlighten me.

Stan Freihofer
1981 CD25 #794
Ft. Lauderdale
www.reefroof.com

[sfreihofer]

Another question: Everything I've read says not to paint the grounding plate. So, what's to keep it from becoming coated with marine growth and thus impede its function?

Stan

[Carl Thunberg]

I'm not sure where you would put a dynaplate on a CD25. A typical dynaplate installation would be in the bilge just above the ballast but still mounted in a vertical plane. I'm going by memory here, but my recollection is that the CD25 has a very shallow bilge. I'm not sure there's enough physical space to mount one in a vertical plane.

Without demonstrating my ignorance by getting into a lot of theory about bonding and lightning protection that I really don't understand, I can say absolutely do not paint the dynaplate. It's made of scintered bronze that's basically a porous bunch of spheres that are fused together. The idea is that the scintered bronze has a tremendous surface area. When hit by a lightning strike, it basically explodes. The paint would clog the pores and inhibit this "exploding" action. All I can say is, I've never had a problem with marine growth over my dynaplate, but I sail in pretty darn cold water. Your mileage may vary, being in Fort Lauderdale.

[Sea Hunt]

This is from the Cape Dory Yacht Owner's Manual at page 28. The Manual covers most, but not all of the Cape Dory models. It appears to include the CD 25. The entire manual is located in this website. Not sure I remember exactly where. I copied it to my computer a long time ago.

3.18 LIGHTNING GROUND SYSTEM

Your Cape Dory is equipped with a lightning ground system installed in accordance with the American Boating and Yacht Council (A.B.Y.C.) specifications. Every shroud and stay is connected to an external ground plate by a #8 A.W.G. stranded copper wire. Other equipment requiring bonding include the engine, fuel tank, mast step and fuel fill cap. Within practical working restraints, the wires are lead directly to the ground plate. (Note - Typhoon and CD-22 have optional lightning
ground systems.)

. . .

Do not paint the external ground plate with bottom paint as this prevents the plate from grounding out with the seawater.

Periodically inspect the connections in the bilge to see that they are tight and clean and free from corrosion.

I do NOT own a CD 25. However, from reading the above, I think one was originally installed on your CD 25. Carl T. and the others who have owned CD 25s for years obviously know a lot more about the "innards" of a CD 25.

[sfreihofer]

Carl, I have read that the Dynaplate can be used as a grounding plate for a Single Side Band (SSB) radio. In this case, maybe it can be in the bilge, but I believe for grounding the bonding system on board, it must be mounted externally, like on the keel, where it is submerged. If I'm wrong about this, I need to know.

My boat doesn't have one, and I'm considering installing one, so I'd like to know what I'm doing, how, and why.

Sea Hunt, in spite of what the manual says, I can assure you that my CD25 does not now have, and never has had, a bonding system or grounding plate. I don't think it was included on any of the CD25's, so I don't think mine is an exception.

Stan

[Bob Owens]

Stan,
On my CD27, the factory installation of the grounding plate is on the side of the keel, well below water line and about 8" below the cabin sole. In Long Island Sound marine growth is a major problem on my dynaplate. I follow the instructions and never paint it. Consequently, the thing is covered--and I mean COVERED--with a mass of barnacles as thick as my fist at the end of each season. I grind it clean every fall with a wire-brush attachment on my electric drill, since I don't want to risk breaking loose its seal by going after the sea-life with a hammer and chisel, etc. This is such a pain I have wondered what I would really sacrifice by doing away with the dynaplate altogether and fiberglassing the hole.
Bob

[sfreihofer]

Bob;

Thanks for your input. I was hoping to hear from someone who has a grounding plate as an original installation.

My understanding is that the grounding plate serves several functions. The main reason I'm interested in including one is because, if I understand what I've read, it helps avert lightning strikes by preventing the mast etc. from accumulating an electrical potential which would attract a strike.

I understand it will also prevent stray current electrolysis in submerged metal parts. I'm seriously considering using Marelon (sp?) through-hulls and seacocks to avoid this concern, but I still have the rudder shaft and engine in the water to worry about.

The reason you shouldn't paint it is because the paint would serve as an insulator, preventing the grounding plate from dissipating any accumulated charge into the surrounding water. So, I wonder if marine growth doesn't also insulate the plate and reduce its effect. Damned if you do, damned if you don't...? But since the plate is copper (a biocide), is the marine growth a big problem? From what you've said, I'd say "yes". That's valuable feedback, and I thank you.

South Florida is the lightning capitol, and the strikes can be frequent and severe. Anything that would ameliorate that threat seems like a good idea. I'm thinking that installing a grounding system is worth the trouble and the cost, if for no other reason than to boost my safety if I get caught in a thunderstorm, which is a real possibility here.

I'm sure others here understand this better than I, hence my questions....

[Sea Hunt]

Stan:

There are several different "manuals" posted on this website. I looked at another one (1978 edition) this evening that appears to be for CD 25s and a few other CD models (27, 28 and 30). At page 53 of this manual (Section 2.8-4), it states the lightning ground system was installed on the CD 27, 28 and 30 models. By implication (and exclusion ) the lightning ground system was NOT installed on the CD 25 models. Strange. I thought only the Typhoons (Daysailors and Weekenders) were built without a lightning ground system being installed at time of construction.

I learned something new today about Cape Dory sailboats

[Carl Thunberg]

Perhaps I wasn't very clear. The dynaplate itself is very definitely externally mounted on the side of the keel. The backing plate and all the bonding wires attach on the nuts that are located in the bilge. I remain concerned where you would actually mount one on a CD25. You need a certain minimum amount of exposed bilge/keel surface above the ballast and below the water line to mount one. From my memory of the very shallow bilge on my old CD25, I just don't think you have enough room to do it. I'd love to be proven wrong on this.

Robert, thank you for correcting me on the reason why not to paint the dynaplate. I had the right answer, but for the wrong reasons. Being right for the wrong reasons is still being wrong. Thanks for correcting me.

[MoJac]

I have a 1979 CD25 hull 712 which I bought several years ago. It had a grounding plate installed, which "appears" to be factory installed, maybe... Installation is neat, clean and a far a I can tell appears to be professionally installed. Thru bolts @ the backing plate are connected with four (i think) very heavy gauge wires that run to two stays and two shroud backing plate locations. The location of the plate is as follows. Exterior of hull, Port side, approx midship, on vertical side of keel just below where the hull begins to curve, which on my CD25 is directly adjacent to the bilge.

For what it's worth this is only my second or third post since joining, but i've learned tons. Thanks to all.

[CruiseAlong]

I "believe" that Cape Dory installed bonding on those boats which had engines (i.e. battery charging) thus requiring AC power. In such cases it is important to protect individuals from accidental AC activation of metal components by AC electrical hot phase power. This is why the metal parts are all joined together and brought to ground potential.

Now for the separate discussion of lightning...does it protect you from attracting lightning....answer NO. In fact an ionizing "cloud" of electrons may form at the top mast tip which may attract the lighting should it want to strike within your "cone" of protection. It does, however, provide for a better mechanism for it to be directed into the water (ground potential) without establishing a fireball within the cabin of the boat bouncing around to who knows where. But that is no insurance that the boat will not sink, nor save electronics or electrical equipment...just a better chance for human safety.
Dana

[jbenagh]

After a very active electrical summer last year (and many days I didn't dare sail due to a remote threat of storms), I looked into lighting protection for my CD25 (Carl's former boat). Here's a summary of what I did -- I would appreciate your comments since I'm not an expert, I just did what I read about.

There was an article about lightning protection I read by a professor from Florida (which I can no longer find, but I included some references below). There were also some amateur radio articles. I also read several articles about protecting telecommunications equipment on the top of telephone poles. My interpretation of the advice was a dynaplate as the ground, which would provide efectively 1 sq. meter of surface area. A singe 4ga conductor from the mast, which due to the high conductivity of aluminum, would carry most of the current. Each shroud or stay is connected with its own 8ga conductor. I connected the dynaplate to the bonding zinc with another 8ga conductor. I did not follow the advice to ground all the genoa tracks becuase this seemed awfully difficult.

I placed the Dynaplate on the port side, as low in the locker as I could, just behind the head bulkhead. While it might be better to locate it lower in the boat, I think this position is adequate. I chose the location using from the Dynaplate manual (I used the 4080C):

"Description
... The model 4080C Dynaplate meets ABYC requirements for use in a lightning protection system.
...
"Step 1: Choosing a mounting location
Choose a mounting location that will always be submerged, even when the vessel is planning [sic] or heeling over.
...
"On a sailboat, a flat location on the aft half of the hull and close to the centerline is best."

I hope I never need to test the system as the article I read said "95% of properly grounded boats suffer no damage" -- I would hate to be in the 5%!
Jeff

references:

http://www.cdc.gov/nasd/docs/d000001-d0 ... 00007.html
http://www.arrl.org/tis/info/lightning.html
http://www.polyphaser.com/technical_notes.aspx

[Bob Owens]

Am I correct that a barnacle-covered dynaplate would be as ineffective a lightning ground as a dynaplate that has been given one coat of bottom paint? Would a really high-cuprous oxide paint lessen the interference with the plate's conductivity? I don't usually have to pay a diver to clean any of my hull each season, except for a single go at my prop about two-thirds through the summer. But maybe making certain that that dynaplate is clean always should be a top priority.
Bob

[Oswego John]

jbenagh and all,

It seems that there are so many questions about lightning and so few definite answers. Continuous studies are being conducted and some of the things that were truths about lightning are being restudied with new revelations being revealed.

I am not positive but I think that the study you are referring to is one by Professor Ewan Thomson when he was with the University of Florida. His extensive writings on the subject of lightning were very enlightening and in many instances surprising.

Unfortunately, Dr Thomson is no longer associated with U of Fl and his findings are no longer available on the web. He is now with a private agency doing studies in the same field. The good news is that there are other findings published by the U of Fl in re: boating and lightning that are well worth investigating. I am having trouble finding the proper URL to get to it.

http://www.cdc.gov/nasd/docs/d000001-d0 ... 00007.html

Now scroll down to "NASD Boating-Lightning Protection" by Professor Wm. J Becker, Extension Safety Specialist-U of Fl.

This thread was discussed a few years ago and some more info is available by going to "Search". Type in keyword "Lightning" and Author- Oswego John.

I don't remember if this was ever mentioned before or not. If you are ever caught in an electrical storm, go below and stay centered in the cabin. Keep your hands in front of you but don't touch anything. Probably one of the worst things that you can do is sit at the helm in the cockpit. You could very well be a link in the chain between the aluminum mast, boom and the rudder post.

I don't know if this, too, was ever mentioned. Harbour and baymen practice this when caught in an electrical storm. At the first sign of impending lightning before the storm hits, we drop the anchor and chain and if there is a metal sampson post, secure the chain and wrap it a few times around the grounded post. Any bonded metal on the boat will do. On my old work boat, I used a phase jumper for bonding the chain to the bond system, which I borrowed from a utility lineman friend of mine.

Ask a half of a dozen persons what is real and what is fantasy when preparing your boat for lightning and you might get seven different answers. I tend to rely on the results of controlled experiments and the suggestions of people who are experts in the field. I'm not certain if anything is definitive.

Also, knocking on wood and keeping one's fingers crossed helps a lot.

O J

[WaywardWind]

Grounding plates on boats (sail or power) do not reduce the chance of a lightning strike, nor mitigate the damage of a strike that does occur.

They are, however, a fine talisman.

The reason for not painting a DynaPlate was (was) that paint "filled in the pores", thus supposedly reducing the "effective surface area" for radio transmission. Much hoopla behind the claim, but no science, no positive experience in the ham radio community.