OK its not easy
Need to be planned well in advance
Needs to be cancelled if the weather is not OK and winds are above f2
SPCC have a guide available here http://www.stpancrascc.co.uk/thames-cruising-guide.html
You cant do it in a NB from Limehouse or Teddington without pushing a lot of tide the only sensible place to leave from is Bow Locks ( needs to be pre-booked)
Its basically a case of follow the buoys
Best day to go is on an early morning tide 7-8am
Leave Bow Locks 1-1.5hrs before HTLB means you arrive at the barrier at High tide ( I leave as soon as I can get over the cill at Bow).
You should reach the entrance to the Medway at low tide then ride the tide up to Allington. Its a long day in the region of 12-14hrs hence the need to leave Bow Early.
Its much easier if you have a chart plotter as a couple of the Buoys are 3 miles apart and it makes sighting them easier.
PM me if you need more details its an easy trip but has to be planned and you need to be prepared to cancel I know of some NB that waited 3 weeks to get back from the Medway as the weather window just wasnt there
Canal boats going under Rochester Bridge on the way back round to the Thames.
In good company.
Look at this site.Cameras and wind at Sheerness.Its wind that causes all the unpleasantness.Once above the Gillingham Forts the weather cannot do much to you.If you need any local info just ask. http://www.iossc.org.uk/weather/index.php