Bonding and DC ground.....

[NYSail]

Hello all.....
Have a question regarding grounding of DC electric. My ground goes to the engine block..... Also I have a bonding to only my stays (not through hull fittings) to the keel. Is there also suppose to be a connection from the engine block ground to the keel where the bonding wires are attached?? btw, none of my through holes are attached to bonding or ground..... What is the opinion of this? Pearson apparently didn't think it was necessary however see most boats do have.

Thanks!!
Greg

 

[Stu Jackson]

http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems

 

[Ken Cross]

Really it depends on your purpose. If you bonding is for lightning protection the through hulls have little purpose.

Without knowing your boat I don't see a reason to connect the engine to the keel.

The grounding to your engine is another matter altogether. Think of grounding as just another wire to make complete circuits.
For some reason people don't seem to understand that grounds are simply conductors. There would be good reason to isolate your bonding system from your grounding system if your propeller and shaft weren't conductive (or if your coupling electrically isolates them). It could go along say toward eliminating electrolysis. That stray current that seems to flow where we don't want it to is what causes electrolysis. On our previous boat I installed a composite propeller. A benefit I hadn't thought about: Our zincs seemed to last forever. The only thing they had to protect was a few inches of propeller shaft. After 2 years they were nearly like new. 2 more years; same story.

Ken

 

[Charles Erwin]

Both AC safety green and DC negative need to be connected together and that means they are also both connected to the motor block but the purpose is different. AC safety green connected to the motor block is a second path through the water to earth/ground in case AC safety green in the shore power cable or elsewhere becomes broken.
Also if AC were accidentally shorted to a DC conductor on the boat there is a path to earth/ground and - one hopes - an AC breaker or GFI would trip instead of energizing your DC system with AC power. Obviously the shaft cannot be isolated from the transmission for example via a shaft saver or other flexible joint. If so you need a shaft jumper wire.

Bonding is a bit different. Bonding (connecting) the the keel to the motor block means your shaft anodes will protect your shaft and propeller assembly and now your keel as well. If the rest of the underwater metals are connected the shaft anodes are protecting all the rest of those underwater metals too. So put a zinc on the keel or do not - but do not connect (bond) the keel to the motor. There are other threats as well by the way.

Connecting the rigging to the keel is completely silly. This permits a path for stray current to to pass via your vhf antenna wiring up the mast down the shrouds to the keel and back to your battery. I can think of no reason whatsoever to connect the rigging to the motor or keel or anything else either.

Get rid of the above water rigging to keel connections. Do not bond/connect the keel to the motor block. Keep your bilge dry, your low lying wiring well maintained, and out of the water - and skip bonding the underwater metals.

There is one exception in my opinion. Bond (connect) the rudder post to the strut and bolt an anode direct to the strut but no further connection to the motor. That will provide cathodic protection for the rudder post and the strut separate from the shaft zincs.

Charles

 

[NYSail]

You guys are smart! Thanks as always for your insight into this..... Going to boat to check

 

[Maine Sail]

Connecting the rigging to the keel is completely silly. This permits a path for stray current to to pass via your vhf antenna wiring up the mast down the shrouds to the keel and back to your battery. I can think of no reason whatsoever to connect the rigging to the motor or keel or anything else either.

Umm one word, lightning.... In the PNW this is not a huge issue but I would never personally own a boat without a lightning bond from spar to keel.

The evidence we have on-hand, and I have consulted with Beth L. at length about this at Boat US, is that well grounded boats are hit slightly less (Dr. Thompson's data-set also agrees) and suffer less hull damage. The data leaking out every few months from Boat US, about lightning, was at my nudging Beth to look into this... Unfortunately lightning data collection, on the insurance side, is pretty lacking so every word has to be poured over to dissect any relevant data..

As an electrician who does about 7-15 lightning damage consults per year, in my own pool, the well lightning bonded boats suffer considerably less hull damage. When my own boat was hit she suffered zero hull damage and the lightning exited the bottom of the keel where the longest keel bolt is and where the massive lightning bond wire to the spar was connected. Every piece of electronic and electrical gear was toasted, including stuff not even plugged in, as is normal in a bad hit, but our hull remained 100% undamaged. My boat is not "bonded" for galvanic bonding just lightning bonding...

A well installed VHF whip has no path to the spar. Creating a whip-isolator takes about 15 minutes... .

 

[RoyS]

There are plastic VHF antenna mounting brackets available also. I installed one about five years ago with some concern about longevity, however, so far no issues.
Also, at one time the IEEE recommended connecting the shrouds to the keel for additional lightning protection. This presumably created a Faraday cage to protect the ships occupants in a lightning storm.

 

[JamesG161]

This presumably created a Faraday cage to protect the ships occupants in a lightning storm.

No presumption! At least the US Navy practices this science. For sure your Microwave Oven!
Every wonder how you can see inside your Microwave to monitor your delicious home cooked meal, while the Admiral is way, without cooking your eyeball too?

A Faraday Cage!!!
https://en.wikipedia.org/wiki/Faraday_cage

BTW there are a few ways to get Lightening Damage on you boat.
1) Direct Hit.. Normally you will measure the size of the hole in your flaming boat, as it sinks.
2) Side branch... Less amps but the wire to your grounds will be melted or exploded.
3) Boat to boat... A bolt hits a nearby boat and then discharges to water and passes up through your keel too.
Usually evidenced by keel bonding wiring damage.
And IMHO the most common....
4) Ground strike nearby that powers up your AC Green and/or White common grounds, thus reversing the current flow. Evidence would be damaged shore power boxes, melted shore power cords and in a smaller strike, AC breakers damaged or tripped.
Since the AC Green and DC ground should have a common point, the may be more DC than AC circuit damage.
5) Other ways that are truly random... Power Ball win.. kinda odds.

If your marina has a frequent problem, as the manager to improve is AC ground to allow a ground strike to dissipate faster.
Jim...

PS: You can only reduce the odds of a strike by good grounding, not prevent.

 

[Charles Erwin]

Umm one word, lightning.... In the PNW this is not a huge issue but I would never personally own a boat without a lightning bond from spar to keel.

The evidence we have on-hand, and I have consulted with Beth L. at length about this at Boat US, is that well grounded boats are hit slightly less (Dr. Thompson's data-set also agrees) and suffer less hull damage. The data leaking out every few months from Boat US, about lightning, was at my nudging Beth to look into this... Unfortunately lightning data collection, on the insurance side, is pretty lacking so every word has to be poured over to dissect any relevant data..

As an electrician who does about 7-15 lightning damage consults per year, in my own pool, the well lightning bonded boats suffer considerably less hull damage. When my own boat was hit she suffered zero hull damage and the lightning exited the bottom of the keel where the longest keel bolt is and where the massive lightning bond wire to the spar was connected. Every piece of electronic and electrical gear was toasted, including stuff not even plugged in, as is normal in a bad hit, but our hull remained 100% undamaged. My boat is not "bonded" for galvanic bonding just lightning bonding...

All true - however lightning suppression includes a rod and robust down conductor. That conductor does not exist on the boat in question and neither does he have VHF isolation. Bonding the shrouds alone will not improve things.

Anyway - at least now you know why I said what I said - Now he can certainly add these items to the calculus but until then I am still clinging to my opinion - so far


Charles

 

[Maine Sail]

All true - however lightning suppression includes a rod and robust down conductor. That conductor does not exist on the boat in question and neither does he have VHF isolation. Bonding the shrouds alone will not improve things.

Anyway - at least now you know why I said what I said - Now he can certainly add these items to the calculus but until then I am still clinging to my opinion - so far


Chalres

An aluminum spar makes an excellent and robust down conductor. If you had carbon fiber or wood then yes you would need an additional down conductor. I agree that bonding the stays is of less value especially when the SS offers a much higher resistance than the spar and we often wind up with conductor radius in the boat that don't led well do conducting the strike to the water... The idea of a bonded spar is not to minimize or reduce chances of a strike, that won't happen, just to try and minimize the potential for hull damage. I don't mind sitting on my boat with dead electronics but I don't also desire a hundred pin holes because the strike found its way through the hull.... Bonding the spar to keel can help to minimize that risk.

 

[JamesG161]

I agree that bonding the stays

If your Aluminum mast is bonded AND your metal stays are electrical connected to your mast, the stays are bonded.

Nothing minimizes your chance of a strike, but a well grounded boat makes your boat's chance of a hit, the same as the community water tower, local bridges, tall grounded buildings, etc.

Put it this way...
If I am on my well grounded boat (BTW it is!), next to a ungrounded boat with same size mast as mine. I am NOT moving to the neighbors boat for safety or 2 martinis, during a lightening storm.
Jim...

PS: Hmmmm? I wonder why sailboats are not Banned from marinas?

 

[Maine Sail]

If your Aluminum mast is bonded AND your metal stays are electrical connected to your mast, the stays are bonded.

The risk is that if the chain plates/stays are not bonded to the keel or immersed lightning ground point and the strike follows the stay down it can side flash.. Yes they are bonded, by sheer connection to a bonded spar, but only in the pure sense of Earth potential but they are not "path" grounded to the keel..

Nothing minimizes your chance of a strike, but a well grounded boat makes your boat's chance of a hit, the same as the community water tower, local bridges, tall grounded buildings, etc.

Absolutely but the data we do have suggests that lightning bonded boats are hit slightly less often and non-bonded. Course trimarans and cats are hit the most often regardless of bonding, so surface are must also play a role..

PS: Hmmmm? I wonder why sailboats are not Banned from marinas?

Don't know why they would be my brothers old Mako center console was hit in a mooring field with 1100 sailboats..... Blew the terminals right off the battery... He was surrounded by 40+ foot sailboats less than 65' away... Lightning seems to hit what it wants...

 

[Ron20324]

Then there was the film footage on the evening news. A bodacious rain storm was blowing through a marina. It was being filmed from the office when a lightening bolt hit a power boat- and it was in the slip next to a tall-masted sailboat! All caught on camera.

 

[CYQK]

Mainsail
was planning a cable with a zinc on it to be able to hang over the side while at the dock or moored
Will a battery jumper cable work for this an attach fitting on the mast and a large fish zinc on the other end?

 

[Ken Cross]

Mainsail
was planning a cable with a zinc on it to be able to hang over the side while at the dock or moored
Will a battery jumper cable work for this an attach fitting on the mast and a large fish zinc on the other end?

This is an old suggestion which has been discussed for years. The problem with the cable over the side is the exposed to water area of the cable may not have surface area to accommodate the huge energy of a lightning strike. While it may help, it may not be enough. The keel would make a great ground due to large surface area, but most likely it's covered with something (fiberglass, epoxy, etc.) which would be likely blown off during a strike. It may prevent the boat from perforation and sinking, but the boat would still need hauled and rebuilt. This assumes you know the boat was hit although you may be able to guess when all your electrical and electronics fail to operate. If you search archives you should find lots of lightning protection information.

I'm just happy to live up here where we don't actually get lightning each year.
Ken

 

[JamesG161]

Mainsail
was planning a cable with a zinc on it to be able to hang over the side while at the dock or moored
Will a battery jumper cable work for this an attach fitting on the mast and a large fish zinc on the other end?

Yes, better than no grounding at all.

Are you sure your boat is not "bond grounded" as mentioned in this post and especially the best concise discussion from West Marine I have seen. The link is shown in @Stu Jackson post #2 above.

Bond = Tied together electrically. Grounded= all at 0 volts DC ground and hopefully to the ocean.

Test...
1) Rub a cleans spot on your drop zinc with sand paper size of a quarter.
2) Hook your jumper cable to the drop zinc cable and the other jumper end near your mast.
3) Set you DVM to continuity or Ohms.
4) Suspend your drop zinc in the water near your mast. Wait a few minutes.
5) Use your DVM probes ... one to the jumper, the other to touch the mast.

If you get low resistance (ohms) in few minutes, then your boat is probably already "bond grounded".
You are using the zinc as an extended "test probe", in this example.

At minimum, your idea would help prevent a "static charge" build up on you boat.

Near mine, there is a 45' ketch, with no "bonded ground". He has a "bronze grid plate" 16x16" with a big big ground wire. He hangs it, like you suggested, clamped to mast and over board submerged, but he forgot a ketch has two masts. He had some extensive electronic damage in a summer storm. My boat, 50' away, had none.
Jim...

PS: A cloud "sees" ground charges and not elevations, just like you get a "static zap" from static electricity. As the ground charges build up, the opposite charge in the clouds will jump to the easiest path. ZAPPP!
You can only hope to be in a spot not under, the charged cloud and "invisible electrically" by grounding your boat.

 

[mitiempo]

Short video of a sailboat being struck by lightning in Greece.

https://gcaptain.com/sailboat-light...GN&utm_term=0_f50174ef03-d9a0162148-139850237