# Twist



## ctlow (Apr 10, 2011)

Hello, all. See if this sounds about right.

First, I'm a fairly new club racer, nothing serious, several years of weekly (seasonal) skippering and many more of crewing behind me.

Secondly, I believe that much confusion on this topic stems from twist vs. flatness. To the beginner, they sound contradictory, like a twisted sail must be a full sail. The books say no, that one can have twist without fullness. The hows and whys are for another thread or later in this one.

Thirdly, I hear and read that one doesn't usually want twist in the sails "except when" ...

My personal take on all of the exceptions is that one _usually_ wants twist except in one specific scenario.

If we make a grid with wind strength on one axis, and wave state on another, each on a 3-point scale of "mild, medium, severe", that would be nine boxes. I would like to look at only some of them, to illustrate my understanding and ask for comment.

1. Let's take light winds in flat seas (not such light winds that it's virtually calm - that's a different story). The difference between winds aloft and alow is such that twist is desirable to keep all parts of the sail optimally trimmed.

2. Let's take heavy winds. One wants twist because the struggle is to keep power out of the sails (reduce heeling, weather helm, etc.).

3. Medium winds and lumpy seas - the boat's not going to track exactly straight no matter how skilled the helmsman, or in more extreme lumps there will be relative calm in the troughs, so having twist always keeps some part of the sail under power.

4. Medium winds and calm seas. This is the only situation I can think of when less twist is desired, the fabled "upper batten in line with the boom" scenario.

Of course, I'm talking as if twist is either on or off, and it's more nuanced than that.

I'm also not talking (yet) about "how" - a bit of a struggle on my boat currently.

Making any sense so far?

Thank you.

Charles

P.S. See previous threads by others on this topic:
http://www.sailnet.com/forums/learning-sail/6221-depowering-sails-twist.html

http://www.sailnet.com/forums/learning-sail/9336-whats-up-sail-twist.html


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## SchockT (May 21, 2012)

It looks like you have a pretty good handle on the various reasons you might want to add twist to your sail. Just be careful not to over think it. Remember they are not hard and fast rules, they are guidelines. Whether to use twist and how much really depends on YOUR boat, YOUR sails and the conditions YOU are sailing in.

The "HOW" is something you should be addressing before you read any more about twist! All that theory doesn't do you a bit of good if you can't apply it and see how it works on your boat.

Why is setting twist "a bit of a struggle" on your boat?


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## ctlow (Apr 10, 2011)

Thanks, ShockT.

I have a 1981 US Yachts 33 (i.e. feet), built on a Buccaneer plan (long story, they tell me), and it's a lovely, fast boat in many ways, but prone to weather helm and needs delicate attention to trimming when up to weather. So when we're racing, getting the crew to coordinate and play everything well together in concert is a challenge, and we are working on that and getting there. They're all such busy people that most of them absolutely cannot get together on evenings or weekends for practices -most frustrating.

So, that's my "struggle": both technical and human factors.

We have busy races in a 1-mile-wide river, so short legs with lots of tacks, jibes and roundings, so the skipper cannot realistically verbalize every control adjustment on both sails (at least 7 for the main and 4 for the foresail), especially on nights when the winds are gustier and/or shiftier. The crew has to understand what's going on and learn to be semi-independent, and we're working on that too, and making gains.

We have a specific challenge with the main back-winding. A bubble in the forward third is acceptable, but sometimes to reduce a heavy weather helm, we end up flogging the entire sail (but the streamers on the leech are happy!), so we're working on that too. That can't be good, although I know two experienced racers who say "just live with it". I can usually get it all to settle down when I'm sailing alone ... fiddle with things for a few minutes, mainly bring the traveller way up, ease the main-sheet but also ease the foresail. "If in doubt, let it out." "Keep 'er full and footin'!" The boat seems to like to have the main reefed early, say in the 12-15 knots true-wind range, and is quite happy at 20 degrees of heel even in (only) 8 or 9 knots of true wind - it's unclear to me whether that's good, and is specific to this boat, or whether I should be cranking on unbelievable amounts of backstay tension, making other adjustments, etc.

So, the struggle I referred to isn't "twist" alone, but it plays into all of those deliberations. Twist is the thing I hear talked about most, and it became apparent the other day that my crew was confused about the distinction between twist and depth, which has befuddled me in the not-so-distant past as well. For example, raising the traveller and easing the main, leaving the boom just below mid-line on a close haul, is said to add twist but also flatten the sail. That's hard to visualize why that works (but it does work), and I believe that many casual racers never get to that degree of sail-trim knowledge.

Thanks again.

Charles


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## SHNOOL (Jun 7, 2007)

Charles, sounds like you are well on your way... US Yacht 33 eh? Interesting...

But they are masthead rigs with low-aspect narrow mains. The reason why your main bubble isn't a huge factor is, the boat drives almost entirely off the genoa.

I am betting when you are racing with that bubble, and pointing, you are sheeted in hard with the genoa. Getting more drive from the genoa is MORE important than using what's left of the main honestly. But if you can get point, and good genoa trim, AND get your main working for you as well, you'll be golden.

And it sounds like all your assessments are correct... Couple observations, and I am still sorting all this out myself sailing with a smaller masthead rig myself... Take what I say with my own novice observations.

Reef the main if you find that you are sailing a lot with a bubble ALL the time (regardless of these tips below).

To prevent the bubble, (or reduce it), you can crank on the outhaul and flatten. You can also (and want to as you sheet in hard, or vang hard) apply cunningham. If you don't have one, and your main is not brandy new, you'll want to add one (they are easy to build, just a 3:1 becket and blocks with a cleat... with a hook on top (to go through the cringle above the tack), and a hook on the bottom to attach to the bottom of the mast. Anyway the cunny pulls the draft forward as the vang/mainsheet flatten and pull the draft back. You may have a lot of bubble because your draft is deepest at the exit angle of the genoa... getting that draft forward, puts the deeper part of the main towards the deeper part of the genoa (and gets the shape better for lift)... General rule is draft should be in the first 40%, I am betting your draft in yoru main has gone to 60% or more when you are sailing like this.

Dump the traveler in the puffs to depower some (as soon as you feel that puff drop in power, get that traveler back up!), don't release sheet unless you have to (if your vang is on holding the boom from lift, releasing the sheet is less a problem), or/and head up, take advantage of the temporary lift. If your point is good and you are still overpowered, you can add twist to the top of the genoa by moving the cars back a bit on the tracks, to depower that as well. 

MOST of your trim focus should be on that genoa (keep low, medium, and high luff teltales streaming, know when they should stall and when they shouldn't). Keep up as much genoa as you can racing, pick headsails for your non-puff winds, as large as you can go where you aren't overpowered (keep heel under 20 degrees use all the rail meat you got to determine that)... REEF the main before you lower headsail size. When you downsize headsails, go in small increments. 155-140-130-110.. if you can (if you have them).

One of the things I find MOST useful to climb upwind, is to feather.... head up for a couple seconds, adjust trim, until you feel the boat starting to slow, then foot off, retrim, pickup speed, then repeat... don't ROW while doing this, make the steering adjustments slow, otherwise for sure you'll slow down. Practice this before you race, it takes a bit to know what is too much adjustment, or to fast.

On another sailing site (SA), there was a huge racer's discussion on "sailing by the luff." That I've just started to understand myself. I found it interesting and yet another confirmation of genoa trim (it's harder to see with a tuff-luff or furler, but it's still usable).

PS: it hadn't dawned on me that adding twist in the light stuff (although I had been doing it, I hadn't realized that's why it worked) because of the differential between low altitude and high altitude winds. I've observed it by looking at differences between shroud tale and mast head though.

Oh one final note... with a masthead rig, you can usually get away with a larger spinnaker (symmetric) than these fractionals are allowed to run (think square footage). That's where your advantage is biggest. I can walk away from most of the fractionals downwind, but they beat me up, coming upwind.


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## SchockT (May 21, 2012)

> We have a specific challenge with the main back-winding. A bubble in the forward third is acceptable, but sometimes to reduce a heavy weather helm, we end up flogging the entire sail (but the streamers on the leech are happy!), so we're working on that too. That can't be good, although I know two experienced racers who say "just live with it". I can usually get it all to settle down when I'm sailing alone ... fiddle with things for a few minutes, mainly bring the traveller way up, ease the main-sheet but also ease the foresail. "If in doubt, let it out." "Keep 'er full and footin'!" The boat seems to like to have the main reefed early, say in the 12-15 knots true-wind range, and is quite happy at 20 degrees of heel even in (only) 8 or 9 knots of true wind - it's unclear to me whether that's good, and is specific to this boat, or whether I should be cranking on unbelievable amounts of backstay tension, making other adjustments, etc.


It is true that on the '70s and '80s era high aspect masthead rigs it is normal to carry a bit of a bubble in the luff of the main when sailing upwind in breeze, but you still want to try to minimize it. The genoa is where most of your power is coming from, and the main is little more than a "trim tab" for the genoa. First, make sure your genoa is set properly. On my boat in upwind trim the foot of the genoa is almost touching the shrouds, and it is a couple of inches off the spreader. Make sure your genoa car is set correctly so that your upper, middle and lower telltales break evenly. (in other words, the right twist!) Also, if the car is too far forward you will have too much leech tension which could cause a "hook" in the leech. The hook can also be caused by a over tensioned leech line if you have one. That hook will exaggerate the backwinding of the main.

On the mainsail, you want to try to flatten the sail out as much as you can. If you are running old dacron sails that will most likely mean cranking the cunningham (to pull the draft forward) and cranking the outhaul on hard (to flatten the sail). As the wind picks up you will also want to start cranking on backstay tension. If you have an adjustable backstay you should be in the habit of pulling it on for upwind, and letting it right off for downwind. Don't be afraid to crank it on hard. Even unbelievably hard! (It is not uncommon to see 3000psi on my hydraulic backstay) That will do 2 things; it will reduce headstay sag, flattening the genoa, and it will bend the mast flattening the mainsail. Both are desireable for upwind work. I believe the US33 has a baby stay as well? If it is adjustable crank that on too. That will help to induce more bend in the mast.

Once you have done all that set up the main so that the boom is on centerline and adjust the sheet tension so that the top leech telltale streams about 50% of the time. Once the sheet is set for the wind conditions, leave it alone and work the traveler to control heel angle/weather helm. That maintains your desired sail shape, and just changes the angle of attack of the sail. Every boat is different, but typically 20 degrees is too much heel, and that could be why you have a weather helm issue. The more the boat heels, the more rudder input is required to keep it going straight, and more rudder angle slows you down. I try to keep my boat at 10-15 deg. If you have a trimmer on the traveler you have to communicate constantly and let him know when you need it eased. I prefer to control it myself for quicker response. When sailing through gusts I may ease it to the point where the whole sail is backwinded except the last couple of feet of leech. You can also control gusts by "pinching" into them. (what Schnool refers to as feathering).


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## ctlow (Apr 10, 2011)

Schnool and ShockT

I wrote a long reply and the forum software lost it.

The short version is that I have learned some new things, confirmed some old things, and will be working on the new ones.

Thank you both very much!

Charles


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## SHNOOL (Jun 7, 2007)

Shock I am quite glad you followed on, confirmed what I was saying and added to it... TONS more expertise than me Charles, his word is golden.. Also glad I wasn't dead wrong. I've always know to crank on the backstay to depower, had no idea you could crank on so much... The adjustable on my Capri 25 is slow to add bend, I'll be looking to add more backstay quicker here on out.

Amazing the quality of sailors here though!


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## SchockT (May 21, 2012)

SHNOOL said:


> Shock I am quite glad you followed on, confirmed what I was saying and added to it... TONS more expertise than me Charles, his word is golden.. Also glad I wasn't dead wrong. I've always know to crank on the backstay to depower, had no idea you could crank on so much... The adjustable on my Capri 25 is slow to add bend, I'll be looking to add more backstay quicker here on out.
> 
> Amazing the quality of sailors here though!


I appreciate the kind words, but really I am just passing on what i have learned from much better sailors than myself! (and a fair number of years racing helps I guess!) That's what makes this community great!

One word of warning on backstay tension. Some boats have tree trunk stiff masts that really don't bend very much, in which case you are only tightening the forestay, but even that is worth while. Don't forget, if you do crank the backstay to bend the mast, you will have to pull on more sheet to compensate, and of course when you let the backstay off, your sheet will probably need to be eased a click or two.


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## SHNOOL (Jun 7, 2007)

Shock, yes and the Capri 25 fits into that category... mast-bend is very little... but the headstay sag is controlled by backstay... I've found already that cranking on the backstay tightens the luff of the genoa, reducing sag, and providing more point as the winds pipe up, by moving draft forward on the genoa (bringing it back to where it should be, cause it creeps as the wind picks up). I've considered adding a downhaul to the genoa as well but I don't know how much MORE that'd provide.

Another thread on another board commented on "modern sail cut," about how shapes are pre-determined on load-path sails... and moving the draft is a "minimal" movement (I've observed this especially with cunningham)... but on dacron it's can be a huge adjustment.


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## SchockT (May 21, 2012)

SHNOOL said:


> Shock, yes and the Capri 25 fits into that category... mast-bend is very little... but the headstay sag is controlled by backstay... I've found already that cranking on the backstay tightens the luff of the genoa, reducing sag, and providing more point as the winds pipe up, by moving draft forward on the genoa (bringing it back to where it should be, cause it creeps as the wind picks up). I've considered adding a downhaul to the genoa as well but I don't know how much MORE that'd provide.
> 
> Another thread on another board commented on "modern sail cut," about how shapes are pre-determined on load-path sails... and moving the draft is a "minimal" movement (I've observed this especially with cunningham)... but on dacron it's can be a huge adjustment.


I thought the Capri had a fairly "sporty" mast. It doesn't look like an overly heavy section to me. You might be surprised how much it will bend. Next time you are at the dock, attach your main halyard to the gooseneck and pull it tight. Observing the gap between the halyard and the mast half way up. Now crank the backstay on full and snug up the halyard again. That will show you how much bend you can get.

From your avatar I see you have plastic racing sails. They don't typically need nearly as much halyard tension as old dacron. Often times you don't even need a winch, just a good hard yank is enough. I think a jib cunningham is redundant on your boat. you can achieve the same thing with halyard tension. Typically you find jib cunninghams on small boats and dinghies that have locking halyards that can't be adjusted on the fly.


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## ctlow (Apr 10, 2011)

Thanks again, Schnool and ShockT.

I can see the mast bend - mainly the top half. I had to measure it when ordering a new main-order mainsail a few years back.

I think I'm basically up-to-speed on the theory now, and need mileage to turn that into practice. Getting the crew "on-board" will require "firm but nuanced" skippering.

There's for sure an art to this as much as a science, and I know to pay attention to both.

Charles


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## Rezz (Oct 12, 2012)

I just wanted to give a general "Thanks" to the contributors of this thread - I've learned a lot by just reading it. Being boatless, it's hard to put the information into practice, but I enjoy learning the theory behind actions.

Also, SHNOOL, your tagline has me looking at C25's now


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## SHNOOL (Jun 7, 2007)

Resolute... check out Catalina - Capri - 25s International Association for more information on the Capri 25.

The Capri 25 was designed as direct competition to the J/24. It's arguable if Frank was successful with that premise, but it's really intended as a race boat first, and a day sailor second. I however, seem to have managed to turn it into a bit of both. If you can get a back copy (this years) of "Good Ole Boat" magazine... Jan/Feb issue, you'll see a great write-up on the Capri 25 starts page 24.

Plenty of sleeping space in the boat, NO headroom. It's a boat that you can still pick up with a trailer for well under 10k.


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## SchockT (May 21, 2012)

Unless you are One Design racing and there is a strong J24 fleet it is a no-brainer! I would take the Capri over the J boat every time!


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## SHNOOL (Jun 7, 2007)

Well, you can OD race, in one place in the world with the Capri 25.. Wayzata Yacht Club in Missouri. WYC Capri-25 Home/News I can't pull it off even in a long weekend, otherwise I'd try (yep I am little nuts).

So far I am liking how competitive the boat is boat on boat with the S2 7.9, J22, J/24... however, my own abilities.. are not there yet. It's a fun boat though. Maybe I'll give them a run for their money some day


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## zz4gta (Aug 15, 2007)

Shnool, the Merit 25 is very similar to the Capri and the J/24. Tuning guides for the Merit say to keep max backstay tension at 1000 lbs or less. I'm using a 24:1 cascade on my boat and it does help. I have the stiffer of the two mast sections (MORC) on my boat. 

ctlow - how old are your sails on the 33? looks like it's an old IOR design. You'll need lots of headsails...


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## ctlow (Apr 10, 2011)

Resolute_ZS said:


> I just wanted to give a general "Thanks" to the contributors of this thread - I've learned a lot by just reading it. Being boatless, it's hard to put the information into practice, but I enjoy learning the theory behind actions.
> 
> Also, SHNOOL, your tagline has me looking at C25's now


Yes, it has been very helpful, I agree. So I went out a week ago on my own, 33-footer, full main and a #2 in a bit under 10 knots of wind, and got the boat humming, close-hauled. I'm not sure it was fast - in the 5.0 to 5.5 knot range - but all of the ticklers were doing their thing, no backwinding, etc.

And fast does matter! (And bearing off a bit is fast! "If in doubt, let it out!" "Keep 'er full and footin', boys!")

But the problem is to get the crew to do it. With our short-leg races, it really means training them to make many adjustments quickly and with minimal supervision.

I obviously can't race alone because by the time I get the boat all set up I would be at the next mark.

Thanks again to all.

Charles


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## Jeff_H (Feb 26, 2000)

One thing that I might add is that instead of flagging your mainsail because you are trying to get the boom to the centerline, you might try really blading out the sail as suggested, minimizing twist, put on gobs of mainsheet, but lowering the traveler so the sail has a flatter angle of attack. You will get a little more drive, less drag and more style points. The other thing in a lot of breeze you can move your jib leads slightly aft and add twist to the genoa. This should reduce heeling and weather helm and may let you use your mainsail more effectively.


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## ctlow (Apr 10, 2011)

Jeff_H said:


> ... instead of flagging your mainsail because you are trying to get the boom to the centerline, you might try really blading out the sail as suggested, minimizing twist, put on gobs of mainsheet, but lowering the traveler so the sail has a flatter angle of attack. You will get a little more drive, less drag and more style points. The other thing in a lot of breeze you can move your jib leads slightly aft and add twist to the genoa. This should reduce heeling and weather helm and may let you use your mainsail more effectively.


Thanks, Jeff. I've got a few dilemmas in there. Let's say "fairly flat seas but with a bit more wind than 'moderate' for the boat". You're suggesting twist in the foresail but not the main. Did I understand that correctly? The books say that usually both sails will have similar twist.

I'm not sure what "blading out" is. But strangely - and I've come across this in several places and confirmed it with some high-level racing sailors - easing the mainsheet, letting the boom rise and freeing the leech (opening, even though the tack and head are on a shorter line to each other) adds twist but flattens the main. This of course means raising the traveller to restore angle of attack with the boom near centre, whereas you say lower it. I can't quite visualize why that flattens, although I can see how it adds twist. But so be it. It also means having a very tight backstay.

That was one of my original points about "twist": one can flatten and twist at the same time (they say!).

Stronger winds need flatter sails (all other things being equal), and twist. Flatter sails allow more of the sail to be closely aligned with the wind, giving more propulsion and less heel. At least, that's what the books say and how I conceptualize it.

Then there's draft position - we haven't got into that yet.

Can you clarify any of the foregoing?

Thank you.

Charles


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## SchockT (May 21, 2012)

ctlow said:


> Thanks, Jeff. I've got a few dilemmas in there. Let's say "fairly flat seas but with a bit more wind than 'moderate' for the boat". You're suggesting twist in the foresail but not the main. Did I understand that correctly? The books say that usually both sails will have similar twist.


Ideally, yes you want to match the twist of each sail and keep the slot consistent, but when you are over-powered you might want to break that rule.


> I'm not sure what "blading out" is. But strangely - and I've come across this in several places and confirmed it with some high-level racing sailors - easing the mainsheet, letting the boom rise and freeing the leech (opening, even though the tack and head are on a shorter line to each other) adds twist but flattens the main. This of course means raising the traveller to restore angle of attack with the boom near centre, whereas you say lower it. I can't quite visualize why that flattens, although I can see how it adds twist. But so be it. It also means having a very tight backstay.
> 
> That was one of my original points about "twist": one can flatten and twist at the same time (they say!).


"blading out" is just racer-speak for flattening your sails as much as you can. That means cranking on the outhaul, the backstay and probably the cunningham. Once the sheet is set in upwind trim, increasing backstay tension will flatten the sail and increase twist because the curve of the bent mast stretches the material between the mast and the leech. At the same time the mast tip comes aft, reducing the distance between the clew and the head, reducing leech tension and therefore increasing twist. That is why you will find that after you make a backstay adjustment, you will need to make a sheet adjustment as well.



> Stronger winds need flatter sails (all other things being equal), and twist. Flatter sails allow more of the sail to be closely aligned with the wind, giving more propulsion and less heel. At least, that's what the books say and how I conceptualize it.


Twisting the sails off in stronger winds is somewhat of a last resort when you have used all of the other de-powering tools and you are still over powered. High performance fractional rigs are "self-twisting" to a certain extent; when a gust hits the unsupported mast tip will allow the mast to bend and temporarily twist the main off at the top.) Flat sails actually give you less propulsion (and less drag) than fuller sails, but flat is good when you have more wind power than you need. Keep in mind that in this context when I say "full sails" I am not referring to baggy old cruising sails, but good sails that haven't been "bladed"!



> Then there's draft position - we haven't got into that yet.


Draft position is fairly straight forward. Cunningham and halyard tension are draft controls. Typically you want to start with the draft at about 50%. That gives you a nice smooth rounded entry at the luff. Increasing luff tension pulls the draft further forward which will open up the leech. You will find that as you pull on backstay and bend the mast you will have to pull on cunningham to maintain draft position where it should be, hence, the "blading out" procedure will likely include grabbing a big handful of cunningham too!
Older sails usually need quite a bit of cunningham because as sails age, the draft moves aft. If the draft is too far aft, you end up with a very flat entry on the sail which is very hard to steer to, and at the same time the leech is excessively rounded.

It is difficult to get used to visualizing draft position, which is why many racing sails have "draft stripes" on them as a visual aid. Sighting up the sail from under the boom helps too.


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## SHNOOL (Jun 7, 2007)

Jeff and Shock have you covered.
Outhaul is what Jeff is mostly talking about. If you are backwinding that bad on your main still, that means the sheeting angle of your genoa is tight against your main, which is putting wind through the slot at a high enough rate and angle to put high pressure against the main... so you need to open the slot (make it wider).

2 easy ways 
Twist off the genoa (which will lose power - which works under higher winds if you are already at hull speed).
Tighten the main (flatten) by adding outhaul, sheeting in the main, cranking on the backstay and if you do all this, you'll likely need to add cunningham and or adding halyard.

I'll add that flattening the mainsail will allow you to point more, especially if it's combined with sheeting the main in a lot more... don't underestimate where your traveler can go either. You might be able to go several inches higher than windward, keep an eye on the leech of the main, you don't want it above centerline... but if you on relatively flat waters, with the wind coming up, you can sheet on hard, move the car all the way up, outhaul on hard, and get great point!

I wouldn't add twist until you start hitting hull speed...

OH and YES you can crack off a bit (head away from the wind) and ALSO get more speed, but especially in racing you ideally want to get as close to windward as you can at the highest speed possible.

This is the OP's boat (I am thinking). The reason why I thought it was interesting as I spent several years as a kid racing with my father on his (then) brand new US 27... which is a similar boat. Note the picture, the blade main.


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## Jeff_H (Feb 26, 2000)

ctlow said:


> Thanks, Jeff. I've got a few dilemmas in there. Let's say "fairly flat seas but with a bit more wind than 'moderate' for the boat". You're suggesting twist in the foresail but not the main. Did I understand that correctly? The books say that usually both sails will have similar twist.
> 
> I'm not sure what "blading out" is. But strangely - and I've come across this in several places and confirmed it with some high-level racing sailors - easing the mainsheet, letting the boom rise and freeing the leech (opening, even though the tack and head are on a shorter line to each other) adds twist but flattens the main. This of course means raising the traveller to restore angle of attack with the boom near centre, whereas you say lower it. I can't quite visualize why that flattens, although I can see how it adds twist. But so be it. It also means having a very tight backstay.
> Can you clarify any of the foregoing?
> ...


The two explanations above are both essentially correct. To more specifically try to clarify my points, there are two schools of thought on heavy air mainsail trim. Done skillfully, either can work well. The flat and twisted approach is the 'old school' approach. In this approach, huge amounts of halyard, and outhaul are applied. This 'pulls fabric out of the middle of the sail'. The risk is that it moves draft aft, and so some cunningham is applied to move the draft forward. (I personally try to avoid ever having to use the cunningham, and have actually no longer have it rigged on my boat. But as sails get older or are stretchier, the cunningham becomes your friend.)

This is a very old technique and so old, in fact that it used to be called a 'fisherman's reef' from the days when folks fished under sail.

The good news about the flat and twisted approach is that the upper part of the sail is twisted off reducing heeling, when coupled with a twisted jib, the slot remains nearly parrallel, and its pretty quick to play in and out. In smallish boats, when coupled with the vang, a good mainsail trimmer can play the sheet with each wave allowing the boat to be steered with the mainsail and not with the helm reducing drag and building up Popeye arms on the mainsail trimmer.

The downside of this approach is that the geometry of most mainsails mean that as the boom lifts adding twist, it also adds fabric in the middle of the sail, powering the sail up. The result of that means that beyond a very small range of adjustment, this quickly becomes a twisted and  not so flat approach. For that reason, the flat and twisted technique works best on boats with lots of mast bend control and the ability to play the backstay quickly and easily, so that applying the backstay will quickly open and flatten the mainsail without changing the boom geometry.

(Here is a picture of my boat from astern illustrating the flat and twisted approach. This was right after a mark rounding, a little over powered since it was just as the wind had come up to roughly 20 knots apparent. I am single-handing and so was not settled down in a position for subtlies yet. The backstay is on hard, the sails flattened, at that exact moment I am adjusting the traveler to flatten the boat. I am using flat and twisted since that approach tends to be a little more forgiving and so made sense here while I dialed in.)



In my lifetime, the approach to main sail trim in heavy air has changed over to blading out the sail. The idea here is that the sail is very flat and has minimal twist and is rotated using the traveler to increase and decrease the angle of attack. Conceptually, there is comparatively little gradiant wind angle difference during heavy air. Consequently, the sail does not need twist to have the same angle of attack along the span of entire sail. The net result is that the flat sail maximizes drive relative to side force, and then the angle of attack is precisely rotated with each gust and lull.

To do this, all control lines are set up very tightly (that means halyard, outhaul, flattening reef if you have one, vang, backstay, and mainsheet) so that the sail is flat and with very minimal twist. The boom will be below the centerline pretty much all the time. The mainsheet is pretty much cleated off, and the traveler is played between full on to totally flagging, but mostly with a small bubble near the luff.

In practice, on a bigger boat with really good sails, a good mainsail trimmer will cycle through a mix of both techniques, slightly freeing the sheets and lifting the traveler in lulls and blading and dropping the traveler in the gusts.

This cycling can happen with great frequency in waves and the mainsail trimmer really can make a huge difference loading and unloading the helm. In gusty conditions I would cycle through this 3-4 times a minute on the 40.7 I used to race on. Timing is critical on this. As the gust hits the boat, the mainsail trimmer needs to delay a moment so the boat starts to take a bite to windward, and feathers up slightly, but then the load is released just before the helmsman needs to move the rudder to stay on course. As soon as the gust wanes, the process reverses. When trimming mainsail on a boat with a wheel I make sure the center spoke is marked and carry tape in my seabag so I can mark the center spoke if its not. The mainsail trimmer needs to be aware of the angle of helm, and use his sail trim to minimize drag. That is usually easier when the sail trim starts out being bladed out and only uses small amounts of added twist.

The other part of this is communication between the helmsman and the trimmer. The helmsman needs to be able to convey input into feel and simple stratetic decisions such as, "Need point", "Need speed", "lots of helm", "feels slow", "need more steering" and so on so that two can work as a tight knot team. Of course, after a while, a bit of clairvoyance sets in so that team learns to read the other person's mind.

I hope that this somewhat clarifies what I was trying to say.

Jeff


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## ctlow (Apr 10, 2011)

Jeff_H said:


> The two explanations above are both essentially correct. To more specifically try to clarify my points, there are two schools of thought on heavy air mainsail trim...
> 
> I hope that this somewhat clarifies what I was trying to say.
> 
> Jeff


Thank you, Jeff. And yes, the sales brochure material posted recently a few message up in this thread is of my boat.

I'm following everything you all say. It's not wonder I'm confused and some of my mentors are confusing me more. This has helped to clarify my thoughts.

We have some challenges because of the traveller controls, in getting quick adjustments, but that's nothing that time, effort and/or money cannot overcome. And crew-coordination ...

Thank you all again.

Charles


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## SHNOOL (Jun 7, 2007)

Jeff, just got back from racing in our little puddle of a lake this past Sunday, in our informal series.

As always your description is spot on, and I have always set the sheet and played the traveler... Never knew why it worked as well as it did, but now I get it (and I hadn't realized this was a "newer" way to do things, and I recall my brother and I getting into a huge debate over dump the traveler versus dump the sheet to depower). Honestly they both work, but what I've found is if you keep it all flat, and dumping the traveler keeps you on your feet, then bringing the traveler back gets you moving quick again faster than having to sheet back in... I hope that makes sense... So dump the traveler as you get overpowered, and crank it back in as the puff subsides. If you are STILL overpowered, then backstay on more, and outhaul more, and try again (keep the draft where it belongs, and you are right the loadpath mainsail keeps its shape and draft doesn't move much).

One of my crew was concerned that I was "doing all the work," but in our gusty little lake, we'd go from 12mph to 20mph in a heartbeat as we got oscillating winds. And yes I was dumping and reeling in on the traveler with every puff... to keep helm as neutral as possible and to keep the boat on her feet. We spent nearly 2 hours on our course at or above hull speed. Great sailing (a rarity this time of year for us). My legs are burning still today from hiking like it was a centerboard boat.

We cranked on the outhaul to blade out, and I'd firm up or ease the backstay depending on the winds we were MOST experiencing. Then for local puffs, I'd dump traveler. Genoa trim was nearly "set and forget," keeping it drawing as much as possible (trimmer was on it all the time, ready to dump if we too on too much, and always tweaking if needed, but we were pretty spot on), although we DID drop the car back a bit when we were still consistently overpowered but wound up bringing them back into full on mode when the winds dropped. This is probably the most adjusting we've done or had to do in a race, but we were able to keep pace with most of the faster boats, so we couldn't have done all THAT bad (just got results and our hard work paid off we bested all but one other in our fleet, so something we were doing was right). If my start hadn't have been so horrendous (another story all together) we'd have been in the money.

Oh to the OP I post all this so you get an idea of what all we're doing to apply these things...


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## ctlow (Apr 10, 2011)

SchockT said:


> ..."blading out" is just racer-speak for flattening your sails as much as you can....


Thank you, ShockT. Again, this entire discussion has been very helpful.

I had a good long upwind sail yesterday with a mostly-non-sailing-literate crew (brother), put him on the helm and I started tweaking. The background is that my USY 33 seems to like to be reefed earlier than the books suggest. We were in about 9 knots of wind, whitecaps just starting, basically calm waters for a 10m boat.

Using every control at my disposal, and that included jury-rigging a cunningham, and cranking on more backstay tension than ever before, I think I got that boat humming. I found that I was using very firm main-sheet tension to help reduce twist, and found a traveller position half-way up which put the boom just barely to leeward and allowed excellent pointing. The (old) #2 foresail was sheeted in harder than I can usually manage without seriously disturbing the main. (The #2 is easier without a full crew, plus it was already on my roller-furling.) We were doing 5 to 5.5 knots indicated, and making good progress against the current (average about 1 knot). We rarely heeled more than 15 degrees.

A friend in a shorter boat grew smaller and smaller behind us.

At the end when we had a leg a bit freer, close-reaching but not close-hauled, the speed soared into the 6.5 -7.0 range.

Now, doing that in races will be another matter. I need my larger racing crew for that, and we are working together better and better, but it takes time.

All of these things I knew, except that the "twist-vs.-blade" concept needing clarification for me, but running through them again here has helped enormously to sort out the fine details.

Thanks to all.

Charles

N.B. Moderate winds, flat seas, minimal twist - just like I said at the beginning.


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