Marine jet propulsion inlet duct and method

An improved inlet duct for a marine jet propulsion system for a watercraft which includes an inlet duct, a pump, and a discharge nozzle, said inlet duct comprising:

• a) a hydraulically efficient inlet tunnel formed in the hull of the watercraft, said inlet tunnel having a front entrance opening and a rear exit opening with said inlet tunnel being formed by stream lines of generation which commence at said front entrance opening and curve upward to progressively draw water into said inlet tunnel and towards said exit opening;
• and,
• b) an articulating structure attached over said front entrance opening of said inlet tunnel, said articulating structure capable of self-adjusting to control the areas across which water that enters said inlet tunnel so that the velocity of water flowing therethrough matches the velocity of the watercraft in the body of water.

A method of delivering the dynamic head required by a marine jet propulsion system for a watercraft which includes a pumping means and a discharge nozzle, said pumping means capable of receiving incoming water and forcibly delivering the incoming water to a discharge nozzle and exit therethrough to propel the watercraft through a body of water, said method including the following steps:

• a) selecting a watercraft having an inlet duct capable of delivering the total dynamic head of incoming water to said pumping means, said inlet duct including a hydraulically efficient inlet tunnel and an articulating structure attached over the front entrance thereof, said inlet tunnel being shaped so that cross-sectional area progressively increases from the fore to the aft positions, said articulating structure capable of adjusting according to the difference in hydraulic conditions located inside said inlet tunnel and outside said watercraft so that the velocity of incoming water into said inlet tunnel matches the velocity of the watercraft;
• and,
• b) operating said watercraft in said body of water.

An improved inlet duct for a marine jet propulsion system for a watercraft which includes an inlet duct, a pump, and a discharge nozzle, said inlet duct comprising:

• a) a hydraulically efficient inlet tunnel formed in the hull of the watercraft, said inlet tunnel having a front entrance opening and a rear exit opening with said inlet tunnel being formed by stream lines of generation which commence at said front entrance opening and curve upward to progressively draw water into said inlet tunnel and towards said exit opening;
• and,
• b) an articulating structure attached over said front entrance opening of said inlet tunnel, said articulating structure capable of self-adjusting to control the areas across which water enters said inlet tunnel so that the velocity of water flowing therethrough matches the velocity of the watercraft in the body of water, said articulating structure including at least one transversely aligned fixed vane and a plurality of transversely aligned floating vanes, each said floating vane being pivotally attached to enable said floating vane to move according to the hydraulic conditions thereon, thereby adjusting the size of said entrance opening and the length of said inlet tunnel according to the hydraulic conditions.