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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #21  
Old 06-29-2013
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Re: main sail blown?

Am I the only one here wondering what the outhaul tension was, sounds like there was a forward bubble in the main (which is OK as you want to depower, but it indicates the slot was too narrow too, so either the draft was too deep in the main, or the jib was really sheeted in close)?

This is a complicated answer for sure. Overpowered is overpowered. What everyone here has done is given you a way to depower.

Assuming your rig tension is tight (not allowing the mast to pump or drop, so basically not moving).
Assuming your rake (how far back the mast is angled) is correct.

Things to depower:
Move your jib-cars back (allows twist off at the top of the jib)
Vang on, and on harder as the winds go up (pulls the boom down, bends the mast, flattens the leech)
Mainsheet on hard (flattens the leech, bends the mast, flattens the mainsail, changes angle of attack)
Traveler on center and dropped to leeward (to twist off the main, and changes angle of attack) as it gets windier
Cunningham gets tensioned (this pulls the draft forward on the main-lower, as you tension the others, tension this, as the others pull the draft back, this will pull it back forward).
Halyard on harder (pulls the draft forward on the main-top)
Outhaul on harder (flattens the lower 1/3 of the main draft).
Backstay on harder (takes the dip out of the headstay on a masthead, does same on a fractional, but also helps to bend the mast on the fractional, which helps to flatten the main, and also reduce draft)...

So lemme summarize... tighten everything evenly as the winds pipe up, to help depower your rig, except the jib cars, they should just be moved back to depower.
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  #22  
Old 06-29-2013
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Re: main sail blown?

Quote:
Originally Posted by SHNOOL View Post
Am I the only one here wondering what the outhaul tension was, sounds like there was a forward bubble in the main (which is OK as you want to depower, but it indicates the slot was too narrow too, so either the draft was too deep in the main, or the jib was really sheeted in close)?
There's a difference between backwinding the main and a little speed bubble - where the forward 15% or so is just soft & fluttery. No problem with that. If you try to eliminate that, the main will be over-trimmed.

Just blade it out and don't forget about broach control!

If you're having trouble with too much pressure on the tiller or have to turn the wheel 90 degrees to hold course, retrim your sails or your crew-weight or reef the main, your balance is all out of whack.
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  #23  
Old 07-05-2013
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Re: main sail blown?

Hello everyone, Thanks for all your inputs.

Here are a few pictures I took of my main sail (1 reef) at light wind.

Also here is a link to a video I took in the slot with stronger wind.

another sail - YouTube

(only the first 10sec actually show the sail though)

I really feel that the vang helped the sail shape although I think it was less windy at the time I took this video compared with last time.

I have yet to trim the shrouds but I do agree that they are likely too loose and probably increasing my weather helm somewhat. By the way, I don't have to hold the tiller 45 degrees or anything like that, it's just as if the boat is pulling hard on the rudder towards the opposite side. Just want to be clear.
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main sail blown?-p1040058.jpg   main sail blown?-p1040061.jpg  
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  #24  
Old 07-05-2013
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Re: main sail blown?

Here is another shaky one... it's not easy to steer with your foot while looking up!

P1040073 - YouTube
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  #25  
Old 07-08-2013
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Re: main sail blown?

Quote:
Originally Posted by flo617 View Post
oh no, I fly something like a 90%.

About the boom vang, I am embarassed to say that 2 years ago I drilled into the boom to bolt a fitting for the vang. I did not calculate right and although the angle is ok, the distance is only about a fifth of the boom length. I'm worried that would put too much pressure on the mast when tightening it up but I might be worrying for nothing.
The distance along the boom where the vang is mounted, is usually dictated by the distance between the boom and lowest point on the mast where the other end may be mounted.

45 degrees is the most effective angle.

So the normal approach is to mount one end to the mast as low as practical, then mount the other to the boom so as to leave the vang at 45 degrees.

1/5 along the boom does not sound that unreasonable if you did indeed mount the other end as low on the mast as you could.
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Old 07-08-2013
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Re: main sail blown?

It does look like the sail is fairly well blown. Look how far aft the point of maximum draft is. If it's that far aft in light winds it must be really aft in heavy ones. Your focus should be on moving it forward.

But something odd is happening to the lower few feet of the sail. You say this is with the first reef? It looks like the lowest ring is not attached to any slide on the mast track.

The second point up is attached but not tightly. I don't think you should have that huge gap between the sail and the mast.

It looks like there is some kind of loose luff line that isn't working or tensioned properly.
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Last edited by MarkSF; 07-08-2013 at 03:04 AM.
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Old 07-08-2013
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Re: main sail blown?

The first reef is locked onto the boom at the tack with a hook.

there is a set of slugs on the lowest part of the sail that are attached to the sail through a small rope to create a gap. when I put a reef in, I usually have to let a couple slugs get off the track to be able to bring the tack ring onto one of the two hooks at the gooseneck. I suppose I could try to work on the tension of this rope.

Finally, the boom itself in on a track. I can control how high or low I want it to be using a tensionning line at the bottom of the gooseneck going to a cleat on the mast (before tensionning the halyard).
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  #28  
Old 07-18-2013
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Re: main sail blown?

The vang is not there to bend back the mast - that's way too much work to ask of it, and more importantly, the fittings that you would be asking to work against that leverage. If you want to bend the mast by pulling the sail down, then crank in on the sheet until it's in all the way, and then snug up the bang, but to try and accomplish that with a rope vang alone in heavy winds is a lot of work for you and your equipment.

The vang is there to reduce twist in the sail. We want to do this, because the lift that is generated by the sail is pretty much perpendicular to the surface of the sail, so when sailing off the wind and the boom lifts, the lower portion of the sail is looking at the water, and that's where the lift is pulling the sail, inducing heeling of the boat. By reducing the twist, that lift is now directed more horizontally, where we want the boat to be pulled. But it's not going to do much for you on a close haul, because your sheet is a more effective lever arm for flattening the sail. At some point, the sheet starts pulling mainly down and not in, and that's where it can be helpful, especially in lighter winds, to switch to the traveller for sail trim, as it's pull is strictly horizontal.

Flo, from your pics, I'd say the sail is pretty blown. One clue is that your leech line is cranked way in, which suggests that the cloth is pretty stretched (if you can loosen it and keep the leech from flapping, go ahead. That curl is making an uphill climb for the wind exiting the sail, and causing lots of turbulent drag. Get some yarn and stitch a couple telltales in there and you'll see what I mean. If the cloth isn't too worn, the sail can be restitched. I'm not sure what your boat is, but I have a pretty decent Catalina 27 main that came with my boat. The problem is that the PO spilled some West Marine resin on the area near the tack, so it's discolored and still a bit sticky, but I can give it to you cheap, and an hour or so with some vinegar or alcohol should cure the stickiness. I'm over in Sausalito, PM me if I can be of any assistance -

Greg
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  #29  
Old 07-18-2013
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Re: main sail blown?

when i read the title of this thread i was expecting something much more scandalous, but thoroughly documented,
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  #30  
Old 07-18-2013
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Re: main sail blown?

Wow, there are a lot of different opinions on the vang topic.

Lots going on with your videos and photos. First, what was the wind speed? Didn't looks too bad out there, not a lot of white caps. 15 kts? You shouldn't need to reef in those conditions. That being said:

Work on your reefing skills. The sailshape is horrible. You've effectively reduced sail, but have bellied out the bottom of the sail, greatly powering up what cloth you have flying. Take a look at a proper slab reef.

Flat as a board. That is efficient and depowered correctly. There is an extreme amount of fullness in your current main. Try to trim that out first before dropping coin on a recut or new main.

Also, re-set your bolt rope (it's probably shrunk) and check the outhaul bolt rope if you have one for similar shrinkage. This will make a sail seem very blown out. I would also look into bringing out a rigger or sailmaker to make some adjustments to your rig. SF bay in the afternoon is always breezy. Might as well tune for it.
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