The main problem to solve was the mixing of the control lines and the sail.

A separate channel (which contains the control line) is sewn alongside the main sleeve which contains the spinnaker. The spinnaker and the control line are completely separated . The separate channel (side sleeve) is made of a different colored cloth than the main sleeve which shows the eventual twists of the sleeve prior of hoisting it. There will often be some twists in the sleeved spinnaker as it comes out of the bag, especially after long periods of storing and moving it around the sail locker. Needless to say, those twists are to be removed before hoisting the sleeve.

Another problem to address was the opening, the mouth of the sleeve.

It had to be rigid to remain open when pulled against the sail, slippery to enable it to slide over the sail without chafing it, light (weight aloft should always be avoided) and sturdy enough not to break in the bag when stepped on or stored. Fiber glass was, from the beginning, the material of choice by its versatility and ease of manufacturing. While the round shape seems obvious, the oval shape is more spinnaker friendly for it doesn't have the tendency to rotate around the sail as it is guided by the spinnaker leeches and it is easier to slide through the hatch when storing below deck. We make them out of Kevlar and glass which, while expensive, offers a good combination of strength and lightness.

The control line is a closed loop, made of 2 different lines. One side is to hoist the sleeve. It must not kink and it should be small enough to travel in the side sleeve and through the top turning block. The other side must be much heavier as it is handled by the operator to douse the sail. It also must not kink as well as be long enough to be lead through a snatch-block, as Steve Dashew suggests in his very thorough "Offshore Cruising Encyclopedia", in the fore deck and then to a cleat or a winch on bigger boats.

The cloth problem came from the fact that spinnaker or bag cloth doesn't breathe and might bleed. The cloth that is milled especially for ATN is a "tricot", a mesh like material which is light, strong, and doesn't retain water. The sail can dry when in the sleeve and it will not cling to the sail when hoisting the sleeve, even after long period of wet storing.

Finally, the spinnaker is fastened inside the spinnaker sleeve with a swivel shackle to allow gibing.
The hoisted spinnaker sleeve must always remain in the same position at the mast head, on top of the flying spinnaker, while allowing the spinnaker to rotate under itself. This also gives more flexibility when loading the sail.