A hatch is very important to be able to adjust and work on the sails. They have to seal against the force of the sea and wind driven spray.

This illustration shows a circular hatchway in a notional deck plane. Above is the cover with a pneumatic seal, which can be inflated to 50 psi. or 3.45 bar. The seal is a bicycle tyre, large, strong, smooth without tread and a folding bead made from flexible Kevlar. The inflation valve will protrude above and below deck

The cover is sealed into the hatchway.

The cover cannot go through the hatchway because the diameter is greater. Then where to store the cover?, have it hinged?, or attach it with a rope and have it banging about in the wind and waves ? Not good.

Making the hatch system oval makes no difference to the tyre if it is the same effective circumference. I took the opportunity to add a window made from polycarbonate (Lexan ???) for interior light and being able to watch the sails and wind direction. It a double glazed system to reduce interior condensation.

The cover can now go through the hatch way and be stored below, safely. There will  be handles attached to make the operation easier. Also a tether to stop it blowing away in a gust.