how to judge appropriate draft in very light winds?

Aug 2, 2010
440
J-Boat J/88 Cobourg
This is kind of related to my post before about judging the line between more power and less drag, but it seems different enough to ask separately.
In very light winds, 2-4 kts, I have been fairly successful adding some extra draft in the lower part of the main through easing the outhaul. It is almost impossible to judge by the speedo since the winds tend to be so variable in both velocity and direction at these levels so I want to have some guidance for the trimmer as we experiment. Is it fair to say that if the leech telltales are flying there has been no detachment? Conventional wisdom is to flatten the sails in the very light but my slippery boat just seems to die when I do so and lights up a bit when I make the main more full.
Ultimately I want the trimmers to make their own judgements using the various cues available to them including the speedo, but in this case I am hoping to give them the following: Ease halyard, ease backstay, and manage twist to minimum normal levels until the leech telltales start to fall and there is significant luffing at the luff of the main. The twist should be minimized until the upper leech telltale stalls all the time rather than up about 50% of the time.
Obviously the driver has to chase the wind direction and velocity to maintain speed and heel and all the above cues will vary moment to moment but we are trying to be a more proactive crew without killing the speed doing something strange in the middle of a struggling beat!
 
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Feb 21, 2013
3,777
Hunter 46 Point Richmond, CA
Ditto easing the halyard and backstay (just enough to take up the slack) and outhaul to add extra mainsail depth for power in light air. Some additional light air mainsail trim techniques..........easing the cunningham and boom vang also increases mainsail depth, pulling the traveler to windward and easing the mainsheet until the leech telltales stream together. You might find these articles on mainsail trimming in light, medium and heavy air Guidelines for Good Mainsail Shape (sailingbreezes.com) AND QuantumSails_TrimGuide_Mainsail.pdf.aspx and this one on mainsail leech telltale adjustment How to Sail Faster with Mainsail Leech Telltales (skippertips.com) helpful.
 
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May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
If a sailor can sail in light air they can sail in anything. The main sheet trimmer is responsible for the traveler, outhaul, halyard (or cunnigham) and boom vang. The jib trimmer can't be asleep. On a masthead rig, he's calling the shots and the main trimmer has to match his moves. On a fractional rig the jib trimmer has to match the main trimmer.

The following are my opinions and are general in nature and have to be tweaked to any particular boat plus they are not in any particular order.

The first thing I'd install are telltails on both sides of the middle of the mainsail. I also added telltails to the side stays which helped me stay "in the groove".

Keep the mast straight - forget the backstay. The traveler should be almost centered. There's a technique called "trim to a point of draw". The trimmer eases the sheet until the luff ripple and then trim in until the ripple just stop. Ease the main halyard slightly, which will move the draft position to about 50% to 55%. A cunningham is a better devise than the halyard and easier to deal with.

Ease the outhaul slightly. Here's the most important aspect to keep in your mind when sailing in light air. In light air the wind just doesn't have enough power to get around both sides of the sail and one side stalls. How many times have you seen boats trying to sail in light air with a lot of draft in the main mistakenly thinking they are grabbing as much of the little air available and going nowhere!! So you have to be ever watchful that the wind, whatever little there is, doesn't become detached.

if you have a vang release it - you want the boom to rise slightly. In light air you can cheat with the topping lift. If you have a leech line - tighten it because you don't want the leech fluttering.

Twist is a speed killer in any wind speed and deadly in light air- eliminate all twist..

What I've provided is contained in my SAIL TRIM CHART. Light wind is one thing but as the wind increases all the setting change accordingly and the SAIL TRIM CHART outlines the new adjustments for both the main and jib.
 
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May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
Danstanford: Sail SFBay made me think of something. I said release the vang but be careful when you do that because when you release the vang and fool with the topping lift you're inducing twist, which is exactly the opposite of what you want to do.

Neither the cunningham (halyard) or the boom vang has anything to do with draft depth. The Cunnigham/halyard adjust draft position and the boom vang adjusts twist.
 
Aug 2, 2010
440
J-Boat J/88 Cobourg
Thanks Don and SF, this is the kind of subtlety it is hard to find someone to discuss this with. Most charts and guides stop giving much advice at wind velocities at 5kts and above and I see nights, Windless Wednesdays we call them where we are sailing in less than that. Our boat seems to have an advantage which I want to leverage in these breezes vs the bigger boats in my fleet that have a big advantage in the 8-12 kt ranges due to waterline length.

I did buy your sail trim guide and have endorsed it here several times and I would like to thank you and recommend it again to anyone needing a guide to work against.
Hopefully I haven't missed some element of the guide, but this is referring to really light winds which can occur in our racing much too often. I feel I have diverged from the conventional wisdom somewhat successfully but cannot tell as all the boats I am competing with are different than mine which makes the results harder to interpret.
If you looked at the 5 steps in the skippertips example above, it gives something similar to what I want to give to our trimmers to work from on those nights when we have not much wind and fortunately for us, a pretty quick but hard edged trimwise boat. Don, your paragraph re-stated below is exactly what I am trying to prevent and my hope was that the leech telltales would be sufficient evidence that we weren't stalling the sail.

'Ease the outhaul slightly. Here's the most important aspect to keep in your mind when sailing in light air. In light air the wind just doesn't have enough power to get around both sides of the sail and one side stalls. How many times have you seen boats trying to sail in light air with a lot of draft in the main mistakenly thinking they are grabbing as much of the little air available and going nowhere!! So you have to be ever watchful that the wind, whatever little there is, doesn't become detached.'
 
May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
danstanford: Thank you for purchasing my book. Now buy it's companion, the SAIL TRIM CHART, which is an outline of the book.

I think the telltales in the middle of the main will be a big help - they were to me anyway. I needed all the help I could get even though I knew what I was looking for and telltales gave me that extra bit of info I needed. With the middle telltales you'll see instantly when the wind detaches. Sailing in very light wind is an art, which not a lot of sailors have mastered. Just look around the fleet and notice what a lot of the boats are doing, or not doing, trying to get their boats moving. A lot of them are working against themselves and don't know it.

Actually, I developed the CHART first. It tells you WHAT to do. There is a certain but sometimes small segment of any population - including sailors - that wants to know the WHY of things. Some of that group, who bought my CHART, approached me about writing a book, which I did. Looking back on it, I don't know how I accomplished the task and it's something I never would want to do again.

Anyway, with the book, the WHY of sail trim is explained and the WHY is EVERYTHING - otherwise a sailor is just guessing at sail trim. To me, the most important thing to know is the function of each sail trim control for the main and jib and exactly WHAT each sail trim control is adjusting. With each SAIL TRIM CHART I include FREE a QUICK REFERENCE, which performs that function.

Interesting side note: My original QUICK REFERENCE was OK - I understood it - but one of the gals at sailboatowners.com, who handles the distribution of my stuff, asked if she could make it more understandable and user friendly. She did a great job and I'm very thankful for her help. I love the folks at sailboatowners.com!!
 
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Aug 2, 2010
440
J-Boat J/88 Cobourg
Will start to look at the telltales in the body of the main Don, it has not been something we have really utilized. Our focus has been on the luff and leech (one quite high on the jib) telltales on the jib and the leech telltales on the main. The 3D elements of changing the sail shape are not hard for me to understand but I can see how these telltales will inform the required shape.
Thanks, Dan
 
Oct 22, 2014
16,099
CAL 35 Cruiser moored EVERETT WA
Ultimately I want the trimmers to make their own judgements using the various cues available to them including the speedo,
If you read Bethwaite “Fast Handling Techniques” or study the engineering works of Arvel Gentry you’ll find they used more than leach telltales to give them clues as to sail performance.

If you want to know when your main sail is dragging then add another set of telltales to the sail. Set them in 16-24 inches in from the leach. The will flutter when you see the flow change across the sail.

In exploring the sails for the Americas Cup Gentry placed telltales all over the sails. A bit overboard for what you seek. Though a few more will give your trimmer the insight you seek, when feel is not enough.
 
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May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
On a masthead rig the most important telltales on the jib are the middle ones - not sure on a fractional rig but it's probably the same. The most important on the main is the top one - it's your "twist indicator" and the middle ones.
 
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Feb 26, 2004
21,951
Catalina 34 224 Maple Bay, BC, Canada
On a masthead rig the most important telltales on the jib are the middle ones - not sure on a fractional rig but it's probably the same.
Depending on "the cut of your jib" :), it could be that the top one is also important because it could mean that you have too much twist is the head of the jib. For example I have a fixed, non-adjustable, fairlead car which is as far forward as it can be. But it's on a 110 and 85 jib high clews boat. Others have adjustable fairleads with lower clews, (same small jibs but decksweepers, or bigger jibs/genoas) so they have a lot more "adjustability."
 
May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
:), b. For example I have a fixed, non-adjustable, fairlead car which is as far forward as it can be. But it's on a 110 and 85 jib high clews boat.

Stu: For sure I thought you would have the Garhauer adjustable system.

I started out with a 150 on a C30 but didn't like it - it was too much for me to handle alone so I sold it on the old C30 forum, which was in play years ago and in fact where I got my start and met a lot of you guys. Next, I purchase a 135 deck sweeper and didn't like that either and sold it on the old C30 forum. Next, I purchased a 135 high cut. My wife said I hope you like it because you sell that one I'm going. I thought about for a while and decided I liked the 135 high cut!!
 
May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
I have been following the folks at Quantum Sails since asking for a sail quote.

John: Have you asked sailboatowners.com for sail quote? They're good folks and they provide these forum which are not found anywhere else on the web.
 
Oct 22, 2014
16,099
CAL 35 Cruiser moored EVERETT WA
Thank you Don. It was back in 2019 that I explored the sails. And yes I looked into sails through SBO by Doyle.

Dave Groshong and I have enjoyed a salesman/buyer relationship since 2015. It is also good to chat with someone who understands sailboats.

It is good to remind viewers here that SBO is a good market resource
 
Feb 26, 2004
21,951
Catalina 34 224 Maple Bay, BC, Canada
Stu: For sure I thought you would have the Garhauer adjustable system.
Don,

I raced back in SF without it. Moving my car back with the two jibs I had (but I did use my "BIG" 110 for racing!!!) would only serve to open the top up, not helpful. So I never did get the car system, although I know all about it and have friends with C34s with them. I also don't have an outside track. My PO did some nice things (Harken batt car system, rigid vang, adjustable whisker pole ring) but left a lot of other "sail oriented stuff" out of the package. I ain't complanin', though. :)

My ProFurl raises the tack high, too, deliberately.
Aquavite strbd tack 2010 (Medium).jpg
 
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Sep 18, 2021
2
Searunner 37 Halifax
i just joined this forum because of this thread and others like it. i learned about this forum from another sailing forum that has a different emphasis but almost never talks about sail trim. Thanks to all of you for this resource.
 
May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
I received an Email from a Cape Cod, Ma lister on the sail trim forum this morning. He wanted to know if I could give a scientific explanation as to why easing the boom vang would not increase draft depth because he felt it would. I'm just a country boy and not very scientific - with a lot of things I don't really know why they work but they just do.

You could try this at your dock or even with your hand sitting at your computer. Your halyard should be at full hoist, the outhaul should be tight and the boom vang cranked all the way on. The primary mainsail sail trim control for draft depth is the outhaul. The secondary draft depth control is mast BEND - not to be confused with mast RAKE. The primary sail trim control for TWIST is the boom vang. When you release tension on the boom vang the outhaul is holding the bottom 2/3 of the sail tight. Maybe, but I doubt it, a very little draft depth will be induce but it will quickly be over powered by the top 1/3 of the sail twisting off because the leech has nowhere else to go.

Raise you hand in front of you as if to salute. That's a flat mainsail. Now tilt your hand forward as if releasing the boom vang. Again, the leech has nowhere to go except twist off.

That's not very scientific but it's the best I can do.
 
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May 17, 2004
2,032
Other Catalina 30 Tucson, AZ
i just joined this forum because of this thread and others like it. i learned about this forum from another sailing forum that has a different emphasis but almost never talks about sail trim. Thanks to all of you for this resource.
longjonsilver: Glad you've found our forum. If you have any sail trim questions please fire away. I don't have all the answers but there are sailors on this forum that really know their onions about sail trim and I can't think of any questions over the years that haven't been answered.
 
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May 17, 2004
3,470
Beneteau Oceanis 37 LE Havre de Grace
I received an Email from a Cape Cod, Ma lister on the sail trim forum this morning. He wanted to know if I could give a scientific explanation as to why easing the boom vang would not increase draft depth because he felt it would. I'm just a country boy and not very scientific - with a lot of things I don't really know why they work but they just do.

You could try this at your dock or even with your hand sitting at your computer. Your halyard should be at full hoist, the outhaul should be tight and the boom vang cranked all the way on. The primary mainsail sail trim control for draft depth is the outhaul. The secondary draft depth control is mast BEND - not to be confused with mast RAKE. The primary sail trim control for TWIST is the boom vang. When you release tension on the boom vang the outhaul is holding the bottom 2/3 of the sail tight. Maybe, but I doubt it, a very little draft depth will be induce but it will quickly be over powered by the top 1/3 of the sail twisting off because the leech has nowhere else to go.

Raise you hand in front of you as if to salute. That's a flat mainsail. Now tilt your hand forward as if releasing the boom vang. Again, the leech has nowhere to go except twist off.

That's not very scientific but it's the best I can do.
Good explanation. Maybe more scientifically I also think of it like this - At a set sail trim if you pick a spot along the luff of the sail you can draw an imaginary straight line horizontally to the leech. Call that line’s length a. Then measure the actual length of sail cloth between those two points, and call that b. The difference between b and a is what causes draft. Now, the only way you can change draft is by changing the difference between those two lengths. The sail cloth is built in, so if you want to change draft you must move the point on the luff closer/further to the point on the leech. Like Don said the two primary ways to do that are mast bend (moves the luff forward and back) or outhaul (moves the leech forward and back). When you adjust the vang, (at least when the boom is within a few degrees of horizontal), the boom is still holding the clew a set distance from the mast. Since those distances are still the same you’re not really changing draft.