Abstract: A jet propulsion system for boats in which the thrust force center line is below the boat reaction center line to urge the propulsion system thrust line to tilt downwardly. The tilting of the propulsion system thrust line downwardly lifts the stern of the hull to create a suitable vertical vector. As a consequence thereof, the boat is urged into a planing position for the reduction of drag on the boat in the lower speed range. At the higher speeds, dynamic water pressure reacts on the intake to urge the tilting of the thrust force center line upwardly toward a horizontal position to reduce the depth of the bow of the boat submerged in water for reducing the drag on the boat. A tension spring controls the angle of the tilting of the thrust force center line to attain the changeover at a selected speed for optimum operation.