I’m not sure that I would want to put yacht varnish over white as it comtains UV filters which give it a yellowish tint. Yacht varish is intened to provide a flexible coat over exposed wood – which it does very well.
As has beeb stated on here previously, you can go for one of the specialist products as dave recommends or alternatively Ronseal Interior Matt or Satin Polyurethane varnish. (Don’t use the quick dry acrylic type)
Colin