Thanks Sean for reminding me of the bridge. I knew it was there but had forgotten what it's clearance was.
From Great Bay's web-site:
"...the General Sullivan Bridge, with a 52' vertical clearance, spans the river. NOAA chart #13285 covers this section. A quarter mile west is Great Bay Marine
. Please note that NOAA chart depths do not reflect recent dredging by our docks to at least six feet."
Besides clearance under that bridge (which may be somewhat greater at low tide), the other issue getting in and out of Great Bay is the tidal current
on the river.
FWIW, Great Bay Marine will unstep and step masts down river, for time and materials plus crane charge, if that's what you want to do.
Given jimsea's big new boat, maybe GBM wasn't such a good suggestion, although I've seen some pretty big boats in storage