| Prop Shaft Diameter. | How To | |||||||||
| A reasonably accurate and reliable rule of thumb states that propshaft diameter should be | ||||||||||
| one fourteenth of propeller diameter. | ||||||||||
| Formula | ||||||||||
| D = cube root ( ( 321,000 x SHP x SF ) / ( St x RPM ) ) | ||||||||||
| 42 | Shaft Horsepower | |||||||||
| INPUT > > > | 3 | Safety Factor (3 for yachts, 5 - 8 for commercial / racing) | ||||||||
| 20,000 | Torsional Shear | |||||||||
| 2000 | Shaft RPM | |||||||||
| 14 | prop diameter | |||||||||
| 1 | Shaft dia in inches + eighths | 1 | one fourteenth | |||||||
| 1 | average | |||||||||