# Homework Help: A ship's propeller shaft transmits 7.5 MW at 440rev/min.

1. Jan 6, 2010

### TC13

1. A ship's propeller shaft transmits 7.5 MW at 440rev/min. The shaft has an external diameter of 230mm. Calculate the maximum permissible bore diameter if the shearing stress in the shaft is to be limited to 150MN/m squared. The modulus of rigidity for the shaft material is 79 GN/m squared

2. Relevant equations: P=omega*T therfore T=P/omega
T/J=tau/r therfore J=Tr/tau
J=pi (D power of 4*d power of 4)/32 therfore d power of 4=D power of 4 -J*32/pi

3. Are my transpositions of the equations above correct? I realise if I want d i will have to find the fourth route of my susequent answer. I came up with 162760.42 Nm for T, 1.248*10-4 m4 for J and 0.1977m for d.
I also need to find the legth of the shaft if the angle of twist does not exceed 10 degrees. I've used the equation: tau/r=G*theta/l which I transposed to get l=G*theta*r/tau. My answer came out as 605.666m which to me seems a tad large. Any help would be very much appriciated. Cheers.

Last edited: Jan 6, 2010