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tell tales

lyclaser

New Member
I wanted to see what everyone here thinks about this. With tell-tales on the laser I have heard that both sets (windward and leward) should be horozontal. I have also heard that the leward ones are the only ones that should be flying horizontal. This is all heading up wind. How does everyone else sail them?
 

49208

Tentmaker
It all depends!

If you're footing off to a shift ahead, or putting the bow down to drive over the top of someone, you'd have them both streaming back.
If you're trying to pinch off someone on your windward hip, you'd want the windward one dancing up.
If you're in a lot of chop, both streaming back
If you're in smooth water, at max speed, windward side dancing up...

(It also depends on how far back from the luff you put the telltales)
 

GeoffS

Member
Basically, the behavior of telltales placed near the point of maximum draft on a cat-rig mainsail is:

Leeward tell-tales:
1) flipping around all the time or hanging = stalled = bad = ease or head-up
2) streaming straight-back = attached flow = good

Windward tell-tales:
1) flipping around = pinching
2) streaming straight back = good attached flow = normal power
3) streaming up (ca. 45 degrees) = footing = max. power
4) hanging limp = stalled (leeward will also likely be in state 1) = ease/head-up

So, in reality (like 49208 writes) there are really two (maybe three) desirable configurations:
1) Windward: flipping, Leeward streaming = pinching
2) Windward: streaming back, Leeward streaming = normal power
3) Windward: streaming up, Leeward streaming = max. power (footing)

In any case, the leeward tell-tale should never (almost never?) be doing anything but streaming back; IMO a leeward-side stall is *always* very slow.

How you use this information is very situation dependent. As 49208 says, in flat water with steady wind, you might want to pinch a bit as you don't need so much power. In chop, or when you're trying to get in front of someone to leeward, you would want to be in "max. power mode".

There's probably a drlaser article out there with *way* more detail and description than this...

And don't forget the upper leach tell-tale...

Cheers,

Geoff S.
145234
 

Canadalaser

New Member
Depends, just like everyone said. You also want to factor in windspeed... in really slow wind, (specifically under 6 knots) you'll want your upper telltales streaming and your lowers limp with just a little dance. Generally otherwise, just keep them streaming, and make sure your not making too much drag with your rig. Also, make sure that your tell tales are positioned far enough back on the rig that they are clear of the separation bubble caused by the mast. Otherwise everything will be really wonky.
 

drLaser

Member
> make sure that your tell tales are positioned far enough back on the
> rig that they are clear of the separation bubble caused by the mast.

I disagree with the above. Because the Laser sail luff is sleeved and that sleeve rotates with the boom angle, there is no significant separation bubble on the Laser mainsail -- except in very very light air. Effectively, the Laser has a small "wing mast."

And there are serious advantages associated with having telltales very close to the mast, which are then used just like the steering telltales on the genoa of a sloop.

Details are provided in the drLaser web site in several articles, including statistics on where the "pros" have been locating their Laser telltales.

Shevy Gunter
 

GeoffS

Member
Re: tell tales (sleeves aren't wings...)

Actually, luff sleeves can't compare with true wing masts. Frank Bethwaite goes into gory detail about this in "High Performance Sailing". The main problem with a sleeved mast is that the leading-edge radius of the foil (i.e. the mast diameter) is much to large for anywhere near optimal performance.

With that said, I've never personally investigated the flow over the forward part of a Laser rig. If you say that forward tell-tales are useful, I'd be inclined to give them a try.

I seem to remember that most (all?) of the tell-tale locations described in the drLaser article on "Telltales of the 2002 Laser Worlds" were near the mid-line of the sail. I was going to check the page, but for some reason none of the combination/permutations of space and no-spaces in the username/password would work... :-(

Cheers,

Geoff S.
DN US-5156/Laser 145234/Renegade 510
 

GeoffS

Member
> I seem to remember that most (all?) of the tell-tale locations described in
> the drLaser article on "Telltales of the 2002 Laser Worlds" were near the
> mid-line of the sail.

My mistake (mostly). My fat-fingers finally got the ILCA-NA drLaser password right and I was able to look at the article again:
http://www.drlaser.org/ILCA/tells2002.html

The centroid of the lower tell-tales is distinctly forward of the the midline of the sail, much closer to the 25% mark. I wish I could remember where the tell-tales on my sail were...

Cheers,

Geoff S.
 

drLaser

Member
> much closer to the 25% mark.

???

Geoff,

You are still not reading the diagrams correctly! Or your bias shows :))

Note that almost no one uses a single telltale in the lower (steering) telltales group. If I were to qualify the locations of these steering telltales, I would have said "the most forward one of these steering telltales is at 7%, at most 15%, of the chord from the sleeve."

Check out the drLaser "Gentry Tufts" locations in that article. My forward tuft is at about 4" (10 cm) from the sleeve stitching. And I can consistently out-point (achieving the same speed) any competitor in my fleet who has telltales further aft. Regardless of the hull I'm using.

Yes, there are those who can do better than me with just one telltale at about 20% aft, but that's because they are either better sailors overall or taller or lighter or heavier or have a newer sail, etc.

It is a scientific fact that bad (sub-optimal) flow near the sleeve will make you slow. A telltale near the luff sleeve makes you see that airflow. Some of us can see it (feel it) without a telltale close to the luff. I'm not one of those talents. Neither are most of us.


Shevy
 

GeoffS

Member
> > much closer to the 25% mark.
>
> You are still not reading the diagrams correctly! Or your bias shows :)

The former. I just glanced at the diagrams and saw the "blob" of tell-tales were substantially nearer the front than the half-way point.
15%, 25%, eh - they're both "up front"... ;-)

I really have no bias on tell-tales. Being more on the geek end of the spectrum (and less on the "really talented sailor" end...), I tend to favor having more data than less. My DN and Renegade iceboats (with *real* wing-masts, BTW), have very different tell-tale setups than the keelboats I sail on, but they all have pretty complete sets of tell-tales.

FWIW, I've been a fan of Gentry (and Marchaj) since reading his papers on sail aerodynamics in the bound volumes of the proceedings of the AIAA's "Symposium on the Ancient Interface" (now the "Conference on Sailing Technology ") when I was in graduate school back in the '80s. At the same time I spent a couple of seasons sailing on a couple of keelboats with North jibs that had the leading-edge horizontal series of "Gentry Tufts". From that practical experience I became a huge fan of the ability to watch the leading-edge stall progess back along the sail.

Even today, when I'm teaching sail-trim I always add a set of leading-edge tell-tales to the jib and have students observe the correlation between pinching and footing and the behavior of the tell-tales. I find that after that lesson they have a much better (empirical?) grasp of the basic aerodynamics of sailing.

With all that said, I have to admit that my Laser sails just have the tell-tales the previous owner had applied (high, low, and leech). When I'm getting everything put together this year I'll have to add a series of tufts near the leading edge!

Cheers,

Geoff S.
DN US-5156/Laser 145234/Renegade 510
 
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