I am surprized that no one seems to have mentioned Marine Spar Varnish that is recommended for boats. This stuff has been around for years and is well proven. Has a lot of natural ingrediences. I am not ready yet for my bed boards put this will be my choice. I know of a friend who has a 53, he has had his varnished since 2000, still looks very good. (6 coats)
Ayone who wants a natural clear finish will also benefit from the natural hew that all woods developp over time.
This just an example. Click on site below to check it out.
http://www.jamestowndistributors.co...p;familyName=Circa+1850+Exterior+Varnish