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Old 23-10-2021, 02:17   #1
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Aluminium boat next to steel in the marina

What are the potential problems when mooring an aluminium sailboat next to a steel one during a winter layover (~ 5-6 months)?
Which one of the two should be more concerned?
What is the minimum that could be done by both to prevent problems?
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Old 23-10-2021, 02:54   #2
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Re: Aluminium boat next to steel in the marina

Aluminium should worry more.

However, as an owner of an Aluminium boat with a few steel-boats close by, the risk depends on a long list of factors and it's hard to make predictions. Best is to be very attentive to what's going on to catch problems early on. If your anodes get eaten at a high rate, it's time to take measures. If you're suspicious of your neighbour, add a few additional anodes between the boats.
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Old 23-10-2021, 03:47   #3
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Re: Aluminium boat next to steel in the marina

If you are seeing rapid anode consumption, you can also hire a qualified electrician to verify your aluminum boat is a properly isolated system and then identify who is the "leaker". The boat that is creating the electrical feedback into the water is costing every boat near it money and time- easily proven by the rate of zinc consumption and cost. If the leak is bad enough it can even be a serious safety hazard.

This information can be used to make a formal request from the marina to the owner that they need to hire someone to repair the boats improper wiring.

Unfortunately there are multiple reasons this might not be effective: marina doesn't care, or owner of offending vessel doesn't- people are strange creatures.



You can also help yourself by not using the shore power. Which means your boat will have less ground potential and be better isolated from electrolysis.



Finding a properly qualified electrician who understands the nuances of aluminum boats might be a challenge depending on your location.



Otherwise they make large "zincs" (use ALUMINUM anodes: they are better in every way) that you can drop over the side of your boat. An anodes effectiveness/protection is largely based on surface area in order to "give up" or exchange material. These are often called "Grouper Zincs".



In a perfect world, it should not matter the hulls construction material, every electrical system would be properly set up, steel, fiberglass (which often has grounded shafts and bonded through hulls), aluminum. In the real world you have to look most often for the "DIY boats" and derelicts as these boats have often been modified my the unknowing with improperly wired systems.




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Old 23-10-2021, 05:44   #4
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Re: Aluminium boat next to steel in the marina

The galvanic series for metals show that aluminum will be the anode, of the galvanic cell, in contact with almost all other metals, and, hence, the one which suffers from galvanic corrosion.
When two different metals are in contact, and subject to a corrosive or conductive environment, there is a current flow between them. This current flow causes the corrosion of the least corrosion-resistant (Anodic, active) metal to increase, and corrosion of the more corrosion-resistant (Cathodic, inactive) metal to decrease.
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Old 23-10-2021, 05:59   #5
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Re: Aluminium boat next to steel in the marina

We protected our aluminum vessel with multiple coats of epoxy and properly done wiring. We have only connected to shore power once and that was during haul out. Who knows whatís going on at marinas or in other boats. Any boat, not just steel boats, can be wired incorrectly. Some marinas are dangerous not just to boats, but people. You can test very carefully, but that does not guarantee things will be the same when someone flips a switch or a wire fails.
Additional zincs might help if itís the only place to leave your boat but do you have any other options?
We removed a number of female connectors from several marina power pedestals and cut them apart. They were only a few years in service. The corrosion was frightening. Itís the reason we avoid shore power.
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Old 23-10-2021, 08:57   #6
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Re: Aluminium boat next to steel in the marina

If your shore power enters your boat via a high quality isolation transformer, then your use of shore power shouldn't be an issue on your boat but who know what the boat next door has installed and therein lies the problem. All the information I've seen that preceded mine is relevant too. I generally haul out every winter but that isn't a great option when living aboard.
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Old 23-10-2021, 09:07   #7
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Re: Aluminium boat next to steel in the marina

This is a tricky subject. As a retired marine engineer, I've seen some strange things regarding galvanic corrosion that defy explanation. While zinc is the typical metal of choice for a sacrificial anode, aluminum is also used.
Do some internet searches and you'll find a variety of discussions on this topic.
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Old 23-10-2021, 10:26   #8
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Re: Aluminium boat next to steel in the marina

Quote:
Originally Posted by BenBowSirocco View Post
If you are seeing rapid anode consumption, you can also hire a qualified electrician to verify your aluminum boat is a properly isolated system and then identify who is the "leaker". The boat that is creating the electrical feedback into the water is costing every boat near it money and time- easily proven by the rate of zinc consumption and cost. If the leak is bad enough it can even be a serious safety hazard.

This information can be used to make a formal request from the marina to the owner that they need to hire someone to repair the boats improper wiring.

Unfortunately there are multiple reasons this might not be effective: marina doesn't care, or owner of offending vessel doesn't- people are strange creatures.



You can also help yourself by not using the shore power. Which means your boat will have less ground potential and be better isolated from electrolysis.



Finding a properly qualified electrician who understands the nuances of aluminum boats might be a challenge depending on your location.



Otherwise they make large "zincs" (use ALUMINUM anodes: they are better in every way) that you can drop over the side of your boat. An anodes effectiveness/protection is largely based on surface area in order to "give up" or exchange material. These are often called "Grouper Zincs".



In a perfect world, it should not matter the hulls construction material, every electrical system would be properly set up, steel, fiberglass (which often has grounded shafts and bonded through hulls), aluminum. In the real world you have to look most often for the "DIY boats" and derelicts as these boats have often been modified my the unknowing with improperly wired systems.




Galvanic isolator or isolating transformer. Then you don't have to disconnect shore power.
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Old 23-10-2021, 14:25   #9
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Re: Aluminium boat next to steel in the marina

A good epoxy paint system below the waterline is a very good start.

I put 6 coats of high build epoxy on my boat in 1984 and it's still in good condition (except for a few spots here and there where I grounded on rocks and had to recoat).

I was once moored alongside copper sheathed piles for 9 months and feared it might cause problems so hung some extra anodes over the side on SS cables bonded electrically to the hull. The anodes were actually pieces of a mangled "mag" wheel and they certainly corroded away quite satisfyingly. The normal hull anodes (zinc) were fine.

"Mag" wheels in the '80s were probably more than 90% aluminium.

When in marinas (rarely) I hang some "mag" alloy pieces at bow and stern. From the same old wheel that I bought for $5 at a wreckers yard all those years ago and cut into pieces on a bandsaw ( I've since been warned to take care doing this as apparently some "mag" wheels can catch fire ).

Since launching the boat nearly 40 years ago I have had to change the hull anodes 4 times.
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Old 23-10-2021, 17:13   #10
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Re: Aluminium boat next to steel in the marina

I owned a steel boat for number of years. The hull was protected by a single 12x6x1 sacrificial zinc plate attached to the hull. I found it interesting to note the dissipation of the zinc varied from location to location. I monitored this with frequent inspections, not only my boat, but also where I happened to be at the time.

There were times, where no noticeable consumption of the anode was noted, but other times, when it seemed to disappear before my eyes.

Despite my best efforts I could not determine why or when, anode consumption was the worse.

Later, in my engineering career, I came across countless examples of anode consumption or protection, that made absolutely no sense to me whatsoever.

I can relate numerous examples for discussion, but can provide no answer to why this was so.

At the end of the day, I determined that some or other makeup in the material that the anode was trying to protect, the placement of the anode, the area that the anode was effective, the distance from the anode, the salinity of the water, the proximity of any electrical current, whether it was shore power or simple the boat's own electrical grounding system, all play a part. It would require an above normal investigation to arrive at an answer, and even then, some doubt would be possible.

In later years I hung a sacrificial zinc grouper over the side over non-steel boats, thinking to add life to the prop shaft zinc, but it made little to no difference.

Whether your boat is steel, aluminum or fiberglass, you best bet is to monitor your particular situation on a daily basis and make decisions accordingly.
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Old 23-10-2021, 17:45   #11
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Re: Aluminium boat next to steel in the marina

First thing ! Do NOT take advice from anyone who uses the word "electrolysis", that is a different but related process that has nothing to do with corrosion on boats. "Electrolysis" is simply a catchy phrase that dock talkers have glommed on to. No one trained in Marine Corrosion will use that term. You are potentially dealing with either stray current or galvanic current.

With either stray current or galvanic current, 99.999% of the time corrosion is caused by ones own vessel. On the other hand, plugging in to shore power does connect you to every other boat on that transformer.

On rare occasions a more cathodic (very close) neigbouring vessel may be an issue. Aluminum is a terrific boat building material but I would not own one that didn't have an isolation transformer. An isolation transformer would give you complete protection from other boats and bad shore power.

If in doubt hire an ABYC Certified Marine Corrosion technician to assess your situation.

.... Retired ABYC Certified Marine Corrosion Technician.
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