Racing Boat Prop
Racing puts unbelievable stresses on mechanical components. A quick look at this prop will attest to that. It is rated at 1500 horsepower. The crack is huge, and luckily it stopped short of breaking the tip off.
The prop pictured here was on a racing boat owned by non other than 4 time off shore champion Rick Bowling. Rick runs twin Mercury Marine motors rated at 1350HP. It is made of a magnetic stainless steel described by Mercury Racing as a proprietary alloy. The prop costs over $5000.
The crack (See picture 2) shows “beachmarks” (Indicated by the red arrow) which distinctly identifies it as a fatigue related crack. A likely explanation here is that the prop received some damage from striking debris in the water. That damage caused a stress concentration. Other blades show damage nicks at about the same area of the blade. These are indicated by black marks on the blades. The other explanation is that there was a discontinuity or an inclusion in the casting, which we are looking into.
The failure of the prop could have been worse. Had the blade separated on the up stroke it could have been thrown a heavy piece of metal at a considerable speed for a considerable distance. It would have made the propeller extremely out of balance (a lot more than it is here), which could have had destructive consequences to the drive system on the boat.
Another factor in this failure are the extremely sharp edges on both the leading and trailing edges of the prop. We understand that these edges are necessary design elements.
One thing that definitely did improve the life of the replacement prop was Deep Cryogenic Treatment (DCT). The treated prop has three times the running hours on it of all previous props used. The prop as of January 6, 2016 is still running strong. We will publish the total hours after the prop is out of service.