Bottom Paint Care
“Thanks for the great work on my haul out - the bottom paint looks great Krabby!” exclaimed the happy yachtsman.
“Your welcome, now you can enjoy sailing and not worry about what's under the waterline” I responded.
“While I have your attention I have a question about my bottom paint. I recall you said to hold off cleaning the bottom for several months; but when I told my underwater cleaning service to hold off on the cleaning they told me that I was making a big mistake and that they have to clean the bottom regularly. I did some research on my own and found that the paint manufacturer’s recommendation is more in line with what you said. What's the deal?" asked the perplexed yachtsman.
“I am going to start out the answer to that question with a story, better grab us a couple drinks” I suggested.
“Only a couple? I know how your stories go!” remarked the yachtsman.
“You know, you're right, this may take more than one after all…When I was a kid, I fixed up an old inboard motor launch from a wreck that was left behind at the yard. Once I had her in the water for a few months, the bottom had a few spots of algae, especially on the sunny side of the boat. As I was quite proud of my little yacht, I explained to my dad that I was planning to go over the side and scrub her clean. To my surprise, the old man scolded me with a stern voice and warned ‘don’t scrub all the good stuff out of the paint - just let the sea wash it when the boat is underway’. That sounded like pretty-good idea - but you know how it was when we were young, we were so much smarter than our fathers - so over the side I went and I scrubbed her clean.
Within a few weeks in the warm, summer water the growth on the bottom came back with a vengeance. The old man walked by and grabbed me by the scruff ‘I thought I told you not to scrub the bottom’. I thought for a moment that I could negotiate my way out of my disobedience, but all I could say was ‘aw, how did you know?’
For the rest of that summer I was a slave to my bottom: each time I scrubbed it more of the ‘good stuff' came off, the fouling grew more severe and took a greater force to remove, which took off more good stuff. This cycle repeated all summer long until the temperatures cooled off in the fall; my old man finally took pity on my soggy backside and let me repaint the bottom,” I paused to take a swig of my drink and relish in memories of lessons learned by trial and error.
“That was a good lesson, I have experienced similar results on my boat. So, why then are there different opinions on the care of bottom paint?” The yachtsman asked, looking for clarity.
“Better have another drink for this one… It occurs to me that very few people understand how bottom paint works, even many of those who are directly involved with the marine industry.
The idea of anti-fouling coatings goes back to the days of wooden ships. The marine organisms that foul the bottoms of our contemporary craft did more than reduce the performance and efficiency of a vessel; ships built of wood were eaten by marine borers. Finding a way to deter this organism was essential to the ships being able to carry cargo and defend the nations for which they sailed.
At some point, it was discovered that oxidizing copper was deadly to marine organisms. Before they figured out how to put oxidized copper into paint, they would put copper sheathing on the bottom of a ship, in much the same way we use copper bottom paint today.
The majority of anti-fouling coatings (bottom paint) today, use copper as the active ingredient to deter the marine growth. There are lots of other agents have been tried over the years, but nothing works as well as cuprous oxide (oxidized copper) - that’s what causes green tinge you see around the water line.
Anti-fouling coating with copper works by suspending the cuprous oxide in the paint – so that it is exposed to the salt water and can slowly oxidize. When the marine organisms first attempt to attach to the painted surface, they die, and you'll notice a brown slimy layer all over the bottom of your boat. This dead biomass washes off very easily. Eventually, other organisms attach themselves to this dead layer and it may appear that the bottom of your boat is becoming hopelessly foul. But since this is all attached to the dead material, it washes off very easily while underway.
As long as the surface is passively washed by the boat moving through the water or a very soft cloth, the cuprous oxide remains on the surface of the paint and continues to kill whatever tries to grow on it.
When the paint is fresh, in the first year, the cuprous oxide is at its highest level. Any aggressive cleaning will remove a substantial amount of it and dramatically reduce the effectiveness of the paint, prematurely. Just like the story from my boyhood, when you remove some of the copper, the marine organisms are not killed by the weaker paint, so when you go to remove them, you have to rub harder and in the process, remove more paint.
This is evident on your own boat when you saw the paint was completely scrubbed away. As the paint manufacturers recommend: minimal, passive cleaning the first year or more will keep your bottom paint effective longer. After two or three years you’ll have to start cleaning more often as the paint becomes weak. When you notice your bottom is fouled more often and your diver is having to scrub harder, then it is time to haul-out and repaint. On my boats, I find that this time comes between two and three years, depending on how carefully I take care of the bottom paint." Taking a long swig after I finished my monologue,
“Okay, that makes sense now, but why then does my diver keep telling me that I need to have my bottom cleaned?” queried the frustrated yachtsmen.
“I think you’ve already figured out that answer, he is likely afraid he will be out of work. It is unfortunate that he doesn't realize there are some useful things for a diver to do besides scrubbing the effectiveness out of your bottom paint- like a quick inspection: checking the sacrificial zinc anodes, running gear, and through hull fittings” I responded.
“Yes, and what about my zincs, propeller shaft, don't those need to be inspected and cleaned?”
“When we painted the bottom of your boat, we coated your propeller with an epoxy barrier coat, followed by anti-fouling paint that should last for six months to a year, but then your zincs will need to be changed and your propeller needs a cleaning, and that is where your diver will come in handy,” I advised.
“Sounds to me like I just need to properly manage my bottom cleaning so that I can keep my paint in good shape and take care of the rest of the underwater maintenance on my boat. Thanks for the stories. I had no idea of the history involved. Speaking of local history and wooden ships, isn’t the Wooden Boat Festival coming up?
“As a matter of fact it is in June, Father’s Day weekend - as is our annual tradition – it’s our 27th year.
Add that to your calendar, there will be lots of interesting things to see and you might learn a few things that will apply your fiberglass boat as well.”