Back winding

nicho · 16 Apr 2003

A novice type question (as usual from me!), but could someone please give me a brief explanation of the term "back winding" (but only as it applies to, and effects sails pls - it's a 'gift' to some of the humour on the forum!!!)

Thanks

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BrianJ · 16 Apr 2003

AndyL would probably be able to give you a better explanation as he is based in Hong Kong. It was something the old sampans on Hong Kong harbour did ,first started by an old chinaman called Far Ting
BrianJ

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MADFISH · 16 Apr 2003

Back winding

1. Distortion of the mainsail luff caused by the airflow between the main and jib.

2. What you do to your watch every Autumn.

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Sybarite · 16 Apr 2003

Might also be applied to stopping the boat upwind more quickly by pushing the boom against the wind.

John

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NigeCh · 16 Apr 2003

Re: Back winding - It\'s all about pointing ability

Assume that you've got your sails balanced (Bermuda rig) and are pointing. You luff up until the luff area on the mainsail JUST begins to loose its shape and begins to sag. This is known as back winding as the slot effect between the genoa and the main is starting to fail. So you bear away till the main luff retakes its proper shape.

So what you are doing when you are pointing and trying to pinch is to continually luff up till the main starts to backwind and then bear away slightly - Repeat ad infinitum .... and it all should be done with very small helm adjustments.

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nicho · 16 Apr 2003

I might have known it was too hard to resist....!!! (do you have a number for Mr Ting?)

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nicho · 16 Apr 2003

Re: Back winding - It\'s all about pointing ability

Thanks Nigel, I've got it now.

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Twister_Ken · 16 Apr 2003

Nigel - a different point of view

What you've described as back winding, I would call luffing the main - actually the genoa will luff at the same time doing it your way. It's caused by pointing further into the wind than the sail trim will allow for. And rather than pointing to windward on the luff of the main, I would suggest Nicho should be sailing on the luff of the genoa, which has a much finer entry and is not disturbed by airflow around the mast or off of the genoa.

To me, backwinding is caused by a trim imbalance between main and genoa, which closes the slot between the two sails, and directs windward air fron the genoa into the leeward side of the mainsail, causing a reverse aerofoil curve in the front 20-40% of the mainsail. Cured by opening the slot - either by hardening in the mainsheet, bringing the traveller up, or cracking the genny sheet.

Not always a bad thing - some backwinding of the main (by dumping the traveller, usually) is a good way of depowering quickly in gusts.

Nicho - congratulations, welcome to the arcane world of sail trim, and sailing vocabulary!

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Spacewaist · 16 Apr 2003

I vote for Ken nm

.

<hr width=100% size=1>A pontification from the Panjandrum of orotund bloviation AD2002

NigeCh · 16 Apr 2003

Totally agree

But how can you say it in a few words? I was looking at the main only. Of course the genoa can also backwind .... But the reality is that you can't describe in a few words the whole thing about sail setup, trim, balance, slot effect, heel, weather helm etc ... because they all interact.

All I was trying to do was to describe a practical demonstration in words of what back-winding is on the main. The last thing I wanted to do was to write a daitribe on the aerodynamics of foil surfaces, interacting foil surfaces and why back-winding occurs. IMO, it's far simpler to look at what's happening and know how to correct the situation than it is to delve into theory and obfuscate everything ... It's sailing with sails that's important and knowing how to trim the sails for nice balance, speed, comfort and an easy helm that's more important .... And it comes about, not by books nor words here, but by firsthand experience of sailing to all points of the wind and under all conditions .... and I'm still learning.

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oldsaltoz · 16 Apr 2003

G'day nicho,

You might find this link handy, it most sailing terms.

<A target="_blank" HREF=http://www2.friend.ly.net/~dadadata/kemp/>http://www2.friend.ly.net/~dadadata/kemp/</A>

Andavagoodweekend. Old Salt Oz /forums/images/icons/cool.gif

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vyv_cox · 16 Apr 2003

Re: Back winding - It\'s all about pointing ability

Agree the definition but not the recommendation. With a big overlapping genoa close hauled and sheeted at less than about 10 degrees there will always be backwinding of the main. In fact this has an almost negligible effect on speed, as the luff area of the main is almost in stalled air. Upwind drive from the mainsail comes largely from the leech and aft part of the sail, so some backwinding is unimportant.

In the circumstances I describe, bearing away until the main fills would stall the genoa and the leeward telltale would lift to prove it. Speed reduction would be far greater than provided by a little mainsail backwinding.

Best thing in lighter winds is to travel the mainsheet upwind of the centre line to get the boom on the boat axis, progressively travelling down as wind speed increases. Sheet tension to get the top batten telltale stalling about half of the time, all others flying. Ignore backwinding.

Alternatively, buy a fully battened main and you won't see it anyway.

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jimi · 16 Apr 2003

All these guys are just talking about backwinding in relation to the main, but I've always thought of it as being more relevant to the genoa.

have a look at or <A target="_blank" HREF=http://www.sperrytopsider.com/sails.asp>this

<hr width=100% size=1>Edited by jimi on 16/04/2003 13:42 (server time).

vyv_cox · 16 Apr 2003

I've read the article on genoas and as far as I can see the only reference to backwinding is talking about the mainsail.

Here's a paragraph copied from the mainsail section of the same website:
Hoist the sails in a medium breeze. With the genoa in its correct beating trim with all windtufts working together, sheet the main in. A small amount of backwinding is normal, but if the whole luff area is really backing, then remove a chock to allow the mast to bend more until backwinding is reduced to an acceptable level.

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Aja · 16 Apr 2003

This months' YM has a very good article on mainsail trim with an excellent picture and sketch showing the relationship between genoa and mainsail set and how this is affected by using kicker, traveller and sheet to control amount of backwinding of mainsail from the genoa and how this is sometimes a good thing (depowering the main).

Donald

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jimi · 16 Apr 2003

Re: Back winding OF THE GENOA

Watching for back winding of the telltales on the genoa is an elementary part of sail trim.

"It is the job of the helmsman to constantly watch the bottom windtuft to keep the boat pointing properly and it is the job of the crew to watch the top windtuft, using the motto “if it collapses sheet in, and if it hasn’t collapsed, ease it out.” He must therefore be prepared to keep the sail constantly on the move. This enables the helm to get the lower windtuft working and keep the boat in the groove, knowing that the leech is on the move to keep the angle of attack, and
the leech opening and closing appropriately in relation to how much wind is going over the sail.

If anything, it is better to have the sail undersheeted, so that one has a nice easy backwinding to spot, rather than to have it too tight and stalled, which is much harder to see. This is important not only in light winds when there is no movement of the jib sideways which makes it very easy to have a choked slot (see diagram 2), but also makes heavy air sailing easier as the boat will not be flattened by the gust before the helm has a chance to feather the main. "

<hr width=100% size=1>Edited by jimi on 16/04/2003 13:51 (server time).

qsiv · 16 Apr 2003

I'd agree with you and Ken - there seems huge confusion between lifting/luffing (which can happen to any sail on almost any point of sail) and backwinding which is caused by the headsail (inculding spinnaker) being oversheeted relative to the main.

As Ken says, it is by no means always a bad state of affairs, whilst lifting almost always is.

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NigeCh · 16 Apr 2003

Tell tails

Top tell tail on the main and bottom tell tails on the genoa - and all 3 flying true - The rest follow once you've made the correct adjustments to everything that affects both sails trim.

I was talking not light airs but a general case say 15 to 25 knots apparent with say a 115% genoa. Perhaps I should have made it clearer ... But I didn't.

Already here there are many discursions into fine points. Nicho's original question was "What is back winding." I think that I answered the question in a general manner.

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MADFISH · 16 Apr 2003

Re: Tell tails

I think I have just lost the will to live..................

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vyv_cox · 16 Apr 2003

Re: Tell tails

Nigel,

No problem with that. But where would the forum be if we just answered the questions? :~)

Vyv

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Back winding

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