Help with translation

Is the following sentence understandable?

Those ain't drowning who cannot swim, but who think they can.    It is understandable, but not really correct.  You can say it like this:

Those who drown are not those who cannot swim.  They are those who think they can.

or

People who drown are not those who cannot swim.  They are those who think they can.

The idea is that those people, who cannot swim usually do not drown (usually), because they are afraid of the water, or whatever. But those people, who think (mistakenly) that they are a great swimmers have a greater chance of drowning.   

They drowned. --  it was an accident.

They drowned themselves.  -- it was suicide.