This buoy is ideal for anchoring small boats. Made from strong plastic. Diameter: 25 cm. Height: 39 cm. Total buoyancy force: 10 kg. Useful buoyancy force: 4.5 kg. The difference between the total buoyancy and the useful buoyancy is the following: total buoyancy: the buoy is underwater. Useful buoyancy: The buoy floats on the water