Old vs. New Laser

#21
In most conditions, block-to-block vang is plenty...and you can put that amount of tension on just by sheeting in to block-to-block and then cleating the vang.

But not all. Leech flutter is slow and there are, (at least for me) many times when just block to blok will not stop leech flutter, but the new vang can get the leech tension needed to stop it. Not with the old vang. At least not me.
If the end of the leech is attached to the end of the boom, which is on the deck when you are block-to-block, how can you increase leech tension by adding more vang when you are already sheeted block to block? It would seem to me that adding more vang might increase mast bend, but since the position of the end of the boom is fixed on the deck when you are block-to-block that would loosen the leech.

It was my understanding that the purpose of greater than block-to-block vang tension was to prevent the boom from lifting as the sheet was eased, thereby preventing the sail from becoming fuller when easing the sheet (in a puff in heavy air, or when playing the sheet in waves etc.)

Anyway, I could super-vang without any sheet tension with the old (mid-90's) vang setup of rope loops. My current vang setup is 6:1 with the old blocks and additional blocks instead of loops. I can easily super-vang with this setup also. The only convenience of the new vang hardware (beyond the unnecessary additional purchase) is the better performance when pulling from an angle, such as when hiked out. When I set up my 6:1 vang, it seemed to work fine, so I have kept it that way. I get funny looks from the young-uns on the race course, but I also have much less vang line floating around on my deck and in my cockpit because of the lower purchase.
 
#22
I never had to do this with the old vang, never had any problems with it
Merrily is talking about a technique that was used before any additional purchase was allowed in the vang (i.e. 3:1) and when the vang cleat block was the one attached to the boom. Before your time Ross, and mine. Back when men were men, and girls sailed Europes. ;)
 

Rob B

Active Member
#24
If the end of the leech is attached to the end of the boom, which is on the deck when you are block-to-block, how can you increase leech tension by adding more vang when you are already sheeted block to block? It would seem to me that adding more vang might increase mast bend, but since the position of the end of the boom is fixed on the deck when you are block-to-block that would loosen the leech.

Check out the bend in the boom of someone using the updated vang in a blow.

If you have not sailed withthe new vang ina blow it's hard to describe, but when you are 2 blocked and that leech flutter starts you just ean forward and pull MORE vang on. Leech flutter goes away.

It works.
 

Rob B

Active Member
#25
I never had to do this with the old vang, never had any problems with it
Back in the day when the regular vang was in use I did not have to do this either. But by '89 I was using the extra purchases and the Harken vang swivel. So the cleat was at the base of the mast.

In '83 when I was young and before the extra purchases were discovered I would go back and fourth as to where to have the vang cleat. We mostly just sailed around with loose vangs compared to today's standards.
 
#26
If you have not sailed withthe new vang ina blow it's hard to describe, but when you are 2 blocked and that leech flutter starts you just ean forward and pull MORE vang on. Leech flutter goes away.

It works.
Yeah, I can do that with my current setup using the old vang blocks and bullet blocks...but why does it work? Seems like the leech should get looser if you move the mast tip closer to the clew by adding more vang. I suppose it's possible that by adding mast bend you are flattening the sail, moving the draft forward and changing the angle of the leech, thus reducing flutter.
 

Rob B

Active Member
#27
I'll take a stab at this. I'm no engineer, but I did stay in a Holiday Inn Express last night.

The downforce from the vang pulling on the boom transfers directly to the end of the boom which is where the leech is attached via the clew. The downward force is tied directly to the leech, which connects to the top of the mast.

So, all of the force used to create mast bend is through the leech, but the vang in the lever.

If you draw a scetch of the boom, mast and vang and then draw arrows indicating the direction of the forces involved when vang is applied it helps you to see how the leech does this. At least that's how I see it........
 
#28
I'll take a stab at this. I'm no engineer, but I did stay in a Holiday Inn Express last night.

The downforce from the vang pulling on the boom transfers directly to the end of the boom which is where the leech is attached via the clew. The downward force is tied directly to the leech, which connects to the top of the mast.

So, all of the force used to create mast bend is through the leech, but the vang in the lever.

If you draw a scetch of the boom, mast and vang and then draw arrows indicating the direction of the forces involved when vang is applied it helps you to see how the leech does this. At least that's how I see it........
Yeah...I know how the vang tensions the leech normally...but what about when the boom cannot move any further because it has reached the level of the deck (i.e. block-to-block). At that point any additional vang tension can't move the end of the boom. The Laser sail is loose footed (only attached to the boom at the clew), so the only place the boom can apply force to the sail is at the clew. The boom pivots at the mast, and so the boom cannot apply any force to the mast except through the sail (i.e. through the clew). So, when the boom is block-to-block, it has reached the maximum amount of force that it can apply to the sail/mast system. Adding more bend to the boom doesn't move the end of the boom appreciably, and so doesn't move the clew or the mast. (Obviously, adding more vang prevents the boom from lifting when the sheet is released, but we are talking about block-to-block trim here.)

Can anyone explain where I am going wrong here? (i.e. Does adding more vang after the sail is sheeted block-to-block change the leech tension at block-to-block trim?)
 
#29
I think the problem is the assumption that a tighter leech will flutter less. I would have thought that a tighter leech would flutter more.

Pulling the vang beyond block to block (when the mainsheet is block to block) will bend the mast more, which moves the draft further back and opens the leech. An open leech has less tension and depowers the sail.

So, pulling on more vang may well reduce leech flutter, but at the expense of power. A pretty sail is not necessarily a faster sail (in the Laser world especially).
 
R

Ross B

Guest
#30
Leech Lines were messed around with back in the day, one of my sails from my first boat has one, and it worked well. I still think they would be added to the class rules, inexpensive and easy to add, and it doesn't make you faster, whats to loose
 
Thread starter #31
Sounds reasonable, TonyB.

I started this thread after reading the "Understand the un-stayed rig" article on roostersailing.com, where the writer is sort of saying that a lot of people are using too much vang, just because they can.
 

Rob B

Active Member
#32
I think the problem is the assumption that a tighter leech will flutter less. I would have thought that a tighter leech would flutter more.

Pulling the vang beyond block to block (when the mainsheet is block to block) will bend the mast more, which moves the draft further back and opens the leech. An open leech has less tension and depowers the sail.

So, pulling on more vang may well reduce leech flutter, but at the expense of power. A pretty sail is not necessarily a faster sail (in the Laser world especially).
From my personal experience I just don't see how a fluttering, flapping, vibrating leech can be fast. It disturbes the air flow coming off the sail massively. That vibrating has to be taking power away as well.

I know when that flutter starts I pull on a smidge more vang and it goes away. I feel faster anyway.
 
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