When a ship runs a fixed route in a given time, two methods are proposed to reduce the fuel consumption of the ship. The first optimization policy is to keep the engine output power at a constant level, in spite of prevailing conditions, such as wind forces, wind directions, sea conditions, draft, fouling, etc. Even power running saves about 0.6% of fuel consumption, when compared with the constant speed running at full load-halfway and ballasted-half way. Secondly, if sea currents are known, the optimization policy is to correct the above-mentioned speed by about half of the sea currents. These methods can save about 1.0% or more fuel on a Japan-Persian Gulf voyage.