Speaking of engine zincs...

Yesterday, in prep for losing power at the marina at noon today, I fired up the genny to check everything. For the first time in our nearly 7 year history, the NL 16KW genny didn't instantly start/run. It started, ran a few seconds and died. Started again, ran a few seconds and died. Started again, ran perfectly. No, this thread is not about figuring out the issue but it got me to thinking about something else.

Actually this thread is to ask the question, "Did the "need" for having zincs in engines undergo a change sometime in the past?" The reason I ask is that my DDs have fittings for 3 zincs in each engine - one on the RW pump housing and two in the HE (though I only use one - on the outlet side of the HE). The NL genny has no fittings for zincs at all nor any mention of them in the owners or service manual

Near as I can tell, the mains/genny engines are made of the same materials as are the HE cores, etc. So it seems obvious to me that at some point there was data or whatever available to engineers to lead them to believe that zincs were not needed.

A few months ago I pulled the genny HE for the first time since we have owned the boat. I cleaned it but frankly, there were no deposits in the HE at all. So, what was the "data" that made NL realize that zincs weren't necessary? Do currently-made marine diesels have zincs?

This reminds me of conflicting answers rsmith and I gave in the last week (was it a question from Angela??) about pencil zincs in a genny.

If you read about the theory of cathodic protection (as in the Beyn's THE 12 VOLT DOCTORS HANDBOOK by Spa Creek electronics) you find there are a myriad of considerations. I doubt there is a single answer.

Quality alloys are crucial and maybe bronze, for example, with fewer impurities is now generally available. If there is zinc mixed in with whatever metal is used inevitable local (like crevice) corrosion occurs, protective zincs or not. Today US silicon bronze (as in thru hulls, seacocks,etc) should last forever, while manganeze bronze (which most props used to be made of) requires cathodic protection. I suspect Aquamet 22 (recreational) shafts will also last indefinitely, but not the stronger commercial grades which I think still require cathodic protection.

You'll see that a key ingredient regarding internal parts is free ion flow...it carries the corrosion current and the protective cathodic protective current. In small diameter hoses there is usually not enough cross sectional area to carry much of any current....and NONE passes thru rubber impellers....so local zincs are still,maybe, a safety precaution....Hence in DD for example, local zincs were used to protect local metals.....

the other ingredient might be bonding systems and recommendations.....distant zincs don't protect internal engine and genny parts that might corrode. And often they don't protect props very well either...hence local shaft zincs....It was discovered that with stray currents in marina waters, a bonding system (a wire among bow to stern seacocks, shaft logs, rudder posts,etc) actually acts like an antenna and picks up stray currents just like your radio antenna picks up electromagnetic radition from the air. This is made worse by multiple connections between dc,ac ground and the bonding system.....and leaky grounds from shorepower cables where isolation transformers or blocking diodes are not used....and all this can generate ion flows in gennys and engines where they would otherwise not exist.....

all the above boils down to this I guess: if you have pencil zincs, replace them before they flake off and clog raw water cooling passages. Use them because that's what surveyors will expect to see.

If there is any new science on all this, I have not seen it.