Dealing with wind shear

[Davidasailor26]

During last week’s race I noticed that the wind had a very distinct twist. On starboard tack on the first beat the bottom of the sail was luffing while the top was stalled, and my anemometer said I was way off the wind. At first I thought that since it was so early in the season I had something out of tune. But then I tacked and it was all the opposite - the bottom was stalled while the top was luffing.

I know I could compensate for some of the twist with jib car position, but this was probably close to 20 degrees. Are there any other strategies to deal with that? I do have three sets of telltales - bottom third, middle, and upper third. If I have to choose one part of the sail to have proper airflow is there a best section?

 

[jssailem]

David.
You will need to adjust the draft of the sail to maximize the power for the wind conditions. You may need to move the draft forward and up to improve speed. Note as draft is moved up more heel happens. Wind conditions will dictate whether this helps or hinders VMG.

Here is a discussion of draft that may provide insight.

When racing such trim change is important to success. Knowing the trim options is also important to cruisers as it keeps the boat moving under sail rather than the iron genny, or it gets you to the anchorage ahead of other boats for the best sites in the anchorage.

 

[Don Guillette]

I do have three sets of telltales - bottom third, middle, and upper third. If I have to choose one part of the sail to have proper airflow is there a best section?

All the telltales are important but the most important jib telltales are the middle ones. The most important mainsail telltale is the top one, which is your twist indicator. It's also helpful to install 2 telltales (one on each side) in the middle of the main and watch them also. The engine of a fractional rig is the main (on a masthead rig it's the jib) so depending on the type of rig you have you really have to watch the telltales on the sail that's driving the boat.

Draft position is very difficult to see - the 1st time. Once you see it you won't forget it. One of the controls used to adjust draft position on the jib is the halyard, which I never liked using because you'll tend to end up with line all over the deck as you make the adjustment. I prefer a "jib Cunningham" which is easy to set up and very simple to operate. If you have one, the procedure is to go to full hoist and back off slightly. I marked the jib halyard with a piece of tape so I knew where full hoist was and then just backed off from that.

Various sail trim controls on the main are used to adjust draft depth, draft position, twist and angle of attack. On the jib it's different. Every time you adjust the fairleads you're messing with all 4 elements so you have to be careful and understand what's happening or you'll end up with a result you did not want.

 

[Joe]

Adjust the tell tales using the jib cars, don't look at the wind indicator since it only describes the apparent wind angle at one particular point... the top of the mast. Only the tells can give you the complete picture. The reminder is: "bottom - back" when the boat luffs up, if the lower set breaks first, it means that part of the sail is too full, moving the car back will flatten the foot and open the leech...
You also need to insure your mainsail twist is set correctly... again, using your leech tells. A properly trimmed mainsail helps jib performance also.

I highly encourage you to try trimming your sails without looking at the Apparent wind indicator and use your tells and your senses. The apparent wind indicator is going to help you with many things but you want the sail itself to talk to you.

 

[Davidasailor26]

Thanks for all the ideas. I think Don’s point about the middle jib telltales and upper main telltales will be a big help. That gives me some reference for when the wind’s twist is so much that even moving the cars can’t balance it out. I tend to look at the lower telltales the most since they’re closest to my line of sight, but I’ll practice looking at the higher ones more.

The boat is a fractional rig, but I grew up sailing a masthead rig so I instinctively sail by the jib more. I should try to get in the habit of sailing by the main more too.

To Joe’s point about not sailing by the wind vane - I agree. I generally steer and trim by the telltales. I just look up periodically for a sanity check. That day I was looking up a little extra to try to figure out what was going on since the telltales had me going off in different directions.

 

[Don Guillette]

Thanks for all the ideas. I think Don’s point about the middle jib telltales and upper main telltales will be a big help. That gives me some reference for when the wind’s twist is so much that even moving the cars can’t balance it out. I tend to look at the lower telltales the most since they’re closest to my line of sight, but I’ll practice looking at the higher ones more.

The boat is a fractional rig, but I grew up sailing a masthead rig so I instinctively sail by the jib more. I should try to get in the habit of sailing by the main more too.

To Joe’s point about not sailing by the wind vane - I agree. I generally steer and trim by the telltales. I just look up periodically for a sanity check. That day I was looking up a little extra to try to figure out what was going on since the telltales had me going off in different directions.

David: I've never owned a fractional rig and every time I went aboard one I had to refocus. Additionally, I never raced my boats because my wife had so many creature comforts on board that the water line went up 3" when I sold the boats but unless I wanted to sail alone I had to do what I had to do. I'm really a cruiser. I didn't know a lot of the racing rules and didn't want to take the time to learn them. Any race boats I went on I expected the skipper to know the rules - I was there for sail trim.

Anyway, back to the subject -.messing around with the jib (in other words GUESSING at the adjustment) during a race is not a good idea. If I were you here's what I'd do. First, I'd take Joe from San Diego advise and master the fairlead adjustment procedure by reading what the jib is telling you. On a light air day go to full hoist and back off a little - if it's heavy air go to full hoist. That pretty much sets your draft position - it's close enough. Then head your boat into the wind and check what happens to the luff but you have to quick about reading because it happens fast. If the foot flutters, bottom luffs or bottom telltales break first - move the fairlead aft. If the leech flutters, top luffs or top telltales break fist - move the fairlead forward. That's easy to say but how much each way? You have to do it a few times or more until you find the spot where the luffing stops. Make a note of it and unfortunately it changes with each change in wind speed.

Next, you have to focus 75% of your attention on the mainsail. All of the mainsail controls adjust different things and in addition I think you have a "bendy" mast to contend with. With each SAIL TRIM CHART I include a FREE QUICK REFERENCE which tells you which mainsail control adjust what element and tells you which way to push or pull the control to obtain the adjustment you desire. You can mess with the jib all day long during a race and get it 100% correct but you won't win any races because the jib ain't the engine.

 

[DinghySailor]

I have a similar experience currently with my new 125 genoa, also with three rows of telltales, on my masthead C&C 37. Going to weather yesterday, I was able to achieve a steady 40deg angle but couldn't seem to get the twist out of the upper end. Leech about 15" from spreader while the foot was at the shroud, lower yarns parallel, mid/uppers not so much; helm balanced. Cars are not all the way aft as the control lines aren't that long: will a broader sheeting angle flatten the curve at the top of the genoa? Hoping this contributes to the OP's discussion, too.

 

[Davidasailor26]

Cars are not all the way aft as the control lines aren't that long

If you’re near the end of the control line it sounds like the cars are pretty far back? If so you could try bringing them forward a bit. That should close the leech in a little and take some of the twist out. When you say the middle and upper yarns weren’t parallel do you mean they were showing luff or stall? Luffing would indicate too much twist, but stalling would indicate the opposite.

 

[Apex]

so i read there was a lot of wind speed differential from lake to masthead. That is typical of light wind days where surface tension and other low features slow wind further. When in light wind, drawing from the top of the sail is key to getting more boat speed. So apply max twist where you can and then sail the top of the sails to get max boat speed. Twist in Jib = cars back. Twist in Main = traveler up, vang eased, mainsheet eased.

High wind is typically the opposite, wind shear is less pronounced, so less twist and less draft are in order until the wind is up enough you need to twist power out of the top half of the sails, driving on the lower half of the sails.

 

[jssailem]

control lines aren't that long

Sound like you need some new control lines for this season....

I like that your "helm balanced".

You concern about the "twist" of the upper 1/3 of the Genoa is controlled by where you set the car.

• forward position causes the sheet to pull down on the leach and allows the foot to be fuller
• aft position stretches the foot flat and allows the leach to twist off as it is not drawn down.
• You can provide additional adjustment by using a tweaker to pull down or pull in between the car and the sail clew.

Sounds like you had a fun sail in the bay.

 

[DinghySailor]

Thanks, great responses. Just getting to know the new 125. And of course I should’ve known that cars forward would reduce twist. Wind was 15 avg and I had a reef in the main. Couldn’t seem to get the leach as close to the spreader as my 110. Will move cars fwd and report.

Jsailem, yeah it was a nice sail up Puget.

 

[Mac Smith]

During last week’s race I noticed that the wind had a very distinct twist. On starboard tack on the first beat the bottom of the sail was luffing while the top was stalled, and my anemometer said I was way off the wind. At first I thought that since it was so early in the season I had something out of tune. But then I tacked and it was all the opposite - the bottom was stalled while the top was luffing.

I know I could compensate for some of the twist with jib car position, but this was probably close to 20 degrees. Are there any other strategies to deal with that? I do have three sets of telltales - bottom third, middle, and upper third. If I have to choose one part of the sail to have proper airflow is there a best section?

David, your boat size and that you are racing, leads me to think you might want to consider you were actually in a downdraft.
A cold spot on the water can cause the winds to come down, irritating the head and the foot.
In very light air, I have had crew on the lower toe rail, and used that to my advantage.
Very hard to see, feel, etc.
Good luck

 

[Don Guillette]

Thanks, great responses. Just getting to know the new 125. And of course I should’ve known that cars forward would reduce twist. Wind was 15 avg and I had a reef in the main. Couldn’t seem to get the leach as close to the spreader as my 110. Will move cars fwd and report.

Jsailem, yeah it was a nice sail up Puget.

Peter: I'm not sure of what I'm about to say. in fact, I wrote the thought and then deleted it but the more I thought about it I felt I could present it as a question instead of a statement - I wonder if a 135 or bigger sail is easier to set trim than a smaller 125?

Is your boat a masthead or fractional rig and what made you decide on a 125?

 

[DinghySailor]

Don, it’s a masthead rig. The sail replaces an older 125, which seemed perfectly sized for this boat: comfortable in moderate to heavier air and furling easily to 110 when needed. Would not want a larger headsail.
Back to the OP’s question, I found the advice here useful today on a rainy sail. Once I moved the cars forward, opened the leach, AND sailed to the upper/mid yarns (so happy not draft stripes), I found trim to be much easier.

 

[Don Guillette]

Don, it’s a masthead rig. The sail replaces an older 125, which seemed perfectly sized for this boat: comfortable in moderate to heavier air and furling easily to 110 when needed. Would not want a larger headsail.
Back to the OP’s question, I found the advice here useful today on a rainy sail. Once I moved the cars forward, opened the leach, AND sailed to the upper/mid yarns (so happy not draft stripes), I found trim to be much easier.

You have to use what you're comfortable with - I started out with a 155 (Catalina 30) and it was way too much for me to handle alone. I then went to a 135 deck sweeper and it wasn't much better. I finally settled settled on a high cut 135 -- after my wife told me enough is enough with the sails!! As I mentioned, on a masthead rig the engine is the jib. It's like building a old time sports car from scratch and deciding what engine you want to put in it - a 110 is like a 4 cylinder, a 125 moves you up to a 6 cylinder and a 135 is like a small block Chevy.

As an observation - I assume you're not using the jib halyard as a sail trim control so you could squeeze a little bit more power out of your 125 if you went to full hoist and eliminated the wrinkles in the luff. Instead of using the jib halyard you could install a simple jib Cunningham. With the jib Cunningham you go to full hoist and back off a little and use the Cunningham to adjust instead of the halyard. If you're not using either then just go to full hoist and get rid of the wrinkles.

Another item to consider is the Garhauer adjustable fairlead system. You've got a big heavy boat and you need to squeeze as much power as you can out of your jib.

 

[DinghySailor]

Thx again. Yes I’d just re installed the sail on the foil and failed to to bring it all the way—good catch. I do have the Garhauer system and it works brilliantly.