Prop Shaft Brush - Prop Shaft zinc

[O C Diver]

I'm curious to see who uses prop shaft brushes, prop shaft zincs, or both. I'm considering switching to a brush, just not sure if I feel comfortable without the collar zinc.

Ted

 

[Tuttouomo]

OC, I have both on my shafts, normal replacement sched on zincs, brushes show minimal wear.

Bill

 

[kchace]

I have 2 aluminum "zincs" on each shaft - no brushes.

 

[Larry M]

We have an aluminum prop nut, no brush but also have a rudder and plate(on the hull) anode. We can easily go a year between changes. When we're in a marina, we hang an aluminum anode over the side, clipped to the bonding system.

 

[Rossland]

Just a brush

 

[Ski in NC]

Mine is a bit of a hybrid, not on the options. Have shaft zinc and transom zinc. Transom zinc is bonded to engine block among other things. No shaft brush. While setting, gears and bearings conduct bonding current through tranny. Verified via checking for millivolts while sitting- Zero.

Both zinc waste about the same rate and no strange corrosion issues.

I have checked a few shaft brushes and found a voltage differential, so that is why I do not count on them for anodic protection.

 

[eagle419]

I removed my hull zincs and replaced them with half the number of Matrox alloy blocks. My hull is timber, so all these alloy blocks are internally bonded to all hull fittings, including the prop shaft via a 'brush'.

I've kept specific zincs for the bow thruster and rope cutting spurs mechanism.

 

[psneeld]

Both...brush is just insurance....

 

[C lectric]

Don,t depend on brush but just as insurance after I had shaft zinc croak years back.
Don,t want to have to buy new prop.
Have the silver cell and use it to check periodically which is how I found the problem.

 

[Lou_tribal]

Mine is a bit of a hybrid, not on the options. Have shaft zinc and transom zinc. Transom zinc is bonded to engine block among other things. No shaft brush.

Same hereaft zinc, transom zinc and rudder zinc. Thinking about adding brush but don't think it is worth it in my case (fresh water cruising only for now)

 

[O C Diver]

Same hereaft zinc, transom zinc and rudder zinc. Thinking about adding brush but don't think it is worth it in my case (fresh water cruising only for now)

When you say zinc, are you referring to aluminum?

Ted

 

[Lou_tribal]

To be honest the anodes were already in place when I bought the boat and I am not sure in which material they are, I did not check yet when hauling out last autumn. As I need to replace the rudder one I plan to replace all of them with magnesium anodes as I am cruising only fresh water river and lakes.

 

[Steve DAntonio]

With one caveat, see below, there's little or no harm in having both a brush and anode on the shaft. In fact, unless you go with a high end slip ring type brush like the ElectroGuard Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships. the effectiveness of a standard brush is far from guaranteed. Having tested several different types, if you do go the economy route, the 'copper wand-style carbon brush' offers the best chance for low resistance continuity. The resistance threshold here is quite low, Standards state that the maximum allowable resistance between protected metals and anodes cannot exceed 1 ohm. That's often difficult to achieve with wired systems, much less between a contact and rotating shaft. While the shaft is spinning contact is often good, it's when it stops, and sits idle for days or weeks that resistance often changes.

Brushes can, however, be a double edged sword. If the hull anodes are depleted, the shaft anode will, via the brush, provide protection to all bonded hardware, until it’s depleted, which will happen quickly. Ultimately, I’d recommend a brush, while ensuring all anodes are maintained.

This article explains a bit more about brushes and how they work with bonding systems Bonding Systems And Corrosion | | PassageMaker

 

[O C Diver]

With one caveat, see below, there's little or no harm in having both a brush and anode on the shaft. In fact, unless you go with a high end slip ring type brush like the ElectroGuard Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships. the effectiveness of a standard brush is far from guaranteed. Having tested several different types, if you do go the economy route, the 'copper wand-style carbon brush' offers the best chance for low resistance continuity. The resistance threshold here is quite low, Standards state that the maximum allowable resistance between protected metals and anodes cannot exceed 1 ohm. That's often difficult to achieve with wired systems, much less between a contact and rotating shaft. While the shaft is spinning contact is often good, it's when it stops, and sits idle for days or weeks that resistance often changes.

Brushes can, however, be a double edged sword. If the hull anodes are depleted, the shaft anode will, via the brush, provide protection to all bonded hardware, until it’s depleted, which will happen quickly. Ultimately, I’d recommend a brush, while ensuring all anodes are maintained.

This article explains a bit more about brushes and how they work with bonding systems Bonding Systems And Corrosion | | PassageMaker

Steve, thanks for the links. Some good information. Have you done any analysis on aluminum versus magnesium anodes in fresh water. Finding aluminium in all the sizes I needed was challenging enough, but magnesium is just not available in most of the uncommon sizes. While I will be in fresh water for 5 months this year, I will also be in brackish and the ocean. Assume aluminum is generally the best all around choice for me. Just isn't much information regarding how much of an improvement magnesium is over aluminum in fresh water.

Ted

 

[User915]

With one caveat, see below, there's little or no harm in having both a brush and anode on the shaft. In fact, unless you go with a high end slip ring type brush like the ElectroGuard Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships. the effectiveness of a standard brush is far from guaranteed. Having tested several different types, if you do go the economy route, the 'copper wand-style carbon brush' offers the best chance for low resistance continuity. The resistance threshold here is quite low, Standards state that the maximum allowable resistance between protected metals and anodes cannot exceed 1 ohm. That's often difficult to achieve with wired systems, much less between a contact and rotating shaft. While the shaft is spinning contact is often good, it's when it stops, and sits idle for days or weeks that resistance often changes.

Brushes can, however, be a double edged sword. If the hull anodes are depleted, the shaft anode will, via the brush, provide protection to all bonded hardware, until it’s depleted, which will happen quickly. Ultimately, I’d recommend a brush, while ensuring all anodes are maintained.

This article explains a bit more about brushes and how they work with bonding systems Bonding Systems And Corrosion | | PassageMaker

Thank you Steve, very interesting and useful.

 

[Rossland]

The resistance threshold here is quite low, Standards state that the maximum allowable resistance between protected metals and anodes cannot exceed 1 ohm. That's often difficult to achieve with wired systems, much less between a contact and rotating shaft. While the shaft is spinning contact is often good, it's when it stops, and sits idle for days or weeks that resistance often changes.

| PassageMaker[/url]

This is why I like this forum. THE experts are here.
Just tested mine and resistance between the shaft and bonding bar was .09 ohms.

 

[Steve DAntonio]

Steve, thanks for the links. Some good information. Have you done any analysis on aluminum versus magnesium anodes in fresh water. Finding aluminium in all the sizes I needed was challenging enough, but magnesium is just not available in most of the uncommon sizes. While I will be in fresh water for 5 months this year, I will also be in brackish and the ocean. Assume aluminum is generally the best all around choice for me. Just isn't much information regarding how much of an improvement magnesium is over aluminum in fresh water.

Ted

The voltage and current ratings for all three sacrificial anode metals, zinc, aluminum and magnesium are readily available, so no testing or experimentation is needed. Unless the boat will be used exclusively in fresh water, it's best to stick with aluminum. AL can be used effectively and safely in fresh, salt and brackish water, however, magnesium can only be used in fresh water, and zinc should only be used in salt water. For more detail on anode selection see http://http://stevedmarineconsulting.com/galvanic-isolators-and-zinc-anode-selection/

 

[O C Diver]

Steve,
That link doesn't work for me and the one on your website for that article doesn't work either.

Ted

 

[angus99]

This is so timely. I'm at the boat now completely replacing the bonding system--all new #8 and #6 wire, new lugs, heat shrink tubing, aluminum shaft, transom and rudder anodes etc.

The existing bonding system on my boat was a spaghetti plate of wires of different colors and gauges serving both bonding and safety ground functions, tying the cases of electrical components (including AC-powered air conditioners) to the bonding system. Metal tanks are also connected and there may have been an attempt at lightning protection as well since metal seacocks 18 inches above the water line are also bonded.

I found a lot of tarnished wire, corroded and loose terminals and self-tapping screws connecting wires to the long copper bonding strip in the engine room. (ABYC requires machine screws and tapped/threaded holes in the copper bar or nuts/machine screws to secure the terminals.) I could spin many of the terminals secured with self-tapping screws by hand.

The guy I'm consulting with (also an ABYC-certified marine corrosion expert whom you know, Steve) suggested I forego shaft brushes. He considers each prop shaft it's own separate bonding system and uses two (sometimes three) anodes per shaft, depending on the length and how fast they're sacrificing themselves. He says his company was never able to get shaft brushes to work consistently enough to have confidence in them--certainly never as a substitute for anodes.

Through hulls, prop shaft struts, rudders/steering gear and stuffing boxes are all tied to the bonding system. Once all the terminations are tight, each gets a spray of Boshield to limit future corrosion.

 

[Steve DAntonio]

Steve,
That link doesn't work for me and the one on your website for that article doesn't work either.

Ted

Ted:

Not sure why. I just pulled it up again with a search and accessed the article (and I'm in Taiwan, which sometimes makes links act strangely). Try this “Zinc” Anode Selection and the Role Played by Galvanic Isolators | Steve D'Antonio Marine Consulting

If that doesn't work, just go to my site and in the search bar on the upper right plug in "zinc anode" and you'll get it. Or, from Google, "D'Antonio zinc anode", you'll get several articles I've written on the subject in various pub's.

 

[Steve DAntonio]

This is so timely. I'm at the boat now completely replacing the bonding system--all new #8 and #6 wire, new lugs, heat shrink tubing, aluminum shaft, transom and rudder anodes etc.

The existing bonding system on my boat was a spaghetti plate of wires of different colors and gauges serving both bonding and safety ground functions, tying the cases of electrical components (including AC-powered air conditioners) to the bonding system. Metal tanks are also connected and there may have been an attempt at lightning protection as well since metal seacocks 18 inches above the water line are also bonded.

I found a lot of tarnished wire, corroded and loose terminals and self-tapping screws connecting wires to the long copper bonding strip in the engine room. (ABYC requires machine screws and tapped/threaded holes in the copper bar or nuts/machine screws to secure the terminals.) I could spin many of the terminals secured with self-tapping screws by hand.

The guy I'm consulting with (also an ABYC-certified marine corrosion expert whom you know, Steve) suggested I forego shaft brushes. He considers each prop shaft it's own separate bonding system and uses two (sometimes three) anodes per shaft, depending on the length and how fast they're sacrificing themselves. He says his company was never able to get shaft brushes to work consistently enough to have confidence in them--certainly never as a substitute for anodes.

Through hulls, prop shaft struts, rudders/steering gear and stuffing boxes are all tied to the bonding system. Once all the terminations are tight, each gets a spray of Boshield to limit future corrosion.

Sounds as if you are on the right track Angus, I'm glad to see it. While I agree I don't like to rely entirely on the standard carbon brush arrangement (it's far better than the piece of bronze half pipe held in place with a spring, no kidding, that's an off the shelf part, but not as good as the slip ring) for galvanic protection, and thus the isolated, protected shaft has its merits, bonded underwater metals are less susceptible (not immune) to stray current corrosion. It's one of several good reasons to bond. A bonded underwater metal offers stray current a more direct low resistance path back to its source, which will either trip a circuit breaker or blow a fuse, or cause the wire source of the stray current to rapidly corrode and part, thereby stemming the flow of electricity.

I have a manganese bronze prop siting outside my office, as a door stop, that has been corroded almost down to the blade roots (it's pictured in some of the articles on this subject). It's a victim of stray current corrosion. Again no guarantees but if it had been bonded with a brush, my bet is the source would have been shut down more quickly. In light of that, using shaft anodes and a brush isn't a bad idea, and of course, as I mentioned earlier, all of the anodes must be maintained to prevent the shaft anodes from carrying the full load.