Tell-Tales and Mainsail Shape

[gandy]

Hi,

I finally got round to fitting tell-tales. On the main there are four leach tell-tales, one on each batten. I could do with some opinions on what they're telling me.

I was testing close hauled and on a close reach, with all the genoa tell-tells flying (except the very top windward that flicks intermittantly). Last time out it was maybe a F3, carrying full sail comfortably with helm almost neutral.

On the main the best I can get is the top and bottom leach tell-tales streaming, with the middle two being sucked behind most of the time. With this trim the mainsail luff is being back-winded. If I sheet in harder or pull the traveller up until the back-winding stops, all the tell-tales disappear behind.

Opinions?

I wish I'd taken some pictures .. the mainsail shape didn't look very good, sort of flat over some areas and baggy in others in a way that's hard to describe. The main is definitely old and almost certainly past it, but I want to make sure the controls and trimming can be sorted out as well, otherwise I won't get the best out of a new sail either.

Cheers.

 

[Lakesailor]

I found this amonst my bookmarks

"But What About Those Leech Telltales?

Have you fastened some ribbons to your batten pockets yet? Give it atry and watch what is happening to the top portion of the sail. Whereasthe "standard" telltales are for steering, the leech telltalesare for indicating sail twist.

When the leech telltale disappears around the lee side of the main itmeans the sheet is too tight, the sail has too little twist, and an eddyis forming behind the mainsail. Ease the sheet a little.

When the lower telltales stall (depending on their position from thetop of the sail relative to the jib) they can also indicate that the jibis sheeted badly and causing the airflow to separate from the leeward aftsurface of the main. "

This is also a good site for picking up general information.
http://www.psyberspace.com.au/BrassMonkey/numain.htm

 

[Twister_Ken]

There are so many controls affecting mainsail shape it's difficult to know where to start, esp. without pix.

Unless the sail is shot, then some combination of:

Sheet
Traveller
Kicker
Backstay
Halyard
Outhaul
Cunningham

will let you produce an efficient sail shape, which will also have all the batten tell-tales streaming behind the sail. Be aware though, that it's possible to get the tell tales flying, but still not have an efficient sail.

Best place to start is a good book. I can recommend one written by an old buddy, Dick Kenny, called 'Looking at Sails'. Out of print (I think) but usually available from 2nd hand specialists, or even Amazon. If you buy it, you'll also be treated to seeing certain parts of my anatomy in some of the pix!

 

[Skyva_2]

This is a superb site on tell tales:

http://www.wb-sails.fi/news/95_11_Tellingtales/Tellingtales.html

The other articles on the site on sail aerodynamics are equally helpful.

 

[H4B]

I recommend the following book ,
Ive learned loads from it simple diagrams check lists etc
@Amazon -Sail and Rig Tuning - Ivar Dedekam -£9.20


Cheers

 

[dom]

... not to forget batten tension?

 

[Twister_Ken]

Me. Forget batten tension? Errr, wotzabatten?

 

[machurley22]

[ QUOTE ]
Best place to start is a good book. I can recommend one written by an old buddy, Dick Kenny, called 'Looking at Sails'. Out of print (I think) but usually available from 2nd hand specialists, or even Amazon. If you buy it, you'll also be treated to seeing certain parts of my anatomy in some of the pix!

[/ QUOTE ]
An excellent book and only slightly let down in parts by TK's parts. /forums/images/graemlins/blush.gif

 

[chuns]

I had a "doh!" moment when I finally realised that the reason one of my telltales was not behaving as it should was because it was in the slipstream of the radar reflector!!

 

[gandy]

"Looking at Sails", authors Bruce Banks and Dick Kenny. Any significant differences between 1979 and 1988 editions?

 

[Twister_Ken]

"Any significant differences between 1979 and 1988 editions? "

I weighed a bit more in the 88 one. Dick had less hair.

Dunno whether it was revised or just reprinted. If it was revised it will probably have gone a bit more into laminated sails and bendy rigs.

 

[kds]

" I won't get the best out of a new sail either."

I am afraid that you are unlikely to achieve a working luff and the correct flight from leech tell-tales if the sail is "almost certainly past it".
Much easier with a good sail.
Ken

 

[gandy]

Thanks for the links, most useful.

I'm working with a limited set of controls, in particular the traveller is not very efficient, being short and located well off the end of the boom. There's nothing much I can do about that. Currently the outhaul is fixed, but since there's absolutely no camber along the foot of the mainsail, I don't think the outhaul would have any effect anyway.

Some running rigging improvements are planned for the winter.

One thing I haven't tried is varying halyard tension, so I'll have a play with that next time out (no Cunningham).

 

[Swagman]

Re mainsail shape – it’s oft hard to see how it compares looking up the sail and just relying on mark one eyeball and no guide.
A simple home made clear plastic jobbie I've used for years could maybe help.
Hoping these instructions are understood.
Get a piece of clear plastic sheet (like a report cover from a stationers) but rigid enough to stay flat when held in the wind, and cut an oblong say 9 inches long and maybe 3 inches high. Draw onto it with black indelible felt tip a simple graph showing six equidistant vertical lines from side to side, and possibly seven horizontal lines scaled each to 5% of the graphs length.
Then when you are sailing you can go to the side of the yacht, sight up from under the boom through this device, and align the horizontal scale with the sails luff and leach at various points up the sail.
Moving it closer or away from your eye will allow you to check exactly where the chord is located at that height up the sail, plus in 5% terms, how deep it is at each point across the sail.
We tend to use sail seams on cross cut as reference points, or batten pocket levels on D cuts, to ensure we compare eggs with eggs each time.
Using backstay, halyard tension, cunningham, outhaul, boom vang etc it should help you shape up the mainsail and once you've got the best shape with all telltales flying, you can then note the adjustments for differing conditions - and bobs your uncle.
Hope this does not sound too complex as it really is simple - and it works.
JOHN