As a single hander one of the more difficult sail handling jobs I take on is working a genaker. Love the sail and think your champagne sailing experience is downwind at 5-6 knots under twin head sails
without any sort of following sea.
Consequently I have spent a considerable amount of time pondering in how to implement a DIY furler for the genaker and much of the pondering predates top down furlers.
One of the schemes I came up with was using lay flat hose as the furler foil.
I have used lay flat hose to pump water
fairly long distances and one of the things I found intriguing about it was it's capacity to resist torsionally induced twisting when under pressure.
My scheme was to build the top swivel from nylon it being then clamped into the upper end of the hose. The lower end plug
woild contain a schrader valve (from a push bike tube)
In the bag, and whilst being hoisted, the tube would be deflated. After hoisting the tube would be inflated prior to unfurling the sail, the luff of which is attached to the hose. I figured about 30 psi would be sufficient.
After furling the valve on the bottom would be opened to deflate the tube prior to stowing the sail in the bag.
I am now designing a top down furler and was considering how to implement the twist resistant halyard
component a couple of days ago. What I have come up with so far is to experiment
with taking say the outer braid from 14 mm yacht braid and threading it over 12 mm yacht braid thereby doubling the outer braid which is the more torque resisting component of the rope.