Police investigate after two die in yacht race tragedy

Police are investigating after a vessel capsized in a Perth yacht race off the coast of Mandurah, killing Skipper Rob Thomas and sailor Paul Owens on Friday night.

Water police inspected what appears to be a damage point where the keel used to be.

Initial investigations suggest the boat ran in to trouble when the keel, snapped off, causing the yacht to capsize.

There were six crew on board at the time.

It's understood 60-year-old Bullcreek man Paul Charles Owens became trapped underneath the boat.

Four other sailors rescued after about an hour in the water.

The body of 70-year-old skipper Rob Thomas was recovered from the ocean about 13 hours later.

9NEWS understands the yacht had a retractable or wind-up keel - not a solid steel keel that most yachts commonly have.

Police are investigating whether the wind up mechanism is what failed and caused the keel to snap.

Members of the sailing community say their tight knit group has been deeply affected by the tragedy.