为什么船的水线以下是红色的

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have you noticed how boats both large and small tend to be painted a different

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color under the water most often it is red but actually nowadays you can get

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almost any color you like the reason for it goes back to the

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earliest days of sailing ships back in those days wooden sailing ships would

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slowly plot around the world a combination of their slow speed and

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rough hull made them an ideal breeding ground for underwater growth just take a

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look under a pier you will see the sort of growth these ships used to suffer

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we're talking barnacles worms seaweed and things like that so what's the issue

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well all of these things have negative impacts on ships over time you get the

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obvious of things like damage to the hull itself due to worms and the actual

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growth then you get issues like the additional weight that they have to

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carry around and reduction in maximum speed due to the extra drag of course on

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sailing vessels that dragon weight would impact their ability to sail upwind

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which would yet further reduce their efficiency what you need is a way to

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stop marine life from growing on the bottom of the hull and this is where

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antifouling comes in antifouling fairly obviously is just a system designed to

Antifowling

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reduce fouling by animal and plant life on the underwater sections of a boat or

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a ship early solutions were to place copper sheets on the hulls of ships the

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Cutty Sark is a great example of this and I'll link to the greenwich maritime

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museum below if you want to see more about that the primary purpose of the

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copper sheets was actually to stop worms eating their way through old wooden

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hulls a secondary benefit though is that the copper would reduce the growth of

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plant life of course as wooden hulls were a place by iron worm issues did

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reduce but they've never been eliminated just look at the leisure industry today

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and you'll still see plenty of wooden hulls around and of course regardless of

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its construction material we still have the same old issue of drag caused by the

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growth of plant life is probably more important now to keep that under control

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what were the cost of fuel and efficiency savings on long passage

Paint

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we still need antifouling to stop a combination of worms barnacles and weed

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from growing on the underside of hulls but instead of using the old technique

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of copper sheets we now use a form of paint instead that antifouling paint

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works on the same principle and actually still uses copper as a biocide though is

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mostly cuprous oxide is now mixed in with the paint rather than copper sheets

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it's the natural red color of those copper oxides that's led to the

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traditional red color of antifouling modern antifouling systems can be broken

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down into two broad categories hard and soft soft coatings are designed to wear

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off over time continuously exposing fresh biocides as the outer layer of the

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paint wears off hard coatings on the other hand are designed to be a lot more

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durable they're meant to last a lot longer as the biocides are released the

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durable layer of paint remains but of course the biocides contained in the

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outermost layer do get used up both systems work on the same principle they

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gradually release biocides commonly based on the chemical element copper the

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difference is that soft coatings slowly allow the paint to flake off as well

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as you can imagine there are environmental considerations to think of

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no matter what way you look at it antifouling releases via cites and

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possibly paint into the environment that is one reason a lot of ports don't allow

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cleaning of hulls they don't want the extra dose of biocides and paint

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released by the scrubbing process so what are your other options the cleaners

Alternatives

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one is to simply use normal hardware and paint on the other side of the hull but

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that will result in a lot of aquatic growth that's fine on a small boat that

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you can pull out the water and clean quite often but is not so great on a

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container ship running around the world what would happen if for example a

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container ship picked up some seaweed in Asia and carried it into the Baltic Sea

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where it takes hold and overtakes some of the native species similar things

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have happened and do actually continue to happen though it's not so much from

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hull growth because of antifouling is more of an issue for a ballast water but

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that's a topic for another video so aside from just using no antifouling

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what could you do there is talk of systems that slowly use some sort of

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jelly from the hull the theory is that as

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the growth attaches to the hull the using jelly seeps off and takes the

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growth away with it I've never seen it in use but if anyone

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has let me know in the comments below cuz it'd be fascinating to look into

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otherwise there are some silicon based paints that make it hard for barnacles

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and things to stick to the hull itself unfortunately these don't actually stop

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the growth but it makes it easier to clean off send that most ports don't

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allow cleaning anyway not only because of the historical antifouling issues both so

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they don't want to clean off species that are not native to the harbor itself

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the last thing they want is to be overcome by some sort of invasive weed

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from the other side of the world anyway hopefully you've enjoyed today's video

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and have liked learning about the paint on the bottom of the hull for more

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content like this every other Friday be sure to subscribe

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right here on the channel until next time thank you for watching and good bye