Originally Posted by sailingdog
Or you could make an adjustable sliding arm that is attached to the hatch and to the hatch frame that uses something like a thumbwheel to hold in position. Many factory hatches come with something similar. Not too difficult to make, and not very expensive to buy.
Bomar hatches use this type of support.
West Marine used to sell a cheapo plastic hatch support that folded like a pair of scissors. You would use an uncoated aspirin tablet to hold the "Scissor" open. If the tablet got wet, such as during a rain or heavy dew, it would dissolve and close the hatch. I don't know if they are still available but I used them on a previous to keep it aired out. Security wasn't a big worry then.