If you want to understand why we have to protect our boats from the sun, you'll need to read some science. Don't be afraid, some of us went mostly sailing instead of sitting in the school, but it's understandable for everyone.
UV is the abbreviation of the term "ultraviolet". "Ultra" means in Latin "beyond", so UV's meaning is "beyond violet". Ultraviolet has a higher frequency than violet light. Violet is the color of the highest frequencies of visible light - remember to the colors of rainbow! UV is an electromagnetic radiation with a wavelength from 10 nm (30 PHz) to 400 nm (750 THz). This radiation is shorter than visible light but longer than X-rays. Ultraviolet rays are invisible to most humans.
The history behind it: UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, respectively. At the 60's the scientists already knew that UV has an effect the on DNA.
UV radiation constitutes about 10% of the total light output of the Sun, and is thus present in sunlight. It is also produced by electric arcs and specialized lights, such as tanning lamps. Consequently, the biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.
Suntan, freckling and sunburn are familiar effects of over-exposure, along with higher risk of skin cancer. Living things on dry land would be severely damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earth's atmosphere. Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has effects both beneficial and harmful to human health.
Fun fact from the nature: reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow.
We used wikipedia to write this blogpost.