Excessive corrosion on running gear

Ftcara

Member
Joined
Jul 29, 2023
Messages
12
Fluid Motion Model
C-28
Vessel Name
Tuggernaut
I saw this post below on a faceboook page. I recently purchased a 2014 R-27. The prior owner had it on a dock without shore power. I had it connected to shore power at my dock. I immediately noticed excessive corrosion on the running gear. I installed a galvanic isolator and spent a small fortune doing repairs. I thought it was something related to the marina being hot (although the marina ran a bunch of tests and assured me it was not the marina). They spent hours chekcing out to the tug. Has anyone else experienced this?

We were original owners who kept our 2021 RT29S inside a Certified Clean Marina saltwater boathouse year-round. Despite following recommended maintenance and having a diver check anodes and hull condition underwater every 3 months, we experienced excessive corrosion of trim tabs and prop even though the anodes were not excessively affected. The first trim tab corroded and fell off 16 months after we took possession. Our boathouse was checked by 3 different professionals and no stray A/C current was ever found!! RT recommended we add additional zinc to trim tabs. We added extra zinc, also paid RT to install a galvanic isolator just to be sure. Then, we lost the second trim tab and prop to corrosion. Our marina manager, then our mechanic, surveyed and found D/C current going through several wires on our boat that shouldn't have current - our boat was not grounded properly from the factory! Our mechanic told us faulty factory wiring caused a D/C leak resulting in the corrosion of trim tabs and prop. Our mechanic repaired a few other improperly wired RT boats and even spoken to RT representatives about it. Our diver has seen excessive corrosion recently in some late model RT's kept in year-round saltwater, despite performing recommended maintenance, adding additional zinc per RT representatives and no A/C current leak. The diver hasn’t seen this in other boats under similar conditions.

When we contacted RT explaining the latent defect and asked for reimbursement for excessive corrosion damage and repair of faulty wiring, they helped with some replacement parts, but were not helpful troubleshooting the defect. They didn’t seem interested in understanding the improper factory wiring issue. In the end RT refused to pay for repair and wiring defect damage. I just want others experiencing excessive corrosion to understand this could be the cause and urge them to get an electrical survey done.
 
Your describing two different issues, galvanic corrosion and stray current corrosion. Everyone who keeps their boat on a dock connected to shore power should have a galvanic isolator. It's not that the marina is 'hot', that's a common misconception, but that many boats in a marina usually share the same ground connection for the AC electrical wiring. AC current doesn't cause corrosion, but a DC voltage difference can develop on the AC ground and because the AC ground is connected to the DC ground (battery negative) one boat will end up protecting (using up the anode) another boat nearby at the marina.

The other corrosion being discussed in the post is stray current corrosion, which is caused by a +DC voltage being applied to an underwater metal. The easy way to distinguish between galvanic corrosion and stray current corrosion is time. Galvanic corrosion happens over a period of months, stray current corrosion can eat away an underwater metal in a matter of days. You can easily check for stray current corrosion with a multimeter looking for voltage between the battery negative and any underwater metal. If you see any voltage you have a problem. If you measure resistance (ohms) between the battery negative and a bonded underwater metal you should see less than 1 ohm, anything above 1 ohm means you have too high a resistance and need to clean the bonding connection. With proper bonding connections you shouldn't have a stray current corrosion problem, in theory a positive dc voltage applied to a bonded underwater metal should trip a breaker/blow a fuse before it does any damage to the boat.

Marine corrosion is one of my specialties, happy to answer any specific questions.
 
Your describing two different issues, galvanic corrosion and stray current corrosion. Everyone who keeps their boat on a dock connected to shore power should have a galvanic isolator. It's not that the marina is 'hot', that's a common misconception, but that many boats in a marina usually share the same ground connection for the AC electrical wiring. AC current doesn't cause corrosion, but a DC voltage difference can develop on the AC ground and because the AC ground is connected to the DC ground (battery negative) one boat will end up protecting (using up the anode) another boat nearby at the marina.

The other corrosion being discussed in the post is stray current corrosion, which is caused by a +DC voltage being applied to an underwater metal. The easy way to distinguish between galvanic corrosion and stray current corrosion is time. Galvanic corrosion happens over a period of months, stray current corrosion can eat away an underwater metal in a matter of days. You can easily check for stray current corrosion with a multimeter looking for voltage between the battery negative and any underwater metal. If you see any voltage you have a problem. If you measure resistance (ohms) between the battery negative and a bonded underwater metal you should see less than 1 ohm, anything above 1 ohm means you have too high a resistance and need to clean the bonding connection. With proper bonding connections you shouldn't have a stray current corrosion problem, in theory a positive dc voltage applied to a bonded underwater metal should trip a breaker/blow a fuse before it does any damage to the boat.

Marine corrosion is one of my specialties, happy to answer any specific questions.
Thank you for taking the time for a great explanation.
 
Great info Bantam
 
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Your describing two different issues, galvanic corrosion and stray current corrosion. Everyone who keeps their boat on a dock connected to shore power should have a galvanic isolator. It's not that the marina is 'hot', that's a common misconception, but that many boats in a marina usually share the same ground connection for the AC electrical wiring. AC current doesn't cause corrosion, but a DC voltage difference can develop on the AC ground and because the AC ground is connected to the DC ground (battery negative) one boat will end up protecting (using up the anode) another boat nearby at the marina.

The other corrosion being discussed in the post is stray current corrosion, which is caused by a +DC voltage being applied to an underwater metal. The easy way to distinguish between galvanic corrosion and stray current corrosion is time. Galvanic corrosion happens over a period of months, stray current corrosion can eat away an underwater metal in a matter of days. You can easily check for stray current corrosion with a multimeter looking for voltage between the battery negative and any underwater metal. If you see any voltage you have a problem. If you measure resistance (ohms) between the battery negative and a bonded underwater metal you should see less than 1 ohm, anything above 1 ohm means you have too high a resistance and need to clean the bonding connection. With proper bonding connections you shouldn't have a stray current corrosion problem, in theory a positive dc voltage applied to a bonded underwater metal should trip a breaker/blow a fuse before it does any damage to the boat.

Marine corrosion is one of my specialties, happy to answer any specific questions.
Great info. I noticed the other day when I pulled my boat out of the harbor because i was leaving for work that around one mounting screw on each trim tab was quite corroded. I installed the new trim tabs in the middle of last summer 2024 (just upgraded to larger tabs). I’ll have to run some test with my multi meter when I get home. I know that my trim tabs are not grounded to the boat and I do not have a galvanic isolator. I got back and forth keeping the boat on the trailer and in the marina.

Any thoughts on this?
 
Great info. I noticed the other day when I pulled my boat out of the harbor because i was leaving for work that around one mounting screw on each trim tab was quite corroded. I installed the new trim tabs in the middle of last summer 2024 (just upgraded to larger tabs). I’ll have to run some test with my multi meter when I get home. I know that my trim tabs are not grounded to the boat and I do not have a galvanic isolator. I got back and forth keeping the boat on the trailer and in the marina.

Any thoughts on this?
Do you have anodes on your trim tabs? You should, because those mounting screws are always what suffers when there are no anodes on the tabs. I saw a Ranger Tug just recently that didn't have any anodes on the tabs and half the mounting screws on both were broken.
Strangely, my own boat has the starboard trim tab tied into the bonding system for some reason. I didn't realize it until letting the boat sit in the water for 6 weeks and seeing how fast the starboard one wasted while the port did not waste at all.
 
Do you have anodes on your trim tabs? You should, because those mounting screws are always what suffers when there are no anodes on the tabs. I saw a Ranger Tug just recently that didn't have any anodes on the tabs and half the mounting screws on both were broken.
Strangely, my own boat has the starboard trim tab tied into the bonding system for some reason. I didn't realize it until letting the boat sit in the water for 6 weeks and seeing how fast the starboard one wasted while the port did not waste at all.
I just put anodes on the trim tabs this spring. So far this year I haven’t had my boat connected to shore power while in the harbor either. But last fall I had the boat in the harbor for a few months connected to shore power with no trim tab anodes I am thinking this is when the aluminum trim tab bracket around the mounting screw began to decay. Is it recommended then not to bond the trim tabs to the vessels bonding system?
 
Normally the trim tabs are not bonded, which is why they need their own anodes. Just like the thrusters, some manufacturers recommend not bonding their thrusters and using the individual anodes on the thruster to protect them.
I'm feeling the frustration this morning. Replacing all the anodes and my bow thruster anode bolt head broke off on me and it had only been in the water for 6 weeks. Should be a lot of fun to work on inside the tube...
 
I was suffering from excessive corrosion on all of my zincs. So bad that they all needed to be replaced after just 4 weeks in the water. So I went ahead and bonded the trim tabs to the grounding system. It has made a huge difference for me. Now 2 months in the water and the zincs look like they have over 60% remaining.
 
I have never understood why some boat manufacturers do not install Galvanic isolators on any boat that may be connected to shore power.

The first modification I made to my Tug was installing a Galvanic Isolator. In my opinion, if you plan to dock your boat at any marinas, you should (in my opinion must) install a galvanic isolator.

As noted, my tug did not have a galvanic isolator. I do have a generator, I was wondering if all tug with generators do not have a galvanic isolator as the thought is they will not connect to shore power? Do tugs without generators all come equipped with Galvanic Isolators?

Or am I just making an assumption?
 
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