The finer points of sail trim - Page 2 - SailNet Community
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post #11 of 31 Old 10-06-2007 Thread Starter
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Thanks y'all for helping me out.
We are sailing a C&C 29 MK1. She's our first keeled boat. She fits us just fine and is in great shape. Now we're learning how to sail her.
So let me add a few things. First until now we have been happy to go from point a to point b. It hasn't been much of an issue how fast we got there. That's why we bought a sailboat. But now we want to get better at it.
So what about the adjustable backstay? An observation here. When I am going upwind, the uppermost telltale on the main, (there are 4), never wants to get with the program. It always seems to be on the leeward side or at best wiggling around. What is this telling me. I usually sail upwind with the traveler centered, the vang loose, and the backstay adjuster where it was when I bought the boat.
Also, we have a furler on the head sail, should I be adjusting the halyard tension to get more or less lift on this? when to ease? when to trim?
Thanks again.
BP o' the Hannah Lee
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post #12 of 31 Old 10-06-2007
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Originally Posted by bruceyp View Post
Thanks y'all for helping me out.
We are sailing a C&C 29 MK1. She's our first keeled boat. She fits us just fine and is in great shape. Now we're learning how to sail her.
So let me add a few things. First until now we have been happy to go from point a to point b. It hasn't been much of an issue how fast we got there. That's why we bought a sailboat. But now we want to get better at it.
So what about the adjustable backstay? An observation here. When I am going upwind, the uppermost telltale on the main, (there are 4), never wants to get with the program. It always seems to be on the leeward side or at best wiggling around. What is this telling me. I usually sail upwind with the traveler centered, the vang loose, and the backstay adjuster where it was when I bought the boat.
Also, we have a furler on the head sail, should I be adjusting the halyard tension to get more or less lift on this? when to ease? when to trim?
Thanks again.
BP o' the Hannah Lee
The upper main telltale is telling you to put a little more "twist" in the main, meaning let the top part of the leech out a little while keeping the lower part in. So bring your traveler a little to weather, ease the sheet a little, and experiment til all telltales are happy.

On the jib halyard, more tension pulls the draft forward and flattens the sail a little, for heavier air. For lighter air and marginally better pointing, ease the halyard but not enough to make big wrinkles in the luff.

Backstay. I don't know if you're a fractional or masthead rig. If masthead, tighter backstay will tighten up the headstay, so less sag and better pointing. If fractional, it'll bend the mast, and flatten the sail for heavier air. Might also help your top-telltale problem. Looser backstay, and less or no bend for light air.

If you can find a class association or web site, you'll get more boat-specific advice. This is just general.
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post #13 of 31 Old 10-06-2007
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Experiment

go sailing on what ever point of wind you wish to discover. Adjust your sails to get the tell tails flying just right then try things , adjust the back stay see if you move faster or slower move the traveler & check speed again .....
The point is every boat has its own characteristics. mine likes the a little twist in the sails at higher wind speeds my neighbors boat actually goes faster when not all the tell tails are streaming like you would expect. Why?

When you are cruising is a good time to experiment (but not when the admiral is cooking)

Good luck & enjoy learning
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post #14 of 31 Old 10-06-2007
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The outhual should be loose.
The vang has two uses, First is up wind. Up when you tighten the vang it powers down the main, The higher the wind thighten the vang and dump the mainsheet Traveler down too leward. On downwind, Thightening the vang powers up the main.
The traveler:
In light wind you want twist in your main, Traveler up to windward and bring the boom towards center. As the wind picks up start to drop the traveler to remove the twist but keep the main as close to center. As the wind picks up even more apply the vang and start dumping the mainsheet(refer to above). After that you Reef, Furl and all that good stuff.

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Last edited by HGSail; 10-06-2007 at 12:59 PM.
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post #15 of 31 Old 10-09-2007
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Conningham? When to trim etc?
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post #16 of 31 Old 10-09-2007
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I almost never use the cunningham except in extremely heavy air. Otherwise I prefer to use the halyard.

Jeff
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post #17 of 31 Old 10-09-2007
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Originally Posted by HGSail View Post
As the wind picks up even more apply the vang and start dumping the mainsheet(refer to above).
Or, you can keep the mainsheet tight (same as tightening the vang but with more leverage) and lower the traveler to the lee side. This will keep the main flat and reduce it's power in a similar way. When the wind dies down or if it was a gust you can quickly hike the traveler and regain the power.
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post #18 of 31 Old 10-11-2007
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I just received Dedekam's Sail and Rig Tuning yesterday. Started reading it last night. Looks like everything that's been mentioned here is in there, with the advantage of there being lots of pictures and some basic explanations of "why." For example: I'd seen recommendations/suggestions on general/rough positioning of the jib sheets fairlead blocks car on its traveler. After reading Dedekam's treatment of the subject, now I understand why. I also know that the aforementioned guidelines are just that: Guidelines, and shouldn't be slavishly adhered-to, as, sometimes, better performance can be realized by "breaking the rules," so to say.

My initial impression is that, if you want to learn about sail and rig tuning, Dedekam's Sail and Rig Tuning will probably aid you greatly.

Jim
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post #19 of 31 Old 10-11-2007
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Funny name, I have a Honah-Lee...

Anyhow, I just got back from racing the most insane boat I've ever been on. It was a U20 "the U boat" or ultimate 20. I thought it was like a Porsche of racing quasi-dinghys.

I was on mainsheet and traveller control.

Using the traveller is new to me, as I normally don't go 25+ knots in a sailboat, and my big 30 footer doesn't react to it too much since a lot of my sailing is done in less than 15 knots of wind.

We were in constant 28 knots with gusts to 42 which knocked us almost 90 degrees each time the wind kicked up. The traveller we used was kept towards the wind for the entire race, unless we exceeded 45 degrees of heel, then we spilled it almost full leeward to stand the boat back (and reduced mainsheet). The jib stayed locked in most of the time, unless we went over. On downwind runs, we centered the traveller to kep the sails off of the shrouds, and put it to the opposite side we were going to jibe the boom to. *EDIT* oops, I meant to the SAME side of where the boom was going.

We placed third of about 30 boats, so that was sweet. I learned a lot about traveller use that day, because you could really feel what it did. It almost felt like we didn't loose speed when letting it spill wind off of the sail, but it helped us tolerate higher winds by reducing heel.

I am going to be using my traveller in the big boats now. Up until Saturday, I thought it was the same as just easing the mainsheet a little, however, it is IMPORTANT that it has big enough blocks to manage it in strong winds where it becomes important, because little wimpy blocks or rollers just don't cut it. It is also good (in my opinion) to have a loop system, where you aren't pulling one line to get it to move left and then another to pull the other direction.

Outhaul, vang were another form of adjustments and the cunningham we used too. On heavy winds you use these to flatten the sail and you actually get less heel with the same speed. These however, we just set and left for the race. The vang got a firm *tug* and we cleated it, where the cunningham and outhaul were pulled tight and then cleated under tension.

I'm pretty good at sailing in light winds, as far as loosening sails go, but strong winds puts your knowledge to the test in exact reverse of what you know about light air - almost like a whole new sailboat!

Robert

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Last edited by Lancer28; 10-11-2007 at 11:04 PM.
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post #20 of 31 Old 10-12-2007
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I wrote this summary of sail trim for another discussion but thought it might be useful here.

Amongst non- racing sailors, frequently there seems to be a misunderstanding of the term de-powering (reducing the power of the sails) resulting in the term being mistaken for shortening sail (reducing sail area by reefing or partially furling sails). De-powering a sail generally is easier and quicker than reefing, but still results in less weather helm and heeling while moving faster than a reefed sail would permit.

In a general sense, there are a lot of factors in powering up or down a sail but the two biggies are the depth of its camber and the angle of attack. The deeper the camber (curvature of the sail) the more drive the sail develops, but along with drive (which is the forward component of the force generated) with increased camber comes a higher side force as well. This side force causes heeling and leeway. In really light air, the airflow lacks sufficient energy to flow around a sail with too deep a camber so the sail may actually be slightly flattened. As the wind picks up, you can introduce deeper camber which is how you 'power up' a sail. Powering up involves and easing of halyards, outhauls, and backstays.

As the wind builds, so does drive but at some point hydrodynamic drag becomes the limit on speed, and at this point additional drive is not necessary. As this point is approached, heeling and weather helm become excessive. As the boat approaches this point, the sails need to be de-powered. To begin to de-power the sails, halyards, outhauls, and backstays are tightened. This pulls fabric out of the body of the sail, flattening the sail. The sail produces less forward drive, but it also produces less side force.

The second aspect of this discussion is angle of attack (the angle between the direction that the wind hits the sail and the sail itself). For any given wind and sail shape, at any point on the sail, there is an ideal angle of attack. If the angle of attack is too flat, the sail luffs, and if the angle of attack is slightly too steep, the sail generates less lift and more drag and greater side forces causing more heeling and leeway. In the extreme case of too steep an angle of attach, the airflow stalls and very little drive is generated, and side forces go up dramatically.

Because of gradient wind effect, (air moving slower near the water than higher in the air due to the friction between the water surface and the air above) in light air, the apparent wind angle felt by the sail will be 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 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 is allowed to lift a little, and that lifting eases the tension on the leech of the sail allowing more twist to develop.

As the wind builds, gradient effect generally becomes 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 over trimmed developing a lot more weather helm than would occur with proper sail bladed out sail trim.

The backstay tension (especially on a fractional rig) can be used to de-power 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 sail in a horizontal direction, flattening the jib and de-powering 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 de-powering the sail in the same manner that tightening the forestay flattens and de-powers 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, 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 and comfort.
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