Prop speed and the need for zincs

[Brisyboy]

I just got back from a meeting at our Marina, and we were standing around having a beer, as you do and I was bemoaning the fact that each time I slip our boat it seems to get bigger, in direct proportion to my age

Anyway I mentioned that I was having the props and shafts coated in propspeed (as I usually do) which led to the discussion on shaft zincs. There was some emotion expended by a few guys claiming that because propspeed is silicone based, then the shafts don `t need an anode because silicone is an insulator.

I enjoyed the discussion but was a little out of my depth when they started talking galvanic and residual currents etc.

Can anyone comment in lay mans terms on this concept please - is it fact or fiction?

Thanks

 

[Hippocampus]

My feeling is zincs are cheap. Props, shafts etc. aren’t. I put two zincs on the shaft if there’s room and one on the hub of the prop if doable. Know about over zincing so stay below that limit but think that’s rare. I also use some 60 grit to make sure there’s good contact.
Be real hard to convince not to continue to be doing this. Maybe if Steve D’ or Zimmerman said it’s ok I’d think about it. Otherwise no. All it would take is a nick in the propspeed or for it to wear off at the props edges and you get bad stuff happening.

 

[rslifkin]

My feeling is zincs are cheap. Props, shafts etc. aren’t. I put two zincs on the shaft if there’s room and one on the hub of the prop if doable. Know about over zincing so stay below that limit but think that’s rare. I also use some 60 grit to make sure there’s good contact.
Be real hard to convince not to continue to be doing this. Maybe if Steve D’ or Zimmerman said it’s ok I’d think about it. Otherwise no. All it would take is a nick in the propspeed or for it to wear off at the props edges and you get bad stuff happening.

That's my thought process as well. Ideally, the zincs will last a long time with all of the metals coated. But if anything happens to the coating I wouldn't want to risk the metals.

 

[Pete Meisinger]

I guess I should know more about zincs and electralesis ( I don't even know how to spell it) But being a fresh water boater it isn't much of an issue.

All the marinas I have stayed in don't even have any noticeable "stray" current.

There is a big zinc on the back of the boat which hasn't changed appearance in ten years. My boat is well grounded.

Am I being naive?

pete

 

[Comodave]

I guess I should know more about zincs and electralesis ( I don't even know how to spell it) But being a fresh water boater it isn't much of an issue.

All the marinas I have stayed in don't even have any noticeable "stray" current.

There is a big zinc on the back of the boat which hasn't changed appearance in ten years. My boat is well grounded.

Am I being naive?

pete

Pete, if it is indeed a zinc anode that would explain why it has lasted 10 years. Zinc anodes don’t work in freshwater. They get a coating on them that essentially insulates the anode from the water. There is corrosion going on in freshwater, your anode just isn’t doing anything. You actually want it to gradually erode away. Better the anode than something like the prop eroding away. Go with aluminum or magnesium anodes in freshwater.

 

[Ken E.]

I use Propspeed and at haulout, the shaft zinc anodes are eroded. I'll keep using them.

 

[Each finger a marlinspike]

Prop speed will reduce the wear on the anodes, but not eliminate the need for them.