Stern Access Hatch

[2ndCurse]

Has anyone replaced the access hatch in the engine well w/ a larger rectangular hatch? I currently have a 6" round snap-in hatch. I would like to replace it for 2 reasons, 1st is I can't get 2 arms down there to do any thing and can't see anything w/ 1 arm down there. 2nd is I want to be able to secure the cover. I had a friend who almost sunk his boat when he took on water and his snap in hatches opened up. All the water went directly into the bilge. Any input? Thanks