Sail Trim Puzzle

[Dockhead]

I've been having an odd problem with sail trim while beating which has me stumped. Perhaps someone has some insight.

I have started to get this condition while sailing hard on the wind where the luff of the mainsail stalls out, and I can't seem to do anything about it. Just the last couple of feet of sail next to the mast -- the rest of the sail apparently is drawing correctly. But those couple of feet -- all the way from boom to masthead -- sag and are obviously not drawing. It seems to be some secondary effect from the yankee jib.

I have tried everything I can think of -- more or less outhaul tension, more or less main sheet tension. I've even tried putting on a little kicker (at the suggestion of one crewmember). Nothing. The one thing which seems to help is to pull the jib cars all the way back, which opens the leech of the yankee jib. But then the yankee is not drawing properly. Likewise, slacking the yankee sheet seems to reduce the stalling.

I am especially puzzled because I seem to be getting plenty of drive. I just did a Channel crossing overnight hard on the wind last week, and had this condition the whole way across. I still managed to keep up an average speed of just under 9 knots in 20 knots apparent, which is about as fast as my boat will go hard on the wind. Still, that stalled luff just can't be right.

In this particular case I don't know what the real wind angle was, because I was sailing across strong currents -- up to 6 knots -- we were having a spring tide. So the boat was moving in not the same direction as her heading, so the wind instruments were not giving meaningful data about wind angle. Maybe I was pinching without realizing it? But then I would expect the boat to slow down.

I'm really stumped -- anyone have any insight?

P.S. I have an in-mast furling main without battens.

[heron237]

sail fatigue, how old is it.

[Unicorn Dreams]

You expect answers this early in the week, LOL.

My first thought was the jib back winding the mainsail, but you thought of that.

Have you changed any sheet leads or angles.

Almost sounds like the sails blown out, except for the location it's where it's stalling at...

[Dockhead]

Well, the sails are original to the boat, 11 years old. The boat was little used when I bought her two years ago and the sails seemed to be in very good condition, without any signs of being blown out. I have sailed her a LOT in the last two years, 52 sea days last year, and in some pretty hard weather sometimes. Maybe they're getting blown out, although other than this luff stalling issue, I haven't noticed any signs of it.

Yes, it appears to be the jib backwinding the main somehow, but I don't understand how this is happening or what to do about it.

[Unicorn Dreams]

Also, could it be sag on your in-mast furler?

It could be sagging when driving hard.

[Jim Cate]

ONe thing to consider is that as the foresail ages the draft moves aft. This in turn may cause the apparent (and also real) backwinding of the main. The fact that moving the leads aft (tends to flatten the foresail) reduces the bubble in the main seems to support this hypothesis.

On the other hand, it is common practice to ease the main traveler down as the wind increases, and this too will lead to a bubble at the luff while still driving the boat well.

My guess is that you will soon be looking at some new sails...

Cheers,

[Seahunter]

Sagging mast furler.

[Multitalent]

Yes your main is showing its age. You might try decreasing halyard tension which moves the draft aft...which may then possibly be flattened with the main outhaul. But realistically with such a compromised rig (in - mast furling) there is not much to be gained.

[savoir]

The main is just showing signs of age. The forward sector is blown out. Get your sailmaker to remove the luff tape then take a vertical dart out of the sail just behind the luff and sew the luff tape or bolt rope back on. The max width of the dart at the mid point shouldn't be more than 5 cm.

No need to touch either head or clew. The dart is just a long skinny crescent.

[NCountry]

I've seen this is called a racers trim when sailing close hauled but I don't like it when my boat does it either. Generally you're really close to the wind when this happens? What's the apparent wind angle when you see this happen? Have you tried tensioning the back stay just a hair?

[cwyckham]

Sounds to me like you're just backwinding the main a bit. If it's just the section next to the mast (which is disturbed by the mast itself anyways and doesn't draw that well), then I wouldn't worry about it too much. I've heard this referred to as a "speed bubble". You're obviously getting good speed with it like that.

If you can get it to go away by fiddling with the jib, then I'd say it isn't a worn out main or anything to do with the furler. It could be made worse by a blown out jib with the draft moved aft, causing the wind to hook into the main more. Have you fiddled with jib halyard and headstay tension?

Also, you mentioned that you couldn't tell if it was affecting your pointing because you were in large current. The boat's sails only know about apparent wind angle, not true angle, so when you're comparing changes to the trim to see what will allow you to point better, your instruments should be set on apparent anyways. The current won't matter.

Chris

[Dockhead]

Wow, lots of great advice. Thanks everyone. I'll try fiddling with halyard and backstay tension.it seemed to me that the backstay was a little slack and I forgot to do anything about it.

One quibble with the last post: wind instruments can only measure relative wind angle relative to the boat's head. If your boat is not moving in the direction of her head due to a strong cross current, this data is meaningless. That's why you might sail well with even 20 degrees indicated relative wind angle on one tack, and can't get within 60 on the other, if there is a strong cross current. I found this quite astonishing when I first started sailing tidal waters.

[cwyckham]

Originally Posted by Dockhead

One quibble with the last post: wind instruments can only measure relative wind angle relative to the boat's head. If your boat is not moving in the direction of her head due to a strong cross current, this data is meaningless. That's why you might sail well with even 20 degrees indicated relative wind angle on one tack, and can't get within 60 on the other, if there is a strong cross current. I found this quite astonishing when I first started sailing tidal waters.

I also have spent years sailing in tidal waters (gulf islands, BC). I think your confusing true and apparent wind angle. You're correct that the wind instrument is measuring the angle of the apparent wind with respect to boat's head. This is also the angle that matters to the sails. The TRUE wind angle is calculated by most wind instruments by assuming that the boat is moving strait ahead through the water and doing a vector subtraction of the boat's velocity. In this case, the fact that you're in a tidal stream means that your TRUE wind angle will get screwy and you could very well be showing 20 on one tack and 60 on the other. However, the APPARENT wind angle, which is the one that you're interested in keeping an eye on as you tweak your backstay tension to see if you can point better (you will, if it was loose) will show 40 and 40, no matter what the current is.

[Dockhead]

Even true wind is relative to the water, not to the land. So the current shouldn't matter, should it? But I've experienced this 20 on one tack and 60 on the other (wind instruments always on Apparent) in strong currents, and know others who have. Need to think about this a bit.

[cwyckham]

Originally Posted by Dockhead

Even true wind is relative to the water, not to the land. So the current shouldn't matter, should it? But I've experienced this 20 on one tack and 60 on the other (wind instruments always on Apparent) in strong currents, and know others who have. Need to think about this a bit.

There may be fancier wind instruments out there that take GPS COG and SOG into account, but on every boat I've been on, true wind is calculated by the instrument using only the boat speed through the water. The current will therefore have a significant effect on this.

There is just no way that I can see that a wind indicator set to apparent will show that the angle of the wind coming over your bow is 20 degrees. Your sails would have been flogging all over the place. When set to apparent, the instrument is simply telling you the exact same information the windex or a bit of audio tape tied to a shroud would tell you (or a wet finger). It`s just showing you the angle that the wind feels like it`s coming from, relative to the boat`s bow, regardless of the motion of the boat or current.

In your 20,60 experience (I assume close hauled on each tack), somebody must have accidentally pushed the true-app button on the wind instrument.