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Windseeker
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Discussion Starter · #1 ·
While I'm posting this with a specific case it would be interesting to see pictures of different sail trim issues and resolutions.

I've put two mainsail pictures below. One a race sail from the North Sails tuning guide for my boat, the other a performance cruising sail on my boat. I took the picture on my boat as I just started looking at rig tune and loosened everything up. At the point the picture was taken we hadn't tried to trim but the boat was sailing fairly nicely in light (~4 knots?) winds. The North Sail's photo is described as being well setup for light-medium winds so I'd guess about 8-10 knots - which happens to be the wind range Kraken is tuned for.

There are some obvious differences - but rather than trying to lead your eyes with what I see I'd be interested in peoples commentary on what they see wrong and how they would approach fixing it through trim or rig tuning.



 

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Windseeker
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Discussion Starter · #2 ·
I thought more people would bite on this...

The image size might not help - do I have to presize the images or can I rescale in the posting? They are here on blogspot, easier to compare.

My sail has way more twist than the NS reference and is deeper off center-line (see backstay for comparison). Is the depth a little more aft? I slacked the halyard further in that sail as the TWS dropped to a couple of knots.

I you looked up and saw my sail, and were sailing upwind in 2-3 knots of wind and a very gentle two foot swell, what steps would you take to try and improve speed?
 

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White sail has nice clean telltale flow off the leach. Maybe could be trimmed in a little more, or moved up more on the traveler in order to point higher, but I can't say without 'being there'.

Dark sail looks to me to be trimmed down too hard (closed leech) and too close to centerline. The windflow would seem to be kind of "strangled" with the draft that far aft and that little twist in the sail. But again, I don't know what kind of boat we are on so cannot be sure, but this is just my impression based on the photos only.
 

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Windseeker
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Discussion Starter · #5 ·
I guess you need to pre-size images? They look much better on the mobile version of the site as that manages size for you!

The boat is a Beneteau 36.7

What about draft depth and position? Would people push for more draft or less, move it further aft or forwards? In this case we're in ~4 knots of breeze - at what point do you start flattening the sail again to keep flow attached?

That NS sail does look closed off and those tell tales are wrapping back behind the sail a little - I suspect they pulled the traveller right up to fill the sail for the photo - perhaps they were even sitting in a slip....
 

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Quirky
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Paging RichH.... RichH, would you please pick up the red phone....
 

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Q? - What are you attempting to do here? what sea state conditions are you setting up for?

My observations (assuming the 7367 boat is being sailed in light to light-moderate chop):
7367 is of better 'shape' than the NS, although the upper leech section is seemingly 'twisted-off'/open due to a relatively 'light' mainsheet tension.
The NS has obvious high mainsheet tension as seen by that closed-up leech - probably done to enhance the view of the curvature/draft. The one 'real' tell-tale at the leech is being 'sucked' to leeward
Look at the comparisons of both sails to their backstay for comparison purposes. More/deeper draft well aloft in the top panels equates to power aloft, flatter and less draft aloft equates to SPEED. The balance point is max. speed out of the boat and despite differing angles of heel between the two - IMO.

Characteristics of shape (each) details:
7367 has a rounded luff entry - the area from the luff to the point at which the maximum draft occurs. Will be 'more forgiving' for the helmsman to 'follow' and probably a better performer than the NS when sailing into moderate chop. A more 'power-shape' than the 'speed shape' of the NS with its relatively FLAT 'luff entry' shape.
The full batten compression in the 7367 seems more consistently even, batten to batten, as the point of max. draft seems more consistently forward (in% back from the luff) than the NS. It could be that the battens in 7367 are at better/more 'tapered' or of lighter weight/stiffness and are operating at higher end-to-end compression ... to get that rounded luff entry.
The NS battens appear stiffer and at less compression - a FAST shape for FLAT water in light winds (and in the higher wind ranges, too). The 7367 is going to be more vulnerable to separation stalls AT the luff in very light winds.
The hooked up leech on the NS will cause relatively more heel (slower). The open leech of 7367 will allow a better 'footing off'.

The flat luff entry shape of the NS will require the helmsman to be always 'on' as the range of the angle of attack of the NS sail will be considerably narrower than the 7367

I see no mast pre-bend in the 7367 ... but such seems OK as the point of maximum draft seems consistent all the way down at each panel. The NS mast seems to have a slight pre-bow ... probably resulting/contributing to that more flattish overall shape. Put a straight edge across both masts in the pic, although the different view angle is 'difficult' to discern between the two. The NS has less halyard tension - definitely set up for 'light' to 'very light' winds; 7367 is set up for moderate chop.

The differences between the two:
7367.
lighter weight and tapered battens with 'heavier' batten compression. Tripped/open leech, heavy halyard tension, draft forward, .... will probably beat the pants off of the NS in moderate chop but wont 'point' as well (maybe).

NS.
stiffer and (probably) non tapered battens with less batten compression. Tight/closed (slightly hooked up) leech, light halyard tension, more draft aft than 7367. If that leech is allowed to be more open, will scream at very light wind strength and FLAT water ... and @ higher wind strengths, too.

Rx: The main difference I see here is batten stiffness, tapered battens, halyard tensions .... and of course mainsheet tensions contributing to those leech shapes.



FWIW - There is always 'controversy' about how much batten compression and taper up high ... and it really depends on how much crew / weight is being carried and if one 'dials in' more power (draft) in the uppermost panels ('shoulder') vs. how much 'flatness' is carried aloft by a boat with less crew/weight. Best way to adjust for this is batten stiffness, compression aloft and of course 'taper'. If youre settiing up and once your tell-tales are all flying perfectly, the speedo (or well documented history) in such conditions vs. speedo) will decide for the days sea-state and winds vs. batten adjustment You can trim and shape all you want, but once you arrive at what seems to be 'best' trim and shape, the ultimate 'decider' is the SPEEDO (or VMG) when tweaking the 'final adjustments'.

FWIW - if I were racing against 7367 Id attempt to force you into a moderate leg length tacking duel as my NS flattish luff entry will be better at pointing and with slightly higher speed, although Id have to 'drop down' to accelerate out of a tack.
If racing against the NS I'd 'short tack' him to death ... he's not going to accelerate as well as me with the 7367 with the more rounded luff shape for better acceleration out of a tack. Id also have the advantage going into a tack, as with that already slightly more forward draft if I be able to better 'put down the flaps' by radically closing that leach (hooking it up to weather). Id also better be able to 'power pinch' to the layline than the NS with the more 'flattish' luff entry - maybe for BIG gains because my 'next leg' might be a few fractional boat-lengths ... shorter.

Is this what you wanted? ;-)
 

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Windseeker
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Discussion Starter · #8 ·
That was perfect - thanks!

Q1. Would you ever push for more depth in the sail than seen in 7367?
Q2. What's the best way to approach avoiding airflow delamination in super light winds?

What I'm attempting to do is improve my ability to race in light winds.

In this case we're talking super light winds (2-5knots) and a smooth rolling sea, say about 2-3 feet base swell level at a 14second period. This is quite common where I sail and conditions in which I've struggled - so am trying to improve.

You opened up a whole new can of worms with batten taper, makes complete sense but a step beyond the level I've been thinking about until recently.

There is a little bit of mast bend on 7367, I'll get a photo of it. I've reduced it a lot in the last few weeks and am contemplating more, but will race on current settings first.

My main aim at the moment is to get my on the run tuning - the backstay, mainsheet, outhaul, cunningham and halyards as effective for the conditions as possible. Until recently I've had my rig way too tight on the outer shrouds and at the same time loose on the inners, this is the way a rigger set it up a year ago. So pretty flat shape and (I think) mast middle sag in higher winds leading to overpowering. Now I've kept the inners loose and loosened up the outers - aiming too reduce mast bend and continue to allow it to sag in the belly. If stronger winds seem likely for a race I will tighten up, but this time pay attention to my inner shrouds to to try and reduce the belly sag.

So hopefully with the current setup I can get lots of depth for acceleration and can use the backstay to flatten out (both main and genoa) and gain more speed once we're moving. Experimentation to be done!!!
 

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My recommendations would be to thoroughly profile each sail by recording their 'output' versus: BOAT SPEED (VMG), vs. (apparent/true) angle sailed TO the wind, vs winds / seastate (wave height/wave period), vs, RELATIVE humidty and wind temperature, vs OUTHAUL tension (Most important when developing a sailing optimization profile - more below), etc. Once such a 'data set' is established, you can easily 'dial in' the previous settings for basic shape and trim to arrive at your 'starting point' for then
tweaking for maximum sail 'output' for the current conditions of wind speed and seastate.
Id recommend that you add 'measuring tapes' to boom, halyard positions, traveller etc. so you have a visible measurable indicator to record and return to when those wind/wave conditions are again the same.

Id recommend the installation of a FULL set of tell tales + steering tales and then follow the 'set up' of sail shaping as found in:
Index of /Publications/Arvel Gentry Articles and then following the serialized articles --->
08_Checking_Trim_on_the_Wind.pdf
09_Achieving_Proper_Balance.pdf
10_Sailing_to_Windward.pdf
11_Are_You_at_Optimum_Trim.pdf
plus ...
(12_What_Goes_Around_Comes_Around.pdf)

#12 is a more scientific explanation of how sails/wings, etc. REALLY work; and, not the 'obsolete - since the time of the Wright Brothers' erroneous stuff that is offered in US 'highschools', sailing books, and even flying schools. If you have a foundational grasp of 'circulational flow' you will sometimes SEE that effect when using a FULL set of tell tales - windward tales pointing 'forward' when your trim/shape are near 'perfect'.

In one of those above listed articles will be found the use of 'barber haulers' - VITAL in correctly adjusting the all important optimization of 'slot distance' between jib & main - smaller slot distance in light winds and more open in heavy winds.

Developing such a 'campaign profile' will be composed and based on 3 elements:
1. Max. developed boat speed (SPEEDO output) due to set/shape/and trim to 'match' the days wind/seastate conditions.
2. Boat prep - smoothness/'fairness' off and 'cleanliness' of the boat boitorsttom, etc.
3. Tactics ... so that yuore always sailing in the correct direction at the highest possible speed and are legally interfering with your better competitors while preventing/blocking gains from 'not-so-good' competitors.

Other articles that may be of benefit:
helm balance and its optimization: How to properly RAISE a woven dacron mainsail - SailboatOwners.com . get used to watching the turbulence wake from you rudder when you encounter so-called weather helm' as it may NOT be 'weather helm' but a SKID off to leeward.. and ONLY that turbulence angle coming off the stern will show this SKID. (Skidding is usually the result of improper forestay tension or improper jib sheet tension.)
proper/optimized rig/wire tensions for headsails/jibs/genoas: http://www.ftp.tognews.com/GoogleFiles/Matching Luff Hollow.pdf

VERY IMPORTANT ---- Also remember or be aware that what controls the speed/power ratio of sail output when in varying seastates (high gear or low gear) is adjusted by the outhaul. Once trimmed/shaped to perfection, then readjust the outhaul to set the correct amount of draft to arrive at the OPTIMUM amount of sail draft ... as indicated by the maximum value on the speedo (or VMG). If you simply 'guess' on outhaul tension, youll not consistently place 'high' in the racing tally results - use your SPEEDO as the final observation for any setting of sail shape or trim. Setting the optimum draft via outhaul while watching your speedo (in less than survival conditions) will more consistently get you to the front of the pack ... such automatic adjusts and compensates for flat water or heavy chop and all in between. Ultimately youll want that outhaul into the cockpit and at a mechanical advantage of 6:1 or higher!!!!! so that you WILL be adjusting it constantly as the wind/wave conditions change --- that outhaul is really your speed/power control !!!!!!!!
Flat sails for speed sailing in FLAT water; full drafted sails (power) for sailing in waves .... even when 'reefed'.

Other: learn how to roll tack and also how to power-pinch (hooking the main's leech to windward by STRONG mainsheet tension when going INTO a tack) as in doing so your VMG will not be affected due to the trigonometry at the end of a leg but you will have LESS distance to sail on the 'NEXT' leg. Racing is a game of 'inches' and power-inching INTO a tack will/can save a lot of distance on the NEXT leg ... I used to power pinch into a tack from several boat lengths out, sometimes beginning from the last 5% distance of a leg (depending on wind strength or wave height)

Keep copious records of your practice trials, fully analyzed each race to see what you did WRONG and what steps can be improved - sail SHAPE / trim, tactics, etc.
Keep copious records and develop an 'empirical' profile all based on the accumulated
data so you more quickly develop your sailing 'instincts' and dont have to 'guess'.

Basic Tactics: "Sailing to WIN" by Buddy Melges (long out of print, so may be hard to find) Eg.: Starting a race on PORT TACK always gives you TWO options .... and really pizzes of a fleet when you roll-over them while on 'port' at a 'start'. Buddy is the all time master of the 'port tack start'.


There's a lot more, but this should get you 'started'.

hope this helps. ;-)
 

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I never gave you my opinion on your two questions ......
Q1. Would you ever push for more depth in the sail than seen in 7367?
Depends on the wind/wave conditions ... and the more important helm balance that results from the current shape that you induce in the sail via halyard, outhaul, etc. tensions .... all set obtain MAXIMUM boat speed.
Generally you want a FLAT and FLATISH luff entry shape for light to 'really light' winds - to retard the vulnerability of separation stalls (as visualized by tell tales) on the leeward side of sail(s) due to the low energy IN the light wind speeds. ditto, for 'depowering' when beyond the design wind speed of the sail ... and the boat is 'struggling' to overcome its so-called 'hull speed'. Flattish is always 'better' when sailing against little to no wave amplitude ... and depth of draft should be adjusted to gain maximum boat speed (notwithstanding 'survival' situations including fear of heeling).
Where you want MORE draft is for 'punching' into and through steep waves - a 'powered-up' (low gear) shape, .... but not as 'fast' (relatively) as when having a flattish shape when sailing in relatively FLAT water. Low gear vs. high gear. This includes when reefed - IMHO.

This included the 'roundness' of the luff entry as when in 'light to very light' winds as when the wind has low or little energy to stay 'attached' due to its 'turning the corner' at the leading edge / luff ..... less halyard tension will yield a more flattish luff entry shape (but will shift the dynamic CE further aft; hence, increased helm pressure. ... Ya gotta balance these forces out or suffer from dragging the rudder at a large deflection angle). MORE HALYARD TENSION will bring the dynamic CE more forward and also cause the luff to become 'more rounded' .... on most sails the highest 'suction peak' occurs 'right behind' the luff.


Q2. What's the best way to approach avoiding airflow delamination in super light winds?
Basics are to have the minimum amount of 'rounded luff entry shape' ... best way is to release halyard tension .... and move the crew well forward to conterbalance the need to re-rake the mast more forward OR if can rake-the-mast-while-on-the-fly do so .... all depending on the changes in 'helm pressure' and being able to sail (beat/point) with no more than about 3° of rudder deflection angle. This includes
A FULL set of tell tales at midcord and leeches + plus a full row of 'steering tales' will 'show' which way to either flatten down or draft up. Just be able to keep the leeside tell tales streaming straight back (and ignore the windward side until in 'stronger' wind flow or as the boat increases its speed and thereby artificially increases the apparent wind speed (making your own wind speed by gettin the boat 'faster') when above a beam reach, etc. .... usually requiring reduction of overall draft to do so and to keep those leeside tell tales flying. For max. output, slowly release/increase outhaul tension until you get max. speed (while concentrating on that the leeside tales should be flowing back) .... and then watch for the indicators of a start of separation stall at the leeside (drooping tell tale) then flatten a bit from there to insure that leeside flow is and remains 'attached' .... all the way from the luff ... back to the leeches (if possible). I like to also apply tell tales 'just behind' the luff as thats where usually separation stalls 'start' to occur, especially if the sail was 'cut' with a 'well rounded' and 'forgiving' luff entry as with a 'cruising cut'.

A flat luff entry requires a very precise helmsman to be constantly 'on' because the range of angles sailed will be much less than the 'range of angles possible' of a sail with a 'rounded' entry that is designed for inattentive cruising sailors. .... BUT if the boat is designed to PLANE then ONLY a rounded luff /draft forward shape is preferred due the sudden changes of apparent wind at those planing speeds.

;-)
 

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Windseeker
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Discussion Starter · #11 ·
Thanks RichH. I'll check those articles, I've probably read some of them before (perhaps you've posted some of them) but as I keep rereading material it keeps making more sense... just picked up "High Performance Sailing" by Frank Bethwaite which seems an interesting read already, biased to the smaller boat from what I've seen so far but really well written and seemingly solid information.

Here's a picture of my mast, 34 on my loos gauge (set to about 10 knots wind - we were overpowered with five on board above 10 knots and dumping the main a little, but not too much).



To my eye this appears quite straight low down but has some bend still up top.

With the rig in this setting the forestay is totally slack and slaps around without a tiny bit of backstay to put some pressure on it. Does that mean I need to shorten it or is that fine?

Hopefully going to be windy this weekend so I may get a chance to tighten up the rig and post some comparison pictures.
 

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Here's a picture of my mast, 34 on my loos gauge (set to about 10 knots wind - we were overpowered with five on board above 10 knots and dumping the main a little, but not too much).



To my eye this appears quite straight low down but has some bend still up top.

With the rig in this setting the forestay is totally slack and slaps around without a tiny bit of backstay to put some pressure on it. Does that mean I need to shorten it or is that fine?
With the forestay obviously loose or not at a typical 15% wire tension you'll not have correct sail shape in the jib/genoa. Sailmakers cut the leading edge shape 'expecting' that the forestay will be in the 12-15% tension range for sailing in winds of 10-15kts., more so above those windranges. Use the backstay to apply tension the forestay.
If the smooth curve that the sailmaker cut into the leading edges doesnt 'match' the expected sag in the forestay wire and that sag if excessive, you will heel over aggressively and the boat will tend to skid off to leewards with the helm mimicking 'weather helm' - difficulty in 'pointing' & 'cranky boat'.

Although your pre-bend (forward bowing) in the mast looks good. To verify - Here's probably the most comprehensive rig tuning guide available on the internet; and, includes proper tension set-up without the use a tension gage. The prime function of precise rig tuning is to provide a predictable 'platform' for the sails to operate and take their proper SHAPE. Sailmakers cut sails to these 'expected' shapes and tensions in the wire: http://www.riggingandsails.com/pdf/selden-tuning.pdf
 

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Windseeker
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Discussion Starter · #13 ·
The Selden guide seems mainly concerned with structural stability and a base setting, the North Sail's guide talks about mast bend - closing the slot down, etc and has more detail for my specific boat.

I'm getting used to the headstay tension, its not really loose at the dock just looser than it was. Downwind it flops about a bit and talking to other owners this is possibly an indication that we're getting closer to correct tuning. Most importantly we're more frequently getting our boat speed up. We blew off a 40.7 yesterday and easily held off some other 40+ foot boat that tried to roll us. A few months ago I wouldn't have even thought to try.

Finally dawned on me that I'm after a draft balance between the head sail (via sag control) and mainsail (via mast bend). What that means exactly in practice remains to be narrowed down.

That being said there is still a lot of room for improvement - which is good because we're not winning....

Those Gently articles you linked are awesome and echo much of what I'm getting from High Performance Sailing: Faster Racing Techniques: Frank Bethwaite: 9781408124918: Amazon.com: [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@514mi1xpfxL. It's going to take a long time to apply these ideas as part of day to day sailing.

I'm trying to document the important things learnt on the blog.

36.7
 
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