Expensive mistake

[Patches]

I swapped out my bronze prop shaft for a stainless one about 1+ years ago, and did a new PSS dripless shaft seal at the same time.  New zincs (2) were put on the prop shaft, and a clam shell-type on the strut.

With the old bronze shaft, I didn't seem to have to replace zincs more than once/season.  I just hauled out, and the zincs on my stainless shaft were completely gone.  Worse, my fixed 3 blade Michigan Sailer (original) had started to de-zinc and had to be replaced.  The zinc on the strut was still in place, although close to spent.

One "boat buck" later, and I have a new Michigan Sailer 3 blade, 15 X10, prop.  I was a bit fortunate to source one locally from the Prop Shop in Mukilteo, WA, who had one in stock.  Everywhere else said it would be 6-14 weeks to get one.  I was told that the "Sailer" types are made offshore, and part of the reason for the wait.  The Michigan MP3 3 blade props are easy to find, and much cheaper too ($600-700).

Anyway, anecdotally at least in my case, it seems the zincs need replacement more frequently with the stainless shaft/bronze prop set-up. 

What is the frequency that others change zincs with this set-up in salt water?  Every 6 months?  More frequently?

Your input is appreciated.

Patches

[waughoo]

I have the divers out every 6 months at Elliott Bay marina just across the Sound from you.  My strut button zinc is often not really attacked but the 2 shaft zincs are due each time they dive.  I have a 3 blade bronze prop and a stainless shaft.

[Ron Hill]

Patches : I don't believe that the change from bronze to a stainless has anything to do with the Zn being "eaten" up faster!!  Unless the new Zns that you are using have a better connection to the drive shaft (ie. the BB in the shaft Zn vrs no BB).  You might have a new slip mate that is emitting stray voltage or some other marina cause??

A few thoughts

[waughoo]

I would also think surrounding conditions would be the more likely culprit than the change from bronze to stainless.  It doesn't even have to be a NEW neighbor.  An existing one could have made changes or have a failure that is causing stray current.

[rmjohns]

Curious on this Patches. Do you keep the boat plugged in when you're not there? And do you have a Galvanic Isolator? I have one I haven't installed yet but I'm hoping by keeping the boat unplugged I won't be part of the marina circuit.

Thanks
Rob.

[Patches]

Rob:

Good questions.  I do not have a galvanic isolator, but have been giving that a lot of thought after replacing the prop.  All the docks and electrical in my Marina were replaced within the past 6 years with new.  So I don't suspect anything on the marina end.

I do not hook up to shore power often.  I upgraded my whole electrical system two years ago with a new house bank consisting of 3 Firefly AGMs.  As part of that upgrade, I added a new Sterling charger, Balmar external regulator, and 105 amp alternator--all purchased from Mainsail.   I also operate as a charter boat doing daysails so the boat motor/alternator comes on for at least 30-45 minutes/day, 5-6 days/week.  That is slowing down now.  But the "state of charge" on my house bank is rarely below 95%, even with my Engle cooler continuously "on." 

So, I'm not sure what the culprit is.  But I'm seriously considering adding a galvanic isolator as soon as I get the boat splashed and home.

Patches

[Jim Hardesty]

So I don't suspect anything on the marina end.

I don't know how it's done but our yacht club does check for current in the water.  We have many aluminum boats that worry about the galvanic corrosion.  It does seem to me that since our fixed docks were changed to floating docks my anodes go faster.
Jim