Why windward middle and top tell-tales stream up at jib?

Static Pressure

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I do not agree with him. He's being dogmatic and maybe humorous.


He's being dogmatic, but is telling them that he believes upwind VMG is better when pinching than footing. He's wrong of course, because the approach to best VMG depends...
He is not being humorous,listen him at 18:35 here, he strognly believe in this..

 

Sail4beer

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BD3E9419-5B9B-43A1-9846-EC72E85BD319.jpeg
 

danstanford

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He is not being humorous,listen him at 18:35 here, he strognly believe in this..


It is pretty easy to figure out if you have a plotter, just look at VMG to weather. There are boats and conditions where he is exactly correct and certainly boats and conditions where he would be dead wrong.

In the very light you certainly want to foot as far as needed to build some velocity and apparent winds.
 

Marty Gingras

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He is not being humorous,listen him at 18:35 here, he strognly believe in this..


Seemed throughout the video he was talking specifically about a few skiffs, so agreed he likely believed it strongly w/regard to 1 or more of those certain skiffs. He won the 2022 Wayfarer world championship against 42 other boats, so I would take his word on tune and trim for that boat and probably those other certain skiffs.
 

dogwatch

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It's not all about VMG. If you are sailing in big fleets and above all, if you are sailing the first part of the first beat in close company, you need to be able to point as high as everyone else. If you don't or can't hold your lane, you will rapidly fall into someone else's dirt and it's game over. Sail in an OD fleet of 20+ boats and in the first critical 10 minutes of the first beat, everyone is sailing higher than best VMG to hold their lane. Those who don't will be spat out the back.

The video is aimed at those new to racing and as a general rule, in average 7-15 knot conditions, windward jib tell-tales at 45 degrees is a good starting point. The main exceptions are very light winds and light wind with chop, both of which are likely to want both windward and leeward tell-tales streaming. There are also tactical situations that call for footing but that's a level of sophistication that video doesn't set out to cover.
 

Static Pressure

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It's not all about VMG. If you are sailing in big fleets and above all, if you are sailing the first part of the first beat in close company, you need to be able to point as high as everyone else. If you don't or can't hold your lane, you will rapidly fall into someone else's dirt and it's game over. Sail in an OD fleet of 20+ boats and in the first critical 10 minutes of the first beat, everyone is sailing higher than best VMG to hold their lane. Those who don't will be spat out the back.

The video is aimed at those new to racing and as a general rule, in average 7-15 knot conditions, windward jib tell-tales at 45 degrees is a good starting point. The main exceptions are very light winds and light wind with chop, both of which are likely to want both windward and leeward tell-tales streaming. There are also tactical situations that call for footing but that's a level of sophistication that video doesn't set out to cover.
My main question is what cause spanwise flow(flow from foot to head at 45degress) at windward side of jib, too much twist, boat hull, jib sweep or jib heel?

If you heel mast to horizontal on beam reach then wind blow parallel with mast(100%spanwise flow).
How boat heel angle affect airlfow at the jib?
 
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El Borracho

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My main question is what cause spanwise flow(flow from foot to head at 45degress) at windward side of jib, too much twist, boat hull, jib sweep or jib heel?

If you heel mast to horizontal on beam reach then wind blow parallel with mast(100%spanwise flow).
How boat heel angle affect airlfow at the jib?
Spanwise flow towards the tip is normal for all common airfoils. It is part of the vortex generation process. Whether such a flow is a bad thing depends on whether the crew wants to make changes in power, pointing, speed, heel, etc.

Yes, in 3-d, some upward pointing of the flow is actually horizontal in geographic coordinates. Also it is the path of least resistance for the flow to get past the obstacle presented by the sail. Likely more power generated if the flow can be directed more aftward. If more power is desired.

A flatter entry, moving the camber aft might be useful. I.e. forestay tension or a newer sail.
 

Marty Gingras

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My main question is what cause spanwise flow(flow from foot to head at 45degress) at windward side of jib, too much twist, boat hull, jib sweep or jib heel?
My sense is that the instructor's manner of speech has left you with the wrong impression of what he wants the luff telltales to do, such that your search for mechanisms is difficult or impossible. Pretty darn sure he's describing luff telltales that flutter due to turbulence (or maybe separation) rather than stream steadily aft or stream steadily at +45 degrees. Has anyone see telltales stream at +45 degrees for more than a few seconds at a pop?
 

Steam Flyer

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My sense is that the instructor's manner of speech has left you with the wrong impression of what he wants the luff telltales to do, such that your search for mechanisms is difficult or impossible. Pretty darn sure he's describing luff telltales that flutter due to turbulence (or maybe separation) rather than stream steadily aft or stream steadily at +45 degrees. Has anyone see telltales stream at +45 degrees for more than a few seconds at a pop?

Yep. They'll go 45 up and hang there for as long as you can steer accurately to hold 'em there. Straight up, usually by that time the fabric along the jib luff is starting to show a little bit of "bubble" too.

I think Borracho got it right, spanwise flow... what that increases at lower angles of attacj, I dunno. C.A. Marchaj's book has some photos and graphs on the topic.
 

βhyde

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1st Gear : Windward +0, leeward slightly breaking - Footing for power/Recovery
2nd Gear : Windward +0, leeward +0 - Max power
3rd Gear : Windward +45, leeward +0 - High pointing
4th Gear : Windward +90, leeward +0 - Pinching

Leech telltails always streaming

Low/Medium wind - Adjust jib lead so all telltails breaking at same time.
High wind - Adjust jib lead so upper telltails break first.
 

Steam Flyer

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If it's choppy, you won't see it. But it's a steady-state flow condition, Marchaj draws out a force vs lift/drag ratio and where the different telltale "signals" fall on that curve. As you'd guess, both streaming back is max force but also higher drag IIRC.

"Aero-Hydrodynamics Of Sailing" C.A.Marchaj is a book that is very well worth having for technical/science -minded racing sailor.
 

dogwatch

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Has anyone see telltales stream at +45 degrees for more than a few seconds at a pop?
Yes, for long periods. For example, plenty of boats go best to windward well into force 5 with #1 genoa. You helm it in what's described above as high pointing mode. It's hard because the groove is narrow, pinch and you slow, let the bow down and you are slammed. But done right, it is the fastest way to the windward mark. Maybe because we sail in quite a windy part of the world, we get a lot of practice sailing like this.
 
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CaptainAhab

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This all depends on what mode you want sail. Pointing or footing. Horizontal when footing(speed). More vertical when pointing(almost luffing). The difference top to bottom is combination of the straight line of the luff, cut of the sail, angle of attack. The major variable is apparent wind speed. You need to twist the jib just like twisting a main. The basic idea is to set the lower where you want it(pointing vs footing) and move the cars for & aft to correct the twist. The idea that they should always be horizontal or vertical is false.
 

dogwatch

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How boat heel angle affect airlfow at the jib?

Not much. Others have described well why there is a upward flow and I won't repeat that. Remember though, that video uses the Wayfarer as an example, which is a dinghy, best raced flat (except, maybe, in very light airs). Since it is raced flat, heel doesn't come into how the jib tell-tales are streaming.
 

Static Pressure

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Not much. Others have described well why there is a upward flow and I won't repeat that. Remember though, that video uses the Wayfarer as an example, which is a dinghy, best raced flat (except, maybe, in very light airs). Since it is raced flat, heel doesn't come into how the jib tell-tales are streaming.
Hull that redirect wind up at the sail is not so logic to me. I admit that hull can redirect some flow but very low and induce some dirty air but not at 4m height..You can not blame hull/bow that is responsible for happend with top telltales at 4m(or more) height at the sail...

Also I didnt know that pressure differential at windward side of sail between foot and head (caused by twist) is so strong to redirect all the flow upward.
 

JohnMB

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Hull that redirect wind up at the sail is not so logic to me. I admit that hull can redirect some flow but very low and induce some dirty air but not at 4m height..You can not blame hull/bow that is responsible for happend with top telltales at 4m(or more) height at the sail...

Also I didnt know that pressure differential at windward side of sail between foot and head (caused by twist) is so strong to redirect all the flow upward.

If the physics of this really interest you I would recommend you read Marcaj.

If you just want to improve your sailing, all you need to know is that; when you are sailing high, before the sail stalls out on the inside, the tell tales will lift.
Ideally you (usually) want them to all lift at the same time, if the bottom ones lift earlier flatten the bottom of the jib, if the to ones lift earlier flatten the top of the jib.

I suspect its not so much that the pressure differential from bottom to top is large, but that in the 'high' mode the horizontal pressure differential at the luff becomes quite small, and the vector sum of the horizontal flow and vertical flow gives a nice angle to indicate that if you push it any more bad things will happen. I should probably dig out my copy of Marcaj :).
 

Static Pressure

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If the physics of this really interest you I would recommend you read Marcaj.
Fors sure I interested in physics, doesnt make sense doing something just becuase everbody tell me what to do and dont understand why telltalse doing what they doing...

Is it possible to set windward telltales stream horizontaly when mast is lean to leeward at 40degress?
 

Static Pressure

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Since it is raced flat, heel doesn't come into how the jib tell-tales are streaming.
You dont agree that flow at the windward side of sail will become more and more spanwise when sail in angled toward horizontal?
(picutre show beam reach)


If you now apply my picture to close hauled, then you again get some spanwise direction when lean mast to leeward but in very smaller amount because apparent wind comes from different angle to the jib then on beam reach...3D geometry stuff

So I think some of this upward flow "comes from" sail lean to leeward.

Dont agree?
RFFR.png
 

pqbon

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You dont agree that flow at the windward side of sail will become more and more spanwise when sail in angled toward horizontal?
(picutre show beam reach)


If you now apply my picture to close hauled, then you again get some spanwise direction when lean mast to leeward but in very smaller amount because apparent wind comes from different angle to the jib then on beam reach...3D geometry stuff

So I think some of this upward flow "comes from" sail lean to leeward.

Dont agree?
View attachment 539743
nope dont agree - not even a little bit...
 

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