Rolla Prop Lost a Blade While Underway

2010 September 26
by Chris Brown

Boken and Lost Prop Blade

One of our good customer’s lost a prop blade while underway in the Caribbean last winter.  The angle of the picture is a bit deceiving – approximately 50% of the blade was gone from this 40″ 5-bladed Rolla prop.

The Captain reported running at low speed in relatively calm conditions in clear water when suddently there was a bang and horrible vibration.  No sign of hitting anything.  There was no damage to the other four blades – no “sanding” of the Prop Speed anti-fouling paint indicating a light bottom touch.   It is hard to imagine a single prop blade hitting a floating object at speed without nicking one of the other blades.

This prop had markings from as many as three other prop shops indicating a fair amount of work had been done to these props.  The vessel owner and crew are fairly new to the boat so there is no history on past events.

It is possible that past prop shop work included extensive heating and/or welding.  This process can cause weaknesses in the blade which eventually lead to a complete failure.  There are times when props have had a bit too much work and the blades get thin and weak. 
Listen to your prop shop when they tell you the props are getting beyond their life – get a second opinion.  If opinions match up it is time to retire these props to spares or “get homes” and invest in a new set.   Investing in a new set can also be an opportunity to try new styles of props if you think there is room for better performance in your vessel.
One last comment on the lost prop blade – prop shops can do welding repair to lost blades up to a point.  Most shops will not repair a blade that is over 40% missing.  The ability for the repair to fail and the subsequent liability is not worth it.

Metal Fatigue Causes a Lost Prop Blade?

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