Hey Glen,

I position my hatches like Rod. It makes it easier to wet out the inside seams at tips of the boat and when loading you can load the hatch in both directions instead of shoving everything toward the ends. The downside is that the closer you go toward the ends - the smaller the opening gets. So you be the judge as to whats too small.

As for the shape of the opening, I like to cut straight lines with rounded corners so I follow the run of the strips for the sides. Then finish it off as you can see in some of the pictures at the link below. This pic gives you an idea of the positioning I use.

Happy Building.

Charles.