How to know if you need more power or less drag?

[danstanford]

We are lagging behind some good boats upwind in 7-9 knots of breeze. 90 degree tacks (COG) and velocities close to the polar targets but just enough slow as to lose lengths on the way to the windward mark. Assuming reasonably flat water and not being overpowered by any stretch, what clues do you use to decide to go for more sail depth or less (increase power or reduce drag)? We have a high leech telltale on the jib and good telltales on the main and we do understand twist so all the elements are there, we just need to find some tells to indicate what we should chase.
The good news is that the crew is gaining experience and offering up suggestions so I want to avoid 'no' answers and trend toward a good path with reasons thereby heightening everyone's enjoyment. The bad news is when the suggestions are opposed to each other and practice season is over in favor of racing season....

 

[jssailem]

Study Frank Bethwaite' ideas on going fast.

ANGLE OF HEAL FOR RACING

I race a Hunter 33.5 that has the elliptical blub with the little wings. I am wondering if anyone has knowledge of the optimal angle of heal for upwind performance?

forums.sailboatowners.com

 

[JRacer]

Do you have sets of telltales toward the luff of the jib? See the photo, we have three sets, one low by the sailmakers logo, one mid and one just above the sail number. Your 90 degree tacking angles seem awfully wide to me for a J-88. Perhaps you are not sailing as close to the wind as the boat can, "footing", and losing distance in the angles rather than being slower.

 

[danstanford]

Do you have sets of telltales toward the luff of the jib? See the photo, we have three sets, one low by the sailmakers logo, one mid and one just above the sail number. Your 90 degree tacking angles seem awfully wide to me for a J-88. Perhaps you are not sailing as close to the wind as the boat can, "footing", and losing distance in the angles rather than being slower.

Absolutely, I steer by the jib luff telltales. The tacking angle is actually COG by GPS and so the angle we call on board is closer for sure before leeway is taken into account but you may be right that I am footing. I normally wrestle with pinching when competing with other boats but an examination of our track looks pretty solid without too much wandering. Nobody will be asking me to helm a VO65 any time soon but I can keep her in the groove.
Imagine beating in solid shape with everything flying the way it should but feeling a bit slow and finding the other boats slipping away. My question is how to decide if more power is going to hurt or help. Certainly a puff can make it all feel better which indicates more power could be used.
Do you fatten the main till you start to lose flow over the leech or do you haul on the backstay and outhaul to blade the main out a bit? We seem to be solid with the other boats as the breeze picks up but I think we should be better in the light than we are.

 

[jon hansen]

tension on the forestay, driving the puffs and lulls, walking the vessel up a sailing lane or two, shaping the sail for the given wind, ...........
there is allot that goes into getting to the windward mark first.

bethwaite baby. all your answers there, then have the crew all working for the same outcome

 

[JRacer]

Well, IMO, you definitely want to flatten out the sails in the lighter stuff as too much depth can/will cause the flow to want to detach rather than flow all the way to the back of the sail and flow smoothly off the back.

And, footing a little in the light stuff is not bad as you will generally pick up enough additional speed to offset the greater distance sailed (better VMG). But a little is good, a lot is not and results in just driving further.

Here is something you might want to view: How to set up and trim for light airs sailing | Yachting World - YouTube

Melges IC37 | Upwind Setup & Sail Trim - Light Air - YouTube

 

[jssailem]

Learn to steer your tacks, working with your crew to make your tack smooth.

Try slow.
Slow is smooth
Smooth is fast.

Nothing like throwing the helm over, the crew is struggling with the jib and the sheets, the boat whips past 90 degrees of turn, the crew struggle with triming the jib. The boat stalls, everyone is yelling trim the jib. Only gradually do you start to pick up speed and regain your angle of attack.

Mean while the other boats have picked up 2 lengths on you.

 

[danstanford]

Well, IMO, you definitely want to flatten out the sails in the lighter stuff as too much depth can/will cause the flow to want to detach rather than flow all the way to the back of the sail and flow smoothly off the back.

And, footing a little in the light stuff is not bad as you will generally pick up enough additional speed to offset the greater distance sailed (better VMG). But a little is good, a lot is not and results in just driving further.

Here is something you might want to view: How to set up and trim for light airs sailing | Yachting World - YouTube

Melges IC37 | Upwind Setup & Sail Trim - Light Air - YouTube

This Melges YT is awesome, thanks.

The leech telltales indicate we have no detachment as they are flowing smoothly. I was hoping somebody would tell me to add chord depth till I had detachment in the same way you ease trim to just before luffing but it is starting to sound like we just have to start testing and adjusting.

Dan

 

[jssailem]

Arvel Gentry worked on the connection of aerodynamic theory to practical application on sailboats back in 1971. His work can be seen on his website. Gentry Sailing | Theory and Practice

A current update applying the ideas to sails can be found in the two additions of "The Art of Science and Sails" by Tom Whidden and Michael Levitt. They use Gentry's concepts and develop the building of North Sails based on Gentry's work. Their first edition is a bit more pure. The more recent "Revised Edition" includes the marketing of North Sails and pretty pictures to distract the reader.

One of the illustrations that might be informative concerning your tell tails...

It would be nice if getting a boat to go fast was as simple as watching a tell tail.

Gentry's work opens your eyes to all of the elements that can confound the sailor as they seek optimum performance.

It is no wonder competitive racers spend so much money on their boats.

 

[shemandr]

According to Melges in one of his books you are not really supposed to sail in a straight line, or necessarily always in the groove. You are supposed to test your upwind angle by bringing your boat up so that the inner tell tails lifts up to about 45 degrees and then sail down again as the tell tail drops. So you actually steer the boat on a subtle s shaped course. If you don't test the upwind you'll probably foot too much. It's analogous to the need to have the highest tell tail on the main curl to leeward about 1/2 the time. It's not that you want the tell tail stalling, but you want to know you are on the edge.
As for the depth of the main I've come to believe that flatter is better going upwind. You can place a tell tail set on the luff side of the sail about 1/3 of the way aft. If you have too much belly in the main it will stall, because the wind cannot remain attached to that much curve. If you flatten the main, and the tell tail begins to stream the flow is remaining attached and that's good. Those tell tails won't stream like on the jib luff but they can give you an idea of how fat the main should be. If you have an overlapping jib put the tell tail aft of the bubble ("Ranger Bubble").

 

[JRacer]

You might also want to pick up a copy of Bill Gladstone's, North U books or the whole course. I have found them to be helpful. We have had Bill in to do seminars at our Club over the years. Good Stuff. Racing: Sail Trim - North U

 

[Stu Jackson]

Have you read Don Guillette's excellent book?

 

[Davidasailor26]

7-9 doesn’t sound so low that you need to worry about light air flow separation. It also doesn’t sound so high that you need to worry about being overpowered. Since it seems to feel better in the puffs, not overpowered, I would say you need to add a little more draft. A little more shape will add some power and a little more helm to fight leeway.

 

[danstanford]

Have you read Don Guillette's excellent book?

Yes I have and I will review it again to see if it references this rather narrow topic in some way.
The simple principles I read it the book and in this forum over the years has given me the tools to change the shape and to generally know what direction to go, and that has helped me a lot. In this case it is about finding clues/tells to know which way I should chase.

 

[danstanford]

7-9 doesn’t sound so low that you need to worry about light air flow separation. It also doesn’t sound so high that you need to worry about being overpowered. Since it seems to feel better in the puffs, not overpowered, I would say you need to add a little more draft. A little more shape will add some power and a little more helm to fight leeway.

David, this is how I felt as well but it is very hard to get a handle on the result with the shifty breezes as the speedo is up and down a lot due to puffs and lulls. We have a new Vakaros Atlas which gives us GPS speed so perhaps we can get a better feel for the changes in speed.

 

[Don Guillette]

The bad news is when the suggestions are opposed to each other and practice season is over in favor of racing season....
[/QUOTE]

Practice session caught my attention. Years ago when I lived in So CA I worked with a "all gal" crew. I don't remember the make of the boat but it wasn't a C30. Each gal knew her crew position down cold. She knew exactly the function of her sail trim control and knew how her sail trim control effected other sail trim controls so they were not working against each other - it was a well oiled team and a joy to watch in action. They knew the sail trim settings for each point of sail and wind condition, which isn't very hard in Long beach, Ca because it doesn't change much.

We were tired after our practice sessions but trying to get 100% efficiency out of the boat is best done during practice and not the race. At a Catalina National race in San Diego I decided to give the traveler a little tweak and we dropped from 2nd to 4th!! We never did recover in that race and it was totally my fault.

The practice sessions were pre planned. On a given run in existing conditions we set up the boat for what we felt was 100% efficiency. If you don't do that you're no where. Then we tried to push for a bit more in very small increments and waited to see what happened - it's like adjusting the jets in a carb (when you could adjust them) or adjusting the hot water in your shower - you have to wait a minute for the results. Even to the point of adjusting crew positions side/forward to see what happened. Most crews don't bother with crew position - they set anywhere they want and sometimes it's the little things that add up to increase or decrease efficiency.

I've read all the books and watched a million videos but it all comes down to your boat and not the boat in the book or video. Eventually, we got to a point where we realized the boat/sails was giving us everything she had and the result was "it is what it is". Danstanford, you may already be at that point and don't realize it.

 

[Don Guillette]

Regarding lift and drag. I do discuss it BRIEFLY on page 22 and it's true balancing act. It's called the "lift/drag ratio" and what you're looking for is the highest amount of lift and the lowest amount of drag. I don't know the science of it but I know what it "feels" like when I experienced it. The boat just feels light and balanced and the key control is the traveler. After setting all the controls for the main and jib for the wind condition while sailing closehauled don't touch any of them except the traveler. Play with it in SMALL increments and wait for the results. The beauty of only using the traveler is your not effecting the set of the main, which hopefully is matched to the set of the jib.

Playing with the traveler cost the position in San Diego. I had it set pretty good and should not have messed with it but I wanted a little more - the minute I did I knew I was wrong because the boat lost it's balance and I felt it. So did the rest of the crew. They are all looking for who did it so I looked at the driver and tried to blame him - didn't work!!

 

[danstanford]

Don, I believe our boat is capable of more and we just need to access it. We know our maneuvers are a little slow and as always tactics can make you or break you. Where I am searching is the draft of the sails, particularly the main. I can manage the draft through the backstay, twist, and outhaul and the rig settings though they are set at approximately the right values for 10 kts so I am happy there.
We have telltales all down the leech and through the body of the main so I should be able to see detachment as I search for power, and it seems like speed is going to be the ultimate test.

Thanks everybody for the input,

Dan

 

[danstanford]

So, out for a sail on my boat yesterday in 8 knts flat water and the guy on the main loosened the outhaul till we had probably 10" of camber at the boom going upwind and quite the bubble up the luff of the main from the jib. I expected the boat to be draggy and slow but I shut my mouth and let it play out finding that the boat was easy to steer and did pretty well angle wise up wind. The leach telltales on the main were flying like mad all the way up but I would never normally have that much camber. This guy was very experienced in the same model of boat as mine.

How do you Guys decide how much camber is too much?

 

[Davidasailor26]

Neil Pryde is the OEM sailmaker for my boat and their tuning guide says to run the sail 8” off the boom in winds up to 8 knots, and 4” in 8-12 knots. I find that to be pretty good for performance. When I’m out just day sailing I run it about half that, especially in the 8+ knot wind range, and I definitely find that depowers the boat.

At 8” I do get a pretty good luff bubble. In very light air (below 5) I flatten a little bit to cut down on the bubble and help keep the flow attached. In 12-15 knots I pull the outhaul about as tight as it will go to depower.