A maritime tour-de-force begins in Astoria Thursday morning. Pilots will guide a ship carrying a massive crane under bridges on the Columbia River. The vessel should arrive at the Columbia River Bar around 4:30 am and take on pilots for the journey upriver. They'll arrive at the bridge just before 8:00 am -- exactly low tide. Even so, there's just a few feet to spare.The Zhen HuaBut Columbia River Bar Pilot Captain Robert Johnson says that's just the beginning. The upriver port of Longview will be an even tighter squeeze. Robert Johnson: "The Longview bridge is down to inches, so the Astoria bridge isn't the critical part. It's the Longview bridge which will be very critical." The Zhen Hua was previously in Seattle, where it unloaded four other similar cranes. The ship is now bound for the Port of Portland. The ship will anchor in Vancouver, Washington, Friday and arrive in Portland Monday to unload the crane. ODOT plans to shut down the Lewis and Clark (Longview) bridge for 15 - 20 minutes as the ship passes underneath. That could halt traffic sometime between 7:00 and 9:00 Thursday morning.