It wont work well
This system is neither a lazy jack system nor is it a jackline. For a naval architect....sheesh.If there is any kind of wind at all, the jib will be flopping and flogging and I dont think that it will fold in all that easy.The block on the bottom of the forestay? I have made downhauls before and I will tell you for fact that there is a serious flaw here. If the block is at the bottom of the forestay, the line will be pulling tight up against the sail that is coming down and trying to buch up and bulge out....trust me , this is true, It wont come down more than about 1/2 to 3/4 of the way. When I made my first downhaul, this is what I had to correct. I did this by moving the block over to the starboard side and attaching it to the bottom of a stanchion. just slightly back of the forestay. This gave enough clearance.Also, If you clip your downhaul line to the top of your jib, when you pull downhaul, the top will try to bend over slightly which will fight against the forestay and be more difficult to pull on. Simply attach your downhaul line to the second or third position down from the top and all will slide down easily. This system will possibly damage your sails.His system is something that sounds good on paper but will not work well as a downhaul. This 'dousing the sail' thing would however, come in handy if you wanted to partially douse your sail partially against the forestay as in an aid for tacking.My suggestion would be that if you want a downhaul, stick to the normal method. If you try this system, let us know how it works. I would like to hear from you. I have been wrong many times before.IMHOTony B