While I have not made square hatches, I have made hatches with sharp corners. So far I have not had cracks at the corners. I agree with the stress riser idea, but the edges of the hatch are usually reinforced by the hatch sealing system.

I now usually round the corners because it is easier to cut with a jigsaw.

: Every once in a while I see pictures where someone has made their hatch
: cutout as a square or some other shape without any radius in the corners.
: Airplanes haven't had square windows for many years because of one good
: reason, it makes a huge stress riser in the corners. Now granted a deck
: isn't very stressed, but what about when one lays across the back trying
: to get in. I know that some of this stress will be dissipated by the fact
: that the built up fiberglass lip probably makes up for more than the loss
: of the sharp corner.

: I'm wondering if this is just a perceived problem, or if anyone out there has
: actually had cracks develop in the corners of their cutouts from doing
: this?

: Not trying to start another flame war.

: Thanks,
: Dale