Too much vang

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Re: Too much vang

Postby TIM WEBB » Tue Dec 01, 2015 8:26 pm

K.C. Walker wrote:The other red line is for the out haul. It's internal and multi-purchase. One yanks on the line and it automatically cleats through the clam cleat, I think his is 4:1. I set up something similar, though mine is external. It really makes it easy to adjust out haul on-the-fly, though Mike says he just cranks it on full and never changes it.

Oh, OK, internal outhaul - kinda had a feeling that's what it was, just couldn't make sense of the eye and block ...

I don't adjust the outhaul much either, except to ease it in really light air.
Tim Webb
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Re: Too much vang

Postby tmittner » Tue Dec 01, 2015 10:21 pm

After looking at maximum working loads for blocks, I'm thinking Harken 40mm, 29mm, and micro blocks or equivalents for 20:1 vang.
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Re: Too much vang

Postby GreenLake » Tue Dec 01, 2015 11:10 pm

TIM WEBB wrote:GL, I did try the vang the other way around, but it's more difficult to adjust that way, so I put it back to how it is in the pic, and I find it to be more than enough purchase.


You have it rigged the right way for the reason you give. The difference between 4:1 and 5:1 doesn't make enough of a difference and you would have to pull in line with the vang to get the benefit, and that's just not going to happen. Good to know, though, that the difference exists.

TIM WEBB wrote:And all that math still makes my brain itch! ;-P


:shock:
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Re: Too much vang

Postby GreenLake » Tue Dec 01, 2015 11:30 pm

tmittner wrote:After looking at maximum working loads for blocks, I'm thinking Harken 40mm, 29mm, and micro blocks or equivalents for 20:1 vang.


Those look like they give you about 480 lbs / 20 you would pull a bit under 30 lbs to reach maximum (rounding up for friction). So that looks reasonable from the point of operation. You could pull harder, but on a small line like this, not too likely.

Now, the bit where I don't have experience is whether your sail could ever load the vang beyond that. Possibly you'd want the vang to fail at some point, rather than the boom.

I see that the ready-made vang system (they have a 15:1) is set up for similar max load. Possibly likely that once you max out, you reach sail forces that would heel your boat even if you are hiked out...but as I said, probably better not to overdimension the vang too much.
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Re: Too much vang

Postby tmittner » Wed Dec 02, 2015 12:03 am

GreenLake, Right, KC starts his first cascades with a 40mm Ronstan and it has held up well for him. That Harken 15:1 vang was rated for mainsails up to 125 square feet and the DS main comes in at just over 100 square feet I believe. I am feeling comfortable the 480# max working load.
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Re: Too much vang

Postby tmittner » Sat Dec 05, 2015 4:41 pm

One more thing, in looking at the picture of Mike Gillum's boom vang for a pattern for my own, I come up with 24:1. I know Mike says in other posts that his is 20:1 but the one in the picture looks like 24:1, IMHO, although my better half would be the first to say I'm often wrong.
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Re: Too much vang

Postby GreenLake » Sat Dec 05, 2015 11:22 pm

If you mean the picture that appears in this post
http://forum.daysailer.org/forum/viewtopic.php?p=19967#p19967
then it definitely shows a 20:1.

The cascade is a two stage, so it's 4:1 (and that multiplies with the purchase).

The purchase has 4 parts inside it and the pull of the part that leads outside is along the same direction. Since it exist at the "free" end of the purchase, the purchase is "rigged to advantage" that is, you add that part to the total to get (4+1=5):1, for a combined 20:1.

Image
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Re: Too much vang

Postby tmittner » Sun Dec 06, 2015 1:10 pm

GL, I guess I was looking at the block and tackle which appeared to have a triple at the moving end and a double with a becket at the fixed end. Thinking of my 4:1 mainsheet system with 2 fiddles, becket at the fixed end and the mainsheet exiting there but not to advantage, I assumed that Mike's system with the becket at the fixed end and the line leaving to advantage it would have to an even ratio. I'm learning, but slowly...slowly...
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Re: Too much vang

Postby tmittner » Sun Dec 06, 2015 3:03 pm

GL, I think I know the answer, I could not reeve my system with the becket at fixed point and the free line to advantage without having a even ratio. When I looked very closely at the picture I can make out possibly three lines going from the double with a becket to the triple at the top, but could only see two coming back. One in the system and one to advantage (I count the deck block as simply a turning block). It is impossible to have 3 lines going up and only 2 coming down in this picture. As Spock would say, eliminate the impossible and the improbable becomes probable. There are 3 lines coming down, 2 in the system and 1 to advantage, one of the return lines is completely hidden by the 2 clearly visible ones. That would make it 2 X 2 X 6 = 24:1. If there are only 2 lines going up and I can clearly see 2 lines returning with one to advantage it would be 2 X 2 X 4 = 16:1 Mike's earlier system he discarded in favor of 20:1.
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Re: Too much vang

Postby tmittner » Sun Dec 06, 2015 4:06 pm

Boy did a butcher Spock! should read: If you eliminate the impossible, whatever remains, however improbable, must be the truth.
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Re: Too much vang

Postby GreenLake » Sun Dec 06, 2015 11:15 pm

OK, looks like there's a part that's almost fully hidden in the picture, so yes, five parts and the 6th being rigged "to advantage", that is contributing. So, that's a 24:1 system.
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