Main Sail Bubble

sailaway78 · Jun 8, 2010

Maybe

Just maybe your trying to point a little higher than the boat wants to go. What happens if you fall off say 10 degrees.

Rick D · Jun 8, 2010

I'd Try The Cunningham...

...but I am inclined to think you need the main recut.

RichH · Jun 8, 2010

Several things may be going on simultaneously.

"Boom at least centerline if not slightly to windward" ....

Sorry but in a stiff breeze, this usually is a VERY BAD setting. Pulling the boom to the CL or above in a STIFF wind will automatically 'overtrim' the main, produce a HUGE amount of turbulence between the jib/genoa and may be 'reversing the flow' in the so-called slot; hence producing something erroneous called 'backwinding'. In a 'stiff' wind with the boom AT on above the centerline ... you are probably experiencing a SEPARATION STALL on mainsail because the sail is WAY above its correct 'angle of attack'.

A good 'eyeball' method / hint for sailing in ~15kts. and slightly above: keep the AFT END section of the topmost mainsail batten PARALLEL to the boat's centerline .... and only add/subtract 'twist' with respect to THIS batten position ... to keep the LEECH tell tale flying straight back.

In STIFF winds the natural tendancy is to pull in on the mainsheet too hard .... which causes the LEECH of the mainsail to 'hook up' to weather - great for 'power pinching' but not good for beating along at the fastest speed possible. APPLY tell tales AT the batten ends and do ALL THINGS POSSIBLE to keep the leech tales streaming STRAIGHT BACK. In aerodynamics the FIRST requirement for a sail to be operating well is the airstreams coming OFF the leech must be at the same speed from EACH side of the sail/wing (called Kutta Condition) - visualized by TELL TALES on the LEECH.

The Genoa is probably TOO BIG for the conditions and/or the shape of the leech is conflicting with mainsail flow because the leech of the jib is too close to the main.... simple speak: if the main is trimmed/shaped OK either ease jibsheet tension to 'open' the so called slot OR move the jib failead car back to help 'open' the leech. Again, you want the genoa's LEECH tell tales streaming STRAIGHT BACK.
On boats with in/out (as well as fore/aft) jib car / fairleads .... the higher the wind speed, the further OUT (away from the boats centerline) the genoa clew is held.

In stiff winds you MUST be sure that the forestay has correct tension. If the forestay is too loose for the conditions and SAGS off to leeward the SHAPE of the genoa goes all to hell - draft moves aft (bad) and the leech HOOKS UP TO WEATHER ... and so destroys the correct aero flow in the so-called 'slot'. Increased backstay tension is normal in stiff winds.

I suggest that you should get tell tales and apply to the luff and leech of the genoa, and midcord and leech of the main ... and use them for SAIL SHAPING as well as TRIM.
The probable ULTIMATE BEST usage and analysis of tell tales for sail SHAPING and trimming ever written is www.arvelgentry.com ----> magazine articles ----> four articles written as a magazine 'series' :
Checking Trim on the Wind, November 1973
Achieving Proper Balance, December 1973
Sailing to Windward, January 1974
Are You at Optimum Trim?, March 1974

Summary: from your description my 'guess' is: - traveller WAY too far up to weather, mainsheet too tight, jibsheet too tight, backstay too loose, jib car too far forward, main halyard too tight, over-tightened vang. The usage of Tell-Tales (especially at the leeches) will correct most of this.

Joe · Jun 9, 2010

In other words, quit trying to point so high that it slows the boat down... Use the VMG feature on your gps to see how fast your're making progress to the mark... and let those damn sails out a bit.

The small bubble normally created when the mainsail luff is in the mast shadow is being magnified by your over trimming the genoa, which is closing off the slot, which disturbs airflow over the main which you try to compensate for by hiking the traveller too far to windward which keeps compounding the problem. Just let everything out and watch the vmg.

Cobalt · Jun 9, 2010

A simple thanks from a grateful sailor

RichH said:
Several things may be going on simultaneously.

"Boom at least centerline if not slightly to windward" ....

Sorry but in a stiff breeze, this usually is a VERY BAD setting. Pulling the boom to the CL or above in a STIFF wind will automatically 'overtrim' the main, produce a HUGE amount of turbulence between the jib/genoa and may be 'reversing the flow' in the so-called slot; hence producing something erroneous called 'backwinding'. In a 'stiff' wind with the boom AT on above the centerline ... you are probably experiencing a SEPARATION STALL on mainsail because the sail is WAY above its correct 'angle of attack'.

A good 'eyeball' method / hint for sailing in ~15kts. and slightly above: keep the AFT END section of the topmost mainsail batten PARALLEL to the boat's centerline .... and only add/subtract 'twist' with respect to THIS batten position ... to keep the LEECH tell tale flying straight back.

In STIFF winds the natural tendancy is to pull in on the mainsheet too hard .... which causes the LEECH of the mainsail to 'hook up' to weather - great for 'power pinching' but not good for beating along at the fastest speed possible. APPLY tell tales AT the batten ends and do ALL THINGS POSSIBLE to keep the leech tales streaming STRAIGHT BACK. In aerodynamics the FIRST requirement for a sail to be operating well is the airstreams coming OFF the leech must be at the same speed from EACH side of the sail/wing (called Kutta Condition) - visualized by TELL TALES on the LEECH.

The Genoa is probably TOO BIG for the conditions and/or the shape of the leech is conflicting with mainsail flow because the leech of the jib is too close to the main.... simple speak: if the main is trimmed/shaped OK either ease jibsheet tension to 'open' the so called slot OR move the jib failead car back to help 'open' the leech. Again, you want the genoa's LEECH tell tales streaming STRAIGHT BACK.
On boats with in/out (as well as fore/aft) jib car / fairleads .... the higher the wind speed, the further OUT (away from the boats centerline) the genoa clew is held.

In stiff winds you MUST be sure that the forestay has correct tension. If the forestay is too loose for the conditions and SAGS off to leeward the SHAPE of the genoa goes all to hell - draft moves aft (bad) and the leech HOOKS UP TO WEATHER ... and so destroys the correct aero flow in the so-called 'slot'. Increased backstay tension is normal in stiff winds.

I suggest that you should get tell tales and apply to the luff and leech of the genoa, and midcord and leech of the main ... and use them for SAIL SHAPING as well as TRIM.
The probable ULTIMATE BEST usage and analysis of tell tales for sail SHAPING and trimming ever written is www.arvelgentry.com ----> magazine articles ----> four articles written as a magazine 'series' :
Checking Trim on the Wind, November 1973
Achieving Proper Balance, December 1973
Sailing to Windward, January 1974
Are You at Optimum Trim?, March 1974

Summary: from your description my 'guess' is: - traveller WAY too far up to weather, mainsheet too tight, jibsheet too tight, backstay too loose, jib car too far forward, main halyard too tight, over-tightened vang. The usage of Tell-Tales (especially at the leeches) will correct most of this.

Hi there,

Thanks for the post; and above all the link you provided. I'm fairly new to sailing so this was very helpful.

LuzSD · Jun 9, 2010

Rich, Thanks so much,I got most of that but might print it and study it more thoroughly. Joe, thanks for the summary and agree with Cobalt, very helpful. As I was reading the original post I was thinking quite a few of the same points made in Rich's answers...so I must be getting smarter! Yippee. now for more practice......

RichH · Jun 9, 2010

Correct sail shaping and trim is a developed art.

Good knowledge of sail shaping and trim isnt only for sailing fast and winning races as it also can be clearly viewed as a SAFETY ISSUE. It can indeed be a safety issue because when in 'squirrely' conditions if the sails arent trimmed and shaped to close to the OPTIMIUM, then you leave your boat vulnerable to radical and unexpected 'power ups', etc. during gusts and other wind turbulence, shifts, wind instabilities etc.

A good entry level / elemental 'textbook' to begin your journey in this 'art' would be (found on this website's 'store') is: http://shop.sailboatowners.com/books/category-books.htm?cat=1321

LuzSD · Jun 9, 2010

I have that book on my list already and looking forward to getting it. Also enjoying all of the post on Don's guest site here. The more I learn the more I realize I need to learn. Wish I was 20 years younger, I would have so much more time to get it right. Not that I will be slowed down, but I think it will always partially elude me.

Scott T-Bird · Jun 9, 2010

When you have a masthead rig ...

your engine is the genoa. The recommendations seem to be that you trim your genoa for the most effecient shape, making sure the tell tales break evenly (they should be streaming on both sides from top to bottom). THEN you trim your main. With a 150 genny close hauled you WILL have a bubble at the luff of your main (2/3 seems excessive ... ). Don't sweat it. Trying to achieve a perfect shape for your main will be counterproductive as it won't happen until you either fall off too far or lose the shape you need with the genny and it is more important to have the genny shaped correctly. Like Joe says, watch VMG to get it right.

RichH · Jun 9, 2010

Your engine on a mast head rig may be the genoa but in that respect its the mainsail thats responsible for providing the genoa/engine with a good proportion of its FUEL. You simply cant have a well performing jib/genoa without a well trimmed and shaped MAINSAIL.

Dont believe it? ... sail on genoa ALONE and see what happens. The mainsail/genoa 'interaction' is what counts. One sail adding/sharing its benefits to the other is what sailing at near OPTIMUM is all about. Otherwise a 'cat boat' using a sheet of plywood for it sail would be the rig of choice.

The reality of the jib being the 'engine' surely 'doesnt compute' on an aerodynamic field effect plotter .... . You simply cant have a well trimmed jib/genoa without the mainsail FIRST being in a modicum of decent shape/trim .... and vice versa. ;-)

RichH · Jun 10, 2010

Tom
If you intend to 'campaign' a boat successfully you need to consider 3 vitally important and interrelated issues:
1. boat speed - boat & sails set up to perfection to get the fastest speed

2. boat handling & prep. - to keep the speed at maximum (*not skidding off to leeward because you have too much sail up* for the wind/wave conditions, etc.) Steering (& sail shape/trim) so that the rudder deflection is only ~3° off to keep the boat on course and wake coming straight back from the stern, etc. Learning to 'shift the gears' between high speed sail shapes and power shapes with which you accelerate or punch through heavy 'chop', etc. etc. etc. etc. etc.

3. boat tactics - being at the right place on the course at the right time, etc. 'playing the windshifts', 'covering' your opponents, knowing WHEN to 'take a flyer' away from the 'pack', weather (study and knowledge of 'localized wind instabilities' and know how & when to take advantage), etc. etc. etc. etc.

Optimizing speed (and going in the RIGHT direction) is a quite long process involving lots of time and energy input.
Suggest you begin at the BEGINNING ... such with using and KNOWING how to use tell tales to set/shape/trim the sails to 'serious' perfection - www.arvelgentry.com etc. A lot of sail shape/trim info comes from the tales. What you are ultimately looking for is the "feeling" you get when the boat is definitely "in the groove". Its an amazing sensation when you get to 'the groove': high speed, little helm pressure, the keel is LIFTING the boat to weather, the wake is coming almost straight back from the stern, etc. ... ahhhhhhhh.
Consider to set up a 'campaign program' to evaluate ANY change you make versus some 'defined metrics': VMG, speedo, past records of settings, etc. etc. etc. Simple SPEAK: change NOTHING unless you can verify (instrumentation) that the result actually improves something.
Once you learn how to perfectly set/shape/trim the sails ... NEVER EVER make *ONE* sail/trim adjustments as with triangular sails you MUST ALWAYS make TWO. Making ONE adjustment cause a 'reaction' somewhere else and the second adjustment brings the 'reaction' in the sail back to its optimum - the tales will tell you 'which one'.
If you can get the 'Polars' for your boat .... these are your predicted TARGET SPEEDS and if youre not reaching these speeds at the various sailing angles .... something is WRONG, either on the boat, the handling, or the sail trim/sail SHAPING, etc..

You immediate goal should be to find and experience 'sailing in the groove' .... not many sailors ever find it - it takes a lot of work and a lot of practice to continually be 'in the groove'. When you get there .... you'll know it when you find it, I promise.

Start with www.arvelgentry.com website - To get *CONSISTENT max. speed* out of the boat in all wind and sea states; this is the 'job' that only a FULL SET of tell tales (luff/leech/midcord .... AND a row of STEERING TALES on the jib/genoa) can provide. Then get a good sailboat racing textbook. My favorite is "Sailing SMART" by Buddy Melges.
With a serious and determined 'campaign program' (takes about 3 years) you can be winning and placing in many races, .... even with a 'slow' boat that has 'bad numbers'.

For performance sailing issues: a good start from the internet is: http://www.sfsailing.com/cgi-bin/articles/trim/trimchapter7.cfm (but their tell tale info is not as good as the www.arvelgentry.com site.) There are other VERY WELL WRITTEN racing tips, etc. on other 'chapters' on this www.sfsailing site.

Lastly, consider to get a good suit of RACING CUT sails that require very precise steering/trim. Recreational cut sails intended to be 'forgiving' for the inattentive cruiser simply wont cut it for when racing .... especially against others who DO have racing cut sails. Buy your sails from a loft that actually 'specializes' in racing sails - the BIG difference is not the materials but the way the are CUT / SHAPED. Good racing sails can be made from 'woven dacron'.

hope this helps. *<

Stu Jackson · Jun 10, 2010

I have the main sheeted tight and the traveller all the way to windward because that is the position to get any draft on the main at all

The traveler should never be ALL the way to windward unless you have an incredibly short traveler track. What's the vang condition? Your main may also have too much belly for those winds. Have you tried reefing the main?

sailaway78 · Jun 10, 2010

Rich H

While I greatly respect your knowledge, and your inputs, I must respectfully, sort of, disagree with your statement about the main on a mast head rig. I can sail with a 150 jenny, under most conditions, just about as fast as I can with the main and jenny. I can slow the boat down with a poorly trimmed main, but can't gain much speed no matter how I trim it. I still think everyone sorta missed the point, and he is just wanting to sail closer to the wind than the boat wants to. I know assumptions are a no no, but consider what he said. The traveler is past center, so I am assuming that as he comes up he moves the traveler over, which I assume to mean that he had it going OK, before hand.

Scott T-Bird · Jun 10, 2010

I tried something new with my traveler recently ...

We had winds that were generally 15 knots with gusts to 20. Our lake sailing is never condusive to accurate assessments because wind is constantly shifting and gusting, which means that you can never have more than a few seconds to read how a sail adjustment is impacting performance. But ....

My normal close-hauled set is to trim the genoa for the twist that I desire by setting the fairleads appropriately. The track is set at the toe rail and I never have a barber hauler because our tacks are far too short to mess with such things in order to gain a few degrees upwind (my wife would kick my ass if I attempted

) so I live with what we have. I will then normally set the traveler at midships and sheet in for close-haul. We will have frequent round-ups when the gusts can't be overcome by the rudder, unless we spill wind with the mainsheet. I know, I know, it may be more effective to move the traveler down, but with stops instead of a sheet system, moving the traveler frequently during a single heading is really impractical. But the issue I have is that there is no twist in the main when I am close hauled. The vang serves no function in this scenerio because the main sheet is tight and over-rides any capability that a soft vang can have when close hauled (it might be different with a rigid vang which can induce the boom to be lifted).

So on this particular occasion, I moved the traveler to windward substantially, maybe 2/3 of the distance from midpoint to the windward end, and eased the mainsheet so that the boom is midships. Because the mainsheet is eased, twist gives me a much better sail shape on a close hauled setting. We found far fewer round-ups, less need to react to gusts by easing the sheet, and a better overall upwind heading with more speed.

This experience reinforces my thinking that getting twist 'right' is one of the singularly most important functions of sail shape. Twist isn't just about spilling wind when gusts begin to overwhelm. It is more about setting the optimum shape and angle of attack from top to bottom and maximizing overall performance. There is stratification of wind speed from bottom to top and as apparent wind moves abeam near the head of the mast, twist improves air flow, speed and helps keep the boat on her feet, instead of heeled over.

I am pretty well convinced that in gusty conditions, instead of moving the traveler down, which just changes the angle of attack (not for the better, either), I am going to move the traveler to windward and use the mainsheet to set the angle of attack and twist.

I agree with Nice, while you don't just 'throw out' mainsail trim on a masthead rig, you also shouldn't place too much importance on getting mainsail trim right at the expense of setting the genny properly. When close hauled with a big genny, I still believe that some backwinding of the main sail can't be avoided unless you dump the trim on the genny, and lose some of that airflow thru the slot.

RichH · Jun 10, 2010

tomgrigsby said:
Nice N Easy you are right that I was trying to point as high as possible. Had the genny trimmed tight. Main was flat (tight outhaul, tight downhaul, vang not too tight) and luffing without the traveller all the way up. From what I can tell so far from the comments here, I was probably overcanvassed (20kts of wind). Being a relative novice and having a heavy boat, we were thrilled to have the lee rail in the water and still have control. Had waaaay to much weather helm though too, so there were lots of areas for improvement. At a minimum, I think I should have moved the genny car aft to spill the genny. That would have reduced the backwind on the main in the slot and allowed easing the traveller a bit to keep the boom centerline or to leeward. Probably would have pointed better. The wind snuck up on us though going from 15 up to 20 relatively quickly. I had a really green crew, so doing a headsail change wouldn't have been fun. Doable, but not fun.

Tom - describe what you mean by 'traveller all the way up' means.
Do you mean 'on' the centerline or do you mean the traveller car 'pulled all the way to the 'weather rail' (as far as possible from the genoa) or other?
????????????
When the traveller was 'all the way up' ... on what side of the CLine was the 'aft' end of the boom? windward side or leeward side?.