TotalBoat Lust marine varnish is not designed for use below the waterline, as delamination of the varnish may occur with prolonged submersion. Certain applications such as varnish on oars, or deck rails on a boat that may experience temporary submersion for up to a couple hours at a duration, should not be affected. However, results will vary based upon application type, how the varnish was applied, and how long it is submerged.