Hi Alick,
I built a small motorboat last year where I did that http://www.flickr.com/photos/59209887@N07/6400709273/in/photostream/lightbox/
however I wouldn't recommend hinges on a Kayak:
- first of all, having more than one hinge is tricky on a curved surface as the opening angle of both hinges needs to be parallel.
- from my experience, not being able to get the lid fully out of the way can be annoying when you load/unload
- the attaching surface is prone to break at some point.
- depending on where you are and what you want to do the side of preferred acces to the hatch might change, rendering the hinge/lid to be exactly in the wrong place.

I'm nowhere near thinking about the hatches with my builds yet but I am planning to construct some kind of magnetic locking mechanism (not sure how this is supposed to work though either ;-) ).
You might also think about a lid with a bayonet-like connector.
cheers,
Matt