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Posted: Mon Jun 15, 2020 2:30 pm
by Robert Biegler
Here is a news item on an antifouling, superhydrophobic diamond film, which is supposed to be robust, too: ... amond.html This is still basic research, so it will be a while until it becomes clear whether it will ever come to market.

I have been wondering, though, about another way to inhibit growth, and whether it would be environmentally friendly. Tie a tarp around the hull, pump most of the water out, and pour enough salt into what remains to raise salinity to the point where marine growth becomes quite uncomfortable. The less water is left inside the tarp, the less salt is needed. Now, salt can be a problem, as shown by desalination plants pumping very saline brines into the sea. Those very die-offs caused by brines do demonstrate that salinity can inhibit growth. And it may be that the amount of salt that would be released from opening up the tarp every time you go sailing would not be enough to be a problem. Of course, the outside of the tarp would have stuff growing on it, but you could turn it inside out the next time. I expect that the brine inside the tarp would also be more corrosive to metal fittings than sea water, so this might not be good for boats with metal hulls, inboard engines, or spade rudders. It might work for boats with outboards and transom-hung rudders. It might even reduce osmosis in polyester resin hulls.


Re: Antifouling

Posted: Tue Jun 30, 2020 7:41 pm
by John Perry
At the recent AYRS Zoom meeting on anti-fouling methods we briefly mentioned 'boat bags' - see These are roughly as you sugest although sodium hypochlorite (domestic bleach) rather than salt is normally added to the water in the bag. According to the website, only half a cup of bleach is sufficient to dose the bag for an 8m yacht. This has to be repeated each time the boat enters the bag. According to the website, the bleach will in due course decompose into salt, so the claim that in these small quantities it is harmless to the environment seems believable.

I like your idea of reversing the bag to keep both sides clean since one would imagine that the outside would otherwise be rather a horrible thing to have to store out of season. The boat bags have flotation independent of the vessel inside and there is a closure arrangement with some kind of seal to allow the boat to enter and leave, I don't know if these features would prevent reversing the bag. From a quick internet search I noted that having the bag tied to the boat rather than being independently floating can result in big loads on securing ropes and fixings since if there is swell the boat and bag do not move exactly together.

I am interested in the relatively new silicone antifouling treatments that work by making it hard for marine organisms to stick to the hull rather than by toxins. It is claimed that what does stick will wash off once your craft exceeds about 8 knots - a challenge for many sailing boats but should be possible for the faster multihulls. I suspect that some people are tempted to try this but are hesitant since if you do apply it and find it unsatisfactory it is a job to get rid of it so that you can get an alternative antifouling paint to stick properly.