Which Varnish to use for wood outdoors - Acrylic or Yacht? Is it possible to varnish over stain?

We are often asked which varnish to apply on staintreated wood or untreated wood so that it can be used outdoors.
Both Acrylic and Yacht Varnishes are perfect for outdoor work. Acrylic Varnish is absolutely transparent and it dries faster than Yacht Varnish. Yacht Varnish, which is based on alkyd-urethane, is more resistant and durable than the Acrylic one, but it has a slight yellowish tinge. It can be visible on light-coloured wood, but it is not visible on a stain treated surface.
There are the same instructions for working with these varnishes. After applying the first coat, the wood grain will rise and the surface will become roughened. Therefore, it is recommended to wait till the varnish dries sufficiently and the surface will be ready for sanding. Acrylic Varnish dries for about two hours, Yacht Varnish - for about three hours. After that you should carefully sand the surface with the fine sandpaper, removing the raised grain. After sanding, remove the dust from the surface with a brush, a vacuum cleaner or compressed air. And then you can apply two more coats of varnish. The intercoat drying for Acrylic Varnish is from 5 to 10 minutes, for Yacht Varnish - from 10 to 15 minutes. Dry to handle time, at +20° С, for Acrylic Varnish is 2 hours, for Yacht Varnish - no less than 3 hours.
Please note that Yacht Varnish is still hardening after drying and will reach its final strength in about two weeks.

More info
https://eng.bta.rs/