auto focus at night. Night shots.

Hi there , i have just got the SX50 . After taking it out at night i was trying to get some reflections of lights on the water of the harbour.

I had real trouble to get a green focus box.

Tried several apertures and ISO values but a lot of times it just would not lock a focus on the scene.

can anyone recommend settings for shooting at night. ?

Like settings for the autofocus ?

Thanks .

Andy