by Shimon Mor on 28 May 2010 in Yacht Services
Are you familiar with the terms hot marina, electrolysis, and galvanic corrosion? Are you curious to know what divers actually do under your boat? These are questions that will be answered under today’s topic: galvanic isolators.
We’ll begin by addressing the second question first. Divers spend their time under boats changing zincs (sacrificial anodes). These zincs are electrically connected to all underwater metals and prevent the boat metals from corroding by sacrificing itself to corrosion. Anytime you have two dissimilar metals immersed in salt water (an electrolyte) you have galvanic corrosion. A battery is a beneficial type of galvanic corrosion. And as long as your zincs are working, your boat is under controlled galvanic corrosion and only the zincs corrode. But if all your zincs are consumed by galvanic corrosion then your boat metals (most likely your bronze propellers) will be next so it’s important to ensure you install new zincs at the appropriate interval.
So what is the appropriate interval? There are many factors that go into how quickly zincs are consumed. Some of the factors are how much metal the zinc is protecting, the types of metals, water temperature and salinity, currents, and possibly, other boats in the marina (more on this soon). It is best to have your zincs inspected very three months for the first year to establish a baseline of consumption. Once you establish your baseline, you can modify the inspection schedule to reflect your pattern of consumption. If you change marinas or even slips, it’s best to establish a new baseline. Timely inspections of zincs can prevent very costly corrosion damage to props and other underwater metals.
There is another type of corrosion called electrolysis. This is similar to galvanic corrosion except now we have an electrical current (stray current from a problematic electrical component onboard) which greatly accelerates the effects of corrosion. These stray currents can wreak havoc on your underwater metals and cause extensive damage very quickly. This stray current can come from your boat in which case there is not much you can do other than recognize the problem and repair the faulty electrical component. But stray current can also originate from other boats in your marina (hence the term hot marina). How can someone else’s problem become your problem? Well, if you are plugged into shore power then you are connected to every boat in the marina via the green, grounding wire in your shore power cord. This is where the galvanic isolator comes into play. This device blocks any electrolysis-causing stray current from entering your boat. It prevents other boats from consuming your zincs and eventually your precious boat metals.
Galvanic isolators are recommended by the American Boating and Yacht Council (ABYC) for all boats–regardless of age or composition–that utilize shore power. More information can be found in Chapter A-27 of the 2010 ABYC Standards manual.
Zincs and a galvanic isolator can offer protection from galvanic corrosion, electrolysis and a hot marina but neither of them will protect you from onboard stray currents. Having a bonding system survey performed will ensure your boat is fully protected.
Shimon is a service technician at North Harbor Diesel and ABYC certified.
Tags: electrolysis, galvanic corrosion, hot marina, sacrificial anodes, zincs
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by Fred Phillips on 21 May 2010 in Mechanical Services
When winterizing icemakers, please remember that the machine must be cycled to fill the tray with water, otherwise the electric water valve will be closed and not allow the flow of water to reach both the tray and more importantly the interior of the valve itself. We have come upon a number of these conditions this spring as we awaken boats from their winter naps. It is just a matter of understanding how the icemakers work. To receive this information and how to prepare your vessel for the spring please contact Fred Phillips direct at 360-299-1910.
Fred is a service manager at North Harbor Diesel
Tags: icemakers, winterizing
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by Justin Mitchell on 14 May 2010 in Mechanical Services
Did you know that an exhaust elbow should be checked every five or six years? Did you know that the average life expectancy of an exhaust elbow is 6-8years? Generators elbows have even a shorter life span.
The exhaust elbow is also known as a mixer or mixing elbow. This is where the seawater used to cool your engine or coolant is mixed with the outgoing exhaust in order to cool your exhaust gasses down enough to pass safely through your rubber exhaust hose and fiberglass muffler. The exhaust elbow is subjected to temperatures of 1000deg or higher and needs a good steady flow of cool saltwater to keep it from overheating. This saltwater is like an acid on the welds of stainless elbows and the steal of a cast elbow and eventually the plug and fail. When this happens seawater either cannot flow fast enough to continue to cool the engine or it back feeds into the cylinders of your engine causing great damage. The genset exhaust elbow often has a secondary problem not associated with age but with under loading or idling too long. A genset that is not ran at a high enough capacity tends to carbon up the exhaust elbow and can cause back pressure problems for the seawater and for the exhaust gasses. This often shows up as soot in the water and the engines inability to reach maximum RPM or horsepower.
HAVE YOUR EXHAUST ELBOWS INSPECTED
Justin is a service manager at North Harbor Diesel.
Tags: exhaust elbow, maintenance
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by Justin Mitchell on 7 May 2010 in Mechanical Services
What is the difference between an oil change and an annual service?
An oil change is simply that- Change the engine oil and filter. This may or may not include the generator. An oil change does not include items like fuel filters, heat exchanger zincs or checking belts and hoses. It does not include the often overlooked and underrated impeller the heart and life-blood of your cooling system. It never includes a gear oil service.
An annual service includes all of these things. Did you know that after only 100hrs of running your engines (mains and generator) your fuel filters can plug up from asphaltine or debris in your fuel tank? Did you know that fuel sitting in a fuel filter breaks down and can plug a filter without actually running the engine? This is caused from the asphaltine dropping out of your fuel and the fuel going bad. What about that impeller? A lot of boat owners do not know what an impeller is. One boat owner told me last week the impeller has never been changed in the 10years he has owned his boat and wanted an estimate for the service. An impeller is a rubber piece that pumps saltwater through the seawater side of your cooling system. Instead of having air like in your car to cool the coolant, your boat has seawater to cool the coolant. The impeller is the one and only devise to push this cooling seawater through your engine and keep it from overheating. If left alone it wears, rots or takes a set causing low or minimal seawater flow. My philosophy is when in doubt change it out!!! The consequences of not changing it are possible major internal engine damages. The impeller should be changed every two years or two hundred hours regardless of what your buddy tells you. The transmission is also often overlooked. Change the oil in it every other year or better yet every time you are due for an impeller change, change the marine gear oil (transmission).
GET AN ANNUAL SERVICE NOT AN OIL CHANGE
Justin is a service manager at North Harbor Diesel.
Tags: annual service, asphaltine, fuel filters, heat exchanger zincs, oil change
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