Grounding Shaft with a DriverSaver

[psneeld]

Originally Posted by SV Escape Plan

Sounds pretty neaat and all but Why? Im still wondering what all of this actually accomplishes?

look up electrical potential and galvanic corrosion...lots of literature on it..

here's a bit from wiki...

Overview
Dissimilar metals and alloys have different electrode potentials and when two or more come into contact in an electrolyte a galvanic couple is set up. A galvanic couple can also be set up on a single metal or alloy due the metal surface not being homogeneous or if the electrolyte varies in composition, forming a concentration cell.

The marelon doesn't require any bonding...and there is the thought that good bronze in isolation from other metals doesn't really need bonding...but once you get stainless and/or aluminum in the mix and it's a time bomb waiting to dissolve....yes galvanic action is usually slow...but often boats develope salt bridges and allow minute DC stray current corrosion that will eat zincs fast...but better the zinc than your underwater metal. Bonding seem to lessen the effects by distributing the DC stray current and uses all you zincs in the sacrificial mode.

[osirissail]

Originally Posted by SV Escape Plan

Ok well I guess I will add a wire here and connect the shaft and prop to my DC ground but I have yet to see a really good reason. I do not have a bonding system on my boat and will not add one. All of my through hulls are marelon. I dont understand why these items would need to be connected to the engine block (DC ground) if they have their own anodes? I dont leave my boat plugged in to shorepower except to top off batteries then it gets unplugged. What am I missing here? What does this connection do for me?

The "Bonding System" is there to connect to ground all the various pieces of metal on the boat like lifeline stanchions, chainplates, shrouds and stays, and anything else metal that a human might touch or come into contact with. These are all connected together by a "bonding wire" and then connected to a ground(ocean). Should something electrical, AC or DC, come in contact with these odds and ends of metal on the boat the appropriate circuit breaker will trip and protect the human from a shock. In the very unlikely chance that you should be near a lightning strike or take one, the bonding system will help dissipate the residual electrical energy (corona effect), again for safety of the humans on board.

[SV Demeter]

Im quite familiar with the sources and effects of galvanic corrosion and dont want to debate bonding vs not bonding but my understanding is that there are two approaches to preventing galvanic corrosion: One says to bond everything together, all underwater metal fittings and tie them to a centrally located zinc or several zincs. The other approach says do not bond anything but instead provide each underwater piece of metal with its own sacrificial anode. This is why the newer bronze through hulls actually have a provision for attaching a zinc directly to them. My approach would be to NOT connect my shaft and prop to my DC ground (which is tied also to my AC ground) and instead provide each piece of underwater metal (only the prop and shaft on my boat) with its own protection.

Osirissail however brings up perhaps the only sensible reason I can see for connecting the shaft and prop to my engine block (DC/AC ground). Im not interested in lightning protection via this route anyway, but in the event of an AC circuit fault if my prop and shaft were not connected what would happen? Would breakers not trip? I think that may be the case but Im not sure? Can someone explain? This protection seems to be the only sensible reason to connect, NOT for any galvanic protection reasons, I mean what would I be protecting?

[psneeld]

Originally Posted by SV Escape Plan

Im quite familiar with the sources and effects of galvanic corrosion and dont want to debate bonding vs not bonding but my understanding is that there are two approaches to preventing galvanic corrosion: One says to bond everything together, all underwater metal fittings and tie them to a centrally located zinc or several zincs. The other approach says do not bond anything but instead provide each underwater piece of metal with its own sacrificial anode. This is why the newer bronze through hulls actually have a provision for attaching a zinc directly to them. My approach would be to NOT connect my shaft and prop to my DC ground (which is tied also to my AC ground) and instead provide each piece of underwater metal (only the prop and shaft on my boat) with its own protection.

Osirissail however brings up perhaps the only sensible reason I can see for connecting the shaft and prop to my engine block (DC/AC ground). Im not interested in lightning protection via this route anyway, but in the event of an AC circuit fault if my prop and shaft were not connected what would happen? Would breakers not trip? I think that may be the case but Im not sure? Can someone explain? This protection seems to be the only sensible reason to connect, NOT for any galvanic protection reasons, I mean what would I be protecting?

I'm no expert..but you seem to be ignoring the potential factor...yes the base metal would be protected as long as there is a zinc on it...but if there is enough potential between two underwater items...I think one zinc would disolve more quickly leaving that underwater fitting unprotected totally. At least with bonding..it gets some protection through the bonding system.

So looking back at your original post...you wouldn't have to if you believe in the don't bond system...but if you bond, the block is usally a tie in point. if you used shaft brushes and tied that into your bonding system, then you wouldn't have to strap over the drive saver.

[SV Demeter]

Originally Posted by psneeld

I'm no expert..but you seem to be ignoring the potential factor...yes the base metal would be protected as long as there is a zinc on it...but if there is enough potential between two underwater items...I think one zinc would disolve more quickly leaving that underwater fitting unprotected totally. At least with bonding..it gets some protection through the bonding system.

Please tell me how I would be getting "some protection through the bonding system"? Are you thinking that there are some other anodes some place else on the boat that would provide this protection or some other device? Im not following your logic here.

[psneeld]

Originally Posted by SV Escape Plan

Please tell me how I would be getting "some protection through the bonding system"? Are you thinking that there are some other anodes some place else on the boat that would provide this protection or some other device? Im not following your logic here.

Yes...any fitting with zinc on it is helping ALL underwater fittings if they are all bonded because they are all at the same electrical potential.

[SV Demeter]

"Yes...any fitting with zinc on it is helping ALL underwater fittings if they are all bonded because they are all at the same electrical potential. "

Okay but there are no other zincs on the boat nor any other underwater metal parts to put zincs onto. There is also no bonding system nor is there anything else underwater that is metal to bond. Also I might add the boat has apparently been this way for quite some time with no abnormal galvanic corrosion present.

The only logical reason I can see to make this electrical connection is to provide a path to ground in the event of an AC electrical fault as Osirissail suggested, but I am looking for more detail on how this works.

There is no reason galvanically speaking that I can see to make the connection.

[psneeld]

Originally Posted by SV Escape Plan

"Yes...any fitting with zinc on it is helping ALL underwater fittings if they are all bonded because they are all at the same electrical potential. "

Okay but there are no other zincs on the boat nor any other underwater metal parts to put zincs onto. There is also no bonding system nor is there anything else underwater that is metal to bond. Also I might add the boat has apparently been this way for quite some time with no abnormal galvanic corrosion present.

The only logical reason I can see to make this electrical connection is to provide a path to ground in the event of an AC electrical fault as Osirissail suggested, but I am looking for more detail on how this works.

There is no reason galvanically speaking that I can see to make the connection.

If you are saying that the only metal underwater on your boat is the shaft and prop...and it has a zinc on it...then yes...you are probably OK...but you entered the world wide forum of "most boats" that have more than one underwater metal situation...thus bonding.

And yes...you ultimately should have some path to ground as Osirissail suggested for a variety of other reasons if you have an AC systen at dock or a genset when away from shore.

[osirissail]

First of all, I think we have got the stern before the bow on this bonding and galvanic/electrolysis thing.
- - First bonding is required by NEC and ABYC to protect humans for accidental electrical shocks caused by accidents where an electrical source comes in contact with "normally non-conducting" metal on the boat such as lifelines, stays, shrouds, masts, etc. Many accidents can occur where an electrical source gets in contact with a normally non-conducting metal. That is what bonding is all about. Add in the common practice of connecting AC and DC grounds to the engine and we have everything being channeled down that to the prop & shaft.
- - The zinger is that you need these items electrically connected to an "earth ground" which in our case is sea water. Since few boats have dedicated grounding plates (they are rather expensive) the common earth ground is the Prop and shaft through the engine. Without an earth ground at the end of your bonding wire system, you are not bonded.
- - So without a dedicated ground plate(s) attached to the underside of the hull installing a "Drive-Saver" wipes out your bonding system (and grounding system) and you are relying instead on bronze through-hulls, if you have them. Not a good idea. So a simple copper braid strap across from one side of the Drive-Saver to the other restores the bonding system and electrical pathway to the prop and shaft. Shaft Brushes can work but over time they wear or become non-functional. And they are just one more thing you have to maintain and worry about.

- - Now the bad news - bonding facilitates/introduces the problem of galvanic/electrolysis between non-similar metals which are both immersed in seawater (underwater). If you had NO underwater metallic items obviously you would have no galvanic/electrolysis problems.
- - Even with Marelon through hulls and seacocks with vinyl hoses there is still one major item - the prop shaft and propeller that (if you have an engine) generally has a stainless steel shaft and a bronze propeller. Bingo, dissimilar metals both immersed in seawater and connected together.
- - In reality there are other items like grounding plates and rudder shafts/bearings, etc. that contain metal and are immersed in water besides the engine/propulsion system.
- - So we use sacrificial zincs to lessen the problem with underwater metal being dissolved.
- - If for some strange reason you had no engine (prop & Shaft) and Marelon through-hulls/seacocks, you would only be concerned with things like the rudder shaft and bearings (barn door or full skeg rudders) which could be protected with separate dedicated bullet zincs. And you would need an underwater grounding plate attached to the hull to provide an electrical "earth ground" - if - you had an AC/DC electrical system.
- - As with most things "boat" one good idea usually raises other bad ideas that have to be dealt with.

[SV Demeter]

Thanks Osirissail this is the explanation I was looking for regarding the AC fault issue. Im going to add the jumper wire and connect the shaft to the engine block.