Thread: GIS Yawl

How have you got the sail lashed to the yard at the throat?

Not sure whether a bendy boom attributes to this as a bendy boom will pull the sail down more over the lenght of the boom that a stiff one, thus removing creases rather than create them (in that area of the sail).

Oh, and I forgot: great to see Bleat finally sailing! She is looking mighty crispy and clean.

I have sailed GISwerk for a few seasons now and am keeping impressed with her performance. It is a great boat: simple but extremely functional and it is a winner in the looks department as well.

I don't get how a bendy boom will take the creases out. BLEAT's boom is bending vertically, not laterally, so that brings the two ends of the boom closer together in a fashion that points them to the sky-- I would also assume like Clint that that would contribute to that strange wrinkle that angles up from the clew along the battens.

Try sailing without the bottom batten. I know the leech will curl and/or flap about there, but this is just an experiment. If the crease goes away, then the batten needs to be moved or adjusted in some way. Perhaps it is too stiff?

Originally Posted by callsign222

I don't get how a bendy boom will take the creases out. BLEAT's boom is bending vertically, not laterally, so that brings the two ends of the boom closer together in a fashion that points them to the sky-- I would also assume like Clint that that would contribute to that strange wrinkle that angles up from the clew along the battens.

I don't think that the two ends of the boom are forced to point to the sky, I rather think that the middle of the bendy boom is forced to bend downwards more by applying downhaul tension (in other words, the ends may seem to point upwards, but the largest bend is in the middle of the boom). This bend than takes a lot, at least for my sail, draft out of the ail as the sail cloth is pulled downwards taking the sail cloth "down" with it.

I am not suggesting at all that there will be any lateral bending (there will not be much since the boom is supported by the mast and the sheet (attached to blocks on the aft end and the middle of the boom).

What I was trying to say is that the crease may (repeat: may, not automatically will) have been caused by the fact that the yard is not peaked up sufficiently (which may have in turn been caused by the way how the sail is lashed on to the yard at the throat: i.e. the downhaul force applied on the luff should continue to the head).

Just some ramblings tyring to feed a discussion on how to resolve this issue.

Joost

Joost, thanks

Indeed a definite issue is that I need to fix the throat of the sail at the yard so that the downhaul tension is restricted to the luff and does not pull through the head of the sail as well. Christophe, aka Callsign, showed this to me and it is quite evident that this needs fixing. I'd like to do it with the spectra I already have. I may glue a wood eye to the yard so the lashings are fixed.

I think you may be on to something, Joost. Maybe the middle does bend down vs the ends up. It is all relative. My sail is loose footed, so I do not have lashings along the foot of the sail.

In fact, I am most satisfied with my yard dimensions. I plan to take measurements of my yard and share them because, so far, they seem ideal. More experimentation will tell.

I sent a file to MIK with my thoughts on a boom and will get started on the new one asap as well as fixing the head of the sail to the yard. That is brilliant.

I think it would pull draft out of the sail is the sail was lashed to the boom, but Clint runs a loose-footed sail which I think is an important detail that wasn't mentioned before.

But great points Joost, I like that perspective.

I keep looking at that crease in capnjon's pictures. And the more I look, the more I think the batten is part of the problem.

Think of the force running down the batten from the leech when the leech is tightened. If the batten is very stiff and is forced inward from the leech, it will create a triangle of stretch in the sail just like you see in the pics.

Possible fixes would be: a more flexible batten or a little more room in the pocket.

Try sailing without it and see what happens.

I like this theory as well. How come we didn't think of these easy things while we were there?

Clint, those creases are not serious at all, as long as the sail is a nice overall shape, which it appears to be. I have those creases as well, and they are even worse on my Laser sail when everything is cranked on. They form because the tension is at 45deg to the warp and weft. Pull the corners of a hankerchief to see this exaggerated. A radial cut helps to some extent, but is not a reason to go for that type of cut.

Have a look at this video of MIK sailing my boat, and you'll see the same creases.

Goat Island Skiff (GIS) - Grahamstown Lake NSW Australia 9 January 2011 - YouTube

Christophe is dead right regarding the attachment at the throat which does need to be fixed to prevent the tension from the downhaul transmitting up the yard. A very stiff yard will help too as one that bends will generate even more tension between the middle of the yard to the clew. I have banged on ad infinitum on this very issue. The throat on my sail is shackled at the throat and the yard is the stiffest alu pole I could find. This lets you play with the yard tension independently to suit the breeze. But seriously, your sail looks fine to me.

What weight of cloth is your sail?

Spot on Paulie,

I was thinking the same. Another way would be just to use a leech batten. But battenless would probably be enough on the trailer to see.

MIK

I saw that crease several days ago when the video first emerged. I assumed it was caused by a line behind it, thinking you may have rigged a lazy jack of sorts.

It seems to run from the clew up and forward, eventually pointing to the yard at the point where the halyard is attached. That leads me to speculate your yard is too flexible. Downhaul tension--opposed by the halyard pulling up on the yard--will tell the tale, IMO. Reduce tension on the downhaul and see if that crease changes or disappears. If so, just sail with less tension until you can stiffen or replace the yard.

MAM, There was an upper portion the the crease that was there but MORE d'haul took care of it. The lower part -- from clew to first batten up (sometimes 2nd batten) is the problem.

Incidentally, when I am reefed it all looks fine.

Bruce thanks for your thoughts...I am sure I am being a bit of a nervous new parent!

Attachment 217281

Interesting to see the large difference in sheeting angles between the first two (Christophe and Clint) and the third (Paulie), for the same wind angle (burgees indicate the same direction). The first two look to be well over-sheeted. This could be contributing to the "problem" with your sail. The other obvious thing here is the crazy amount of twist going on, which I'll discuss further down as a separate issue. On Paulie's boat, note the angle between the yard and the boom. It's about 10 degrees. Then look at the angle between the yard and the boom on Christophe's and Clint's boat. It's about 60 degrees. That's a huge amount of twist!

Are any of you guys using telltales? I could not detect any from these shots or the video, but I would recommend installing some on the reef point lines (two would do). This would help you a lot.

Clint, I have also been thinking back to my first couple of sails in Hakuna Matata, and how my sail looked then. Basically, in above 6 kts my sail was rubbish and it was all down to the fact that my first yard was too bendy. The stiff yard fixed everything. What was happening, was the centre of the yard was bending, creating more tension between the clew and the centre of the yard. The "soft" tip of the yard was also unable to hold the leech tension so it fell away (opened) too much. If your yard is a bit bendy, I am positive this is the issue and adding a stiffer yard will fix it. You will find that a stiff yard will hold the leech tension so much better, and the payoff will be more power.

I've also had a much closer look at the video of your sail, and I think I can detect the leech falling off slightly, starting near the lower batten where the crease starts. There is only one cause for this, and it's lack of leech tension. This will be fixed by a stiffer yard and more downhaul tension. I don't believe the crease has anything to do with a fault in the sail. Also, removing the battens will only create a softer leech and rob more power, so don't do this yet.

With the lug, the sail will automatically depower in a gust by the yard falling away, just as the square top sails do. The last thing you want is a double whammy where in addition to the yard falling away, it is bending in both the horizontal and vertical plane as well. Another benefit of a stiff yard, is that you can apply much more downhaul and limit excessive power-robbing twist.

Of course, a bendy boom will also be contributing to all this instability, so it goes without saying that the boom needs to be stiff as well.

Hope this helps.