When a ship has sailed for a while without hull maintenance, the resistance will increase over time due to increased fouling on the hull. This will lead to a speed loss of the ship. It is difficult to monitor the extent of this speed loss on a ship only due to fouling accurately. This is because there are many other varying added resistance types that include in the total added resistance. The scope of this thesis is to remove by calculations all important added resistance types except fouling resistance from the ship over a period of time. When all other resistance types are corrected for, the only added resistance left should be the added resistance due to fouling on the hull and propeller. These corrections are described in detail in this book. The results of this procedure is also presented.