I have a system that can be done at sea, in high waves and heavy air. I configured it to use a lanyard and ring (I'll explain) and was successful in using it at sea. After more than one occasion of not being able to disengage the ring and douse the reefed sail, I modified the system. But first, the basics.
Why reef? Reefing accomplishes two main purposes. When your vessel has too much sail area you have too much drag. This drag can do a number of unbeneficial things such as slow you down or knock you around. Reducing sail area will reduce drag and therefore you should be able to go faster and have more control of your vessel.
Second, and probably foremost in our case, reefing lowers the sail and thereby reduces the amount of leverage that the sail has against the leverage of your body's weight. So reducing sail area by lowering the sail is the way to go since the primary reason we, as cat sailors need to reef is to keep from being capsized. Being slowed down or tossed around is not as bad as being capsized.
Mast bend is a result of the leech tension on the top of the mast. (The spreaders encourage the mast to bend in a certain direction.) When you lower your sail, you loose most of the power to bend the mast with the leech tension. If the head is lower than the shrouds, you will be pulling the wrong way on the mast. You do no want the reefed sail's head to be lower than the hound. When the mast bends, the portion above the hound comes back, the rest does not move aftward very much. Pulling back on a point below the hound can work against this movement.
When reefed, the head should not be lower than the hound. That way you may attain some mast bend when you sheet hard.
Since you will not have the same aftward leverage as when pulling from the mast top, do not expect as much mast bend and therefore as much flattening. When reefed, you have to live with a fuller draft.
To use a second hook on the mast does not seem like an option to me. I would expect it to stab through the sail when sailing under full hoist.
I made a lanyard of steel cable that would fit between the sail's head and the halyard end. The ring goes on top of the lanyard and bottom of the lanyard attaches to sail's head.
To reef, I would fully douse the sail, add in the lanyard cable, and re-hoist until hooked. This works wonderfully and allows you to once again bend the mast from the top, at least with the downhaul. If you have very high diamond wire tension with spreaders well raked, you can get some decent bend in the mast this way. However, the bending attained solely from leech tension is still limited.
This system has been used a few times on my boat. Twice at sea and twice from the beach. Bill Mattson and I used it to return from Santa Cruz Island, through 'Windy Lane" through winds in the 30-45 knot range. It saved us from being thrown violently over, several times, and allowed us to reduce the strain on a cripled rudder.
However, this system usually required me to tip the boat over to unhook it and I did not like that restriction. That would require me to capsize if I needed to completely douse at sea. So, I went the other route.
If you use the halyard to support the luff tension, you must have a non-stretchy halyard and a strong enough sheaf on top to handle the load. You also need a reliable way to cleat the halyard. First I'll tell you how I have dealt with it. How I intend to deal with it will follow. Then I'll tell you about managing the bottom of the sail. Finally I'll tell you about an even better system that I am not presently using.
I wanted to be able to reef without the fear of being able to douse, fully, later. I also wanted to be sure that the halyard would support the load. Also, the halyard would have to take some abrasion abuse where it would rub against the side of the hook plate.
I also wanted to be sure that the halyard block would support the load. And the bonus to this system is that I don't have to douse and re-hoist. I can do like the big boats and just "take in a reef."
To have a halyard that could manage the load and not do a lot of stretching, I use 1/8" Amsteel. To keep me from having to handle it, I splice on the 3/16" double braid that I usually was using. Many people use 1/4".
To strengthen my halyard sheaf, I dismantled the block and replaced the sheaf, which had nylon or delrin bearings in it, with a high load sheaf. The high load sheaf uses a fiber bushing bearing, not balls. And I believe the high load sheaf is made of aluminum rather than nylon. In my case, I think I just used a bronze sheaf from a wire block (block for wire rope).
Next, I had to make sure this block would not come off of the mast. My boat uses a cheek block for the halyard sheaf. It is mounted on a flat plate on the top of the mast. Instead of re-mounting it with 3/16" hollow rivets, I used #10 machine screws and nuts. Where the cheek block had a hollow rivet for the axle, I used another #10 bolt and continued it through the mast mounting area, making three total bolts to carry the load where two hollow rivets once did the job. I added a washer or two to take up the space between the raised portion of the cheek block and the mounting plate.
If your Prindle 18 is like the P16 that I have looked at, you have a pair of rather stout blocks up there that are on 1/4" axles. I'd feel quite confident with that set up but would probably use a stronger sheaf wheel material than the standard nylon.
To secure the halyard at the bottom, I tied a slip knot in it because I had not yet finished that part of the job. It worked find, but as you can imagine, was tough to get un-done. I think what I will do is to bolt on a small aluminum horn cleat to the luff groove. If all goes well, I will be able to exit the 3/16" halyard before it reaches the turning block at the base. Then I can cleat that on the horn cleat. If I can't seem to fish it out, I'll cleat it after it rounds the turning block.
At the tack of the sail I use a hook, fastened to my downhaul (cunningham) block. There is a new reinforcement patch with a new added cringle in it located at the right spot for attaching the cunningham when reefed. The leech of the sail has a reinforced patch on it with a cringle through which is passed a doubled section of 1" webbing. Each end of the webbing has a ring in it. One ring attaches to the outhaul car on the boom and the other ring just pulls on the cringle, tensioning the foot adn leech of the sail.
In line with the new cringles is a row of about three smaller chringles. These are used to take up the slack portion of the sail. Note: One must not bind this baggage to the boom for you would risk tearing your sail if the boom were to pull on these cringles.
You roll up the unused sail and pass a line through each cringle and and tie the line to iteslf. I use bungie cord. I have a piece that hangs in each hole, knoted on each side of the sial so as not to fall out. With the bungie, you simply, quickly tie a square knot and they are always easy to pull apart later.
Some here have spoke of a problem with a luff rope pulling from the track. I have not had this trouble. If I did I woudl ad a sail slug on the top of the luff. perhaps they have a compost tip or their luff rope is too small.
When I am reefed I try to take it easy on sheet tension. I know I can't flatten as much as I'd like to, so I just take it easy on the mainsheet and the downhaul too. I put up with more draft in the sail than is needed, but it saves my halyard, halyard sheaf, and I guess the luff rope as well.
Finally, you might want to take a look at a newly available system that uses a swage ball on wire rope. There is a swage ball on the halyard for each hoist position. (like the old Hobie 16 had) On top there is a cleat that releases the ball if you first lift it an inch. When you hoist, fully, you hear the first ball "click" and keep on going. As soon as you hear the second "click" you release and it holds. To take a reef, you hoist an inch or so and then the cleat passes the swage ball. After it has passed the second swage ball, you hoist 'till you hear a click and then you ease and it holds.
I remember seeing this system in a catalog, but can not presently find it. I think it was in the apsltd.com "hot new items" but does not seem to be there today.
Skip Elliot told me that he has been using it on the C-cats he has sailed on and that it works very well. Adapting this system to a sealed mast would likelly present some challenge.
GARY
Mystere 6.0, Pacific Ocean