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I'm working on a boom furler design now. I want to keep it simple and least expensive as possible. So far, I have an aluminum roll mounted to a steel shaft. This whole asssembly is then mounted on bearings which fit inside bearing blocks. The bearing blocks in-turn mount to the outer shell. So now, I have a rotating roll capable of rolling and unrolling the main.

I now need to add a take-up drum for the take-up line. I believe I will also add a locking mechanism enabling you to lock the roll in any position. This means you can adjust the sail tension with the halyard alone.

I need to review mounting and sail-feed into the current mast. I will need to use a plain rope system running inside the mast. The trick is getting the sail to feed properly into the mast.

Let me know your thoughts. I want to be sure I have thought this through before I spend the money to build it.

ModsNote:
JJ, CDI makes a mainsail mast furler modeled after headsail flex-furlers (~ $2,000?).
One member here has either built one similar, or purchased that one from CDI.

You can find earlier discussions by searching on mainsail furling, and click the 'all terms' button (Search link at top-center of every page). Then you'll need to review for titles that seem related.

For your info, there are several other threads by MacDealer (Inmon Yachts) on creating a Roller Reefing Mainsail, on the boom (probably ~ $3,000 with sail changes). That discussion is temporarily postponed, pending development of a special Forum to support commercial product design and marketing.

I'm splitting your post into your own thread. If you are planning a commercial product, you really need to postpone your BB discussion. Please post next . . . ~fc

Good problem!
I'm not sure how the store-bought mainsail boom furlers work to get the sail attached to the mast. Sail slugs, either the internal type or the track mounted type seem to me to be out of the question, unless someone is stationed at the mast to feed each slug as the sail goes up.
Using just the bolt rope has possibilities along with a bolt rope self-feeder. I used one of these before I went to sail slugs and it worked 99% ok. Once and awhile, the bolt rope would hang up if entry to the feeder got to far out of whack. That should'nt be a problem here because the bolt rope will always come from roughly the same place on the roller.
Is there such a thing as a loose headed main?
The outer boom "shell" must be quite large to enclose the rolled up main?
Getting battens to line up with the outer shell slot?
Going up is easy, but how will you spin the inner axle to lower the sail?
Sail slugs and lazy jacks don't seem such a bad trade off.
Hmmm, best of luck and keep posting.

We rented a boat with an older in boom furing and the angle of the boom to the mast was critical to allow it to roll up properly when coming down.
We ended up tying the 1/2 down sail to the boom when it jammed while a squall was hitting us. I have to admit after that week of wondering if it was going to work or not every time we dropped the sail, I'm not sure I would spend the money on a home made.

What's wrong with one of these little babies:



They are designed for bolt ropes and work quite well.

As far as locking the sail in position, my old Tri used a system where the goosneck was a basic axle that extended through a sleeve through the mast. A crank handle was attached where the shaft poked through the from of the mast, and was held in place by a grub screw. The handle of the crank was able to slide through the crank itself so that when the desired position was achieved, it could be slid into another hole directly under (that is, including the length of the crank) the axle, thereby locking the boom.

Quite simple, flush and neat.