A somewhat different application, but I have used castable urethane to create a new hub on a prop for a motor once. It worked well and the person I sold the motor to is still using it all summer for the second year now. It was one of those oddball 5hp Johnsons with the 6hp powerhead and the 4hp exhaust leg and lower unit. It had a ribbed / splined hub so a but different, but I'm thinking of trying it for a 10hp OMC prop to see how it works. Not a super cheap solution though.
YouTube handle: Old JohnnyRude