On 11/10/2011 7:32 AM, Perry wrote:
I am preparing to varnish the rails thwart and deck of a newly
constructed canoe. Mahogany and Ash. Any advise on when or when not to
use a sealer first? Also, I have seen how varnish can yellow the
appearance of Ash, any advise on maintaining the white appearance of the
wood?

you might try asking on rec.woodworking