Much better.

 

The horizantal creases in your previous post disappeared now. Thesail is in much better shape now.

 

Looks 100% better, make sure your topping lift doesn't interfere either.

 

Looks way better. I see what you mean about the windex. Looks like the birds have been practicing with it.

A new main is in the cards for you. Don't skimp when you do as it will last 10-15 years which will equate to 300 per year approx. Small pocket change per year on a sailboat.

Dave
X

 

I am guessing that your vang kept the boom too low and you were unable to raise the sail all the way. Once you loosened the vang you got the luff tensioned correctly.

 

How tight should I tighten the main halyard? I don't want to break things and over-tighten it...

The amount of tension you should put on the halliard depends on the wind strength. Generally, the stronger the wind, the more tension you should use, and conversely, the lighter the wind, the less tension. But, instead of thinking in terms of putting X amount of tension on the halliard in a windspeed of X miles per hour, you should learn to think in terms of sail shape. The tension of the halliard affects the leading edge of the sail (the "luff). If you don't put enough tension on the halliard, the luff of the sail will be relaxed and wrinkled somewhat. Usually, you'll want to tension the halliard enough so that the luff will lie smooth and flat, with no wrinkles. If you tension it too much, the luff of the sail will have a long curl in it all along the mast.

Looking at your photos and your representation that they were taken when the wind was very light, I would have eased the tension on the halliard and also on the outhaul. Too much tension on the halliard and outhaul makes the sail flat, and that depowers the sails. When you are in light air, you want to maximize the power generated by the sails. Easing those two controls will give the sail a deeper draft, which is a more powerful shape, and will help drive the boat in light air.

By comparison, when the wind is blowing hard, the sails will generate more power than you need, or can use efficiently, so you should put more tension on the halliard and outhaul, to make the sail shape flatter, and reduce it's power.

The bottom line is that you should apply the amount of halliard tension that is right for the amount of wind on any given day.

The same principles apply generally to the amount of tension that you should use when raising the jib.

Within reason, you don't need to worry about damaging the sails by overtensioning them. Sails are very strongly made and reinforced, and they can tolerate a lot of tension, but they can be damaged if you grossly overtension them, so don't use all your strength and your body weight to tension them. Ordinarily, it shouldn't be necessary.

That sail is a North, full batten mainsail, and, when new, it was an excellent sail. It's hard to say, from photos, how bad it is now, but IMO it's probably still a lot better sail than many of the discount sails on the market. I'd suggest you not replace it for now. If you buy a good quality new sail, you'll begin to wear it out before you have learned how to make the best use of it. I'd suggest you learn the basics of sail trim and practice them on the old sail. There will come a time when you'll look at your sail and can see that it needs a better shape, but you can't achieve that shape through sail trimming techniques. When you are that knowledgeable about sail trim, that will be the time you should think about buying a new sail. I'll guess that you'll reach that stage after about a year of practice.

 

By the way, I notice that your reef lines haven't been affixed to the sail. Some day, soon, you'll be out there sailing, and the wind will pipe up, and you'll begin having enormous difficulty controlling the boat, and you'll suddenly realize that your reefing lines are down below, in a drawer somewhere, instead of affixed to the sail. Do yourself a favor and rig your reef lines now, and learn how to tuck in a reef, so you'll avoid the hard lesson that many of us had to learn.

 

I agree with Sailormon6. It is very difficult attach the reef the first reef linewhen needed. Attaching the second reef lines is nearly impossible.

 

That's a good looking, rugged sail. It has heavy patches and the shape does not appear to be stretched out. Definitely have the reef lines on and ready but you probably knew that. You can judge the right tension by how your helm balance changes. It can make a tremendous difference. It's why I have left my wire halyard in place instead of replacing with rope. I have found that the tension should be as tight as you can make it before distorting the luff. Boltropes are sewn in under tension and at least that amount must be exerted for the sail to attain its correct shape. I just got finished resewing in a boltrope that came loose at the head. The sail (got it used) performed terribly last year when I tried it and I couldn't understand why because the sailcloth is like new. I didn't notice the unsewn boltrope until recutting and making the sail smaller this winter when I restretched the boltrop back to its original position (and then some). That sail is an import, nicely made, triple stitched, but they end their heavy hand thread with burned globs instead of spending the time to knot off and bury the ends properly. The ends break or pull through and unravel after a while.

 

That sail looks like it still has some life left! My North main is older than that, and it still does the job.

With regards to how much tension to put on it, don't be afraid to crank it on fairly hard. Old dacron is pretty stretchy. Clearly your biggest problem was having it sheeted on while hoisting, but the initial reaction that your luff rope has also shrunken may also be true.

To best analyze the shape of the sail, you should take a photo looking from below the boom up. That will allow you to see what kind of foil you are creating. Take the pictures while you are sailing upwind in moderate breeze rather than at the dock. The shape of your sail will be very different when it gets loaded up. Only then will you know if the sail is really bagged.

Even if your sail is a bit tired, a good sailmaker can work wonders to extend the life and improve the shape of the sail, especially with a nice easy cross cut sail like that one. (as long as the cloth is still stable)

 

With no Cunningham, the main halyard is your only way to control draft position. (the point along the sail from luff to leech where the sail is at its deepest).
In any wind strength is should be about 45% back from the leeding edge of the sail. This means that as the wind increases, (and tries to push the draft position aft) the main halyard will need to be tensioned to pull draft position forward to the 45% point.
Use this to determine halyard tension.
sam

 

Looking good.
Your boom is at about 90° to the mast ... indicating a correct 'raise' with good luff tension.

Now get a full set to tell tales on those sails sou you can *see* the result of the sail SHAPING (how to assay the tell tales: ArvelGentry.com -->magazine articles ---> Checking Trim on the Wind, November 1973 ---> Achieving Proper Balance, December 1973 --->Sailing to Windward, January 1974 ---> Are You at Optimum Trim?, March 1974).

For 'better' sail shaping: in 'light winds' set LOW batten compression so that the battens are yielding a FLAT shape to the sail ... in 'light' winds you want FLAT sails
Medium winds: MORE batten compression and drafted-up shape
Generally the 'helm pressure' (so called weather helm) will dictate how much or how little the luff needs to be tensioned. When on a hard beat, If too much helm pressure - MORE halyard/cunning tension; If neutral or lee helm then less halyard/cunningham tension.

How much 'draft'? set the outhaul based on the reading output of the speedo and/or by watching the middle/midcord tell tale on the main, you want the midcord tale to be flowing 'straight back' or occasionally flicking 'up' and the weather side tale to be flying straight back or flicking up occasionally .... set the outhaul tension to get the correct amount of draft (every day is different!!!). Adjust the outhaul while watching the speedo!!!!
Light winds LESS draft, moderate winds flat water LESS draft, moderate winds w/large waves MORE draft.

 

Round sails for light air, flatter for more. Batten tensioning stuff is a PITA. Newport, agreed, your main looks much better. It's a bit tired for sure, but it'll work well for now. Do make the small investment in line and hardware for a cunningham. Lead the line back to the cockpit so it's somewhere near the main trimmer's reach. You can also split the vang lead and run it to both sides of the cockpit if you don't want to run back and forth to the mast. Oh, nice website as well! Is that your html handy work?

 

Round sails for light air, flatter for more.

If you want to use your engine instead of sailing in light winds, carry a full draft and 'round them up' ..... and enjoy the 'separation stalls' that occur because the light winds dont have sufficient energy to stay 'attached'.

Flat sails for 'speed sailing' in flat water, full draft for sailing in 'lumpy' water or when in waves.

 

There is an eye in your sail about 1 foot above where the foot of the sail attaches to the boom. Correct me if I am wrong, but I think this is where your cunningham would attach, with the other end lower on the mast (maybe at the vang connection point).

Your cunningham could be just a simple block and tackel (maybe $50 worth of parts). I find the cunningham requires much less force to tension the main sail than if I were to use the main halyard.

 

Is it just me or are the two middle battens over tightened? The upper and lower ones look about right for the amount of tension on halyard and outhaul, but the middle two… Do you guys in light air venues normally put in that much compression on your battens to develop that deep of a camber? If it were up to me, I’d ease up on the Velcro on those two pockets. I’m thinking that the #2 batten probably still has some bow to it even when the sail is flaked on the boom.

 

I race on the Chesapeake which is notorious for light and flukey air. Ditto used to race/campaign scow classes in mostly the light and flukeys. In all racing and prep we kept volumes of documentation of sail shape as well as set, etc. vs. the speedo - an empirical approach to maximizing, not guesswork.

My base 'vocation' is fluid and thermal sciences. Separation stalls are the bane of light wind sailing .... too big sails and too 'rounded' sails are anathema to light winds - invisible flow separation stalls; its all in the aerodynamics of 'flow attachment'. Aerodynamics is one science that you cant use intuition and logic or youll always be mid-pack and back in the fleet. All the crap you learned about 'wings' in US high school science classes is DEAD WRONG, been that way since the Wright Brothers proved it so.
Fluid viscosity predominates over 'Bernoulli'.

AS an avid amateur sailmaker, a light wind genoa has more roundness in the shoulder/top, not the lower panels for SPEED sailing in light winds. The full drafted drifters are an aero-inefficient abandoned design from the days of DDW racing of the 50s/60s before folks learned to tack downwind to keep the AWA and VMG at a maximum.

 

That all makes sense and isn't that out of line with what I'm thinking... Just another inter webs 'a picture's worth a couple hundred posts. I think I was misunderstanding the degree of looseness / tightness in the discussion, and the all important 'where' in the sail 'shape' is happening in light air.

 

I'm with RichH on this one. While it is true that you don't want your sails board-flat in light wind, you don't want them very full either. The fuller the sail is, the more drag it will produce.

In light wind another important aspect comes into play; sail twist. In light conditions there is significant wind shear. The wind angle and velocity is quite different at the top of the mast from what it is at deck level. As a result the top of the sail needs to be "eased out" or twisted off more than the lower sail. this is accomplished by easing the sheet and pulling the traveller more to weather. Most race boats are also equipped with vangs that are capable of lifting the weight of the boom so that it doesn't stall the top of the sail by putting too much leech tension on the sail with it's weight.

You must also keep in mind that high level racing sailors use sails that are extremely flat compared to the average cruiser sails. The term baggy is not in their vocabulary, except for the thing that holds their lunch!

 

I'm with RichH on this one. While it is true that you don't want your sails board-flat in light wind, you don't want them very full either. The fuller the sail is, the more drag it will produce.

In light wind another important aspect comes into play; sail twist. In light conditions there is significant wind shear. The wind angle and velocity is quite different at the top of the mast from what it is at deck level. As a result the top of the sail needs to be "eased out" or twisted off more than the lower sail. this is accomplished by easing the sheet and pulling the traveller more to weather. Most race boats are also equipped with vangs that are capable of lifting the weight of the boom so that it doesn't stall the top of the sail by putting too much leech tension on the sail with it's weight.

You must also keep in mind that high level racing sailors use sails that are extremely flat compared to the average cruiser sails. The term baggy is not in their vocabulary, except for the thing that holds their lunch!

Yes, this was what I was assuming, and yes, relatively speaking our sails are flatter or can be flattened more than most cruisers we see. It's all relative and again, I think we were all making assumptions... I'm sure Rich was thinking that we were completely bagging things, and I was assuming he was strapping everything down hard and tight with no twist. Interwebz communication breakdown. I' guessing that if we were on the same boat, we'd be pretty much in agreement about trim.

 

Main looks properly raised. Sail looks in reasonable shape. You may be able to get a couple more seasons out of it, and be QUITE happy with it. If you don't like the look of it (where it seems perfectly functional), try sailcare. They'll make it look as good as it works. Plus they can give you an idea if there is too much stretch in the boltrope which is possible.

I'll also second that a "make-shift" cunningham is a helpful tool to adjust luff tension for your main on the fly. On my ratty ole boat, it's the pink line in this picture. It goes from the bottom of the mast ring on the port side, up to the luff first cringle and through, down to the cheekblock on the boom, and back to the clam cleat on the boom. It helps me tighten tension on the luff on the fly as weather conditions change. It's within reach of the jib trimmer.

 

Main looks properly raised. Sail looks in reasonable shape. You may be able to get a couple more seasons out of it, and be QUITE happy with it. If you don't like the look of it (where it seems perfectly functional), try sailcare. They'll make it look as good as it works. Plus they can give you an idea if there is too much stretch in the boltrope which is possible.

I'll also second that a "make-shift" cunningham is a helpful tool to adjust luff tension for your main on the fly. On my ratty ole boat, it's the pink line in this picture. It goes from the bottom of the mast ring on the port side, up to the luff first cringle and through, down to the cheekblock on the boom, and back to the clam cleat on the boom. It helps me tighten tension on the luff on the fly as weather conditions change. It's within reach of the jib trimmer.

SHNOOL is correct but Ill add an 'amplification'. Due to friction in the mast slot vs. slugs, etc. or in the sleeve that the boltrope is contained ... the halyard primarily (after the sail is 'properly' raised) adjusts the fore/aft location of draft in the upper sections of the sail; the cunningham (again due to 'friction) will better adjust the fore/aft position of draft in the lower panels.
And again due to friction it takes time for the boltrope sleeve and/or slugs in the mast track to 'equilibrate' to their 'final' position ... so for precision you really cant make a single adjustment when setting draft position, two or more especially if the friction is high.
For precision, when setting fore/aft draft position when racing, before the start its best to go to the eye of the wind or short tack a few times in succession to help the slugs and boltrope 'equilibrate' to their final positions.

 

This may afford some answer ....
cruising sails are cut with 'rounded' luff sections which enables an inattentive 'cruiser' to 'wander' over a quite broad angle of attack without luffing (stagnation stalls) or without separation stalls.

A 'racing cut' sail is usually made with a relatively flat non-rounded luff entry with very narrow range of 'wander' and requires constant & precise helmsmanship.

The luff 'entry' shape would be the curve or roundness that is designed/shaped into the luff and back to about 12-15% of the sail's cord length. The luff entry is where the highest 'suction peak' (developed force) occurs along the leeside of a sail, the flatter the entry the greater potential for the all important 'boundary layer' (flow) will stay 'attached'; when the air flow doesnt have enough energy to stay attached, the boundary layer 'bursts' and you get a 'separation stall'. The more 'roundness' to the luff entry the more 'work' or more energy is required to keep that luff zone boundary layer attached .... air flow doesnt like to turn 'corners' and if not enough energy in the wind you get an invisible separation stall and the sail essentially stops 'working'.

As stated or implied previously the airflow on the leeside does not 'speed up' to get to the leech rather because of the 'upwash' in front of the sail delivers 'MORE' air to the leeside, a sail is a wing with essentially zero 'thickness' .... and the air does 'work' against the sail only because the air has viscosity (fluid friction). Air at atmospheric pressure that is not contained or 'ducted' is essentially or considered to be incompressible ... and the highschool and almost all 'sailing books' model of the leeside having faster flow because the air somehow 'speeds up' is wrong and has been wrong since the Wright Brothers discovered it to be otherwise.

Light air sailing absolutely requires a flatter, less drafted sail than a sail at 8-10kts, etc. .... or you will most always have a very destructive separation stall on the leeside --- racers apply 'tell tales' to ensure to SEE that the leeside of the sail has 'attached' flow.

 

essentially or considered to be incompressible ... and the highschool and almost all 'sailing books' model of the leeside having faster flow because the air somehow 'speeds up' is wrong and has been wrong since the Wright Brothers discovered it to be otherwise.

Light air sailing absolutely requires a flatter, less drafted sail than a sail at 8-10kts, etc. .... or you will most always have a very destructive separation stall on the leeside --- racers apply 'tell tales' to ensure to SEE that the leeside of the sail has 'attached' flow.

not sure I understand what you mean by the air does not speed up. the air on the lee side of the sail does increase in velocity relative to the surface as the air is compressed due to the curve in the sail ( one half of a venturi), more air going thru a given space equals higher velocity air on the surface of the sail, thus the lower pressure on the lee side of the sail. The 'MORE' air on the lee side is what makes the air speed up relative to the sails surface. Thats what makes the boat move since long before Mr. Bernoulli not the Wright brothers decovered why. What is it that you and the Wright brothers discovered? all the sailing books are wrong?

 

What the Wright Brothers discovered, in their wind tunnel experiments and by using 'empirical methods / data collection of 'observeables', is the "circulation flow" around sails/wings where the vectorial sum of the flow has the flow on the leeside going towards the 'stern' (and creating a (starting) vortex just behind the trailing edge), while the sum vectorial flow on the windward side is 'going forward'. The Wright brothers experiments had the wing fixed in place and therefore didnt have to subtract the forward velocity of the wing and the flow on the 'windward' side was always (relative to the leeside) 'forward' when at aerodynamic functioning angles of attack - circulating flow. It not the leeside 'speeding up', its the weatherside having a components that going forward, and that causes the 'difference' of relative speed (Bernoulli).

This is easy to verify on sailboat even with relativistic flows of 'apparent wind'. If you have a handheld anemometer/wind instrument measure the flow velocity on the leeside vs. the windward side ... and then SUBTRACT boat speed from each side.
With the boatspeed subtracted the resultant relative flow measurement you will have will be the windwards side always a NEGATIVE vector due to the (relative & measured) forward flow on the windward side ... this means that the overall net sum flow is 'circulating' about the sail from an 'absolute' or nonrelativistic basis ...... ie. when on a starboard tack and sailing in aerodynamic mode, the circulation flow is 'counterclockwise', clockwise when on port tack.

This is observed many times when using tell tales on a 'perfectly' shaped and trimmed sail ... when the middle/mid-cord windward tell tale is seen to be sometimes be observed to pointing FORWARD at max. sail and max. boatspeed 'output'.
Commonly this can also be seen without tell tales when the 'slot' is too narrow and the mainsail is 'backwinding' (a bad term but in common usage) ... if you measure the flow during the 'backwinding' you will find the flow going forward, when you subtract the boatspeed from the results = circulation flow.

Ed. - a Sail is not the exact same as wing; or rather, a sail is a wing with (essentially) NO thickness. You can have lift even with a thin flat plate.

;-)

 

What the Wright Brothers discovered, in their wind tunnel experiments and by using 'empirical methods / data collection of 'observeables', is the "circulation flow" around sails/wings where the vectorial sum of the flow has the flow on the leeside going towards the 'stern' (and creating a (starting) vortex just behind the trailing edge), while the sum vectorial flow on the windward side is 'going forward'. The Wright brothers experiments had the wing fixed in place and therefore didnt have to subtract the forward velocity of the wing and the flow on the 'windward' side was always (relative to the leeside) 'forward' when at aerodynamic functioning angles of attack - circulating flow. It not the leeside 'speeding up', its the weatherside having a components that going forward, and that causes the 'difference' of relative speed (Bernoulli).

This is easy to verify on sailboat even with relativistic flows of 'apparent wind'. If you have a handheld anemometer/wind instrument measure the flow velocity on the leeside vs. the windward side ... and then SUBTRACT boat speed from each side.
With the boatspeed subtracted the resultant relative flow measurement you will have will be the windwards side always a NEGATIVE vector due to the (relative & measured) forward flow on the windward side ... this means that the overall net sum flow is 'circulating' about the sail from an 'absolute' or nonrelativistic basis ...... ie. when on a starboard tack and sailing in aerodynamic mode, the circulation flow is 'counterclockwise', clockwise when on port tack.

This is observed many times when using tell tales on a 'perfectly' shaped and trimmed sail ... when the middle/mid-cord windward tell tale is seen to be sometimes be observed to pointing FORWARD at max. sail and max. boatspeed 'output'.
Commonly this can also be seen without tell tales when the 'slot' is too narrow and the mainsail is 'backwinding' (a bad term but in common usage) ... if you measure the flow during the 'backwinding' you will find the flow going forward, when you subtract the boatspeed from the results = circulation flow.

Ed. - a Sail is not the exact same as wing; or rather, a sail is a wing with NO thickness. You can have lift even with a flat plate.

;-)

I have heard about this circulation flow you speak of. I need to do some more reading. Here is a link:
circulation flow around a wing - Bing Images

This sailing thing is more complicated than if looks,
Regards

 

Ok, I am an EE, and my head hurts... I hated fluid dynamics... and I hope I am not the only one who is confused with the above.

I totally am ALL OVER trying to understand Rich... but here's what I was taught, and it's probably wrong (as much of what I've learned could be)...

I thought "Baggy for light winds" tighter for heavy. Watch your tell-tales on the sail port and starboard for "flow," get them streaming aft and the trim is good. Assuming you still have them attached.

Halyard hard to bring the sail strong against the top of the mast (or as high up as it'll go if the boom is fixed). Then VANG on, for beating upwind, and on hard for heavier winds. These were a simplification of course, but simple I can remember. The vang was to keep the boom parallel off the wind as well.

AGAIN I AM NO RACER, so Rich has peaked my interest. My baggy old main (is not as nice as Newports) but my personal experience is halyard medium tight... cunningham on but not firm in light air (take out most but not all crinkles). As it picks up, halyard on hard, cunningham on harder as it picks up take out all crinkles, maybe start to induce some vertical crinkles with the cunningham. Boom Vang goes in conjunction with both. The objective is to keep the boom parallel to the water. Between the halyard the vang, the outhaul, and frankly the leech adjustment (if you have one), or in my case the "Flattening reef" you "shape" the sail and move the draft, depending on conditions.

AGAIN SOMEONE CORRECT ME ON ANY OF THIS.

 

EEs are the same as MEs and CE and ChemEs, etc. were all applied physicists when you boil it all down to 'energy'.

Summary,
the more rounded or full drafted a sail when operating in 'low energy' / ligt winds the more propensity for the flow to separate from the sail. The less 'curve' to the sail the less energy needed to stay attached. Rounded full draft shapes are for accelerating / power; Flat sail are for speed. If you need to accelerate in light winds you 'can' change the curvature; but, its just plain easier to 'bear off' to accelerate.

The function of the halyard (other than the simplistic function of raising the sail) is to correctly position where along the cord of the sail that point of maximum draft occurs - helm balance !!!!!!!! The amount of draft is controlled by the outhaul.
A dacron sail usually has a boltrope with predictable stretch and the sail AS DESIGNED shape will not ever be reached until that 'preload' that the sailmaker purposely cut 'short' is stretched out to the DESIGNED length ... usually about 1" additional 'stretch' for every 10-11ft. of luff length ..... THEN additional stretch or relaxation via the halyard (and cunningham) so that the boat has 'very little' weather helm (not dragging its rudder through the water slightly 'sideways')

A well set up boat is not only 'faster', it also is *safer* because its not as subject to sudden power-ups and crossed sail controls/shape, and wont aggressively HEEL as much and can 'point' higher (and with less heeling) etc. etc.

Raising a dacron mainssail requires more than just raising up the mast; if you just raise it and forget to Shape it by MORE /required halyard tension you will inevitably wind up with baggy/deplorable shape (cranky & SLOW sail).... even a brand NEW boltroped dacron mainsail. EVERY DAYs conditions are different and every day the halyard tension is 'different'.
Repeat: How to properly RAISE a woven dacron mainsail - SailboatOwners.com ... also explains 'old' sails w/r to shrinking boltropes, how to check and what to do.

hope this helps.

 

wind gradient = difference in speed from the bottom of the mast to the top
wind shear = difference in angle from the bottom of the mast to the top.

Two separate things, but yes, they're more present in light air sailing. Really light air, you want flatter shapes to keep the flow attached. And due to gradient, more twist will help keep the top from stalling. As the breeze builds, you can power up the boat, remove twist, and start pointing again.

 

wind gradient = difference in speed from the bottom of the mast to the top
wind shear = difference in angle from the bottom of the mast to the top.

Two separate things, but yes, they're more present in light air sailing. Really light air, you want flatter shapes to keep the flow attached. And due to gradient, more twist will help keep the top from stalling. As the breeze builds, you can power up the boat, remove twist, and start pointing again.

Yes the Wright Brothers are in agreement with you and RichH (Baggy sails no good):
From wikipedia:

"With this knowledge, and a more accurate Smeaton number, the Wrights designed their 1902 glider. Using another crucial discovery from the wind tunnel, they made the airfoil flatter, reducing the camber (the depth of the wing's curvature divided by its chord). The 1901 wings had significantly greater curvature, a highly inefficient feature the Wrights copied directly from Lilienthal. Fully confident in their new wind tunnel results, the Wrights discarded Lilienthal's data, now basing their designs on their own calculations."

 

LOL!

Holy crap do engineers ever know how to over complicate things!

All you really need to know is that air flowing smoothly across a sail, laminar flow, creates the lift. Turbulent air across the sail, as you get when a sail is stalled, creates far less lift. Turbulence is drag. The essence of why we use telltales on the sails is to show us if we have laminar flow or turbulence.

On my last race boat my two most trusted controls were the traveler and the backstay. Once I had the desired foil shape I could change the angle of attack with the traveler. If I wanted to depower I could flatten the main and twist off the roach with one yank of the backstay. I used it constantly in light air. As I accelerated and the apparent wind increased I would flatten the sail, allowing me to point better and go faster. If I encountered wake I would ease backstay to power through the waves. Obviously there was a bit more going on in terms of adjustments but in a nutshell, draft depth was my gear shift.

I would ask that everyone stop using the term "baggy"! Baggy has no place in sail trim!

With regards to the boom vang, I do not consider it to be an upwind tool at all. I uses sheet tension to maintain the desired twist, and the traveller to adjust the angle of attack. The vang is intended to maintain twist when you are sailing off the wind, and the traveller is at the end of its travel. Then the vang becomes the leetch tensioning tool, and the sheet becomes the angle control. (Of course if your boat doesnt have a traveller, you must use the vang all the time!) the angle of the boom relative to the water is not really relevant, the important reference is the twist.

How do you know if the twist is right? You put telltales on the leetch of the sail near each batten pocket.(careful they arent too close or they might get atuck on the velcro.) Your goal is to have the teltales streaming aft. The top one is the most important. Keeping the boom on centerline, ease the sheet until it is streaming, then tighten it until the teltale flickers a bit. Ideally the top should be streaming 50% of the time. A main trimmer should always pay attention to that little piece of yarn!

 

LOL!

Holy crap do engineers ever know how to over complicate things!

All you really need to know is that air flowing smoothly across a sail, laminar flow, creates the lift. Turbulent air across the sail, as you get when a sail is stalled, creates far less lift. Turbulence is drag. The essence of why we use telltales on the sails is to show us if we have laminar flow or turbulence.
On !

First LOL when people knock engineers. From Nova:
NOVA | The Unlikely Inventors

"Engineers build things. They build machines, they build bridges, they build buildings, they build systems. Their task is to design and build something that's going to work. That means that they're sometimes less concerned with uncovering absolute truth. They're gathering data that's going to help them to build more efficiently this thing that they're building, whether it's an automobile, a bridge, or whatever."

What do you think this world needs more of: politicians, lawyers, stock traders, bankers, sports figures or engineers?

And laminar flow does not necessarily mean less drag. Try to figure out why a golf ball has dimples, why does a piture rough up a baseball? Flow separation leads to drag, laminar flow actually has more drag than turbulent flow (flow in pipes is turbulant for good reason- lower pumping cost). BTW, you will never have laminar flow across your sail- wind velocity is way to high and sail too rough, the flow will always be turbulent. You are confusing turbulent flow with flow separation- totally different things. If you do not want to deal with these problems, then thank an engineer.