Doyle Stackpack were invented by Doyle sails as a way to enclose the mainsail after flaking in an easy manner. The mainsail cover is basically part of the system so you do not need to store and retrieve the cover every time you go sailing. The lazy jacks capture the sail as its drops and then all you need to do is zip up the top of the cover.
Introduced in 1983, DOYLE StackPack is the original trouble free mainsail furling system for the cruising sailor The simplest, easiest way to handle your mainsail Proven to be the most innovative and cost-effective mainsail handling system ever Maintains mainsail speed & shape – lies flat against the sail while sailing Available as a retrofit for your existing sail
StackPack is a fully battened mainsail with integral lazy jacks and a cover that opens automatically to accept the sail as it is lowered. The cover and lazy jack system neatly flakes and holds the sail as it is lowered or reefed. The folds at the foot of a reefed mainsail also lie neatly in the StackPack cover, eliminating the need to tie off the excess fabric with ties. With the sail completely stowed, the StackPack system presents a neat appearance and automatically protects the sail from harmful UV rays. While sailing, the integral cover lies flat against the foot of the sail for a clean aerodynamic effect.
More Sailmakers these days are producing their version of the stackpack, so ask your sailmaker