Water properties such as density, visoosity, corrosive, etc. are important parameters to be considered in the design of a boat. This paper demonstrated the effects of these water properties to the boat design and disoussion on the effective ways ti deal with the problem. The change of water properties due to the change of temperature influence the resistance and power required to propel the boat. Resistance and effective power changes of a boat due to the change of temperature are calculated using Froude Soaling. The change of draught of a small planning boat when it travels in different parts of the world is also calculated and discussed. The statical stability of ship as the sea water density change is also calculated. Briefly discussion has been made for the prevention of hull corrosion and hull roughness. It is very important to obtain exact values of relevant density and kinematic viscosity in the design of a boat.