Tell-tail Question

[Ward H]

Had a nice long sail today in winds 10 - 15. Started out with full main and full 110 jib.
On close reach and close hauled points of sail I could get the jib luff tell-tails to fly on the leeward side and sometimes both leeward and windward tell-tails would be flying.
With the main I had very little success getting the leach tell-tails to even flutter.
Then the wind picked up a bit so I reefed the main. Immediately the leach tell-tails were flying.

I am guessing the the old main would not allow the air to stay stuck to it because of the deep draft. When I reefed, there was less draft/the sail was flatter, so the air stuck to the entire sail reaching the leach and flying the tell-tails.

Am I close?

 

[RichH]

For an OLD woven dacron mainsail ..... here's how to PROPERLY RAISE it; and then, how to examine it once 'properly' raised to see if the sail has or has not developed shape problems: http://forums.sbo.sailboatowners.com/showthread.php?t=120970 see post #1.

If the 'aft end' of the leech is *too tight* and is 'pointing towards windward' (the leech has a 'cupped' shape) instead of being parallel to the boats centerline when you are beating, it means:
1. the sail wasnt 'properly raised', or
2. there isnt enough tension on the mainsail halyard, or
3. the luff boltrope has shrunken and needs to be 'eased' by a sailmaker (or DIY if you know how).

If the mainsail has developed a 'cupped up leech', then you will definitely not be seeing leech tell tales that stream 'straight back'; severe 'cupping' at the leech - and the tales probably wont be flying at all. The usual 'fix' is more halyard tension ... as described in that link above.

;-)

 

[shemandr]

Yes, I think you are close in concept. If the main has too much draft in it the airflow will stall, indicated by lack of tell tail streaming.

 

[Ward H]

RichH,
I did not notice any cupping of the leach but will follow your directions on how to raise a dacron main on the next time out.
I am curious about this statement:
"Woven dacron mainsails are the most commonly found mainsails on ‘cruising’ boats. If you ‘just raise’ a woven dacron mainsail, you’ll most probably have sail trim and shape problems, problems that can adversely affect a boats performance, ‘helm balance’ and ultimately safety."

How is it unsafe to have sail trim and shape problems? I understand performance and helm balance but not quite getting it as to making this unsafe?
Thanks

Andrew,
Yes, that is what I was thinking. Thanks

 

[shemandr]

Well I guested on a J34C last night with wind in the 16 to 19 kt. SW. We put the main up, in the "Just raised" mode, and before we were done I said let's try this. We cranked on a good deal more halyard tension, to make sure the luff was stretched. We didn't ease any because of the wind velocity. The skipper noted an improvement in sail shape i.e. draft forward and flat leech. The sail was more deep than I would have liked but that is what it is. We had a very good night finishing just behind an Etchell's and with the rest of the fleet in the rearview mirror. That boat likes a breeze but still the little extra effort in getting the halyard tension on seems to have been a great help.

 

[RichH]

How is it unsafe to have sail trim and shape problems?

Shape problems can result in the sail unexpectedly 'powering up' during unstable/changeable wind conditions. If you are at 'optimum' shape for the present conditions, the sail will be producing near MAXIMUM output, then such surprise 'power-ups' are minimized. .....or more simply stated: you cant get 'better' than 'maximum'.

An example would be having insufficient mainsail halyard tension that results in draft-aft, too much draft and hooked up leech ... and you encounter a gust ... with the result that the boat wont accelerate well, and will aggressively heel over while developing extraordinary 'weather helm' as it goes 'over'.
In contrast, a well shaped sail will promote rapid boat acceleration and much less heeling, but with constant 'weather helm' throughout the time of the changing wind strength and heeling over.

Another example would be: In the higher wind ranges, a well shaped sail will more overall respond to such wind changes with the entire sail acting almost instantly to any change ... a mis-shapened sail can easily start with wind-flow attached only in one 'corner' or edge and then the flow-attachment propagate across the rest of the sail ---- leaving the helmsman sometimes 'confused' and unable to correctly react to steer/respond to the 'power-up'.

Another way of saying this would be, in the case of jibs/genoas, if the foot of the sail is 'overtightened' (fairlead set too far aft in order to 'depower') and you need to 'release' to prevent over-heeling, the flow attachment will incrementally change 'across' the luff from top to the bottom of the sail .... top luffs first, then the middle, then finally the bottom of the luff - the total change taking a relative extra long time to accomplish. With an accurately shaped jib, when you 'release' or 'luff up', the entire luff section will 'break'/luff simultaneously from top to bottom - called 'blading out' and much easier and faster (no guessing) to 'follow' and control (steer) with the tiller/wheel to control how far the boat will 'go over'.

As an aside, jibs/genoas on furlers will take better shape (for the present conditions) by adjusting halyard tension - although you may probably jam/bind the furler in doing so; thus you will/may need to ease the halyard before you 'furl'.

 

[Ward H]

Thanks for the thorough explanation Rich. It really helped to better understand what is going on and highlights the need for new sails for better control.

Thanks again.

 

[RichH]

Not necessarily new sail but perhaps better 'shaped' sails. Especially examine your mainsail for a 'shrunken luff boltrope' as this is probably the most common developing fault in woven dacron sails.

I notice that you sail on Barnegat Bay .... light winds in the AM and 'roaring' sea breeze winds in the afternoon. If you get your boltrope 'eased', talk to the sailmaker for re-setting up the boltrope with more slack than 'normal' so that the sail sets a bit 'flatter' as such will greatly benefit in both 'light winds' and the 'blammo' PM sea breezes. For Barnegat I always set up my mains with 3/4" boltrope 'pre-load' for 11-12ft. of luff length ---- FASTER especially in 'flat' water ... but then you need to apply a bit more of mainsheet tension to keep the leech pointing 'straight back' when beating. Youll also be reefing less due to the relative 'flattening' of the sail.