Its Rob Kemp here of Kemp Sails, i have a Dufour 34E hence commenting on this forum. With my work head on we do a lot of top down and bottom up furling systems and conversions to existing sails so i thought some insights might help as this is a common subject. I spend hours a day at boat shows on this subject alone.
Its well worth getting expectations managed with these systems from the start as calling a top down system a fuller is potentially a bit misleading as it imply s the sail will furl in the same way as your Genoa, it wont!Its best to think of a top down system as a wrapping system. Due to the depth of an asymmetric sail the top section will roll fairly well but the leach will shorten very quickly which means the section below the clew is rather loose and messy.
In terms of the systems i share the view that its a common mistake to buy on price and under spec the system, its far better to ensure the system is the correct size and if in doubt go to the larger model as this will help with durability. This is linked also to the AT cable as the larger systems allow for a bigger cable which transmits torque better and avoids kinking the cable, once kinked the cable is never going to work properly again.
We recommend on boats over 35-40 feet to use a system with a metal drum as apposed to composite systems as these have far more flex and can allow the line to skid which in turn damages the drive system and causes more skidding. Also select one with a drum lock or ratchet as this massively helps control the furling.
If using a current sail get the head and tack fittings changed from metal rings to soft webbing loops as this again helps furling but more importantly helps reduce the chance of the head rolling one way and the tack the other ( a twist). This is nightmare to sort out usually resulting in a trip to us or another sail maker to sort out in a sail loft.
A couple of dos and do nots.
Avoid too much halyard tension as this will cause the head swivel to bind up
Wash the drum after use to get rid of salt build up
Do not allow the sail to flog when rolling as this can cause a twist
The big one, DO NOT leave it rolled up all day or on a mooring, spinnakers are made of nylon and nylon is not u/v stable, if you do this the sail will rot very quickly so an expensive mistake. I see loads left rolled up and even call our customers if i spot one doing this to advise not too. Its so easy to drop the rolled sail back on deck and into a launch bag.
Hope this helps.
If you would like any more advise please feel free to call the sail loft