Bonding

Post your technical questions or solutions about your boat's electrical systems or electronics here.

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knitchie
Posts: 27
Joined: Mon Nov 09, 2015 4:30 pm

Bonding

Post by knitchie »

None of the metal fittings on the 350 are bonded to ground, as I understand. Has anyone gone to the expense and time to install a bonding system to reduce galvanic activity?
jbd3
Posts: 60
Joined: Sat Nov 22, 2008 6:44 pm

Re: Bonding

Post by jbd3 »

Having had 2 lightning hits, I've explored this also. A frustrating convo with Catalina lead to my conclusion that they do no grounding primarily to avoid responsibility for any damage sustained from someone making the case that the grounding was inadequate. The tone went from friendly/chatty to corporate the moment I asked about this. My last surveyor strongly suggested adding a grounding plate but the marina where the haul out took place didn't want to do it, again I assume for liability reasons, unless every stanchion, shroud, pulpit mount, etc. was included which created an astronomical expense once the boat was post-construction. There is a lot of conflicted data on the web as to whether or not grounding was really protective, often from the perspective that lightning would do damage regardless of grounding. I opted to pass but I do believe this was a corner that should not have been cut in the design and assembly of these otherwise stellar boats. Since we currently own 2 of them, I think this is much less important in fresh water since that isn't particularly conductive and more important in salt water which is. I see your question is about galvanic activity so this is a bit of a side bar..
knitchie
Posts: 27
Joined: Mon Nov 09, 2015 4:30 pm

Re: Bonding

Post by knitchie »

In addition to protection from lightning, bonding can also reduce the difference in electrical potential between underwater fittings that can cause galvanic corrosion. Fortunately, it is a lot easier to bond all the underwater fittings than all the metal above water.
wolfe10
Posts: 587
Joined: Mon Dec 11, 2006 2:58 pm
Location: Ft Myers Florida

Re: Bonding

Post by wolfe10 »

Ya, the jury is definitely out on whether to bond or not for lightening protection.

Had a friend with a Dickerson 37' on Kentucky Lake (upper Tennessee River). Bonded and extremely well built.
Struck by lightening.

Asked me to come over and help him figure out how water was leaking into the bilge which had always been dry before the lightening strike.

Found close to 1,000 pinholes through the hull at the waterline.

Lightening is powerful enough to go through thousands of feet of AIR (an excellent insulator). Where it goes when it hits a boat is not something that our best laid plans are likely to significantly affect.

So, bond if it makes you feel better, but have insurance in the event you are stuck!
Brett Wolfe
C350 #180
"Vindaloo"
Ft Myers FL
User avatar
D&M
Posts: 69
Joined: Thu Aug 06, 2020 5:02 pm

Re: Bonding

Post by D&M »

knitchie wrote: Fri Oct 25, 2019 8:49 pm In addition to protection from lightning, bonding can also reduce the difference in electrical potential between underwater fittings that can cause galvanic corrosion. Fortunately, it is a lot easier to bond all the underwater fittings than all the metal above water.
This is an old post but one I wanted to expand upon. The C350 has three underwater fittings which could be affected by galvanic corrosion. The prop shaft, the prop and the rudder. (This assumes you have not replaced the marelon through hulls with metal ones). If you have a zinc anode (or aluminium, or magnesium) depending on where you sail, in good condition attached to the prop/shaft this will protect these items. There is no need for any other "zincs". A bonding system is not required because there is nothing to bond.

BTW the story of the lost rudder when the rudder stock became electrified with +12volts is not galvanic corrosion; but man made current corrosion - a big difference. (You can hardly call it stray current when it was created from within the vessel) In that case the rudder stock became the anode (as opposed to the zinc) and with current corrosion it happens much faster than galvanic corrosion. In that case the +12 volts found an easy way back to the source (battery) via the prop shaft through the engine and then the 12 volt negative terminal. For those who believe the transmission fluid provides an isolation from the engine to the prop shaft, I suggest you put a multi meter from your engine negative terminal (some people call this a ground, it is not) to the prop shaft. You will get a reading of probably less than one ohm.

On the lighting protection side of things as mentioned earlier, if you feel better for it spend the money but know it will not protect your electronics. The electro magnetic pulse from a direct lightning strike should induce enough current in your equipment to destroy it all. Expect it and insure against it. There is a reason the lightning conductors on NASA launch pads are ringed around the pad at a distance. They are sacrificial towers trying to draw lightning away from the launch tower. Try to do that on your boat!

Finally, lightning is the only case where electricity leaves the source and does not try to get back to the source - naturally. In all other cases electricity simply returns to the source. This applies to AC and DC. IT DOES NOT "GO TO GROUND".
Regards,

David
Sea Lanes #281
Cairns, Australi
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