First, I want www addresses on online engineering forums which they will answer-solve related engineering problems,quickly and accurately.

Second, " A propeller for a lightwave speedboat capable for been used in inland waters or at sea is currently made out of brass (a copper alloy).In service, the blades are deflecting too much a high rotational speeds i.e(it is not stiff enough).Use a chart of Young's modulus (stiffness) against density to choose three alternative metals which are stiffer, but which will not lead to a heavier component, i.e(they are not greater in density than brass).If possible mention briefly the relative advantages and disadvantages of the alternatives, bearing in mind the service conditions.