Early Rotostay. I have one on my boat..
I can let you have a PDF of the maker's instruction leaflet if you need it. I also have photos of the drum dismantled.
That' s good point. There should be two vertical bars attached to the rope guide to prevent that happening. Like this:The line on your drum looks a bit beefy as if it might easily fall off the drum and wrap round the forestay. I only say this as we have a locally, Australian, made furler, without a cage, and we had issues. I made a new device to feed the furling line and downsized using dyneema.
Jonathan

That' s good point. There should be two vertical bars attached to the rope guide to prevent that happening. Like this:
View attachment 131787
The line diameter recommended to me by Rotostay is 8mm
No need for a sketch, that's all very clear. Although it might help the OP.The drum is old, pre popularity of dyneema. 8mm would be fine, actually might be a bit thin, for handling by hand (much depends on how big the sail is). Now we can use dyneema for the wraps and add a tail of say 10mm. Our similar drum had no guards and we used it, still use it, for a 45m^2 headsail. It originally had 8mm rope but the rope filled the drum and the feed if only slightly off true bunched top or bottom and inevitably fell off. The other issue is that as you sail over big swells the sail fills and unfills (there must be better words? luffs and fills?) and the drum rotates - as it rotates, maybe 1/3 of a turn the last turn of rope goes slack - and again falls off. Out drum is carried on a bowsprit and I had to get out on the bowsprit to put the turns that had fallen off the drum back on the drum - as unsurprisingly the furler does not work if the first turn is not on the drum. You only realise all this when the headsail is too big for the wind and that is not the time when you want to be perched on the front of a bowsprit. The answer was dyneema and a larger tail. I also measure fairly accurately the lenghts of rope required. I ran the spliced on tail down the sidedeck and attached another tail of bungy. When the sail is fully unfurled the tail is kept in tension by the bungy but the bungy still has sufficient stretch to allow you to grab the tail and furl the sail.
If this does not make sense I could make a sketch and re-script.
Jonathan
No need for a sketch, that's all very clear. Although it might help the OP.
I find the 8mm furling line recommended by Rotostay easy enough to handle and so have not felt the need to splice it into a larger diameter line. The sail area is only about 25m2. A friend of mine with a similar boat who suffered from arthritis in his hands did as you suggest so he could more easily grip the line.
The guard on mine has always been entirely successful in preventing any of the furling line dropping off.
The only improvement I could think of on my system would be to lead the halyard up to the masthead and down to a cleat on the mast, instead of the present arrangement where the halyard leads up to a sheave on the swivel and down the front of the foil to the drum, where it is made fast with a lanyard. But it's not a great priority.
Hi Poignard I also have this Rotostay model on my Moody. Would it be possible to have a copy of the PDF and photos? Thank you ?Early Rotostay. I have one on my boat..
I can let you have a PDF of the maker's instruction leaflet if you need it. I also have photos of the drum dismantled.