^^^
This is what I did as well, there was a group buy on a motorbike website I read recently and I got a gopro hd hero. They work very very well, the casing is weather proof and that suction cap works well on the front deck of my tinny (as well as on the motorbike). I still put a safety line around it though just in case.
Not the sleekest looking camera but the video quality is simply the best available in the price range.
Highly recommended. I'm going to take the tinny out on Sunday so I'll take some videos and link them here.