Rapid Bow thruster zinc decay

[Haifisch]

After about a year with my boat (R31, moored full time in saltwater, with a galvanic isolator and needs to be full time on shore power) I have been able to track the decay of my zinc Anodes:

The prop anode gets hit hard 6 mo. max, trim tabs and transom barely at all. Stern thruster lasts about a year; bow < 6 months.

I added a HangTuff Zinc anode clamped to the bonding system on the transom which has really helped slow down decay on the prop zinc and you can easily see it is doing its job as it is getting eaten away.

I can change all of the zincs in the water with a snorkel and mask except for the bow thruster. For that I need to put on a tank as it is just a little too low to see in the tunnel. I would like to have that zinc be slower to decay, so a couple of questions for the group:

1) is the bow thruster zinc decaying faster than the stern thruster zinc because it is 31 ft further from all the other anodes and the hang tuff?

2) Would adding a 2nd HangTuff near the bow help and is there anything bonded near the bow that I could clamp it to? Like is the anchor chain, windlass, rails?

Thanks for any advice on this and keeping me out of the water at least one more time per year!

 

[Kevin Lamont]

After about a year with my boat (R31, moored full time in saltwater, with a galvanic isolator and needs to be full time on shore power) I have been able to track the decay of my zinc Anodes:

The prop anode gets hit hard 6 mo. max, trim tabs and transom barely at all. Stern thruster lasts about a year; bow < 6 months.

I added a HangTuff Zinc anode clamped to the bonding system on the transom which has really helped slow down decay on the prop zinc and you can easily see it is doing its job as it is getting eaten away.

I can change all of the zincs in the water with a snorkel and mask except for the bow thruster. For that I need to put on a tank as it is just a little too low to see in the tunnel. I would like to have that zinc be slower to decay, so a couple of questions for the group:

1) is the bow thruster zinc decaying faster than the stern thruster zinc because it is 31 ft further from all the other anodes and the hang tuff?

2) Would adding a 2nd HangTuff near the bow help and is there anything bonded near the bow that I could clamp it to? Like is the anchor chain, windlass, rails?

Thanks for any advice on this and keeping me out of the water at least one more time per year!

Hello,

I would venture to guess that with trim tabs, transom zinc, thruster zinc, prop zinc and the HangTuff zinc you would be correct. It wouldn't hurt to try hanging another off the bow or just put the one in the back up front and see if it helps. Also you could try just putting it in the middle to see if they will all wear down about the same rate.

Thanks,
Kevin Lamont

 

[baz]

Can you say, or did you record how much the galvanic isolator helped in extending the life of the underwater zincs ? In the past I've used the galvanic isolator on my R25 Classic here at the Port of Edmonds (PNW) that was kept in the eater all year round, and found it did squat for extending the under water zincs life. Because of this, and now owning the 2019 R29 CB, I'm very hesitant in paying for and installing a Galvanic Isolator.

At this time all my underwater zincs last for about 9 months, at which time they are close to being completely eroded. The prop zinc has the worst track record and it can be completely gone after 6 months.

 

[iggy]

I would look at the boats around you. I bet one of the has a problem and its discharging into your boat.

 

[baz]

I would look at the boats around you. I bet one of the has a problem and its discharging into your boat.

Well, at first blush I would agree with you. However, I've now been in 4 different slips in my Marina, and the same issue with having the Galvanic Isolator was readily apparent.

 

[Cutwater28GG]

6 months seem pretty reasonable for marina storage. You won’t stop anode depletion with the galvanic isolator. The thruster anodes are very small so get eaten quick. It’s just a maintenance item. I don’t have an isolator and get 6 months from my zincs.

 

[Chimo]

I was getting about 4 months on my zincs before they eroded to the level where they don't provide protection. I could measure DC voltage in the AC circuit o I then installed a GI and that problem ended. Life to the same point of erosion went to 8 months. I understand the idea of disconnecting and reconnecting shore power but I like to leave my fridge, battery charger and a dehumidifier on all year round. In the winter I have heat on board.I am actually happy with changing on a 6 month cycle, May and November. In May I usually haul for a day or two and bottom paint + polish. In November, tied in with engine maintenance schedule, I do a half lift. It gives me the chance to change zincs and inspect running gear at a low cost for the lift (about $100 US last week.)

Just my experience

 

[BB marine]

I can't comment on how long an (Sacrificial) anode should last because there are all kinds of reasons why they don't. Poor wiring, metal in the water, several boats linked together through the shore power ground ( galvanic isolator helps with this) only to a point though. Voltages higher than 1.2 V dc can still pass through.

Replacement of (sacrificial) anodes should be done when 50% has eroded away. The more surface area the more protection. When removing the anode look for oxidation at the contact points of the anode (Sacrificial) and the Anode( metal being protected). There must be a good connection for the sacrificial anode to do its job protecting the metal.

If a transom plate Sacrificial anode is making a good connection to the bonding wire of the boat (green wire) it is protecting all the underwater hardware that is attached to green wire. Rudder, swim platform brackets, all thru hulls and if there is continuity thru the reverse gear to the prop shaft and prop it is protecting those. If there is very little erosion to the plate but an extensive amount of erosion to the Hang tuff. I would speculate the hang tuff has a better connection (continuity) to the boats ground and the transom plate is just protecting itself.

I think of the prop sacrificial anode as the protector of the prop only. There is a 50/50 chance that the prop shaft is connected to the bonding system. If it is not making good contact to ground, the prop shaft (stainless steel) becomes the cathode and the prop becomes the anode. The sacrificial anode mounted to the prop protects the prop only. How can there not be continuity thru the reverse gear. There is an input shaft and an output shaft, bearings and gears in-between with an oil film ( simple description) all components must be touching for continuity. Sometimes they do and sometimes they don't.

Trim tabs are not connected to the bonding system so the sacrificial anode is just protecting the trim tab nothing else.


The thrusters are not bonded to the boat. The Sacrificial anode mounted to the housing is only protecting the bronze housing gear box ( Side Power) and the sacrificial anode mounted to the housing should be aluminum not zinc.

There are several articles that state Aluminum alloy anodes will give better performance in salt water than the forever used Zinc. It will out perform zinc in brackish water. In fresh water zinc should not be used at all. An oxidation coating forms which will eliminate the sacrificial anode's protection.

In the 1990's the outboard and sterndrive manufactures recommend the use of aluminum alloy in place of Zinc for sacrificial anodes. Mercruiser sent a service bulletin out stating the corrosion protection warranty will be voided if Zinc anodes are used. The aluminum alloy is -.05 V lower, doesn't seem like much but it is enough to make a difference ( I'm told )

I would try Aluminum alloy anodes on your next replacement. When doing underwater anode replacement use a scotch-brite pad to clean contact areas to insure good continuity between the sacrificial anode and the anode (attachment point)

You can try hanging a Hang Tuff off the bow. I would use an aluminum to match the anode used with the side power.

I'm posting my opinion of how I understand what the anodes to be protecting my C26.

 

[Haifisch]

Thanks all for the ideas and advice. I've had the boat for year and it came with the Galvanic Isolator installed. So Baz, sorry to say that I don't have a baseline of erosion both with and without. Finding out that this will be a twice a year maintenance item came as surprise to me, but glad to hear from others that there is nothing freakishly long. My marina is across the harbor from the Washington State Ferry shipyard, so god only knows what kind of current they are putting in the water...

I wish a haul and hang around here was just $100... It's closer to $300, so I will just continue doing it myself. A 7mm wetsuit does a decent job even when the water gets down to 48 degrees.

Brian: Very helpful, I will try aluminum next time. I thing RT parts only sells Zinc, so I will see if boatzincs have the right sizes.

Last question... I am going to do a second Hangtuff near the bow after the next change. Do I even need to worry about it being bonded since the SidePower unit is not bonded to the boat? If I should, is the windlass or anything else near the pointy end of the boat bonded?

 

[Cutwater28GG]

no need for a lift. I have a diver do mine. they clean the boat and install the zincs. also take photos to show whats going on.

 

[baz]

Brian wrote - "The thrusters are not bonded to the boat. The Sacrificial anode mounted to the housing is only protecting the bronze housing gear box ( Side Power) and the sacrificial anode mounted to the housing should be aluminum not zinc."

Where did you get the info that states aluminum anodes should be used for the Side Power thrusters, and is this for both bow and stern units ?

The thruster metal protection is my biggest concern as they are expensive to replace. I also note that the bolt that secures the anode to the thruster can also get eaten away and removing the bolt can become problematic with the threads being compromised.

I fully agree about replacing anodes when they have been eaten away leaving just 50% remaining. The trick is to know when the 50% has been reached because from one year to the next the erosion rate can vary.

Thanks. 🙂

 

[Haifisch]

Hey Barry,
To check for erosion, I bought an inexpensive lighted waterproof endoscope from Amazon that uses WIFI to transmit images to my phone. I tape the lighted camera end to a stick and move it around to see how things look in a real time video feed. For the bow thruster I find the tube and insert the camera in. Usually just takes about 5 minutes to check the whole thing out without getting cold or wet. So far it works great.

 

[BB marine]

Where did you get the info that states aluminum anodes should be used for the Side Power thrusters, and is this for both bow and stern units ?

This is from Side power website. recommend anode , All Side power units so yes bow and stern.

Description- Aluminum Alloy Anode (AL-Zn-In)
*The mil-spec alloy includes about 5% Zinc and a trace of Indium to prevent oxidation resulting in a layer reducing the sacrificial properties of the anode.
*Provides more protection and will last longer than zinc anodes of the same size (up to 50% longer).
*Less than half the weight of of a similar sized zinc anode.
*Provides superior support compared to zinc anodes in fresh or brackish water, while still giving excellent pro­tection in salt water, and is the only anode that is safe for all applications.

Last question... I am going to do a second Hangtuff near the bow after the next change. Do I even need to worry about it being bonded since the SidePower unit is not bonded to the boat? If I should, is the windlass or anything else near the pointy end of the boat bonded?

I'm not sure, I guess I would sway more to bonded. I actually would go with Kevin's suggestion and place the bonded Hang tuff anode midship instead of off the stern.

 

[baz]

The thruster anodes should be aluminum as posted here. Also, note these anodes are small cone shaped, and finding them as zinc rather than aluminum is nigh impossible as well...

 

[ohioan55]

I decided some time back that aluminum would be best for me. If I go to salt water, it is usually the Chesapeake Bay, where the water is a mix of brackish and salt, and aluminum works best in these conditions. And from experience, I can tell you that stray current corrosion ate the inside out of my 8 hp Honda faster than the zinc anodes on the outside of it. Like many have said above, aluminum anodes will serve you better. I currently have magnesium on my boat as these are best suited for fresh water.
.