The type of Mooring buoy you require will depend on the type of mooring you have.
As a general guide we would recommend
Swinging Mooring - Use Polyform US A Series or Polyform US CC Series
 Fore & Aft Mooring - Use Polyform US CM Series or Majoni Rod Buoy

Polyform US - CM Series Mooring Buoys
Cm Mooring Buoy Advice
To work out what size buoy you require you need to determine the weight of the chain it has to support.
  1. To calculate the amount of chain needed -
    You will need to know the depth of the water at high tide and multiply it by 1.5.  This is the length of chain from the ground tackle to the buoy.
  2. All chain has a stated weight per foot.  Calculate the total being used and add another 25% of the total for safety.   This will give you the amount of buoyancy required. 
  3. Always use chafing gear where mooring lines run through bow chocks or are likely to contact deck hardware, and a thimble on the shackled end will prevent chafe at the buoy.
  4. When picking up a mooring, always use the top ring to pick the buoy with a boat hook. Then shackle the mooring line to the mooring chain shackle at the bottom of the buoy, rather than to the buoy itself. This puts all the strain on the anchor chain, rather than the buoy.  You can  now be confident that your boat is attached to the ground tackle and not just relying on the buoy.