$2-$ A twin screw ship has a design speed of $18\mathrm{.}0$ knots. Its propellers have a diameter of $3\mathrm{.}0$ m and are designed to operate at an advance coefficient $J=0\mathrm{.}7.$ the corresponding open water thrust and torque coefficients being: $K_T=0\mathrm{.}350,10K_Q=0\mathrm{.}560.$ The propulsion factors are: $w=0\mathrm{.}050,t=0\mathrm{.}060,{}_R=0\mathrm{.}980,{}_S=0\mathrm{.}960.$ Determine the design propeller rpm and the brake power of each of the two engines. What is the effective power of the ship at the design speed?