Please explain to me what a traveler for a main sail does

[HighTemp]

We are fairly new to sailing and have been regularly going out on a Jeanneau SO 409, that has a traveler for the main. I need help understanding exactly what it does, that the main sheet doesn't or can't.

As I see it, there is plenty of adjustment via the main sheet to ease the boom sufficiently enough get the sail well into the spreaders. So what does the additional adjustment offered by the traveler do with respect to the boom's position relative to the centerline of the boat that can't be done with the main sheet?

Since the sail head and the tack are fixed to the mast, both the traveler and the main sheet appear to do the same thing, allowing the boom to adjusted away from the centerline of the boat, albeit one is corse adjustment and one is a fine adjustment. I was told that it had to do with sail twist, but I am having a hard time understanding this concept.

My apologies if my inquiry is not worded clearly.

[fstbttms]

Sailing - How to Use a Mainsheet Traveler

[four winds]

From the link above.....

A primary use of the traveler is to keep the boom centered when sailing close-hauled. Because the mainsheet tackle covers a span between the boom and the boat attachment, the boom will move to leeward no matter how tight the mainsheet is sheeted in. Moving the traveler car slightly upwind when sailing close-hauled can bring the boom back over the centerline to gain the most power from the mainsail.

[Stumble]

The mainsheet's primary controls the leech tension of the main.
The traveler controls the angle of attack of the main to the wind.
The boomvang controls the leech tension once you have run out of available traveler track.

[OldFrog75]

Over simplification but once you have "set" the shape of the sail for the wind conditions by adjusting the halyard, outhaul, and main sheet, you then adjust the traveler for the various points of sail - up for close hauled; down for a beam reach.

Without the traveler, if you ease or tighten the main sheet when you change the point of sail you are changing the shape of the sail which affects the performance.

[thomm225]

In a heavy air upwind situation, you can ease the traveler out a bit to keep the boat from heeling so much and still have a flat mainsail since the main is still sheeted in tight. (wings on a fast bird are flatter less rounded than on a slower bird). If racing, you may still have to play the mainsheet during wind gusts for max performance

If you just ease the mainsheet with the traveler centered, you would get a more rounded mainsail which you do not want in that situation. (draft moves aft)

Downwind, easing the traveler again gives you better control of the shape you want the main to have

[barnakiel]

Travelers are not required in leisure sailing but they still may add plenty of comfort, eg. allowing for sail trimming from the position of the helm (in two helm boats and in very beamy boats - if the sheet exits at the traveler). Also, you can move the sheet to one side of the boat and keep the center clean for traffic, etc.

In normal sailing, the traveler improves & simplifies sail trim. You can dump the boom to the lee in a fraction of a second with a traveler, not so with the sheet, so it is essential for fast and responsive boats in gusty conditions. In a very beamy boat you can also do without a kicker - provided the top is square to allow for opening of the top portion of the main.

BTW To keep the main off the spreaders you normally trim the kicker, not the traveler. Then again, running and on the broad reach the main will be on the spreaders to some extent (and depending on which style of spreader angle you opted for).

b.

[skipmac]

More in regard to downwind. Yes you can ease the mainsheet until the sail reaches the spreaders without adjusting the traveler, but if the traveler is centered when you ease the sheet the mainsail will belly out and rub on the spreaders sooner than necessary.

If you ease the traveler IE move it to the end of the track on the side where the boom is then the sheet pulls down on the boom so holds the sail flatter. This allows you to let the sheet out more before the sail rubs on the spreaders and the flatter sail "catches more wind" so you will go faster and also most boats will tend to roll less.

[HighTemp]

Thank you all for the insight. I am a visual learner, and this is starting to make a bit more sense to me now. I'll experiment with the traveler this weekend to put some of this into practice. Thanks again!