Uhhhh, not shooting at night? Lol.
I have an HG-10 as well, and generally shooting at night hasn't worked out well for me. However, I recently made a time lapse of a chunk of my drive back to campus, and with the street lamps on the highway that I was using, I actually got some really good quality footage.
You're trying to film the rider I'm assuming? If that's the case, I'd recommend throwing a back behind the boat on a tube, and having them shine a light on the rider to help illuminate them. I'm not sure how well that would work with the HG10's light sensor, but it's worth a shot. One thing that has to be realized is that the HG10 is really only a consumer quality camera, so it's capability of filming at night is relatively restricted compared to say, the cameras that are used for professional videos and such.