zincs on NIALBZ propellers, are they required

[Singleprop]

I had an e-mail correspondence lately with a commercial propeller manufacturer.*

*

He claimed that zincs are not required on propellers made of NIALBZ or on the stainless steel shaft it is connected to.......that's a new one for me so I thought that it would be a good question for the forum.

*

Is he right?

 

[RickB]

Singleprop wrote:
Is he right?

*Only if the boat is in clean fresh water or electrochemical reactions are different in his world.

 

[Edelweiss]

RickB wrote:Singleprop wrote:
Is he right?

*Only if the boat is in clean fresh water or electrochemical reactions are different in his world.

*Now, Now!!* Maybe they were referring to using it in the creek*in front of the Olympia Brewery.* Their motto was "It's the water" So I always assumed it was filled with*distilled water?

Hmm, that would make the prop's the sacrificial metal then.* A novel idea, but I think that has been tried before!!*

 

[C lectric]

_______________
Is he right?
__________


I'm no expert but Not in my book., not in seawater and even in fresh unless you know it is truly clean.
The stainless shaft, even the really good stuff will corrode if circumstances are right. and the variables that cause trouble cannot be controlled. Same for the NIALBZ nickel aluminum bronze, good stuff but not immune either, and then there will be a reaction between the shaft and the prop.

The best way is a zinc which will protect both, cheap and effective.

 

[JAT]

NIALBZ= Nibral Bronze..... which mounted on a stainless steel shaft, and even possibly with a key of another metal....or not...still has "two dissimilar metals" in contact with each other..... No zincs?? Only if you want to put in a repeat order every year or so depending on where you are.... I hate to ask this... But are you sure you weren't talking to the janitor??

 

[FF]

"Only if the boat is in clean fresh water "

In clean fresh water the usual is magniesum on rudders and props.

 

[RickB]

FF wrote:In clean fresh water the usual is magniesum on rudders and props.

Or aluminum.

 

[Art]

RickB wrote:FF wrote:In clean fresh water the usual is magniesum on rudders and props.

Or aluminum.

By coming from SF Bay SW I found that Zinc works well*in FW... as long as... you swim under at least*every couple to few months with a*bronze brush and scrub off the film Zinc acquires as a thin surface layer in FW.* In SF Delta warm FW*I get to do that with no problem; matter of fact I enjoy doing it kind of a ritual of mine!* Then, its sacrificial anode qualities work great and Zinc lasts a long time in FW (3 +/- years).* That is so long as your boat experiences not too much stray current at berth when she is left alone.* Mine gets next to no*current.

 

[Singleprop]

World it be ok if the shaft was equipped with an inside brush/shaft whip running on the shaft and connected to a zinc installed nearby on the steel hull.
Would his statement then be valid?

-- Edited by Singleprop on Friday 16th of December 2011 03:02:39 AM

 

[RickB]

If you mean would grounding the shaft make a nickel aluminum bronze prop and stainless steel shaft immune to electrochemical corrosion? If that is what you meant the answer is still no.

Shaft grounding devices were developed to protect the shaft bearings and reduction gears on ships and boats with oil lubricated shaft bearings and seals that when in operation effectively insulate the shaft and allow sometimes larg currents to develop.

The passive brush systems are difficult to keep clean so the resistance quickly rises to the point where they don't work very well.

The guy who told you NiBrAl props don't need protection is just plain wrong.

 

[Chrisjs]

When we first bought our boat (47ft Selene - single screw) there were no zincs on the (mostly unexposed) shaft, the shaft cutters, or the large Nibral prop. There was no sign of any corrosion on any of these parts, even thought the vessel was then 6 years old. Being kind of anal, after reading a number of other postings related to corrosion and looking at other vessels in the yard at haul-out, I subsequently adapted the prop shaft to fit a modified large prop zinc and added the cutter zinc (very small). Since adding these, there is no doubt that they do erode/dissolve over time. Question is what are they really protecting -- if anything??
I am not convinced that they are really needed but I shall keep on replacing them regardless!!

Chris

 

[Singleprop]

I guess the PO of your Selene was a bit lucky that nothing happened to his prop or shaft....

Anyway - a manufacturer of a well known shaft cutter (I will not name the company) also said that it was OK without zincs on the prop and shaft as long as the mentiononed shaft whip was connecting the shaft to the hull - through the shaft whip on the inside...........

I tend to error on the safe side so I would not follow the advise from any of these two commercial manufactureres.

Zinc or sink - I prefer to zinc.


-- Edited by Singleprop on Friday 16th of December 2011 10:57:00 AM

 

[Chrisjs]

Maybe!! But luck does not really explain why there was no corrosion problem without the zincs for a 6 year period of active use in salt water. We continued to use the boat without zincs for a couple more years before adding the prop zinc and needed to modify the shaft to even accept the shaft zinc. Obviously, the designer had not intended for there to be a zinc or there would have been accommodation for it on the shaft. Perhaps electrical conductivity via the engine block was adequate to protect the shaft/prop, though it seems unlikely? Nevertheless I agree that zincs do give a belt and suspenders type of warm feeling!!

 

[Edelweiss]

Just reading through these posts is the idea that there were no zincs on the boat at all or just no zincs on the shaft, but there are hull zincs?*

If there were hull zincs and the engine, transmission, shaft, prop, were*bonded to the hull zinc, that would explain having gotten by with no shaft zincs for years.* But still a risky adventure for recreational boaters; Lose the bond and in the wrong envionment, lose the prop!*

Nickel Aluminum Bronze; Ni-Al Bz, "Nialbz" also called "Nibral" and sometimes*spelled*Nibrill is corrosion and errosion resistant up to a specified*current flow level measured in "mv".* But I*don't hear anyone claiming they're corrosion proof.**I have seen examples of NIALBZ props with electrolysis, so it does happen.*

My marina for years has been very safe, with two shaft zincs usually lasting me nearly one year and I have Nibral props.* But I look at it the same as insurance.* I can control the electrical issolation on my boat, but what my neighbor and the marina do are beyond my control and puts me at risk.* Zincs are a small price to pay.

 

[sunchaser]

Chris

As you admitted,* "there is no doubt they do erode --" It seems to me your shaft needs for zincs, although small where you are berthed, has been demostrated. Mine last about 5 - 6 months in good clear Pacific salt water. Many decades ago my father purchased a vessel in Antioch that had no shaft zincs, after taking it to SF, the prop was gone in 3 months - lesson learned. Sometimes one has to accept the greater marine knowledge base (of at least*200 years) of professionals and assume zincs do indeed do the job.

It is akin to helmetless motorcycle*and seat beltless car riders smiling happily as they trundle down the road - or as Alfred E Neuman said, "What, me worry?"