Why are ships painted red below the waterline?

have you noticed how boats both large
and small tend to be painted a different color under the water most often it is
red but actually nowadays you can get almost any color you like
the reason for it goes back to the earliest days of sailing ships back in
those days wooden sailing ships would slowly plot around the world a
combination of their slow speed and rough hull made them an ideal breeding
ground for underwater growth just take a look under a pier you will see the sort
of growth these ships used to suffer we’re talking barnacles worms seaweed
and things like that so what’s the issue well all of these things have negative
impacts on ships over time you get the obvious of things like damage to the
hull itself due to worms and the actual growth then you get issues like the
additional weight that they have to carry around and reduction in maximum
speed due to the extra drag of course on sailing vessels that dragon weight would
impact their ability to sail upwind which would yet further reduce their
efficiency what you need is a way to stop marine life from growing on the
bottom of the hull and this is where antifouling comes in antifouling fairly
obviously is just a system designed to reduce fouling by animal and plant life
on the underwater sections of a boat or a ship early solutions were to place
copper sheets on the hulls of ships the Cutty Sark is a great example of this
and I’ll link to the greenwich maritime museum below if you want to see more
about that the primary purpose of the copper sheets was actually to stop worms
eating their way through old wooden hulls a secondary benefit though is that
the copper would reduce the growth of plant life of course as wooden hulls
were a place by iron worm issues did reduce but they’ve never been eliminated
just look at the leisure industry today and you’ll still see plenty of wooden
hulls around and of course regardless of its construction material we still have
the same old issue of drag caused by the growth of plant life is probably more
important now to keep that under control what were the cost of fuel and
efficiency savings on long passage we still need antifouling to stop a
combination of worms barnacles and weed from growing on the underside of hulls
but instead of using the old technique of copper sheets we now use a form of
paint instead that antifouling paint works on the same principle and actually
still uses copper as a biocide though is mostly cuprous oxide is now mixed in
with the paint rather than copper sheets it’s the natural red color of those
copper oxides that’s led to the traditional red color of antifouling
modern antifouling systems can be broken down into two broad categories hard and
soft soft coatings are designed to wear off over time continuously exposing
fresh biocides as the outer layer of the paint wears off hard coatings on the
other hand are designed to be a lot more durable they’re meant to last a lot
longer as the biocides are released the durable layer of paint remains but of
course the biocides contained in the outermost layer do get used up both
systems work on the same principle they gradually release biocides commonly
based on the chemical element copper the difference is that soft coatings slowly
allow the paint to flake off as well as you can imagine there are
environmental considerations to think of no matter what way you look at it
antifouling releases via cites and possibly paint into the environment that
is one reason a lot of ports don’t allow cleaning of hulls they don’t want the
extra dose of biocides and paint released by the scrubbing process so
what are your other options the cleaners one is to simply use normal hardware and
paint on the other side of the hull but that will result in a lot of aquatic
growth that’s fine on a small boat that you can pull out the water and clean
quite often but is not so great on a container ship running around the world
what would happen if for example a container ship picked up some seaweed in
Asia and carried it into the Baltic Sea where it takes hold and overtakes some
of the native species similar things have happened and do actually continue
to happen though it’s not so much from hull growth because of antifouling is
more of an issue for a ballast water but that’s a topic for another video so
aside from just using no antifouling what could you do there is talk of
systems that slowly use some sort of jelly from the hull the theory is that
as the growth attaches to the hull the
using jelly seeps off and takes the growth away with it
I’ve never seen it in use but if anyone has let me know in the comments below
cuz it’d be fascinating to look into otherwise there are some silicon based
paints that make it hard for barnacles and things to stick to the hull itself
unfortunately these don’t actually stop the growth but it makes it easier to
clean off send that most ports don’t allow cleaning anyway not only because of the
historical antifouling issues both so they don’t want to clean off species
that are not native to the harbor itself the last thing they want is to be
overcome by some sort of invasive weed from the other side of the world anyway
hopefully you’ve enjoyed today’s video and have liked learning about the paint
on the bottom of the hull for more content like this
every other Friday be sure to subscribe right here on the channel until next
time thank you for watching and good bye

Dereck Turner

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