RJ,
It may depend on whether you have anything else added since it was new. Our 53MY had 16.5 ft clearance to the top of the flybridge windshield railing from the factory, but our hinged radar arch takes it up to 18 ft. with the arch down. The bridge at mile 300 on the Cal-Sag channel in Chicago is the limiting factor and it 19.1 ft low steel at standard pool stage. The dam near there keeps the pool reasonably at or below that. I've been under it a number of times and I think it's been closer to 19.5 ft.
Call Hatteras to get the original clearance from the factory. I can't imagine it's anywhere near 19 ft, but you may need to know exactly for some of the other choices like the Champlain canal (17 ft.), the 2nd half of the Erie canal (15.5 ft.), the Chicago iver (17 ft.), the Welland canal (20 ft), or the Trent Severn canal (22 ft.).
Note that you may also have to worry about depth restrictions if your boat draws more than 5 ft.
We're doing the Great Loop Route starting from Chicago in Oct. 2006. I can recommend a couple of good reference books if you like.
Doug Shuman
