As Per Marine Department of Hong Kong, If your boat is smaller than 11 ft, and has less than 4hp engine. The person who is operating the boat does not require a operating license (That means a boat driving license). However, anything that floats on the water and is attached to a motor requires a certificate of ownership and an Operating License (like a boat number). Just like your car has a car plate, your boat also requires a license number which is called as Certificate of ownership number in Hong Kong.
You will not require a license if your small craft does not have engine. That means an inflatable boat you are paddling and using around the shore and beach is ok. Of course if it is a sailing yacht you will require license.