Re: prop zincs ,WOB Corrosion, more than you ever wanted to know about...and a message to Kent from Olivier


Hello everyone and here is yet another installment of more than you ever wanted to know about…

During my first visit to Chantiers Amel in the early 1980’s  I spent several hours each day under the tutelage of Jacques Carteau, the Technical Manager at Amel. His job was to take Captain Amel’s thoughts and ideas and turn them into the diagrams, lofts and procedural instructions to make these ideas into a boat. At that time, Mr. Carteau knew more about everything Amel than anyone else at the shipyard. Mr. Carteau could tell I was enthusiastic to learn about all the technical and construction details and, over the years, gave me an incredible education about just about everything that happened, start to finish, when building an Amel boat. Amel insiated that anyone who made representations about their boats to really know what they were talking about and they spent lots of time over the years making sure I was fully familiar with the entire boat and all systems aboard.


There were in depth instructions about all the systems. He explained that Amel boats, every one/every model, had a full earth return/full floating DC electrical system. Simply, this means every bit of electrical energy comes out of the batteries , supplies power to the device to which it is connected and then returns left over energy back to the batteries. If this system is not corrupted, it just about precludes electrolytic corrosion.

When I asked why none of the Sharki, Maramu or Mango boats had zincs on the prop shafts or propellers, even the ones on the way to be launched, he took me to his office and showed me the diagrams for the galvanic anode/zinc system we all have on our Amel boats. This joins every piece of metal near or below the waterline and carries any stray current back to the two zincs on the rudder. He explained in great detail ( I should have taken notes as details dim after nearly 40 years ) how this system was perfectly galvanically balanced and no additional zincs were needed anywhere. He also explained that to introduce more zincs can have a negative effect on the whole system and actually cause metal wasting when the system goes out of balance. It was all kinda like alchemy to me but, hey, this was Mr. Carteau, Amel’s right hand man.


Why all this explanation? Because it is imperative to the good health of our boats that these carefully conceived systems be kept as designed and well maintained. Keeping connections clean and securely fastened is imperative. Don’t let someone totally unfamiliar with the totality of these systems ever give you guidance about changing them to something they are more familiar with. Over the years I can’t tell you how many times that shipyard/repair managers have called me  to tell me how stupid the Amel drive system is, how the bow thruster was conceived by a moron and built by a monkey, or that all those wires carrying DC electricity back to batteries was just plain old stupid and entirely unneeded…I could bore you with more but you get the picture.


I call it “The not invented here syndrome”. If some well experienced marine tech sees something unfamiliar, well, it can’t be any good and probably doesn’t work well for very long and blah blah blah.  Don’t let people like this on your boat.


Oh, in closing, no Amel built boat with an Autoprop ever left the factory with a zinc on the prop. Not one. Only got the red plastic cap. Honestly, you really don’t need a zinc. Some folks follow the if enough is plenty, more is better rule and put a zinc on. Probably won’t hurt anything but it does not help anything either. Just to be safe incase my recollections are suffering from geezage, I checked in with Olivier. He said the ONLY boats that had zincs on the props were boats with a Maxprop and only because they didn’t make a plastic cap as a replacement and the stuff inside the prop lasts longer if foreign bodies are kept out.


Kent, Olivier suggested the next time you do your testing, do it while turning on just one electrical device at a time and see if there is any major difference and if so, investigate that fully. Kent, your boats first owners were nice folks but not mechanically sympathetic. You are to be highly commended for your rescue of and continued efforts to improve KRISTY.


Have fun with your Amel boats everybody!




                                           THE  EXPERIENCED AMEL GUY


                                   Office 954-462-5869  Cell 954-812-2485



From: <> On Behalf Of karkauai via Groups.Io
Sent: Sunday, March 29, 2020 2:30 PM
Subject: Re: [AmelYachtOwners] WOB Corrosion


Oops forgot to attach pic:



On Mar 29, 2020 1:53 PM, "karkauai via Groups.Io" <karkauai@...> wrote:

Thanks, Mark.  Interesting to know.  I have a MaxProp Classic.  They sell stainless steel hex bolts for the zinc.

Anyone have suggestions for something I can put between the zinc and aft side of the prop to improve contact?


I was able to remove the bad WOB by drilling two holes and using screws to pull it out.  It came out with just a little coaxing.


See pic.  The galvanic damage extended about half way through the WOB.


I tested continuity between the prop shaft and bonding system and found NO LOAD!!!

Further investigation showed bad connections between the CDrive and engine bed.  After cleaning those up, still NO LOAD. Cable was bad, too, inside the connectors.

I've now confirmed no resistance between the prop shaft and the rudder zincs.


If this had been worse, I could have had catastrophic failure of the WOB, and who knows what kind of other damage...I got lucky this time.


Soooo, bottom line for me is that while hull potential is a good measure of overall bonding efficacy, we must REGULARLY measure continuity at ALL metals exposed to sea water to confirm that they are protected.  It goes on my quarterly maintenance list today.



SV Kristy

SM 243


On Mar 29, 2020 1:17 PM, Mark & Debbie Mueller <brass.ring@...> wrote:

Hi Kent, 


I do like the Dremel idea; it will allow you to section the WOB and remove it like a dentist removes a wisdom tooth. 


I wanted to let you know that every time I have ordered prop shaft zincs they have come with the plastic screws.  The zinc has exhibited “normal” wear but has never fallen off.  The Autoprop website has a video showing the rebuild of an H5 and references removing the plastic screws when disassembling the prop.  I believe metal screws provide a preferential contact area on the mounting tabs enhancing the destruction of the tabs whereas the plastic screws spread out the contact area to the body of the zinc – just a SWAG.


Good luck with your project.

Mark Mueller
Brass Ring  A54



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