When in a emergency situation when stopping is necessary, throw all engines into flank astern, and if possible, steer hard to port/stbd, this turning movement will help slow your vessel down even more.
I would like to point out, that if your in a fixed propeller vessel, this information is bad advice. Especially if you need to turn to avoid hitting something.
By throwing your engines into reverse, you severely reduce the flow rate across the rudder, thus severely reducing your ability to turn. Reducing power, and going full port / starboard would be a much better option IMO.
This information is not correct for water jet powered vessels such as the sea cat though, throwing your engines into reverse and then turning hard will still allow you to turn very sharply. This is because water jet powered vessels make use of thrust vectoring.