Emsworth Yacht harbour in Chichester harbour.

I highly recommend Emsworth yacht Harbour which is at the north end of the channel leading from the entrance to Chichester Harbour to the Village of Emsworth. We spent several months there. The owners and staff are incredibly friendly and helpful and there are several repairers who are also helpful especially for wooden boat repairs. There are all the normal services such as travel lift etc.
The marina has a sill and is only accessible at high water, have a look on their web site for times and depths to clear the sill. http://www.emsworth-marina.co.uk/
The marina is generally fairly shallow but it is all soft mud and many of the yachts permanently berthed there
 have their keels in the mud at low water. There are just a few berths for larger yachts and calling ahead is recommended. Very good shelter is provided by the high banks one side and the buildings on the other.
The village of Emsworth is a few moments walk away and has everything needed including a reasonable supermarket. The town of Havant is a cycle ride or bus ride away and Chichester and Portsmouth are easily accessible by bus. There is a number 700 bus which travels all the way along the coast from Portsmouth to Brighton and can be caught from the top of the lane about half a mile from the marina.
Going up the channel there is a harbour authority pontoon just before Emsworth where you can wait before entering the marina and another pontoon at the village where you can moor for a short stay and walk ashore to go shopping etc. There is a charge for using Chichester harbour and the pontoon will cost about £10.00 a night, that is if someone appears for the money. There is a tap on the pontoon near the village, however, the harbourmaster will need calling to make sure it is turned on as it was off when we checked during the winter. This is the link to the harbour conservancy http://www.conservancy.co.uk/page/home/1/