The 58 meter long ferry Monnik went aground on a sandbank near Schiermonnikoog, Netherlands.   The ferry had some 100 to 150 passengers on board when a strong wind and tide kept the Monnik firmly on the sandbank for eight hours.   Two lifeboats from the KNRM were able to pull the ferry free.  The Monnik continued under its own power to the island.  No reports of injuries, damage or pollution.