TECH TIPS

BOAT ELECTROLYSIS

When different metals are placed in salt water you create a ”battery”.  Think about it, you have a stainless steel prop shaft ,with a stainless steel or nibral props with bronze or brass strut on a fiberglass or aluminum or steel hull,  perfect "basket case" of electrolysis waiting to happen.  Each building material has its evil or matter of deterioration. Wood attracts worms, fiberglass spurs blisters and, steel and aluminum hulls are the only building material with electrolysis issues that will eat your investment alive. Let’s touch on my favorite material that I have used for over two decades, and some stories to follow.

Aluminum: to me is the easiest metal to work with (as far as building). Aluminum is remarkable for its metal’s low density and for its ability to resist corrosion due to “PASSIVATION”.  Over twenty years ago, when I worked for a premier aluminum yacht builder in the U.S., aluminum yachts were being built dozens at a time. Easy to cut, easy to weld and easy to form if you knew how. But what wasn’t easy was electrolysis. You have to image back then, we slapped on zincs as normal, thinking we covered all areas properly. Well, lessons learned. Over the years when the aluminum yachts returned for routine maintenance, we began taking notice the areas exposed to electrolysis.  We started setting zincs in proper places and bonding all different metals from shafts to piping to motors. It was truly schooling to see every type of issues with different applications.

 I remember one aluminum yacht that had eaten or deteriorated almost all  the welds on its hull plating. The owner insisted that the aluminum hull and welding was defective. We investigated and found out that the owner hired some back yard welding company to perform a flybridge modification.  The "wannabees",  welded on the yacht for a period of 4 months in the water behind his waterfront home, not knowing that welding without proper grounding of the welding machine is a No-No and the yacht should have been hauled-out for that type of work. The owner and captain learned the hard way and we hauled out the yacht and had to replace the entire hull plating. That was painful, watching the owner cry when he was told what the estimate would be, but he knew he had made a mistake and paid for it.  Another issue is...., it is WORSE to over zinc then to under zinc on an aluminum vessel. By over zincing you’re inducing electrolysis creating a very active area and the results will be costly then to under zinc.  You should use a zinc calculation formula to determine the zinc weight and location.  One should consider the cost of “his/her investment”,  comparing it, its a small faction to hire a naval architect to ensure the hull is fully protected below the waterline.

Also you might want to make sure the boat docked next to you is not sending stray current back through the ground bouncing from boat to boat.

 Its good practice to check the ground at the dock. Docks are notorious for bad wiring and often the ground lead is not connected to ground, is connected to the neutral, and is being used for carrying current to a miss-wired boat, and then, all other sorts of problems. So the ground lead should never be directly connected to the ground bonding system.  Check the shore power ends for any signs of current waiting at the ground.  Another good method to check on your aluminum vessel is when at dock, make a separate ground fish for you.  Meaning, get a long grounding cable attached to a zinc bar and throw it over board and leave it during your stay. Just make sure the other end it bolted to a ground point preferably from your engine room out the porthole. This is a safe guard but you should always consult with a knowledgeable marine electrician.

Shaft zincs are a pain to take care of and also create cavitations on higher RPM vessels. You should invest in a brush zinc that’s mounted on the shaft inside the engine room. The brush zinc is a thin flat bar with a zinc mounted at the end and it and it rests on the shaft as it rotates.

It’s connected with a ground cable attached to your bonding system. By doing so, you can now eliminate the underwater shaft zinc and know that the shafts are properly bonded.

Bottom paint millage is extremely important and is thee factor in protecting aluminum hull plating. Do you agree? Well in my years, I have seen the strangest vessels, application and owners. Bottom paint is preached to us for ultimate protection against marine growth and salt water environment. Think again???

About 10 years ago my office received a service call to visit a vessel at the local marina. Myself and one of my service managers made our way down the docks to visit. The vessel turned out to be a trimaran about 80’ft in length and 40’ft beam but, what struck us the most about this vessel, it was constructed from aluminum and NO paint, bare topside and hull, yes I mean the entire vessel was bare anodize aluminum for 13 years. The purpose of our visit was to perform repairs to one of the generators and propeller, so we hauled the vessel out. I couldn’t wait to get her out and view the bottom. Upon haul-out the bottom looked fantastic, no sign of deterioration or electrolysis, just a couple of scares and dents but no pitting, it was amazing. For 13 years, the vessel never seen paint, the owner always dove the sailing yacht and cleaned the bottom, the owner explained how he and his wife sailed the world and never performed any repairs to her hull, truly amazing, so I ask you; do you think bottom paint is needed for aluminum hull??  HEY, Don't e-mail me about my grammer, I TELL IT AS IT IS.