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
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.