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Mainsail Leech Upwind


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Hi all - question of main trim...  I'm referring to generally light(er) winds, say 8-12 kts.

I have an X-34... fractional rig with 106% blade, BIG mainsail.

I typically go upwind with noted twist in the leach of my main.  I've pulled it to align with centerline (often top telltale curls to leward) but found that the speed decrease outweighs the pointing benefit.  It feels like the boat want to be sailed like a dinghy and 'comes to life' letting the leech breath some.

Recently I've raced on a 41' boat with a similar rig (fractional with blade) and they are convinced to pull the main in with tight leech upwind.  It feels like a brake to me (and we in fact don't do too well) but the highly experienced crew are set on the main trim.

What's the collective thoughts here?  Sorry, no pics...

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Renegade,

Find a pic of the Farr 40 world champions from Italy, upwind in 8 TWS:

1. Boom well above cl.

2. Lower quarter height leech on the cl

3. About 20 degrees main twist

4. Main chord depths around 11%

For 12 TWS, depths reduced and boom near cl, little or no perceptible twist reduction.

Less twist raises the ce and increases the tip vortex...

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There's no single answer. If you are coming off a crowded startline and need to hold your lane, leech hard for pointing mode. Same in flat water. Twist in waves or when you need to build speed e.g. after a tack or a bad wave.

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20 minutes ago, dogwatch said:

There's no single answer. If you are coming off a crowded startline and need to hold your lane, leech hard for pointing mode. Same in flat water. Twist in waves or when you need to build speed e.g. after a tack or a bad wave.

^ this^

Driving up, immediately after a start... approaching another boat on starboard... pinching to get around the windward mark... there are a few circumstances in which a temporary tactical consideration outweighs max VMG.

Otherwise, you want max VMG for that wind speed/wave condition. Same wind, more waves = more twist. But in general it's easy to overdo twist and lose a bit of pointing.

FB- Doug

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I have seen many boats having their leeches too tight which then drop the traveller to reduce heeling. Inefficient. I think some of this due to sailors moving up from dinghy classes where you can use vang and boom to induce mast bend and flatten the sail. This usually does not work on yachts.

Generally stalling the sail is not fast as it creates less drive force and more heel. You might have to play with the upper part of the sail. With a fractional rig this area will not benefit from the inflow from the jib and thus stalls more easily. In certain conditions it thus might make sense to stall it, but only the upper part.

Mainsail trim also depends a lot on the characteristics of your boat and conditions. For example in a high performance boat with slender appendages if in doubt I would rather trim for speed and add twist to get the appendages to work. Same in waves where you need more power and have more risk of dynamic stall due to boat motions.

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I always thought I should take twist out till the upper leech telltales start to stall or you have too much heel. Benchmark is upper batten parallel with the boom .

 

Am i giving up speed by doing this? If so, how do you decide how much twist you should add? 

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3 minutes ago, danstanford said:

I always thought I should take twist out till the upper leech telltales start to stall or you have too much heel. Benchmark is upper batten parallel with the boom .

 

Am i giving up speed by doing this? If so, how do you decide how much twist you should add? 

My boat has a rig similar to the X, and I have to carry a lot of twist  in the main with the 110.  The upper batten is definitely to leeward of the boom to keep the upper batten (full batten main) tale at least partially flying as it is not in air directed by the jib.  In light air, to get that much twist, I sometimes have to have the traveler up to windward and the mainsheet eased.  I do have a pretty heavy boom section though, it is the same section as used for the mast.  As Neuronz wrote, stalling the upper main seems to slow the boat down and add helm.    I need to carry even more twist with the 155.  I like fractional rigs as I sail solo mostly and the jibs are smaller for the boat size (33.5'), but it seems more fiddly to get the main correct compared to the mast head boats I have had in the past.

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Look at the telltales on the leech of the main.  Are they flying?  No?  Ease trav or sheet.  Yes?  See if you can pull it in some more (then watch the speedo)

Look at your friends.  Are the falling over because the boat is flipping over?  Yes?  Trav down

Look at the helmsman. Are his or her arms getting more ripped by the second from pulling on the tiller so hard?  Yes?  Trav down

Pull the main in as hard as you can get away with, watching those 3 things and mostly the speedo.  Main trimmer is the throttle man.  Also depends on tactical situation (fighting to hold lane?  Footing toward the shift?  Overstood?)

YMMV

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11 hours ago, Renegade-27 said:

we in fact don't do too well) but maybe because the "highly experienced" crew are set on the main trim

Maybe convince them to try something different and see if it makes a difference?

I think conventional wisdom for moderate air is boom right around centerline and get the top telltale stalling about 70% of the time.

If you start getting too much heel or helm, some boats like traveler down and others like easing sheet and letting the top twist off a bit.

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Batten parallel to the boom is from the old IOR ribbon main day where you had to press the boat uphill to overcome the genoa.  

Fractional rig the traveler sets the angle of attack and the mainsheet the twist/depowering. 

Main trim also has to do with the efficiency of your keel.  These guys like to point, but they need speed to do so with their narrow keels.  So traveler down can help with speed build.   1131491787_ScreenShot2021-08-19at9_02_15AM.thumb.png.14738a886f3f7f378946d201515e9095.png

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I like trimming main especially when it's for a driver with whom I have a lot of confidence/experience. Having done this for several decades, I have a pretty good idea what the main should look like for given wind speeds and sea states. IN GENERAL. Modify that theoretical ideal shape for a particular boat's characteristics.

After I have a good-looking sail (should take under a minute) I turn my attention to the helm/helmsman. You can tell when a helmsman is in the zone and a lot of that has to do with the feel of his/her helm. If the helmsman has to dial in too much weather helm -- drop the traveler an inch. Wait 2 seconds and see if that's enough or if it needs another inch. Small increments. By concentrating on the helm, I can help the driver "walk" that boat upwind. I will glance up at the sail every minute or so to make sure I haven't lost touch with the basic shape but that very rarely happens; by starting with good base trim and then staying in touch with the driver's inputs, you tend to stay pretty close to where you need to be.

I have been known to use my super-powers for evil (use my experience with main trim to subtly dictate tactics.) Without saying a word, you can "suggest" that maybe the driver should be going for more point... or driving for some more speed. When you have a lot of confidence/experience with a driver, you get to know what they would like to do in a given situation. The brief conversations should take place on a fairly high level, not at the nuts and bolts level. This is extremely satisfying and fun.

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You have to know how your boat performs best.  Some get best vmg sailed high with a tight leech, (many) others will respond better to footing and sometimes a surprising amount of twist.  

But you also need to know/read your helmsman,  a bit more twist (in conjunction with matching heady trim), will usually make an average helmsman more comfortable and be quicker simply through being less demanding to steer to.  Often you will have different baselines for different helms on the same boat.

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9 minutes ago, Livia said:

That was not the question, and obviously maths is not a strong point.

OK, putting 500# on the rail will increase the the righting moment be approximately 2,500#, which will allow the traveler to be raised approximately 2.5" and the mainsheet to be eased approximately 1" and improve boat speed by .15 knots and pointing by 1.2°.

What would really help would be to have a picture from dead astern, but while they are waiting for the photoboat to maneuver around, they might block the mast forward at the partners to induce some lower bend and then try putting on some topmast to take about 30% of the draft out of that main, and open up that airbrake of a lower leach.  Then try traveler up and grind on some sheet.  And have a beer.

 

Really, WTF does "maths" have to do with recommending hiking?

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5 hours ago, Left Shift said:

OK, putting 500# on the rail will increase the the righting moment be approximately 2,500#, which will allow the traveler to be raised approximately 2.5" and the mainsheet to be eased approximately 1" and improve boat speed by .15 knots and pointing by 1.2°.

What would really help would be to have a picture from dead astern, but while they are waiting for the photoboat to maneuver around, they might block the mast forward at the partners to induce some lower bend and then try putting on some topmast to take about 30% of the draft out of that main, and open up that airbrake of a lower leach.  Then try traveler up and grind on some sheet.  And have a beer.

 

Really, WTF does "maths" have to do with recommending hiking?

And that’s outta the park and still rising

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On 8/30/2021 at 2:37 PM, some dude said:

Look at the telltales on the leech of the main.  Are they flying?  No?  Ease trav or sheet.  Yes?  See if you can pull it in some more (then watch the speedo)

Look at your friends.  Are the falling over because the boat is flipping over?  Yes?  Trav down

Look at the helmsman. Are his or her arms getting more ripped by the second from pulling on the tiller so hard?  Yes?  Trav down

Pull the main in as hard as you can get away with, watching those 3 things and mostly the speedo.  Main trimmer is the throttle man.  Also depends on tactical situation (fighting to hold lane?  Footing toward the shift?  Overstood?)

YMMV

In lighter airs (4-8 kts), we are struggling with the boat feeling more sluggish then it seems she should. With no weather helm at all beating up the course we go down a similar analysis, boom at CL, all main leech telltales flying, both sails pretty flat, and still no feel in the helm or acceleration. 

Do we have to accept that this is as good as it gets when it is this light or where would you search for more speed? The only thing we haven't really done is try for lots of twist in the main because we are focused on leech telltales and they seem fine. We have in-haulers which we try to set with the North Sails guide even though the sail always looks like it would be better with less in-fucking. 

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On 8/31/2021 at 2:45 PM, Left Shift said:

OK, putting 500# on the rail will increase the the righting moment be approximately 2,500#, which will allow the traveler to be raised approximately 2.5" and the mainsheet to be eased approximately 1" and improve boat speed by .15 knots and pointing by 1.2°.

What would really help would be to have a picture from dead astern, but while they are waiting for the photoboat to maneuver around, they might block the mast forward at the partners to induce some lower bend and then try putting on some topmast to take about 30% of the draft out of that main, and open up that airbrake of a lower leach.  Then try traveler up and grind on some sheet.  And have a beer.

 

Really, WTF does "maths" have to do with recommending hiking?

Still not good at counting!

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Set the boom on the centreline and the top batten parallel to the boom, then ease the mainsheet very slightly to open the top an inch or so from parallel.  Try that setting and see if it works better.

There are so many factors at play here.  Some boats need the extra sheet tension to shape the main properly and to get enough forestay tension.  Others prefer the top batten a little open.  

If your boat has running backstays, check the sag in the headstay at each main setting you try.  The sag must be kept constant by the running backstay tension in order to conduct proper mainsail trim testing.  If the sag is changing that will make as big or a bigger difference to the way the boat sails and feels.

Check your halyard tensions too.  Just enough halyard tension to remove the horizontal wrinkles is what you want.  Many sailors are sailing around with too much halyard tension because it makes the sail "look good".  The sail does look good but the entry angle is too large, so you can't point.  This is a very common way to lose races - if you can't point off the starting line you are quickly shuffled to back of the pack and will struggle to make gains from there on.  All because you had too much halyard tension on.  This is a painful lesson that has to be learned.

YMMV.

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1 hour ago, Frogman56 said:

Dan,

Boom above cl will help.

Try bottom batten at cl

Agree with this. Some boats like a lot of twist in the main especially in light air. Travel most of the way up and adjust sheet tension & traveler position so bottom batten is in line with the backstay and top telltale is stalling on the leeward side of the sail much of the time. Also remember to ease outhaul to put some depth in.

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9 hours ago, Rain Man said:

Set the boom on the centreline and the top batten parallel to the boom, then ease the mainsheet very slightly to open the top an inch or so from parallel.  Try that setting and see if it works better.

There are so many factors at play here.  Some boats need the extra sheet tension to shape the main properly and to get enough forestay tension.  Others prefer the top batten a little open.  

If your boat has running backstays, check the sag in the headstay at each main setting you try.  The sag must be kept constant by the running backstay tension in order to conduct proper mainsail trim testing.  If the sag is changing that will make as big or a bigger difference to the way the boat sails and feels.

Check your halyard tensions too.  Just enough halyard tension to remove the horizontal wrinkles is what you want.  Many sailors are sailing around with too much halyard tension because it makes the sail "look good".  The sail does look good but the entry angle is too large, so you can't point.  This is a very common way to lose races - if you can't point off the starting line you are quickly shuffled to back of the pack and will struggle to make gains from there on.  All because you had too much halyard tension on.  This is a painful lesson that has to be learned.

YMMV.

Funny, my main trimmer and I were swapping emails to discuss the feel of the boat and we mentioned the fact that the last time this happened someone added main halyard tension as well and we probably had too much. Will try that for sure along with getting the boom above CL. 

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I'm generally looking at the leeward luff telltales on the main to determine halyard tension. If they're not flying I ease to flatten the entry and make sure the luff isn't stalled. This also keeps the draft further aft in light air and helps give the boat some helm.

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13 hours ago, danstanford said:

Funny, my main trimmer and I were swapping emails to discuss the feel of the boat and we mentioned the fact that the last time this happened someone added main halyard tension as well and we probably had too much. Will try that for sure along with getting the boom above CL. 

On  your boat, I would recommend boom on the centre line.  Boom above centre line only for pinching someone out after the start or staying above someone who is doing that to you.  I think you will find that putting the boom above centre line costs too much in speed.  If you have VMG on your boat try it and see what the effect is.  

Pointing higher than the keel can point without stalling is a common problem.  Some boats are designed to point super high and carry additional sail area to be able to achieve that - TP 52's for example.  I doubt pointing super high will work for you, but it is worth a try.

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