We did the loop in 2003-5. Clearances at that time were: Erie canal from Albany to Oswego Canal, was officially 20', but we made it all the way at our 20' 10". Lock 19 was the closest at 21'. We dropped mast to 15' to detour south to lakes Seneca and Cayuga, raised mast again for the Oswego and all Canadian canals All of the locks in Rideau and TS canals allowed for 22'. We made a round trip to Ottawa with no air draft issues. As for trawler shopping, almost all moderately sized trawlers allow dropping the mast to provide about 15' clearance. Modifications to masts are not that difficult on most. Bob Kunath Sans Souci Pacific Seacraft 38T