Why do ships have the bottom half of their hull painted red?
In: 4566
The company I work for makes this paint, and a lot of it had been answered already but let me add some to it.
You’re talking about antifouling or fouling control coatings. There’s different kinds with different properties and principles behind it, but the goal is the same: prevent or manage “fouling”, meaning the barnacles and all kinds of marine life to stick to the hull. Not only does this accelerate the corrosion of the metal, it also increases drag by a very significant amount.
There’s silicone based fouling control coatings that reduce friction so the ship sailing through the water is enough to basically wipe the growth off the surface. Positive side is that it doesn’t rely on harmful chemicals and even reduces drag compared to other similar coatings. Downside is that it’s more fragile, more expensive and doesn’t do anything when the ship is laying still. As with others below it adds to the rule that a ship that’s not moving is costing money. A lot of it.
Other antifouling coatings contain copper, biocides or even use nanotechnology to kill off any growth on the ship. Self polishing ones will rely on the water flowing along the surface to slowly polish off a thin layer of depleted paint and expose the fresh, active paint below. The exact type of paint depends on the climate the ship will mostly be in since temperature affects the efficiency, and of the expected time at sea, the average speed and what have you. The faster the ship goes, the harder the paint should be. Of course since it’s basically a marine pollutant it’s heavily regulated and because it wears down it means the ship will need to be repainted every x number of years. This can be as little as 5 years and same as mentioned above this costs a lot of money.
A very interesting thing you might notice is when the antifouling layer is basically depleted. Typically there’s a layer under it that’s the same colour but discolours when it gets into direct contact with water. When you see a ship with the red below the waterline turning white it’s an indication that it should be due for the drydock soon.
But that’s not what you asked. You asked why it’s painted red.
I work in IT for this company, it’s been over a decade since I actually sold the paint so I might be getting details wrong..
If I remember correctly it started with red lead paint used as fouling control paint on ships. It was relatively cheap, very toxic and it was red. This got banned due to environmental factors ( just killing everything that gets close to your boat is not a good idea, who knew). The following fouling control coatings stuck to the same colour due to tradition and having the ships in your fleet look the same even when changing systems. These days it’s most definitely not the only colour that’s around and every brand will have a number of standard shades, usually red and black. Yachts will have similar coatings in white or whatever the latest fashion dictates and big shipping companies can use enough to justify producing batches in their own colours. But typically standard colours do the trick because as it’s been mentioned already 1. this paint is expensive and 2. the big vessels require pallets full of the stuff. A few cents per litre difference can mean a big difference in the total cost plus standardization reduces risk in supply chain.
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