On Aug 9, 8:10 am, "Edgar" wrote:
....
My boat came with a nearly new Profurl system which has been entirely
satisfactory and easy to use. The foil cames with two grooves so
theoretically you can hoist one sail before you lower the other as I have
several extra halliards. ...

But not when using the "furling" option. If you have a furling sail
up it will be attached to the swivel and if you hoist a new sail
before lowering the old you will not be able to lower the swivel or
the old sail... There may be other justifications for dual slots
(twin headsails for trade wind sailing, redundancy, or racing sail
changes when the swivel (and therefore the furling) is not used) but
they aren't for changing sails when cruising.

-- Tom.