Portishead is usually a departure point for most...
it does have a very deep tidal lock system (doesn't take long) which leads into the rather nice modern Marina with a few Eateries and Watering holes...but not a lot otherwise.
If you are in that neck of the woods and can time High water a run up the River Wye a few miles up the Severn Estuary...you pass Tintern Abbey ect with some lovely scenery a nice run.... and you can moor up for pint or two at the Pub side too
Why not consider a run to Bristol Docks as well/instead??? Easy launching (Also tidal lock) Great scenic run under Brunell's famous worlds first Suspension Bridge up the Gorge to the Centre of Bristol ...where there MUCH more to see and do in a Big City MUCH more choice!..pontoons (at both) and it takes you into the very heart of Bristol with loads of places Eat and drink see within walking distance
If you're in the Bristol Channel for a couple of Days A Lundy trip is a nice,though longish run but defiantly worth the trip too!
Just remember all harbours are very tidal and (apart from Cardiff...again with locks) only accessible (variable times) over high water periods because of the huge tidal range.
