Proper use of a traveler

[dryclean]

What is the proper use of the traveler?
I know it is used for sail shape, but for just cruising on a starboard tack should it be more to the port side of center or starboard. How exactly (tough choice of words) should it be set depending on a particular point of sail. I believe on a close haul it should be at center.

Appreciate any opinions on setting the traveler.

[legarots]

For upwind, move to windward in light winds, and leeward in strong winds to increase sail twist and spill wind. Otherwise, using the main sheet, adjust the sail so the top batten is parallel with the boom, and use the traveler to position the boom over the boat's centerline.

For downwind, let the traveler out on the same side as the sail.

[farmboy]

There has been some major discussion on this before. If you spend some time searching and reading, you should find some good advice. Here's one post that has helped me out a lot: http://www.sailnet.com/forums/369306-post.html. I was amazed when I started easing the main and bringing the traveler up while pointing up in light wind how much boat speed I could gain. I used to sail with the main sheet way over-trimmed. Play around with the traveler/main sheet interaction and see what works. Best of luck.

[Jeff_H]

I apologize that this is a bit long and wanders off topic since it was written for another purpose:

To some extent this is a question about adjusting sail trim to changing conditions, some times referred to as shifting gears. I will touch on some basics of sail trim. Most sails, but especially coastal cruising sails are optimized for a narrow range of conditions. Without changing halyard tension, sheet tension, or sheet lead, a sail is only at its best in a wind range that is often well less than 5 knots in width (i.e. 7 to 12 knots, or 5 to 10 knots). By making adjustments to the 'flying' shape of the sail you can easily extend this range by 5 or more knots either side of this ideal setting. These changes can include 'powering up' or 'depowering'.

In sail trimming terminology these terms have very specific meanings. They do not mean reducing sail area.

In sail trimming terms, power is the force (lift) generated by the wind passing over the sail. This force is thought of as having two components. One component is seen as being perpendicular to the length of the boat. This component causes heeling and leeway. The second component of this force is drive, a force considered to be parallel with the direction that the boat is going.

If you make a sail fuller (meaning more rounded and in sail trimming terms 'powered up') you generally increase the force generated by the sail. This means an increase in drive but it also means an increase in that side component that causes heeling and leeway. Conversely, if you flatten a sail, you produce less force, both drive and side load.

Beyond power, there is second and very important aspect of sail trim, which is incident angle. The angle of the sail to the wind is referred to as the 'incident angle' or ‘angle of attack’. To give an example how angle of attack works, if you think of what it is like to drive down the road with your arm out the window, if you hold your hand flat, you feel a small force pushing your hand back away from the wind. That force to the rear is drag. If you turned your hand so the front of your hand pointed slightly upward, you felt a little increase in pressure rearward(drag) and your hand would be pulled upward (lift). As you increased the angle of your hand, lift would increase but so would drag. At some point of rotation, as you hand approaches vertical, the amount of lift begins to decrease and the amount of drag increases dramatically.

I want to clarify two more terms for our discussion, luffing and stalling. Anyone who sails understands luffing but those who are not into sail trim terms will often use stalling and luffing interchangeably. They are two very different terms but both refer to a particular type of incident angle. Luffing is an incident angle that is too flat to the wind to generate lift (like your hand in the flat position).

Stalling is a bit more complicated to explain but it is that condition where the incident angle to the wind is too steep. To generate lift efficiently, the air needs to be able to flow aft on both sides of the sail, ideally all the way aft to the leech of the sail. When the angle of attack gets too steep the air can’t make the necessary sharp turn aft. The leeward side of the sail is a low-pressure zone and the air that fails to make the turn is sucked backward into this low pressure, tumbling turbulently as it does. The failure to maintain flow is stalling. In the example of having your hand out the window of a car, it is analogous to having your hand at too steep and angle to the wind, which is increases drag and decreases lift.

So, back to the questions at hand. As the wind increases in speed, the sails will automatically generate more lift in the direction of both components drive and side force. This happens due to a number reasons.

First and most basic is that the amount of lift generated is roughly proportional to wind speed. So as wind speeds increase the amount of lift increases. There comes a point with displacement boats where almost no matter how much additional drive you add, the boat will not make greater speed. At this point the lift force of the sail can only go into heeling and leeway.

But besides the simple effect of increased wind speed, the increased force on the sail will cause them to power up on their own. This occurs in a number of ways. Because sail cloth can stretch, as the sail stretches more length of fabric is added and so adding more curvature is created and with that more lift is added. But control lines, (halyards, sheets, and outhauls) stretch as well further allowing more curvature in the sail and further powering up the sail. Stays and shrouds stretch as well and they further add to the fullness of the sail. So as you enter a gust, you sails are automatically powering up (becoming fuller) just when you want flatter sails to reduce heel, you have fuller sails increasing heel.

Another aspect of angle of attack is the difference in apparent wind direction felt by the sail between the head and the foot of the sail. If you were to precisely measure the windspeed at various heights above the water, you would find that due to friction between the water and air, right at the water surface there is little or no windspeed relative to the water. As you took measurements at higher levels you would find that the windspeed increases until it hit the ambient windspeed unaffected by friction. Because of gradient wind effect, in light air, the apparent wind angle felt by the sail will be very different at the head of the sail than at the foot. The apparent wind at the foot of the sail, will appear to be more forward than the air at the masthead. To allow the sail to have a proper angle of attack throughout the entire luff of the sail, twist is introduced into the sail so that the upper part of the sail has a different angle of attack than the bottom of the sail. Here is where the traveler, backstay, and the boom vang come into play.


By bringing the traveler to windward, the pull of the mainsheet becomes more horizontal than vertical. In doing so, the boom is held inward toward the centerline, but the boom itself is allowed to lift a little, and that lifting eases the tension on the leech of the sail allowing more twist to develop through the middle and upper portions of the sail.


As the wind builds, gradient effect generally becomes increasingly insignificant, so the whole leading edge of the sail wants the same angle of attack and in general, that angle of attack needs to be much flatter than it would be in moderate winds. To unify the angle of attack, the traveler is lowered to leeward and the mainsheet tightened, which increases the downward force on the leech of the sail. This increased leech tension removes the twist from the sail. As the wind builds the angle of attack can further be lessened by lowering traveler further to leeward. As you bear off on a reach, the traveler can be further lowered to maintain the proper angle of attack without powering up the sail, but at some point the sail needs to be eased broader off than the length of the traveler can permit while still generating the proper downward force, at that point the Vang takes over the main role in controlling twist and the sheet then simply controls the overall angle of attack of the sail.


Simply easing the mainsheet in a strong breeze does allow the head of the sail to twist off and reduce heel, but it comes at a price. In easing the sheet the boom rises and allows more fabric into the body of the sail increasing power just when you need to reduce power, and also in order to obtain enough drive, the lower portion of the sail is overtrimmed developing a lot more weather helm than would occur with properly bladed out (flattened) sail trim.


The backstay tension (especially on a fractional rig) can be used to depower the rig further. On any rig, even one with a stiff mast, tensioning the backstay removes sag from the forestay and is doing so, draws fabric out of the jib in a horizontal direction, flattening the jib and depowering it. As the forestay is tightened the mast moves aft and that also changes the relationship between the jibsheet lead and the head of the sail, allowing the leech of the jib to open slightly, reducing the angle of attack of the upper portion of the sail. On a boat with a bendy rig, and more dramatically and controllably on a fractionally rigged boat, as backstay tension increases the mast bows forward, in doing so it also draws fabric out of the sail depowering the sail in the same manner that tightening the forestay flattens and depowers the jib. Also similar to the jib, the masthead moves aft as the backstay is tightened and that opens the leech slightly at the head of the sail, easing the angle of attack and further reducing heeling, weather helm and leeway.


There is a tendency to dismiss this as 'racer stuff' but these kinds of subtle sail trim adjustments can make for a much more comfortable and controllable passage as well as adding significantly to the speed of the boat.


Lastly, I really disagree with the idea that "if your sails are basically trimmed correctly, and you are making the kind of fine adjustments that a skilled racer would use, those fine adjustments can't be measured by your knotmeter". Small adjustments to backstay or traveler positions can tremendously reduce weather helm and heel angles. On my prior 28 footer, these fine tuning items were good for a half-knot or more, and on bigger boats or in higher winds, these kinds of minor adjustments can yield enormous gains in speed.


Jeff

[dryclean]

Originally Posted by farmboy

There has been some major discussion on this before. If you spend some time searching and reading, you should find some good advice. Here's one post that has helped me out a lot: http://www.sailnet.com/forums/369306-post.html. I was amazed when I started easing the main and bringing the traveler up while pointing up in light wind how much boat speed I could gain. I used to sail with the main sheet way over-trimmed. Play around with the traveler/main sheet interaction and see what works. Best of luck.

Thanks for the link I've searched and found bits and unrelated pieces but this helps explain things

[denby]

And try here for other useful info.
http://www.sailnet.com/forums/sailne...on-videos.html

[captbillc]

thanks Jeff H ---- you put out a lot of information. on my nimble 30 express i have a fully battened main with profurl in boom furling . the vang is solid and cannot be adjusted. the PO installed this system. i got the boat in 2003 . is the traveler setting different with a solid vang?

[farmboy]

Originally Posted by dryclean

Thanks for the link I've searched and found bits and unrelated pieces but this helps explain things

No problem, dryclean. Glad I could help. There are some other good posts about this that I can't find right now, but if come across them, I'll post links to them in this thread.

Jeff, thanks for the fantastic post.

[Jeff_H]

The problems with a rigid vang that cannot be adjusted is that it removes the ability to adjust twist in the sail and it places an enormous load on the boom when beating. These are potentially serious problems.

Without being able to control twist, (ignoring light air) the leech of the sail will inherently twist off to leeward in a breeze as the leech of the sail stretches. This means that you either have your sail badly luffing if you try to drop the traveller to reduce the heeling force of the lower sail, or you have the sail over trimmed resulting in excessive heel. In either case you are really limiting your ability to go to windward in a strong breeze not to mention the negative impact on crew comfort.

With the permanent vang position the vang is always exerting force on the boom. Since vangs have inherrently less mechanical advantage, every time you ease the mainsail going upwind, there is a large load imparted into a concentrated area of the boom. This problem is especially acute beating in heavy air, where leech loads can exert a lot of force on the boom. On most boats that I have sailed on there is a removable pin or a slide and track that allows the vang to at least ease some. I would suggest that you investigate some way of allowing the vang to move through a small range of motion.

Jeff

[SEMIJim]

Originally Posted by dryclean

What is the proper use of the traveler?
I know it is used for sail shape,

More accurately: It's used for allowing you to adjust angle of attack without affecting sail shape.

Originally Posted by dryclean

but for just cruising on a starboard tack should it be more to the port side of center or starboard.

That all depends on conditions and what you're trying to achieve.

Originally Posted by dryclean

How exactly (tough choice of words) should it be set depending on a particular point of sail. I believe on a close haul it should be at center.

Ok, you're close-hauled. The wind is strong, the main's already sheeted-in and you're still on your ear: You can drop the traveler down a bit, thus dumping some air, and get her on her feet again. Conversely: Same tack, but light air, so you're seeking more drive: You want to add some depth and induce some twist: So you ease the mainsheet and use the traveler to bring the boom back up to (near) center. Third example: You're close-hauled and want to fall off to a close reach. If you're happy with the main's shape, just ease the main traveler leeward a bit and Bob's your uncle .

The examples are endless, because the combinations of points-of-sail and wind conditions are endless. It helps to understand how each mainsail control (mainsheet, traveler, outhaul, halyard, Cunningham, vang, backstay, checkstays, leech lines - even the topping lift) affects the sail's behaviour and interaction with the wind. To that end: Suggest you pick up a copy of Ivar Dedekam's Sail and Rig Tuning. It's a great book, with lots of examples and pictures that will help you gain a better understanding of your mainsail controls.

After that: There's no substitute for getting out there and experimenting .

Jim