Anode Plate on stern

During our survey, it was noticed there was no anode plate on the stern, nor any sign that one had previously been mounted. The prop had one as well as both trim tabs, but a "whole boat" anode was never installed by the factory. Was wondering if other boats are similar? We looked at many during our search and all had a stern mounted anode plate.

Paul&Wendy said:

During our survey, it was noticed there was no anode plate on the stern, nor any sign that one had previously been mounted. The prop had one as well as both trim tabs, but a "whole boat" anode was never installed by the factory. Was wondering if other boats are similar? We looked at many during our search and all had a stern mounted anode plate.

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It would help if you specified the boat. Inboards and outboards have anodes, but in different places.

Based on your previous post New owners of a C28 Cutwater. the answer to your question is yes this is similar to other Fluid Motion boats. Hull anode protection was an option?? All underwater hardware is bonded but no sacrificial anodes and no galvanic isolator installed. The Prop and prop shaft are protected by the prop nut anode but not bonded to the bonding block unless the previous owner installed shaft bonding brushes. The tab planes may or may not have anodes this too was an option. The planes are not bonded so the anodes on the planes are protecting the planes only. The Thruster does have anodes but not bonded so the anodes protect the thruster only. The boat should have a hull anode. All underwater hardware, rudder, thru hulls, keel shoe and exhaust outlet are bonded. No anode protection to help reduce Galvanic corrosion. If you keep the boat in the water, keep the boat in a marina. use shore power, I would advise installing a galvanic isolator and a divers dream. There is a recent post in the Ranger Tug Forum that shows the results of lack of hull anode protection. The R27's rudder is severely damaged and in need of replacement. Hopefully the other underwater hardware is not also damaged. Good luck and enjoy your new to you C28.

BB marine said:

Based on your previous post New owners of a C28 Cutwater. the answer to your question is yes this is similar to other Fluid Motion boats. Hull anode protection was an option?? All underwater hardware is bonded but no sacrificial anodes and no galvanic isolator installed. The Prop and prop shaft are protected by the prop nut anode but not bonded to the bonding block unless the previous owner installed shaft bonding brushes. The tab planes may or may not have anodes this too was an option. The planes are not bonded so the anodes on the planes are protecting the planes only. The Thruster does have anodes but not bonded so the anodes protect the thruster only. The boat should have a hull anode. All underwater hardware, rudder, thru hulls, keel shoe and exhaust outlet are bonded. No anode protection to help reduce Galvanic corrosion. If you keep the boat in the water, keep the boat in a marina. use shore power, I would advise installing a galvanic isolator and a divers dream. There is a recent post in the Ranger Tug Forum that shows the results of lack of hull anode protection. The R27's rudder is severely damaged and in need of replacement. Hopefully the other underwater hardware is not also damaged. Good luck and enjoy your new to you C28.

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Possible solution. My RT25SC has donut anodes on the 4 swim platform supports which all are tied to the bonding system. These are fairly hefty anodes and I would think they would be sufficient to provide a similar protection of a hull anode. I am certantly not an expert on this subject and would like to get some feedback on my assumption. In addition, being a 2014 boat that has been in brackish water 6 months of the year for the last 12 years, I have not "seen" any corrosion on underwater metals including: rudder, thru hulls, or metal strip on keel; which are all tied to the bonding system. Am I missing something?

RTC said:

Possible solution. My RT25SC has donut anodes on the 4 swim platform supports which all are tied to the bonding system. These are fairly hefty anodes and I would think they would be sufficient to provide a similar protection of a hull anode. I am certantly not an expert on this subject and would like to get some feedback on my assumption. In addition, being a 2014 boat that has been in brackish water 6 months of the year for the last 12 years, I have not "seen" any corrosion on underwater metals including: rudder, thru hulls, or metal strip on keel; which are all tied to the bonding system. Am I missing something?

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Yes, the other anodes, as long as they are tied into the bonding system will help protect all of the other metals. Since you are in brackish water, hopefully you are using aluminum anodes.

The large anode on the prop shaft will also help protect the bonding system on the inboard boats. I verified that my shaft has only a .1 ohm of resistance to the battery negative and bonding system on my 25 SC with a Yanmar 4BY3, so there is a connection through the transmission and engine. Also, somewhat strangely so I don't know if the factory did this or a previous owner, but my starboard trim tab is tied into the bonding system. Normally the trim tab would be isolated with the anode only protecting the tab just like the thrusters, but in this case it along with the shaft anode are doing the bonding protection for everything. Not a problem in that the trim tab anode is super easy to replace, but it's not the way boats are normally set up.

Like BB marine said, they (and unfortunately most boat builders do the same) are built from the factory without galvanic isolators. Anyone using shore power should have a galvanic isolator, so I had to install one myself even after 11 years of previous owners.

Thank you all for your input. The C28 we purchased has no isolator and has been on a dock for for 7 years. The rudder and all the fittings surveyed well. It was pointed out that the antifouling paint on the hull around a bronze intake strainer was actually hinting of some galvanic action. The fitting was solid, but paint itself was showing an electrical reaction.

I will look into tying the bonded system into an external anode.

Paul&Wendy said:

Thank you all for your input. The C28 we purchased has no isolator and has been on a dock for for 7 years. The rudder and all the fittings surveyed well. It was pointed out that the antifouling paint on the hull around a bronze intake strainer was actually hinting of some galvanic action. The fitting was solid, but paint itself was showing an electrical reaction.

I will look into tying the bonded system into an external anode.

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Unfortunately, many surveyors are not also corrosion experts. Seeing the bottom paint disrupted around a bonded hull fitting is not indicative of a problem, even though many people who don't understand it think it looks like a problem. What we normally call 'haloing', or a circular pattern of damaged bottom paint around a metal bonded fitting is a sign of overprotection, or being 'over zinced'. It's not a problem. The goal of the anode is to cause a voltage shift of the metal you are trying to protect by -.02 volts which will protect the metal from galvanic corrosion. Shifting the metal more than -.02 volts is the 'over protection', but it does not damage the metal. In an extreme case it can damage aluminum, but for bronze or stainless steel there is no damage as the part being protected is still the cathode in the anode/cathode relationship. The haloing is caused by the very, very small electrical field from that -.02 voltage shift interacting with the copper in the bottom paint. It's really a sign that your anodes are working. It's only a problem for the coating (you'll lose the bottom paint protection where it comes off) not for the metal parts.

The reality of most North American built inboard boats, including fluid motion's, is that the only real component that is susceptible to significant corrosion is the propeller. That's because the props are actually brass, even though we call them bronze. Brass, and almost all propellers, are 40% zinc so if they are not protected they will eventually become brittle copper that breaks easily. The bronze through hulls themselves won't corrode, and many boats are built with bronze through hulls and no bonding system without any problem. Stainless needs protection, hence the need for anodes on the trim tabs and thrusters (shaft in the thruster mixed with bronze housing). The main reason for bonding bronze through hulls is to prevent the rare, but extremely damaging, case of stray current corrosion. This protection happens because the bonding wire provides a path back to the battery negative to allow the overcurrent protection to work in the rare case of a stray current corrosion problem.

Adding the galvanic isolator is a must. It should significantly slow down the anode use. Adding the transom anode is always a good idea.

Andy, thanks for the reply. No, most marine yards don’t for the most applications use aluminum anodes on the Chesapeake. I do use them on the thrusters. I will look into aluminum anodes further, however I have not had any issues on several boats including a motor yacht that I only pulled every 2 to 3 years to paint. I also installed a galvanic isolator when I purchased the boat 12 years ago.

RTC said:

Andy, thanks for the reply. No, most marine yards don’t for the most applications use aluminum anodes on the Chesapeake. I do use them on the thrusters. I will look into aluminum anodes further, however I have not had any issues on several boats including a motor yacht that I only pulled every 2 to 3 years to paint. I also installed a galvanic isolator when I purchased the boat 12 years ago.

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I think a lot of it depends on where in the Chesapeake you are. Southern bay I think you're fine with zinc, but where it gets closer to fresh than salt is where you have the problem. I work in the Melbourne to Ft. Lauderdale area of Florida and I've seen problematic use of zinc a few times. Once was in Stuart florida on the North Fork of the St. Lucie river, part of a salt water estuary and on a boat near the Grand Banks facility if you look at a map. This boat had always used zinc and not had a problem. The owner told me that the water was normally very clear, but the day of the survey it was foul smelling and brown soup. They had started water releases through the lock from Lake Okeechobee two weeks prior to lower the lake level, and the water had become much closer to fresh than salt. When we hauled the boat out the zinc anodes were the consistency of toothpaste, and I could easily smear it with a finger.
The other time was on a large motor yacht kept full time in the water at Safe Harbor, Harbortown Marina in Ft. Pierce. This marina is only about 1/4 mile from the ocean inlet, but a small river dumps into the intracoastal waterway next to the marina. Especially when it rains the water in the marina becomes brackish enough that I've seen tilapia under boats and a family of river otters used to live in the marina, even that close to the inlet. Anyway, when that motoryacht was hauled I saw the same thing, zinc anodes that had turned to paste.
I've been told by experts I trust on freshwater that they see boats come in with zinc anodes all the time and the anodes just shut down, but don't turn to paste like I've seen. So I don't know exactly the criteria that makes zinc dissolve in brackish water sometimes, but I know it happens.
There are several advantages to aluminum. Mainly that aluminum is the one anode material that is effective in all 3 conditions: salt, fresh, and brackish. If you're going between them it's always the best choice. Additionally, zinc anodes are made with trace amounts of cadmium, a heavy metal that dissolves into the water as the anode is wasted. Aluminum anodes are supposedly more environmentally friendly for that reason.
All that said, I put aluminum on my boat (I always recommend FL boats use aluminum because we have so much brackish water around) but ended up moving it to a place where I'm entirely salt water. I was surprised by how fast the anodes were eaten up, and I verified everything correct with a reference electrode and testing. So this season I'm switching to zinc to see if there is any difference. I'm also going to add a donut anode to my swim platform brackets as you mentioned on yours, I think that's a good idea and in a place that's easy to change. I'll have to check whether or not my brackets are tied into the bonding system.

Thanks for the information. We have always used zincs in our area, so I never questioned or researched aluminum verses zinc. You make some very good points. My prop zinc always shows some deterioration, but the swim platform supports zinc and trim tabs zinc don’t show much if any. I always replace all zincs each year. I will look into changing to aluminum next year.

Thanks