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Problem with shape of roller furler sail

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jwilliams
Captain

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USA
357 Posts

Initially Posted - 08/24/2003 : 11:48:14

Hi all,

Need some technical advice.

I have a CDI furler with a 150 sail. From the time I bought it I felt that it may have a shape problem. Lets stick to when it is fully deployed, because I grant that sail shape goes to hell when you roller furl it.

This weekend buddy Paul and I took our two boats for an overnighter. I followed. When we were under sail, and autosteering, I could study the sail shape on Hey Jude and reference Sparky's sail shape ahead of me with a similiar size sail.

I was clear that when I have my fairleads set properly to cause the telltales to break at the same time, the sail has a cupped shape. Sparky's was much flatter.

When the wind came up, theory says you want to spill off the head by twisting the head, i.e. moving the fairleads back. Sparky did that, kept his drive and manageable heel. I could not get the head to twist on Hey Jude. I kept moving the fairleads back and back, 6 inches at a time, until I had it at the stern pulpit upright(what do you call he vertical part of the stern pulpit where it bolts to the deck?). Of course I had to route the jibsheet forward around the winch. Lucky I have both jib and spinnaker winches. Still, the fairlead was a foot aft of the rearmost winch.

At this extreme position, the head had a little twist, but not enough to take the pressure off the heeling. I tried pulling the foot so tight it was a straight line! The sail was still cupped. I eased out to cause the head to twist, but could not get enough to reduce the heel. Easing out more just caused all shape to collapse.

As the wind was still coming up (15-20) I furled the jib 50%, lost most of my drive but kept the balance and gave up any hope of keeping up with Sparky. Now I know that I could have reefed the main and kept the jib all the way out. But, Sparky had everything still flying and was gaining the whole time.

Paul was also coaching me from Sparky on the VHF, looking back his perspective was different than mine. We tried various combinations over an hour period, but could not get the shape he had, or even close.

Now, what can anyone tell me about your experience? Is it unresonable to assume that a roller furler sail, properly shaped at the loft, should be able to twist like a hank on, if you move the fairleads aft, given the problems of the fat luff extrusion interfering somewhat with the air flow? Or is this cup shape just what you have to live with? If so, I'm thinking of going back to hank on.

I wonder if the sail needs work. I have not talked to the original loft (Monterey), or a local shop that has done good repairs for me, but I plan to tomorrow. I may take the sail down to him to look at too.

Jim Willias
Hey Jude C25fk 2958
Half Moon Bay, CA

Edited by - on

PZell
Admiral

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USA
548 Posts

Response Posted - 08/24/2003 : 18:30:18

Jim,

I was using a 125 hank on. I figure my 150 is too much
for most afternoon winds. Maybe you just had too much
fabric out there. With the 150 I expect my leads would
be well back also. I've been procrastinating on trying
out the big one. Will give it a go in the fall when the
winds moderate. Before I got that 125 I was using the 100.

Paul C25FK Sparky
'PZ' W7JVY KFS/KTK/KLB/KOK/WNU/KPH/WCC/VAI/VAJ

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 08/24/2003 : 22:27:37

Jim: I didn't do the math, but it would appear to me that if I roll up half the foot of my genny, I have no more than 1/3 (maybe less) of the sail left. That tends to give me a flatter shape, but the big roll apparently spoils the airflow over the sail.

You can't expect to get the shape with a 150 that Paul got with his 125... I can't respond on car placement, 'cause I have a 130, but I'd say you weren't far off--except going board-tight isn't going to help induce twist. Also, your roller sail probably has a higher clew than Paul's hank-on, which means you have more downward pull, which reduces twist.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - on

frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 08/24/2003 : 22:27:43

It sounds like the 150 you have on your furler is just a 150 that had the hanks removed and then mounted on a furler. A furling sail is cut much flatter. The shape you described sound exactly like my 150 shape and in winds above 15 knots you just cannot move the lead back far enough to twist it. If it is a correctly cut furling sail you should not have much extra material when you roll it up. When you rolled in 50% of it you lose the power section of the sail and basically end up with a bed sheet,i.e, flat sail with no dihederal so no lift. I read an article recently were a guy went to Home Depot and got a 2" piece of pipe insulation, split it so he could slide it over the furler as high as he could reach. Then when he shorten the sail from a 135 down to a 110 he did not lose all his lift. Sounds like it might work. Anything is worth a try. I would definitly take it to a loft an have it checked for proper cut. By the way with my 150 up and telltales flying in 18 knots Penny rolls right on up to 35 degrees. The general will go overboard unless I ease her out and then reef the main before I tighten it down again.

Good luck

Frog and the General
79 C25 Wing #1166
Orange Park, FL

Edited by - on

n/a
deleted

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163 Posts

Response Posted - 08/25/2003 : 08:39:18

First, check that your leach and foot lines are slacked all the way out. If they were tightened to cup the sail on a run and never released, that may explain at least part of the problem.

Edited by - on

deastburn
Captain

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USA
334 Posts

Response Posted - 08/25/2003 : 09:52:19

A good post from "Frog and the General", full of useful information. I would just add that RF genoas are tricky to evaluate in the abstract, without knowing, for example, the cloth weight ("Wood Duck" has 6 1/2 oz. Dacron for example) and the type of anti-UV treatment (again, "Wood Duck" has sunbrella material). Mine is a 130 and is too full at the head (too much twist, even in light air). If your 150 is a light air sail, say 4oz Dacron, and has a lightweight material for UV protection, then I would be concerned by the symptoms you describe, and would agree with Frog that it may indicate a cut problem. If it is a heavier sail, then maybe it never got fully powered up when you were trying it with your friend. Generally speaking, the bigger the sail, the lighter the cloth, but many Gennys I have seen break that rule. A 7oz 150 when fully powered up would probably bring a C25 onto a plane! In anything less than 15 knots of wind, the sail is prob too heavy to fully power up, and over 15 knots of wind, a 130 is more than enough sail for a C25 (IMHO). A RF sail is always a compromise...

Dave on "Wood Duck" (2616)

Edited by - on

Steve Milby
Past Commodore

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USA
5932 Posts

Response Posted - 08/25/2003 : 12:11:32

Jim,

Don’t be too quick to blame it on the cut of the sail, and have your sail re-cut. Only consider that possibility after you have eliminated all other possibilities, because you could ruin a good sail. The probability is that the sail is okay.

The fact that Sparky was flying a 125% jib and you were flying a 150% genoa is one of the most likely causes for the difference in performance. That 125% jib is just about right for that range of wind speed. If Sparky had been flying a 150 and full mainsail, he probably wouldn’t have been significantly faster than you. Your boat was laboring and you needed to reduce your sail area.

Moving the jib fairleads aft is a technique that can be used to slightly depower the jib, and help keep the boat on her feet. It helps a little, but if the boat is seriously overpowered, moving the jib fairleads aft is no substitute for reducing sail area. It is very time consuming for a boat that is flying a hanked-on jib to lower a sail and to hank on and raise a smaller sail. Therefore, moving the fairleads aft enables a sailor with a hanked-on jib to stave off the need to make all that effort to change sails. But, moving the fairleads aft is not a very helpful technique for a roller furler.

Moving the jib fairleads aft is not very beneficial to a boat with a roller furling jib, because, if you want to depower your jib, it is easier and more efficient to roll it up a bit. If you leave the fairleads in the same position when you roll up the jib a little, you are not only reducing sail area, but you are also inducing a little twist in the sail. But, if you roll up a lot of sail area, you should move the fairleads progressively forward, so that the telltales continue to break evenly. The sail is more effectively depowered by rolling it up, and the sail shape is better able to point to weather if the fairleads are set so that they break evenly.

When I sail a boat with a roller furler, I roll up just enough of the jib to allow the boat to stop heeling excessively, and no more. That way, you are always flying as much sail area as the boat can efficiently carry. If the wind grows stronger, and the boat begins heeling excessively, then I roll up a little bit more. If I bear off downwind, then I usually roll out more sail area.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote> Is it unresonable to assume that a roller furler sail, properly shaped at the loft, should be able to twist like a hank on, if you move the fairleads aft<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

A roller furling sail will twist when you move the fairleads aft, just like a hanked-on jib, but the amount of twist induced in either type of sail is very slight, and it’s difficult to see. Moving the fairleads aft by about 10-12 inches is about as effective as moving them all the way back to the stern pulpit. After the fairleads have been moved back 10-12 inches, the angle doesn’t change very much more as you move them farther aft. [If the foot of your jib is high-cut, you can probably move the fairleads aft another 12 inches.] When you move your fairleads aft, the jibsheet should be tensioned so that the foot of the sail is fairly flat. When the tension on the foot increases, the tension on the leech of the sail will decrease slightly, but that effect will be spread over the entire leech, and it won’t be very noticeable. Don’t expect to see a pronounced twist. Unless you have a keenly trained eye ( which I confess I don’t) you have to take it on faith that the sail twists a little when you move the fairleads aft.

In the conditions that you described, I would suggest that you tuck a single reef in the mainsail, and then roll up just enough of the jib to keep the boat from heeling excessively. By reefing the mainsail, you would have reduced the amount of weather helm and heeling, and that would have enabled you to carry the largest possible jib area with a well-balanced sailplan, and the least amount of rudder drag.

If your bottom and keel were as smooth and clean as Sparky’s, you should have been able to keep pace with him. If you’re racing in a competitive fleet, roller furling is not as fast as hanked-on jibs, but in ordinary sailing in medium to strong winds, a roller furler should be virtually as fast.

Steve Milby "Captiva Wind" C-25 T/FK #2554

Edited by - Steve Milby on 08/25/2003 12:30:32

Edited by - on

PZell
Admiral

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USA
548 Posts

Response Posted - 08/25/2003 : 12:13:16

Jim's sail is cut so that it has a very high foot. I guess that's probably inevitable so that it will roll up. My 125 is a sweeper, so I'm getting every bit of wind I can. That's another reason I'm getting more drive.

Paul C25FK Sparky
'PZ' W7JVY KFS/KTK/KLB/KOK/WNU/KPH/WCC/VAI/VAJ

Edited by - on

PZell
Admiral

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USA
548 Posts

Response Posted - 08/25/2003 : 12:24:55

Jim,
Steve's reply is very good. Much of what he says has been what I have been thinking. It is very noticeable that much of the time your heel is too great. Basically, you need to discover the sail combos that balance. I try to keep Sparky around 15-20 deg. max heel and rarely go for very long over 20 deg except in puffs or the williwaw on the
last reach home and then I'm constantly playing the sheets.

Paul C25FK Sparky
'PZ' W7JVY KFS/KTK/KLB/KOK/WNU/KPH/WCC/VAI/VAJ

Edited by - on

osmepneo
Past Commodore

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USA
1420 Posts

Response Posted - 08/25/2003 : 13:47:22

One thing I tried to avoid was the sag of the forestay, often caused because it set to long before the luff was run up the forstay. I have my forestay set with the same tension that I had before installing the cdi-ff4 - makes it a bear to connect but I've not noticed any sag. What you describe sounds to my like sag from having your forestay to loose. If so, you might want to take up some of the slack.

Don Peet
c25, 1665, osmepneo, sr/wk
The Great Sacandaga Lake, NY

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Steve Milby
Past Commodore

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USA
5932 Posts

Response Posted - 08/26/2003 : 11:22:54

Jim - In re-reading your original post, I noticed that you said the shape of your genoa was not flat enough.

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote> I was clear that when I have my fairleads set properly to cause the telltales to break at the same time, the sail has a cupped shape. Sparky's was much flatter. <hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

The most common reason why a headsail has a shape that is too full is because the jib is not sheeted in close enough. When your 150 is fully unfurled and you are beating to windward, you should adjust the jibsheet until the leech of the 150 is about 6-8” from the tip of the spreader. If the jibsheet is adjusted that way, the shape of the sail will be much flatter. In strong winds, you will need the winch handle to sheet it in that tight, and you will need to put 4-5 wraps of the jibsheet on the winch. If you don’t adjust the jib properly, the boat will heel excessively and it won’t point. Many people are afraid that if they winch the jib in that tight, it will split. If it does split, then either you tried to fly way too much sail for the amount of wind, or the sailcloth or stitching was badly deteriorated. Any decent sail should be able to easily withstand that amount of tension, even in too much wind. I have an old 150% genoa that I have raced hard for 22 years, and that I still tension in that manner in strong winds. Sails are designed to withstand that much tension.

When the genoa is trimmed 6-8” from the spreader, and the wind gusts, the dacron sailcloth will stretch, and the distance between the leech and the spreader will increase. When the sailcloth stretches, the pocket of the sail will become deeper, the boat will heel more, and it will lose its ability to point. Therefore, when the gust hits, you should trim the sheet in even tighter, to keep the distance between the leech and the spreader at a distance of 6-8”. By doing that, you will reduce the tendency of the boat to heel more in the gusts. When the wind gust abates, you should ease the sheet, so that the distance between the leech and the spreader isn’t too close.

As Don pointed out, you also don’t want too much sag in the headstay, because that will also cause the shape of the sail to be too full.

Steve Milby "Captiva Wind" C-25 T/FK #2554

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