There are thinners for every type of paint and each manufacturer offers a wide range. The reason for using thinners is quicker drying, good gradient etc.
Thinners for paints are mixtures of solvents, which are tailored to specific types of paint. Depending on the binder and the desired properties of the paint (fast drying, good gradient,...). Therefore dilution of yacht paint should never be done with "universal" thinner as the result might be fatal: For example, the color might be divided into its different phases, the surface remains tacky, the paint remains soft. This will lead to a surface that is matt / milky etc. Thinning with slow solvents is therefore a good solution for the application with brush and roll. This is because the paint has more time to reach a good gradient. "Fast" solvents are thus more suitable for spray applications.