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Topic Review (Newest First)
08-12-2013 10:19 AM
ctlow
Re: Twist

Quote:
Originally Posted by SchockT View Post
..."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.
08-06-2013 10:58 AM
SHNOOL
Re: Twist

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...
08-03-2013 11:30 PM
ctlow
Re: Twist

Quote:
Originally Posted by Jeff_H View Post
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
07-29-2013 12:40 PM
Jeff_H
Re: Twist

Quote:
Originally Posted by ctlow View Post
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?

Thank you.

Charles
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
07-29-2013 07:56 AM
SHNOOL
Re: Twist

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.
07-29-2013 03:01 AM
SchockT
Re: Twist

Quote:
Originally Posted by ctlow View Post
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.
Quote:
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.

Quote:
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"!

Quote:
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.
07-28-2013 06:54 PM
ctlow
Re: Twist

Quote:
Originally Posted by Jeff_H View Post
... 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
07-28-2013 10:29 AM
Jeff_H
Re: Twist

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.
07-28-2013 09:15 AM
ctlow
Re: Twist

Quote:
Originally Posted by Resolute_ZS View Post
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
07-15-2013 04:22 PM
zz4gta
Re: Twist

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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