Backwinding !!!!

[RichH]

Over on the Sailnet forum is an ongoing discussion on how to correct or prevent 'backwinding'.

This is a somewhat 'advanced' discussion to a common problem in sail SHAPE/TRIM but If interested and especially if you want to 'contribute' go to: http://www.sailnet.com/forums/c-c/72141-c-c-34-mainsail-shape-problem.html


.... and a lot of Sailnetters are coming to this forum to learn/read how to "properly raise a woven daron mainsail" - a 'tease' to get more 'contributors' and activity to this most valued forum.

 

[Bob S]

Thanks Rich,

I have basically learned to sail and maintain my boat from reading this forum. Thank you for everything you and all the other knowledgeable folks have provided me!

Interesting piece on Tayana 37's in Sail Magazine. I'm sure you caught it.

 

[RichH]

"Interesting piece on Tayana 37's in Sail Magazine. I'm sure you caught it"

... no I didnt, thanks for the heads-up.

 

[Don Guillette]

RichH: I'm not sure this is the topic but I think it involves the "bubble" in the main. I always look to you for the scientific analysis of why things happen to the sails.

A couple of years ago I was racing with the Catalina 30 fleet out of Coronado YC in San Diego. I love head to head match racing. I'm not much for beer can racing. The boat I was on had a large bubble in the mainsail, which the mainsail/traveler trimmmer and the jib trimmer were grousing and arguing about. The mainsail guy wanted the jib trimmer to ease out and the jib trimmer wanted the mainsail trimmer to crank in. Since it wasn't my boat and I wanted to race with them the next day I just sat and listened until I couldn't take it any longer. This was further complicated by the fact we were in first place. I casually mentioned to the skipper that since they are a masthead rig and the engine of the boat is the jib and on these rigs you trim the jib first maybe, to settle the debate, the mainsail/traveler trimmer should crank up on the traveler until the bubble disappears since it coming from the backwind off the jib. Actually, the bubble, doesn't cause any trouble - it just doesn't look nice.

Since this suggestion came from a common seaman and country boy, how far off was I with my simple suggestion. Alan, and anyone else, you can chime in also.

 

[Joe]

The mainsail's power is in the back half of the sail... the bubble doesn't affect performance that much... and it is usually a result of the mast shadow rather than the headsail backwinding. If you could rotate the mast it would disappear.

 

[Don Guillette]

Joe: I think it comes from backwind off the jib because I can induce it and make it go away by easing out the jib or cranking the traveler or mainsheet.

 

[Winkfish]

I remember taking a sailing course about 20 years ago, sailing, I believe, a J22. One class, we raced against another J22, same rigging, etc. We did all we could think of on sail trimming, but we always got our butts kicked sailing upwind. At the end of a few races, the instructor let us in on the trick - by intentionally backwinding the main a little bit, he was able to outpoint us by a lot, maybe 10 degrees. We had to tack to make the mark, he didn't.

About a year later, I was crew on a boat with a very experienced skipper. He did the same thing when he was pointing high.

 

[cwkemp]

Assuming moderate to strong wind, I would expect to point just as well (albeit slower) if I relieved the bubble by bringing the traveler to windward. I have sometimes found it to be more efficient to sail with a slight bubble in the main rather than over trimming to "neaten up" the sail, but every day is a little different. Once the lakes thaw I'll gladly experiment some more and try anyone's suggestions and report back.

 

[Joe]

Backwinding is not BAD!

Joe: I think it comes from backwind off the jib because I can induce it and make it go away by easing out the jib or cranking the traveler or mainsheet.

Yes... you can induce or smooth out a bubble by doing that... but... why? Perhaps this excerpt from Tom Whidden's "Art and Science of Sails" regarding "backwinding" will be enlightening to some:

"...........A major theme of this book is that the jib and main have an interactive relationship, and a change in one affects the other. Good sail-trimmers can trim the main and jib; the gifted few can trim the two pieces together as the whole is greater than the sum of its parts. That, indeed, is how the wind "sees" a sail plan: as one long foil, not two separate ones.

The best way to ensure the relationship between these two sails is complementary is to focus on the slot, the area where the two sails come together. It is the width of the slot that is important, and this dimension is controlled by traveler position, mainsail depth, sideways mast bend, genoa-lead angle, genoa sheet tension, and mainsheet tension. Adjusting these controls fine-tunes the interaction between mainsail and headsail.

In medium and heavy air, it is most desirable if the forward section of the main flutters, or shows "backwind" evenly from boom to headboard. Further, this should occur at the same time as the windward telltales of the genoa lift. Let off the traveler to induce this fluttering in the mainsail, then readjust the mainsheet. If the top flutters before the bottom, the mainsail is twisted too much. So trim the mainsheet. If the bottom flutters first, east the mainsheet to induce more twist.

Another indication of the relationship between the two sails is the amount of backwind, or fluttering. Too much means that the slot is too narrow. the size of the slot can be increased by 1) easing the genoa sheet a little bit; 2) trimming the main; 3) flattening main; 4) changing to a headsail with a smaller LP; 5) moving the genoa lead outboard or back; and/or 6) making sure the mast doesn't sag to leeward in the middle.

 

[bria46]

In extremely light air I backwind the jib to help turn (tack) the bow. Once tacked, the jib is secured correctly.

 

[RichH]

I remember taking a sailing course about 20 years ago, sailing, I believe, a J22. One class, we raced against another J22, same rigging, etc. We did all we could think of on sail trimming, but we always got our butts kicked sailing upwind. At the end of a few races, the instructor let us in on the trick - by intentionally backwinding the main a little bit, he was able to outpoint us by a lot, maybe 10 degrees. We had to tack to make the mark, he didn't.

About a year later, I was crew on a boat with a very experienced skipper. He did the same thing when he was pointing high.

What he is creating is a 'happy bubble' ... a teeny bit of 'backwinding' that in no way affects sail interaction (Aerodynamic term: bootstrapping or 'velocity dumping'). This 'happy bubble' will usually only work if there is a 'slight overlap' (or more) of the jib in relation to the mainsail. It also allows the jib to be brought in closer to the boats centerline - doesnt get you more speed, just increases your ability to 'point higher' (at the same speed). The affect is better suited to mast head rigs rather than fractionals, but you can still do this on a fractional if you have some jib overlap.
With either rig configuration you bring the clew of the jib closer to the boats centerline (via barberhaulers, etc.) while watching the speedo, the speedo indicates 'how much' you pull in, and 'regardless' of how much 'luff bubble' is forming. That said, you HAVE to have perfect shaped/trimmed sails for the day's conditions ... and that journey begins with simple use and mastery of Tell-Tales (FULL set - luff, leech and mid-cord + 'steering tales' ..... and then 'working up' your expertise into the more extreme 'sets'.

If you get your 'happy bubble' precisely set, you will usually leave all other boats behind 'in the dust' and your 'turbulence wake'. To do all this you need 'perfect' set via your tell tales and then 'steer' the boat solely by watching the 'steering tell tales' (aka "gentry tufts").

This is not solely a 'racing tactic' .... I use a happy bubble when long distance cruising as it gets me there 'faster' and with much less tacking. Do this and your VMG will 'soar'.