My latest underwater anode servicing shows benefits

[baz]

A little over a year ago I made several modifications to improve our underwater anode erosion issues. Most anodes were being replaced every 3 months. Yesterday my diver service indicates this replacement period will likely stretch out to 9 months or longer.

Yesterday after some 3 months since last checking only two anodes were replaced... the prop shaft and the bow thruster anodes. The prop shaft was replaced even though it had 65% remaining and the bow thruster anode was almost gone. The diver service replaced the prop shaft anode even though it had 65% remaining as they want to monitor the switch over to using Aluminum anodes and because it's important to not have the anode deplete to zero remaining. These new aluminum anodes do seem to be doing a better job.

The stern thruster (65% intact), trim tabs (55% intact), swim step bracing donuts (90% intact) and the transom mounted zinc plate (90% intact) were all in good shape.

The hull surface was also inspected and found to be in good shape. New bottom paint had been applied in March 2012.

Our boat is kept in a covered slip (stern in with starboard tie) with just the port side bow exposed to strong sun light and shore power is always employed allowing battery charging, refrigerator at #2 and a low wattage WM dehumidifier running.

Here are some photos of the underwater anodes.

 

[Irishpilot]

Wow..very interesting perspective. I even called my wife over to have a look ;-)

Mike from Rainy Maryland

 

[circusmar]

We have also undertaken increasing our galvanic protection. we have added tab zincs and a 6x12 transom zinc in conjunction with a galvanic isolator. we keep our boat in the water with shore power also. so far results are promising but thruster zincs are still going quickly (they are not connected to the boats bonding system). not sure i trust the transom zinc mounting as our hull is only about 1/4 inch thick. we may redo with a backing plate of some sort. do boats with factory hull zincs have a proper mounting block?

 

[baz]

A backing plate for the transom anode plate is a good idea. I did not use one but did use large washers for each of the two bolts that hold the plate. A backing plate would be really necessary if there was a load imposed on the anode plate -- but from my perspective there's no load on it.

Yes, the thruster anodes (use Aluminum Anodes even though the SidePowerThrusters.com web site says otherwise -- per my Diver service advice) need special attention. I do recall reading something on the SidePower that indicated much of the metal in their systems are protected from erosion ... but dunno for sure about this.

Check the thruster anodes regularly as if they deplete to nothing the bolt and the threads the bolt engages will be badly damaged and you will have a nasty repair bill.

Here's a snippet about Aluminium anodes... taken from SidePower web site.

Features & Benefits:
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.

 

[circusmar]

We also used washers... we clipped the corner to ensure the water stream from the prop pocket would not put stress on the fragile hull.

 

[baz]

You must restrict all photo images to be no more than 700 x 700 pixels.

My transom mounted anode is outboard of my starboard trim tab and I used just 2 bolts.

[EDIT]
What's that gray looking stuff on your prop and rudder ?

 

[circusmar]

You must restrict all photo images to be no more than 700 x 700 pixels.

pretty sure I used 640x480...

EDIT: Petit Barnacle Barrier is the grey substance on exposed running gear

EDIT2: solved the pic problem

 

[baz]

Yea... some photo's meta data confuses things... I always export my photos to ensure the pixel sizes remain at or below 700 before I upload them to my Dropbox.

 

[nzfisher]

Thanks for this post. I really like to see what more knowledgeable folks do to protect from the issues of keeping your boat in the water. I pull my boat periodically to check it and am always amazed at the amount of corrosion that takes place and have used your suggestions to increase the longevity of the zincs from your past posts. I will be switching to the aluminum zincs on the thrusters. What about the prop zinc? Does aluminum make sense there as well? I am using a hanging zinc near the prop/rudder connected to the main bond which seems to have benefited the corrosion on the rudder and prop.

 

[circusmar]

Dove our boat this morning. We had fresh zincs all around in Jun. We moor in relatively warm salt water on shore power and use a galvanic isolator. Right before I serviced zincs our hull potential was just a bit under "full battery" potential at -1.014V. We have no significant leakage currents on our boat or from our shore power.

Prop Zinc and Hull Zinc were barely used. Tab Zincs were down to ~30%. Thruster anodes were at ~50% by weight.

Engine Zincs - bottom gone, top 50% (reminder to all to make sure engine zincs are part of your routine). Genset zinc was gone too (suspect this was neglected by previous owner).

Disappointing life out of the thruster anodes (we are using the newer aluminum version from BoatZincs.com). I wonder whether another supplier might have a denser zinc for the thrusters?? Anyone??

Suspect the bonding system is preferentially using the tabs for some reason... very disproportionate usage rates. will have to keep an eye on that; may take the tab zincs off again. Maybe its all the crabs that like to hang out on our tabs... We have plenty of reserve protection based on our measurements and it may "encourage" the bonding system to use the hull plate more instead.

Very Pleased with the performance of the Petit Barnacle Barrier spray paint so far.

 

[j&lgray]

Anodes have different metallic compositions for specific purposes. My marine guru says that aluminum anodes are typically for fresh water applications and magnesium ones are typically for salt water applications. The goal is NOT to preserve the anodes, the goal is to preserve the rudder, prop and other metal pieces that will be attacked.

Our Ranger 29, Andiamo, had effective aluminum anodes because it was kept in fresh water. When we moved it to a salt water marina, I dove the boat and changed out the anodes to magnesium ones; a task that I would gladly do repeatedly to ensure that the prop and rudder are protected.

 

[ragman]

Anodes have different metallic compositions for specific purposes. My marine guru says that aluminum anodes are typically for fresh water applications and magnesium ones are typically for salt water applications. The goal is NOT to preserve the anodes, the goal is to preserve the rudder, prop and other metal pieces that will be attacked.

Our Ranger 29, Andiamo, had effective aluminum anodes because it was kept in fresh water. When we moved it to a salt water marina, I dove the boat and changed out the anodes to magnesium ones; a task that I would gladly do repeatedly to ensure that the prop and rudder are protected.

Exactly,

The anode is meant to be sacrificed. There is an electrical potential between the water, the zinc and the metal that the zinc is protecting. If your environment remains the same and you switch to aluminum anodes that don't corrode as quickly, then something else may be losing electrons (corroding).

If you are in a marina, continually connected to shore power, you may be experiencing increased galvanic activity due to a DC leak by another boat connected to the same shore power. In this case, a galvanic isolator could greatly reduce the amount of anode loss.

 

[circusmar]

Anodes have different metallic compositions for specific purposes. My marine guru says that aluminum anodes are typically for fresh water applications and magnesium ones are typically for salt water applications. The goal is NOT to preserve the anodes, the goal is to preserve the rudder, prop and other metal pieces that will be attacked.

Our Ranger 29, Andiamo, had effective aluminum anodes because it was kept in fresh water. When we moved it to a salt water marina, I dove the boat and changed out the anodes to magnesium ones; a task that I would gladly do repeatedly to ensure that the prop and rudder are protected.

Almost right...

Mg = Fresh
Al= Brackish/Salt
Zn = Salt

Derives from the properties (galvanic series) of the metals and not opnion... Next time you dive your boat you may want to consider going back to Zn or Al if you are in salt water.

and we gots the galvanic isolations...

 

[Lobo]

I've improved anode life differently.

Rather than plug my boat into shore power and energize everything, I plug only my ProMariner battery charger into an extension cord that is connected to shore power. As my batteries are always charged, when on the boat at my dock I can play tunes, use the stove (Wallas cooktop), or check anything on the 12v systems -- which is basically everything except the 110v plugs.

This involves:

1. If your ProMariner doesn't have a male plug, cut the line where the ProMariner joins the 110v line and put a male plug on the charger side and a female plug on the 110v line (marine quality, of course).
2. Get an outdoor or marine extension cord of 6 feet or less. Run the female end over the cockpit liner in front of the battery box and stuff it until it comes out below and inside your locker. After disconnecting the charger from the shore power cord -- plug the charger into the new extension cord. Plug the other end of your new extension cord to shore power via an ordinary outdoor extension cord. The short extension cord is a cheap way to avoid having an extension cord coming out of a cockpit locker.

I leave the house batteries "ON" and my fridge "ON" because life with warm beer sucks. Other than that my boat has no power circuits on. In winter I will plug in an electric heater directly into my shore power, also via an extension cord which I bring into the boat via my portside porthole.

My anode life has increased to almost 12 months in salt water. Before, I was lucky to get 6 months.

This solves one other problem for docks that have 15 amp GFI shore power like I do. Bypassing the on-board systems eliminates the shore side GFI breaker from popping.

Dave
"Lobo"

 

[ragman]

I've improved anode life differently.

Rather than plug my boat into shore power and energize everything, I plug only my ProMariner battery charger into an extension cord that is connected to shore power. As my batteries are always charged, when on the boat at my dock I can play tunes, use the stove (Wallas cooktop), or check anything on the 12v systems -- which is basically everything except the 110v plugs.

This involves:

1. If your ProMariner doesn't have a male plug, cut the line where the ProMariner joins the 110v line and put a male plug on the charger side and a female plug on the 110v line (marine quality, of course).
2. Get an outdoor or marine extension cord of 6 feet or less. Run the female end over the cockpit liner in front of the battery box and stuff it until it comes out below and inside your locker. After disconnecting the charger from the shore power cord -- plug the charger into the new extension cord. Plug the other end of your new extension cord to shore power via an ordinary outdoor extension cord. The short extension cord is a cheap way to avoid having an extension cord coming out of a cockpit locker.

I leave the house batteries "ON" and my fridge "ON" because life with warm beer sucks. Other than that my boat has no power circuits on. In winter I will plug in an electric heater directly into my shore power, also via an extension cord which I bring into the boat via my portside porthole.

My anode life has increased to almost 12 months in salt water. Before, I was lucky to get 6 months.

This solves one other problem for docks that have 15 amp GFI shore power like I do. Bypassing the on-board systems eliminates the shore side GFI breaker from popping.

Dave
"Lobo"

I'm trying to figure out why this might work. The ProMariner should share ground with everything else on the boat which is where the unequal potential between your boat and any other in your marina should be and hence galvanic corrosion occurs.

Can you explain how and why this strategy works?

Not questioning that it does work, just wondering why?