Illustrated talk on lightships which were floating lighthouses positioned where land based lighthouses could not be built.  They marked the entrance to harbor channels and the navigational routes around reefs and shoals.  The first American lightship was in 1820 and the number grew to a maximum of 55 lightships by 1900 compared to 1,460 lighthouses. The early lightships were of wood, no engines, with oil lamps and hand- rung fog bells. Later lightships had engines, built of steel, and with electric lights and power operated fog horns.   Almost half of all lightships were in or near Cape Cod waters.  Ten lightships were lost to storms and five in collisions. The last active lightship (Nantucket) was removed from service in 1985.  Nine remaining lightship hulls are museum artifacts. The old Nantucket Lightship is berthed at East Boston and open to visitors.