Abstract
In a previous paper (1980), the author derived analytically a friction coefficient for a wave-current coexisting motion as well as its approximation for practical use. This approximate formula is, however, given in an implicit form so that an iteration is always needed in the calculation. The present paper proposes an approximate formula in an explicit expression. The accuracy is found to be within 3% compared with the exact solution, better than that of the previous approximate formula. The persent formula is thereby useful in reducing the number of arithmatric operation in computer programs.
