Boating Advice: Corrosion case studies (Part 3)

Let’s not make light of the issue of corrosion for it’s undoubtedly the biggest concern and the least understood subject affecting boats, boat-buyers and boat owners. So while we may be up to Part 3 in this corrosion series by *The Surveyor, the information shared within is invaluable.

Author Gavin Clark, The Surveyor, also consulted corrosion expert Brian Gatt, the Technical Director and owner of Logix Group (.com.au), for solutions to the following case studies and others involving corrosion.

The following four interesting cases were unearthed by The Surveyor in the course of normal surveying work about the Sydney waterfront. They range from a US import that was converted from 110V to 240V to some production cruisers and a relatively new yacht living in the water with earth leakage issues.

This conversion on boats was common in the market place, when the Aussie dollar was at parity and there were lots of ‘grey’ imports. The problem is the majority of owners do half the job or, more to the point, are unaware of the real costs of a professional conversion to Australian Standards.  

In this case there were obvious signs during the internal inspection that things weren’t right. The carbon face on the shaft seal was corroded severely and many valves had seized and were unable to close or were very tight to adjust.  

When the boat was hauled up for the out-of-water inspection it was quite obvious the bonding system was not linked.

On the port side only, we had huge amounts of calcium growth on all of the through-hull fittings; the main block anode on the transom had not been active, it was covered in a slime; and the metal supports for the marlin board and rudder housings had huge amounts of growth on them.

The standard zinc anodes were working and for the eight months since installation were at an acceptable level and showed no concerns.

The Fix: This was relatively easy fix, however. We recommended the buyer contact Brian Gatt, the Technical Director and owner of Logix Group and get a Maddox anode (anodes will also be covered in a separate and more detailed article) and that the bonding system be replaced.  

The local electrician on site attended to this advice and found two things immediately. First, the bonding between the transom block anode and the bonding wires was non-existent and the bonding circuit was broken in many places due to the degradation of the wire over the years.  

The starboard side, funnily enough, had just enough connection that it was working.  Naturally the bonding was replaced on all fittings throughout.  This was caught in time and with ongoing inspections, which should be standard for all boat owners, will live a happy life.

Case 2: 44ft sportscruiser built 1994
The vessel was first inspected out of the water and aggressive action to the rear anode and the starboard-side leg anodes was noted instantly. The records for the last known slipping showed these were replaced four-months ago, so this was very alarming. The aggressive action also identified that this wasn’t just a basic bonding issue, but a massive earth leaking issue from shore power.

Brian, the corrosion king, was called in and carried out his thorough on-board testing and found the earth blocker was non-existent and all stray current was leaking to the anodes and passing through the leg.

The Fix: Luckily, we got to this one out of luck, as the purchaser was inspecting the boat. Another month on and the leg would have become the anode and started severe corrosion at a rapid rate. The earthing issue were professionally fixed.

The local boat yard had him convinced he had been unlucky with lightning or that the steel vessel next to him was causing issues. What was causing the issue was a long way from the truth.  

Once again Brian was called in and found there was a rather large current leaking from the mast, traveling down the mast and standing rigging to the chain plates, to the bonding strap and on to the keel. This current was large and the blow out was the current leaving the vessel through weaker metal, that being the keel.

The Fix: The bonding strip was removed from the keel and instantly the leakage to keel was stopped. Now we had a problem; if the mast were to be struck by lightning, there would be nowhere for the charge to reach earth.  

So the source of the fault needed to be found. It could only be two things: a halyard had worn an aerial sheave and this was in contact with the mast section; or the same thing was happening with the mast lighting wiring. It was found to be the latter and the entire wire was removed and replaced.  

Now the source had been fixed, the earth needed to be re-attached to make the mast grounded from a strike.  In this case, and what is now a very good recommendation, is the installation of an electrolysis blocker between the mast and the keel. This will allow any stray current to pass to the keel, but will also allow a major lightning strike to pass through.

Case 4: A 44ft production yacht built 2014
This one had a saildrive completely corroded to the bone! In this case, you could see the internal gearing after three months in the water after an annual slipping.  

This was originally an ongoing issue of “minor corrosion” to the keel.  In fact, the power supply to the 12V nav. lights had been severed in the pulpit and was sending current through the aluminium toe rail, the toe rail had been linked to the chainplates to the keel, hence the issue with the keel.  

The keel had ongoing issues and the saildrive anodes were working a little harder than normal. The lack of education in the industry lead to a very well-credentialled repairer instructing his team to bond all the systems to the saildrive.  

What wasn’t known was that what the repairer was actually doing was spreading the love and the saildrive, being alloy, became the anode (remember aluminium is very low on our galvanic scale).  

What turned this one south was the fact the owner had done quite a lot of night work with the boat, including a major coastal passage under motor. The system is on, the voltage is higher because of the alternator working and, bingo, no saildrive casing.  

Now you may think I’m being harsh on the repairer, not at all, he was working to the best of his knowledge, and the chances of a butterfly effect are low. But if you don’t know and cannot quantify it, please get an expert in.

The Fix: Isolation switch on negative terminal, rewiring, electrolysis blocker and good bonding.

TIP OF THE ICEBERG
There are many more cases and causes of corrosion
I have highlighted a few very common and not-so-common cases of serious corrosion here to get your attention.
As boat owners and potential boat buyers you need to be aware: there are a multitude of possibilities when it comes to corrosion. Here is a short list:

My answer to this is make your boat right, that way boat by boat we eliminate a cause. This is the only way.  The severity of these cases vary, but all can be identified by the right professional, and rectified.

I have taken my time to research and align myself with the right tools and knowledge to identify corrosion issues, then I can call in the experts to offer the solution and immediate prevention.

During the course of putting this article together I have used information directly from Logix group.

I recommend if you are a boat owner, or even run a professional repair yard and you have some of these symptoms, or more importantly are not fully educated in the effects of corrosion, that you contact Brian at www.logixgroup.com.au. Like me, you may find it’s the best phone call you make.

For those hooked on the corrosion articles so far, we will move to the bonding system and anodes, their importance, what you should have and why in our next instalment (Corrosion Pt 4).

Please keep in mind the next article will be specific to the grounding and bonding system. You will be able to understand its working and faults in that article.

*Gavin Clark is a contributor at boatsales.com.au and BoatPoint.com.au who writes under the pseudonym 'The Surveyor'. He is a shipwright and marine surveyor with a business called Slipstream Marine based in Sydney. He has 27 years experience in the boating industry, is an avid boater and owner of a 33ft Sharpie (trawler). Gavin can be contacted at boatsurveying.com.au.