M's concrete-hull boat was floating nicely in the harbour of a little island in the South China Sea.
Concrete? you exclaim.
Hey, whatever floats your boat. Only the boat isn't, anymore. It has sunk.
All that is visible is a broken mast forlornly bobbing up and down on the water's surface. Nearby, the Marine Police have stationed a yellow warning buoy which has a red flashing light.
Still, all is not lost. They say that for every problem there is a solution. Maybe he could turn it into a concrete submarine? Like this one: Popular Mechanics