PROBLEM TO BE SOLVED: To more accurately analyze a frictional resistance reduction effect by means of air bubbles in a marine vessel. SOLUTION: In an analytical method for analyzing a frictional resistance reduction effect resulted in by jetting air bubbles to a flow field in the vicinity of the surface of a hull of a marine vessel under sail, the quantity 1 of a decrease in shearing stress due to the intervention of air bubbles is obtained when the product of a time constant T and a turbulent frequency 1 in a flow field is sufficiently greater than 1 (in case of a high frequency band) based on drag Rv acting on bubbles, which is introduced by the movement of air bubbles in the flow line direction of the flow field, and in the direction normal to the wall surface of the hull in the flow field of the surface of the hull, the constant 1 of a wall law for a case of the existence of air bubbles permitting the diameter db of a single air bubble to be variable, is obtained based on the assumption that a decrease in shearing stress is caused by a decrease in mixing length, an analytical solution for a frictional resistance reduction ratio Cf /Cf0 is thereby obtained based on a relational expression on the constant 1 of a wall law and a local frictional resistant factor Cf when there exists no air bubbles, and a relational expression on the constant of a wall law when there exists no air bubbles and a local frictional resistant factor Cf0 .
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