Plymouth Harbor has many areas from which to launch a Kayak.   Nelson Street Park is  one of the best places to portage from.  You are centrally located and have several choices of destination.

Heading straight out, crossing the harbor and going through the channel-- you reach Long Beach, which is probably the best beach one could  want to visit.  It is miles of flat sandy coastline that is secluded from the mainland.  From there you can paddle out to browns bank at low tide. There are interlinking sandbars that go on for what seems a mile or so.  A virtual private beach of your own, during the week, but not on the weekends. It is a good stop-over if you choose to paddle over to Saquish or to Clark's Island.

There are websites that say you cannot paddle out from Plymouth during low tide???  They are saying that you have to walk through a ways of mud flats, That is not true.  It is not rocket science Navigate out.  You can still head out straight across the harbor with ease.  Common sense  says that boats during low tide will have to stay in the channels so kayakers who can float in just inches of water don't have to look over their shoulders if they are avoiding boaters.

Another place to launch is Stevens Field.  It is more of a portage area than a beach, but when it's low tide you might not want to bother. When the tide is out; there are mud flats to deal with. Have fun cleaning all the muck that gets inside your kayak!!!.  During mid or high tide, it is a great place to do short trips from. After you portage from Stevens Field turning right will lead you south  behind Plymouth Beach to an inlet behind long beach which allows for a short but descent paddle  that borders many "ocean view homes" of  Warren Avenue. 

 http://www.billingtonseakayak.com/