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RBArrowood
Deckhand

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17 Posts

Initially Posted - 11/16/2005 : 15:15:20

Question for any sail trim guru's out there. What causes the mainsail to backwind? What is the best way to correct this problem? I have a 135 roller furler and I notice this most when I am out in a stronger wind, pointing high and have the sail rolled to about 100%. Boat comes out of the water tomorrow and the season is over on Lake Carlyle until about the last of March. I'm just sitting here thinking of work to do over the winter and wondering about things like the above.

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 11/16/2005 : 22:40:55

My finger hurts.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 11/17/2005 : 00:35:31

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by RBArrowood
 ...What causes the mainsail to backwind? What is the best way to correct this problem? I have a 135 roller furler and I notice this most when I am out in a stronger wind, pointing high and have the sail rolled to about 100%...<hr height="1" noshade id="quote"></blockquote id="quote">

As Frank's illustration shows, the mainsail backwinds when the slot becomes too narrow. It can be caused by a number of issues like an over trimmed genoa, under trimmed main, too much draft in the main, not enough twist in the genoa, too much twist in the main, improper traveller position, not enough backstay, too much headsail for the conditions,...etc.

I've found the C25's transom mounted traveller contributes to backwinding due to its rather limited travel.

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RBArrowood
Deckhand

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17 Posts

Response Posted - 11/18/2005 : 16:33:05

Thanks Guys. I've been watching the forum for about six years and I've noticed over that period of time that someone always takes the time to check the forum and answer questions. You guys do a good job.

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Lightnup
Master Marine Consultant

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USA
1016 Posts

Response Posted - 11/18/2005 : 18:41:13

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I've been watching the forum for about six years<hr height="1" noshade id="quote"></blockquote id="quote">
Good grief! Six years and you've only posted 4 times, two of those being this week? Wow. I admire your self discipline.

Steve

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RBArrowood
Deckhand

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17 Posts

Response Posted - 11/18/2005 : 21:56:13

Steve...I've posted under several names. Each time I can't remember my password I get another name. I don't have many posting though.

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SJ
Navigator

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USA
198 Posts

Response Posted - 11/21/2005 : 12:57:45

Backwinding the main is actually fast....Believe it or not. There are times where you just willnot be able to make it look pretty. When the back winding is happening, I'd be willing to bet the wind is up and you are trying to point as hish as you can. You will notice that iyou adjust the jib out the main will settle in nice, but you will now be pointing lower than before resulting in more distance needed to be sailied to get to your destination. I sail on a big boat as well, and when we are going up hillthe main is fastest when its ugly...Just one of those eroneous anomolies I guess....

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atgep
Master Marine Consultant

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1009 Posts

Response Posted - 11/21/2005 : 19:58:13

I feel that the main is on a 25 because a "sloop has to have a main" . The jenny is the workhorse for us. If the Jib is trimmed, It may not be possible to get the main to look right. If you trim the main too much the weather helm takes over and drinks get spilled.

I always set the jib, leave the main a little loose and trim it in till It looks good, or the weather helm takes over.

A reefed main and a 135 is very good on this boat.

Tom.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 11/21/2005 : 21:38:42

While watching the America's Cup race a few years ago, I listened to the commentators discuss the luff bubble that was on the main sail on one of the boats. They said that a nominal amount of backwinding isn't necessarily a bad thing as long as everything else is trimmed properly.

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Steve Milby
Past Commodore

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USA
5909 Posts

Response Posted - 11/22/2005 : 09:54:54

On a masthead sloop, like the C25, the key is to trim the sails so that each is providing the proper proportion of the total driving force. The jib provides most of the drive, and the mainsail provides a little drive, but its main function is to help the boat point. It takes the right combination of the two sails to make the boat perform its best. A small luff bubble is fast, but if it's too big, it means the mainsail isn't generating enough of the forces that help the boat point as high as it could. If the luff bubble on the mainsail is too big it's probably because the jib is too big, or its shape is too full, or the jib is overtrimmed, or the mainsail is undertrimmed, or the shape of the mainsail is too full, or the mainsail needs to be reefed.

Backwinding can be caused by making the slot between the mainsail and jib too narrow, or it can be caused by gathering too large of a volume of air and trying to force it through a slot that is too narrow. If the slot is too narrow, then you can correct the problem by widening the slot. If the sails are gathering too large of a volume of air, then the remedy is to reduce the size of the jib. A smaller jib will gather a smaller volume of air and direct it through the slot. The key is to be flying the correct size of jib (relative to the windspeed) that gathers the maximum volume of air that can be efficiently forced through the slot, when the sails are trimmed correctly for the windspeed.

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mmac
Navigator

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USA
168 Posts

Response Posted - 11/25/2005 : 12:49:49

Robert,

For your winter reading you might like Sail Power by Wallace Ross.

http://www.amazon.com/gp/product/0394727150/104-0384083-5567954?v=glance& n=283155& n=507846& s=books& v=glance

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.