(Portsmouth,N.H.) - A 600 foot oil tanker struck a pier on the Memorial Bridge in Portsmouth  early this morning, but there is no apparent damage to the bridge itself.Bill Boynton of the Transportation Department said the tanker "Seapride" was headed out of Portsmouth Harbor when it struck the pier at about 5:15 this morning. Boynton said the incident did not affect lift operations of the bridge and it remains open to motor vehicle traffic.