In recent weeks, the Oakland Estuary has morphed from an innocuous playground for water sports into what the local boating community describes as a semi-lawless stretch roamed by marauding thieves and patrolled by vigilantes. It’s a drama more suited for the high seas than the placid, 800-foot-wide channel separating Oakland and Alameda. Yet according to those who live and own boats in the area, the situation has escalated into a true crisis. On Aug. 16, half the boats at the Alameda Community Sailing Center, a sailing nonprofit for kids, were taken in the night. At the Marina Village Yacht Club, residents say they have been threatened by “pirates” scouting out the docks. The Encinal Yacht Club, Jack London Square Marina and the Outboard Motor Shop have all been victimized. In total, over a dozen small boats and dinghies have been stolen in the past three weeks.