Yard Sail

[Daveinet]

Yard Sail (formerly sail twist)

So, Spring has arrived and it has been time to get the boat in order. Last fall, I had a long discussion, trying to figure out how to get my sail shaped correctly. You can refer to the previous thread here :
http://forums.sbo.sailboatowners.com/showthread.php?t=166173
So one of the first things I did was lay the main sail out on the ground and accordion fold it vertically. Not sure that worked out very well, as the luff ended up being concave by about 2 inches in the center. Holding the sail off the ground, the middle of the sail seemed very baggy. Its almost like the leach and luff are both tight, but just the middle is baggie.
So either way, I did work on putting some pre-bend in the mast, probably about 3 inches measured at the spreaders. I cranked the back stay on and off, which bends the head.

You can see the bend in the mast here:

But the leach still is tighter than the rest of the sail, and tends to put a fold right after the battons. The photo has not wind. I did get a little wind on it and with the backstay full on, I can get it to smooth out.

Didn't get any wind when I had the camera out, glad I wasn't trying to sail. I did learn a few things. First, if I reduce the out haul, the shape is better, and you don't notice the fold too much. I also have concluded the weight of my boom prevents any kind of twist in the sail. just for grins, I removed the boom, and connected the main sheet directly to the clew. If I messed with the angle just right, I could achieve a near perfect sail shape. Changing the angle of the main sheet, I could put the twist any where I wanted it. I could make the twist low or high, just by changing the angle. But as soon as I connect the boom, it pulls down so hard that the last 18 inches at the leach pull tight, an everything in between sags. One of my other projects for the day was lazy jacks. I did find if I pulled the lazyjack tight enough, I could take the weight off the boom, and recover my sail shape. I'll just have to see if I can make that practical out on the water.

One thing that did work out rather well. When I set the rig tension up, I needed a way to unload the forestay so I could cleat it in place when I step the mast. Once the mast is up, I use the jib halyard to keep it up. Then I use the main sheet fiddle blocks and pull the checkstays forward. This puts bend in the mast, so I can easily cleat the forstay. This will allow me to step the mast without adjusting any turn buckles and still get the tension in the rig.

 

[Joe]

My first comment is this: Without the wind you'll not be able to determine much. The weight of the boom is held up by the wind in the sails.... if you have NO wind then you need a topping lift to rigid vang to hold the boom. The wind velocity also affects draft position

The important thing is that all the trim controls are working which will allow you to learn quite a bit once you're out on the water. The sail is cut so that the luff and foot are NOT straight lines.... I guess you noticed... but that is how sails are designed... and it is why making adjustments like bending the mast, tightening the outhaul, imparting twist have such a dramatic effect.

 

[Daveinet]

I did have wind later on after I put the camera away. The pictures only show no wind, but with wind, there is still a tendency for the leach to be too tight. The normal moving the main sheet car has no affect. The weight of the boom makes the top of the sail hook.

 

[Davidasailor26]

I just re-read the original thread but couldn't find an answer as to whether this is the original sail or if it could be off a different boat? It looks to me as if the boom is well above horizontal, and the clew doesn't go out to the end of the boom. This makes me think the sail is smaller than OEM, but with the luff somehow stretched to match the height of the mast. If this is the case, with the luff proportionately longer than the other 2 sides, that would explain your trouble getting the leach to twist off properly.

 

[Joe]

Either invest in a rigid vang.... or install a topping lift.

 

[Scott T-Bird]

I agree with David ... the leach and the foot look way too short. It doesn't look like the right sail for the rig at all. Also, the mast has nice bend, but does it look like it is raked too far forward? It's possible that the angle of the boom causes an illusion. And the boat does need to be in the water when adjusting the mast rake.

 

[Daveinet]

Before I started, I leveled the boat based on the water line, which seems pretty accurate based on photos I have of the boat sitting in the water. I set the mast rake based on the spec from North Sails, which is what is linked to on the RL forum.
Yes, the boom does angle upward significantly - much worse than any inaccuracy in leveling the boat could ever be. I'm not sure why the sail is cut that way. The boom is not remotely close to 90 degrees from the mast. They way the leach is so tight makes me wonder if the sail was designed for the Mark IV Oz version which had a bendy mast. I lot of bend in the mast would flatten the sail out and release some of the tension on the leach. I'd be very afraid to bend this mast that far.

The history on this specific boat is a little suspicious. The title shows the boat is an '84 model, but the HIN shows a homemade boat built in 1990. No numbers are engraved in the hull anywhere. Original sails seen on other boats built in the US, have RL logo on them. My sail does not. If I had to make a wild guess, I would bet this boat may have been a bare hull that sat around for a few years - maybe after the builder went out of business. I would bet that it was picked up at an auction someone time later and finished in 1990. This is all speculation of course, but to me it seems the most logical scenario that would fit what is known.

I've not found a manufacturer of the sail anywhere. I wonder if the sail was made over seas, which then could easily be made to the wrong spec.

 

[Scott T-Bird]

I think I agree that the sail cut could be based on a very bendy mast. The sail does look a little like a windsurfing sail that doesn't have a enough downhaul (which is what bends the mast). Bending the mast more would also loosen the clew, allowing more outhaul.

I also agree that the mast rake doesn't really matter in this discussion. Besides, I think the boom angle causes an illusion that makes the lower mast look like it is raked forward.

Do you have a spec for mast bend? How do you know that it won't bend significantly more? I guess I would have a sail maker design a sail for the rig, if you can point to those specs.

 

[Daveinet]

I’ve only seen a spec for rake, I’ve not seen a spec for pre-bend or stay tension. In reading the instructions for sail setup, even on the bendy rig, it implies no pre-bend in the mast. While I’ve not calculated the rig tension, it seems like with my current setup, that there is more tension than my personal body weight would put on it, which would mean a few hundred pounds. In how the rig is currently set, the backstay only has a turnbuckle adjustment. When I put the mast up, with the turnbuckle all the way loose, the stay just barely has tension on it. I can crank about 2 inches of adjustment, which is what I had when messing with the sail, once I has some wind to play with. While everything I have done helps, the leach is still noticeably tighter than the rest of the sail. That is when I could lift on the boom and create a twist anywhere I wanted to along the leach. (something I could not do before I put bend in the mast) Something else I’m going to try to do is see if I can change the position of where the halyard attaches to the head. I was thinking to mount pulley to the bracket where the backstay attaches. This would put the halyard about 1.5 inches away from the mast, which would also change the way the leach hangs.

Is loose footed and fully battened on a flexy mast, which combine to make a very versatile sail. The battens should be tied in with enough tension to remove wrinkles whilst sailing, keeping in mind that the sail will wrinkle more as wind pressure increases.
In light airs (0 – 8 knots) the mainsail should look as full as possible for power. Ease the loose foot in so the mainsail skirt sits about 22.5cm off the centre of the boom. Ease the boom vang right off (no tension) and pull the traveller 45cm to windward from the centre line. Then ease the mainsheet and thus boom into the centre line. There should be no luff tension on the main, even to the point that the cosmetic wrinkles develop up to the luff so that the drive moves aft in the sail. In these conditions, the mast will stand straight and the sail will look about the same depth all over with maximum drive at about 45% aft. Rig tension should be set to just hold up the mast with maybe even a bit of slack in forestay (not tight at all).
In moderate airs (8 – 15 knots) you set the mainsail up to be powerful, keeping in mind the boat should be sailed flat, yet with enough tension on luff, foot, battens and mainsheet to remove wrinkles. At this stage, the traveller ranges from the centre line to 15cm to windward with firm sheet tension (that is play the traveller in the gusts). Rig tension should be gradually increased as the wind increases so as to keep a tight forestay with minimal sag.
In fresh winds (15 knots and above) you start to depower the rig so the boat sails as flat as possible. Crew weight should be as far to windward as possible. The aim is to bend the mast through luff, main sheet, rig, batten and vang tension to depower the rig. Pull the foot tension out very tight so the sail sets flat off the boom. The traveller should be eased to leeward before the mainsheet to depower. Only throw the mainsheet in very fresh winds to prevent stalling and knock downs. In these conditions, the boom vang must be very tight so when the sheet tension is eased the mast does not straighten up causing the sail to power up. Rig tension should be gradually increased as the wind increases so as to keep a tight forestay with minimal sag

I've read this about 5 times, and from this description, I get the impression my sail was not made correct for any boat. Even if the sail was blown out, one would assume the leach would have stretched as well, especially with the load of the boom/main sheet on it.

 

[Daveinet]

First sail of the year. Set the mast up with about a 3 inch bow in the center. The leach still tends to hook, even under stronger wind loads. The one thing I did notice is the boat tends to be slower over all. While in some ways, one would expect that, I had assumed there was excessive draft previously, and assumed that was limiting the efficiency. Apparently not.

So the million dollar question is, can one to assume that you can't have too much draft as long as the boat is not healing? (As long as the sail is being back winded)