In the past there were plenty of boat tours that approached the Maunsell Sea Forts and even let people take a look inside of them but nowadays organized tours are rare.
Currently it is dangerous to climb to the forts because the stairs have been removed and most of the structures are in an advanced state of decay.
In the past most of the trips departing to the Maunsell sea forts commenced from the nearby Herne Bay.
Operation Redsand Forts performs regular boat tours to the forts. A return ticket price costs £60 and their exact schedule can be found on their site.
Today, daily tours are performed by a restored Thames sailing barge. Built in 1892 the Greta explores the Maunsell Forts at a very leisurely pace. The 6 hour tours of the Thames estuary commence at Whitstable Harbour, just seven miles north of Canterbury.
Non-regular services are also offered by X-Pilot but you need to call to inquire about the dates the boat goes to the Maunsell forts.
The people at Project Redsand also do regular trips to the Redsand Army Fort for maintenance work. If you want to go to a trip with them and volunteer see Project Redsand for available dates.