Two powerboat riders were fortunate to escape serious injury after their vessel flipped and took heavy damage during high speed training exercises near Coney Island.

The crewmen, aged 17 and 19, were hurled from the speedboat Trim Down for What as the vessel headed out of Castle Harbour near the railway pylons off Ferry Reach at 4.20pm yesterday.

It’s believed a mechanical fault caused the bottom of the boat to strike a rock or reef while the vessel was travelling at 50 knots, or nearly 60mph.

According to a Maritime Operations spokesman, the boat “took off and came down stern first, with the two crewmen thrown out”. The impact tore off both men’s life jackets.

The men swam ashore, and although an ambulance was called, they reportedly refused medical treatment, having sustained “minor abrasions”, the spokesman said.

The powerboat suffered “severe damage”.