Sail Trim Puzzle

[savoir]

Originally Posted by 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.

In mast furling doesn't like too much backstay. The furler starts to jam. On a regular mast more bend would certainly fix it. Don't be too concerned though, 11 years to recut is a pretty good run.

Before reaching for the scissors you might try sailing to windward without the staysail.

[Bash]

Originally Posted by Dockhead

Likewise, slacking the yankee sheet seems to reduce the stalling.

It's called a "luff bubble." The foresail, in your case a yankee, backwinds the luff of the main.

This is NOT--despite what you've been advised in earlier posts--caused by the condition of your main. Rather, it's caused by the shape of your slot. In other words, pay a bit more attention to the slot created between the leech of the foresail and the luff of the main.

One thing you need to do to lessen this problem is pay more attention to the leech of the foresail. You want a clean leech. If it hooks inboard the last bit you've got a dirty leech. That leads to a luff bubble.

The good news is that a luff bubble doesn't slow you down all that much. Chances are that by the time you're getting a luff bubble you'd be cracking off on the traveler anyway--pretty much the same result.

In big air you can't point as high as in medium air. Why? Because you'll get a luff bubble.

So when you're close hauled in a stiff breeze, stop focusing on the jib tell tales and start focusing on the slot--and on adjustments that will give you a clean leech on the jib.

A perfect slot may not help you point higher, but it will certainly increase your VMG.

And that's a good thing.

[boatman61]

I was going to be facetious and say "Release the topping lift".....
But I won't....

[savoir]

[Adelie]

Originally Posted by 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.

It's not a problem. When I crewed on a Tartan Ten (US made Aphrodite 101 knockoff) we saw that all the time with good sails when hard on the wind. The owner who was very competetive had done a lot of investigation figuring out it was the fastest set to the sails sometimes. I have seen it other times on other boats when I thought the boat was doing just fine.

The way to check the air flow is to have leach telltales on the main. When they are streaming aft smoothly the main is properly set and if you are hard on the wind the main may be out enough that the jib backwinds the luff. Find a time when the waters are flat with little or no current and winds are consistent then try playing with the trim of both gib and main watching both the knotmeter thru the water and the GPS to see how leeway is changing.

[daddle]

Cwyckham is correct about the luff bubble. Don't worry about it. If you have enough speed and power it is fine. A new flat sail may fix $$ the bubble. Or some mast bend. Or ease the headsail a bit - but not if pointing or speed suffers. Call it a "speed bubble".

[Dockhead]

Originally Posted by boatman61

I was going to be facetious and say "Release the topping lift".....
But I won't....

Lol! Of course, I've never EVER had a sail trim problem which turned out to be a forgotten topping lift, oh NO!

[Dame.n.Jess]

As a competitive dinghy racer this was a very common sight on certain rig types. Flying Dutchmans were notorious for this 'luff bubble'. it was caused in their case by a LARGE overlapping jib squeezing so much air thru the slot that the volume of air pushed the mainsail luff to windward.

The comments about slot shape are the ones to look at. As the issue stems from the direction and volume of air flowing thru the slot from the yankee in your case to the front third of the main.

Often you would see this issue more so on the dutchmans when they have everything sheeted on, hard into the wind and they get a gust, when this happens the speed and volume of air increases but also its likely they eased the main off a little so as to not get over powered. Easing the main depowers the dinghy and flattens the boat out but it also closes off the slot a little which creates more luff bubble.

Im not sure if you or others can see any bits of this rambling that could apply to you rig but im sure there are some common factors with slot shape that would be a main factor to consider.

[ozskipper]

More halyard- Cunningham. More backstay. Also if the leech on the headsail is old it will be turning in somewhat and disturbing the airflow - you may need to get it trimmed off. It could also be that the main is simply "blown out" and will never trim correctly. But, most likely a mix of all of the above.

But either way older sails arent going to be as efficient as new sales. 11 years is a long run.

I just re read your post again.. you said. "Likewise, slacking the yankee sheet seems to reduce the stalling." I bet the leech is a major cause of the problem. Because as you ease the sheet, the leech would free up and stop stalling the main. A sailmaker should be able to trim that leech a few inches and most of your problem should be solved imho..

[Dockhead]

A treasure trove of information -- thanks everyone! I have learned a lot.

Yes, the headsail leech is turning in a little. I wonder if I have forgotten to ease the yankee leech line???!!!! That would be even worse than having forgotten to ease the topping lift! Arrggghh!

[Blue Stocking]

IMHO, Bash got it right.
Close-hauled is when the foresail/main combination most closely resembles an aircraft wing- turned vertical.
Different leading edge slats (flaps) create different lift characteristics, and negative/ positive areas on the sails.
I'd bet a visit to one of the aircraft forums would provide insight.
In fact, you got me thinking, I'll go there myself, out of curiosity.

[savoir]

Originally Posted by ozskipper

More halyard- Cunningham. More backstay. Also if the leech on the headsail is old it will be turning in somewhat and disturbing the airflow - you may need to get it trimmed off. It could also be that the main is simply "blown out" and will never trim correctly. But, most likely a mix of all of the above.

But either way older sails arent going to be as efficient as new sales. 11 years is a long run.

I just re read your post again.. you said. "Likewise, slacking the yankee sheet seems to reduce the stalling." I bet the leech is a major cause of the problem. Because as you ease the sheet, the leech would free up and stop stalling the main. A sailmaker should be able to trim that leech a few inches and most of your problem should be solved imho..

Messing with the backstay doesn't work when you have in mast furling. It causes the furler to jam.

[savoir]

Originally Posted by Dockhead

A treasure trove of information -- thanks everyone! I have learned a lot.

Yes, the headsail leech is turning in a little. I wonder if I have forgotten to ease the yankee leech line???!!!! That would be even worse than having forgotten to ease the topping lift! Arrggghh!

Try no yankee at all until the apparent gets to 60.