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Old 11-14-2010
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Flattening Reefed Mainsail, or why no Cunningham?

It's my understanding that when one reefs the mainsail, generally, you would want the mainsail to be flat to depower the sail. On an unreefed, fully hoisted sail, most have a cringle at the mast for a cunningham to flatten the sail. But at/above the reef cringle at the luff end of sails, I have never seen a cringle for a cunningham. Since all sails have a fullness or belly (i.e. the sail is not a flat piece of cloth and is designed to somewhat be similar to the upper, curved surface of a wing), this fullness area is greater in the reef cringle areas than it is at the foot of the fully hoisted sail. Thus, it seems (and on my boat) hard to flatten the reefed sail. Why are there no cunningham cringles above the reefing cringles?

I use a single line reefing system. As originally set up by the dealer, when reefed, the bottom of the sail would pull away from the mast, aggravating the flatness issue. I installed two additional sail slides and connected them to the luff end reefing cringle with a large shackle. Now when reefed, the luff end stays snug to the mast, but the sail is still not flat. On the leech end of the sail, the bitter end reefing line is around the boom and through a small cringle at the foot of the sail, and tied off there. The reefing line then goes up vertically (perpendicular to the boom) to the leech end reef cringle, through a block and back down and aft to the end of the boom, inside the boom forward to the luff cringle. You can tighten the reef line as tight as you wish and the sail is not flat. As I explained above, the sail is snug to the mast. The leech end can go be pulled tight towards the end of the boom, but once the leech reefing cringle is at the boom level, the line is pulling against the boom and the end of the sail will not/cannot move aft to flatten the sail.

I know many will say you need a two line jiffy reef, but with the way that the reef line attaches to the boom at the outer cringle, I don't see whether it makes any difference whether it's a two line reef or a single line reef. My situation would be helped a good bit if I could tighten the boom vang and mainsheet to pull the outer end of the boom lower. However, everything is a compromise, and the bimini, which I must use to avoid sunburn, is at the right height, but too high to allow much lowering of the boom end to flatten the sail that way. Any thoughts? Thanks.

Last edited by NCC320; 11-14-2010 at 11:54 AM.
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Old 11-14-2010
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The cunningham/s main purpose is to adjust the draft position by varying the luff tension in the main. You need it because presumably the main is already at full hoist so the only way to further tension the luff is to pull down towards the tack. A reefed sail has no such restriction and luff tension can be set/created by the halyard. - so no need for cunninghams on each reef - not to mention the hassle of transferring the cunningham each time you reef/unreef.

Many older racing sails DO have a 'flattener' cringle 6" to a foot above the clew that is taken in to remove the shelf foot and thereby flatten the lower portion of the sail. With the advent of loose footed mains this feature is not so common.

To truly flatten a reefed sail you need a significant 'outhaul' component in the lead/pull of the reef clew lines, and you need to get as much on that as you can.. in many cases there's a small dedicated winch on the boom just for that purpose. Failing that try tightening and tying the clew in after the tack is on but before you re-tension the halyard. And remember to have your sheet fully released and free during all this.
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Old 11-14-2010
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I have a two line reefing system on my boat. The leech end of the reefing system is attached to the boom in a very similar way to yours. I have a padeye on one side of the boom about 6" aft of where the cringle is when reefed. The line then passes up through the cringle and back down to a block opposite the padeye. The key difference is the leech reefing line is pulled down down and aft.
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Old 11-14-2010
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Quote:
Originally Posted by NCC320 View Post
....
I use a single line reefing system. As originally set up by the dealer, when reefed, the bottom of the sail would pull away from the mast, aggravating the flatness issue. I installed two additional sail slides and connected them to the luff end reefing cringle with a large shackle. Now when reefed, the luff end stays snug to the mast, but the sail is still not flat. ...
Before starting to tight the reef, pull the boom up (with the line that does that).With experience you will find out how much. Tight the reef, let go the boom and pull it down. Now your sail should be tight.

Regards

Paulo
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Reading between the lines I think I see a couple of issues.

Are you saying that when reefed, you can't bring your mainsheet tight because the boom hits the bimini? If that's the case you need to move the reef cringle at the leech up higher.

Second, I don't see why the reef line passes through a cringle on it's way from the boom up to the leech reef point and back down to the end of the boom. I'd skip that cringle, just tie a bowline (or knot of your choice) around the boom, up and through the leech reef cringle, back to the end of the boom.
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Old 11-14-2010
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I've considered adding Cunningham cringles above my reef points for another reason: a powerful Cunningham is a fast, easy way to achieve proper luff tension. My boat is too small to have halyard winches and I have never felt the need to add one. The Cunningham tackle is a 4:1 purchase cascaded to 8:1, giving me the power needed to get the luff really tight when necessary (unreefed.) When the sail is reefed, however, all I have is the 2:1 purchase of the reef line and my muscle power on the halyard.
I have never seen a sail with Cunningham cringles above the reefs, and this may be overkill since my sail does set nice and flat when reefed but it would give me another option and another string to pull!
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Old 11-14-2010
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I[ve thought about it too, as where the sail come down to, is higher than where one wants a luff reef cringle to be. So when the new sail was made, we raised that cringle a bit. At times, I wish I had a cringle a bit higher......

I also use a double line, one for the rear of the sail, and I use the cunningham hook line for the luff part of the reef, works well, altho one does need to go forward, which may be a PITA depending upon the conditions etc.

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Old 11-14-2010
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Reef (luff) cringles and cunningham cringles are NOT directly attached to a mainsails boltrope, they are attached to the sail and the 'sleeve' that fits over the boltrope. This allows the sleeve to slide up and down over the boltrope. So, reef luff cringles and cunningham cringles are essentially the same.

The luff cringles (cunningham and reef) DO NOT help to 'flatten' a sail !!!!! Their purpose when tensioned and adds tension to the FABRIC along the direction of the luff ...which results in the position of maximum draft in the sail moving forward.

To flatten a sail one needs to apply outhaul (or reef leech cringle) tension.

With a 2 rope slab/jiffy reefing system one can mix/match the tensions to attain the desired shape ( flat or 'powered-up'). With a single line reef system - you have no choice of flat or powered up and the 'setting angles' of the single-line system will limit what is the final sail shape when reefed.

Reefing doesnt always equate to FLAT sails ... as reefing chiefly is to reduce the heeling moment. Sometimes you need a powered-up of full drafted shape to punch through waves, even though reefed.

;-)
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Old 11-15-2010
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Thanks for your comments. I was confusing draft position with flattening the sail. The problem is at the outhaul end. If I were to fold away the bimini, I could pull the boom outer end lower with the mainsheet and boom vang and get a better sail shape. The foot of the sail has a bolt rope that slides into the boom, so there is no way to tie the reef line around the boom without going through the sail. When the sail is fully up, that small cringle, through which the line passes at the boom/sail foot, is vertically below the leech reef cringle, and the line is tied around the boom snuggly with a bowline, so one can tighten the reef line as much as you want and it's not going to tighten the sail in the outhaul direction since the bitter end of the reef line (whether one line or two) is not going to move aft from it's position around the boom (maybe a inch, but not more). To get outhaul control, I could possibably add a small piece of track to one side of the boom at the leech end and use the position of a slide (to which the reef line would then be tied) to change the degree of flatness via outhaul tension due to the then controllable position of the leech reef cringle when it is down to the boom. But, the more I think about it, in light of your comments, I think I need to modify the sail by raising the leech end cringle on the sail. As it is, I don't come close to being able to pull the leach flat (i.e. it sags off a good bit). But if the leech reef cringle was raised a bit higher on the sail, I could use the mainsheet and boom vang to straighten that leech edge of the sail without striking the bimini.
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NCC - it does sound like you'd benefit from moving the clew cringle up 6 inches or so - or simply have one added. This interference with a bimini is not uncommon, and protection from the bimini is becoming more important for many.

I would look at modifying your reef line attachment to avoid using that foot cringle and creating a more effective outhaul effort from your single line system.
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