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SMBReno

Cascading Vang System-Help me design one

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For singlehanding a Moore 24, I want to run a double ended vang system back to the cockpit so I can quickly release the vang when necessary. Thinking about something like pictured in the attached image, except 8:1. My current vang has too much friction from double and triple blocks (ok, and too large diameter line as well), and I'm thinking a cascade system will be less friction and tangle. Of course drawings always have terrific reeving, don't they.

 

So I was thinking about a system with two Karver KBO1 single blocks (or equivalent) and a Karver KBO1 double, then led aft. What's the best way to rig this? I have a bail on my mast step where the vang & Cunningham currently attach, so plan to use that. I can attach the blocks using a thimble (or not) and eyesplicing spectra, but it would be nice to diminish the number of lines/connections to the bail.

 

Anyone created or have images of a simple system for this?

 

For example, can you bury splice a second line into the standing part of a spectra line (with a long tail and whipping of course) - haven't seen this but theoretically no different than an eye splice. Anyone done this?

post-45134-0-44194200-1357515406_thumb.jpg

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I have done all those things. I race on a boat with a triple cascade (8:1) although it is single ended but double ending it would not be a problem. I did a sketch of such a system HERE. As far as an Amsteel to StaSet splice, which I think is what you are wanting, I have complete instructions HERE. This particular splice is 1/8 inch Amsteel to 1/4 inch StaSet. I think it would be much easier with larger lines.

 

By the way, the 20:1 vang that I show on the same page as the sketch of the 8:1 is no longer in use on my boat. It was just too much power for an old wood boom. I switched to a 4:1 as then I can let the crew tug on it without worry.

 

It is possible on your double ended system to locate the two blocks on deck on each side of the mast and locate the anchor points for the other two lines aft of the mast. By careful placement of the blocks, you can get an effective pivot point such that you will not change vang tension as the boom position is changed. That was one of the goals of my 20:1 system but I gave it up after reading Denis Conner saying that it is desirable to have the tension increase as the boom is let out. That and not wanting 20:1 power.

 

Allen

L-36.com

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I'll assume that the best system for the job is the 8:1 system shown in post 2.

 

You don't want Karver blocks for the first two blocks beneath the boom. They spend 99% of the race in a fixed position and don't need roller bearings. Use some low tech wire blocks which are cheaper and plenty strong enough. Think about using a Ronstan RF 103 combined with some 3/16" Amsteel Blue or similar for the upper two blocks. I don't know your loads but you might get away with RF 418 and 1/8" Amsteel Blue on the second block. A Karver KBO1 would be ideal for the third and fourth block combined with some kind of 1/4" string. There are lots of options here - XLS extra maybe.

 

Mount a cleat, eye swivel gizmo ( RF60 maybe ) on the centerline forward of the main hatch and run a very long tail back aft. Tie it off somewhere reachable such as the traveller. You could put a Y in the end and tie it off to each side of the cockpit.

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We use a similar type of system but use a couple of triple blocks with a becket along with single and double blocks to gain an additional purchase points required.

 

It's all up a combination of these single and triple becket blocks and a couple of doubles at the base of the mast to feed the vang relesae lines on either side of the boat coach roof.

 

Which tends to keep it all pretty tidy and close together.

RF41510.jpg

 

RF41312.jpg

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Exactly! Is the arrangement at the foot of the mast like this:

Yes. If you look at my drawing you posted at the beginning, you will see that the lower block provides the last 2:1 purchase. and splits the vang either side of the boat.

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I happened to have recently analyzed that cascade using low friction rings. Obviously you won't have 8:1 due to the friction but what will you have? My analysis says 4.6:1 for the cascade but you will also have some loss in the lower turning block so your net using low friction rings will likely be more like 3.3:1. You might consider using real blocks for the more lightly loaded lower sections as you can use cheap blocks there. For example, if you are pulling with 50 pounds, the turning blocks have something like 85 pounds on them and the first block 100 pounds. The second block 200 pounds and the last one 400 pounds (assuming no friction). You could use T2-29 blocks for the first 4 blocks and a low friction ring for the last block and have 6.7:1. The small T2 blocks are about $20, not that different than the antal rings. HERE is my write up that goes through the math and has my test data. The example I used does not have the two turning blocks that you will need which is the difference between the 3.3:1 and 4.6:1.

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The low friction ring cascades I've seen tend to use blocks for the final purchase - 4:1 or 6:1. Too many cascades and you run out of travel.

 

I think there is just too much loss to do otherwise. A single cascade with a low friction ring is about 1.7:1, the first turning block about 0.7:1 To get over 8:1 with just low friction rings you would need a cascade of 4 or 5 stages (5.8:1 or 10:1). Too many.

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The low friction ring cascades I've seen tend to use blocks for the final purchase - 4:1 or 6:1. Too many cascades and you run out of travel.

Like this...post-47735-0-78384100-1418345440_thumb.jpg

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For singlehanding a Moore 24, I want to run a double ended vang system back to the cockpit so I can quickly release the vang when necessary. Thinking about something like pictured in the attached image, except 8:1. My current vang has too much friction from double and triple blocks (ok, and too large diameter line as well), and I'm thinking a cascade system will be less friction and tangle. Of course drawings always have terrific reeving, don't they.

 

So I was thinking about a system with two Karver KBO1 single blocks (or equivalent) and a Karver KBO1 double, then led aft. What's the best way to rig this? I have a bail on my mast step where the vang & Cunningham currently attach, so plan to use that. I can attach the blocks using a thimble (or not) and eyesplicing spectra, but it would be nice to diminish the number of lines/connections to the bail.

 

Anyone created or have images of a simple system for this?

 

For example, can you bury splice a second line into the standing part of a spectra line (with a long tail and whipping of course) - haven't seen this but theoretically no different than an eye splice. Anyone done this?

 

I have done the bury on multiple vangs, here is one for the J/24

post-45198-052199300 1300364188_thumb.jpg
post-45198-059013700 1300364019_thumb.jpg
post-45198-028352200 1300364005_thumb.jpg

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I happened to have recently analyzed that cascade using low friction rings. Obviously you won't have 8:1 due to the friction but what will you have? My analysis says 4.6:1 for the cascade but you will also have some loss in the lower turning block so your net using low friction rings will likely be more like 3.3:1. You might consider using real blocks for the more lightly loaded lower sections as you can use cheap blocks there. For example, if you are pulling with 50 pounds, the turning blocks have something like 85 pounds on them and the first block 100 pounds. The second block 200 pounds and the last one 400 pounds (assuming no friction). You could use T2-29 blocks for the first 4 blocks and a low friction ring for the last block and have 6.7:1. The small T2 blocks are about $20, not that different than the antal rings. HERE is my write up that goes through the math and has my test data. The example I used does not have the two turning blocks that you will need which is the difference between the 3.3:1 and 4.6:1.

I understand about the friction, however if you have an 8:1 purchase, surely it's 8:1 regardless of the pulleys or rings used ie, if you pull 800mm the end result is 100mm movement. Even if you feed it around ratchet blocks backwards and it takes 1000kg to pull a 20kg load, it's still an 8:1 purchase, just poorly executed.

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The issue with purchase calculation is that it assumes a perfect world with no friction. As Allen said, it will remain close to true with blocks, but with rings it will diminish drastically. Top ring is a good idea, and figuring out a way to make sure the lines in the purchase hold themselves if/when the blocks blow up would also be beneficial.

 

HW

 

 

I happened to have recently analyzed that cascade using low friction rings. Obviously you won't have 8:1 due to the friction but what will you have? My analysis says 4.6:1 for the cascade but you will also have some loss in the lower turning block so your net using low friction rings will likely be more like 3.3:1. You might consider using real blocks for the more lightly loaded lower sections as you can use cheap blocks there. For example, if you are pulling with 50 pounds, the turning blocks have something like 85 pounds on them and the first block 100 pounds. The second block 200 pounds and the last one 400 pounds (assuming no friction). You could use T2-29 blocks for the first 4 blocks and a low friction ring for the last block and have 6.7:1. The small T2 blocks are about $20, not that different than the antal rings. HERE is my write up that goes through the math and has my test data. The example I used does not have the two turning blocks that you will need which is the difference between the 3.3:1 and 4.6:1.


I understand about the friction, however if you have an 8:1 purchase, surely it's 8:1 regardless of the pulleys or rings used ie, if you pull 800mm the end result is 100mm movement. Even if you feed it around ratchet blocks backwards and it takes 1000kg to pull a 20kg load, it's still an 8:1 purchase, just poorly executed.

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The purchase calculation is simple maths with maybe an allowance for stretch. An 8:1 purchase means you pull the tail of the purchase 8times the distance the standing part moves. What you and allen are discussing and comparing is the efficiency of the system. If I was going to use friction rings I would probably add another cascade to allow for friction losses, however I would still only use rings on the top 2 cascades. (By the way adding another cascade makes it 16:1 regardless of friction)

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Agreed, apologies was looking at your pull load, not the travel.

 

HW

 

The purchase calculation is simple maths with maybe an allowance for stretch. An 8:1 purchase means you pull the tail of the purchase 8times the distance the standing part moves. What you and allen are discussing and comparing is the efficiency of the system. If I was going to use friction rings I would probably add another cascade to allow for friction losses, however I would still only use rings on the top 2 cascades. (By the way adding another cascade makes it 16:1 regardless of friction)

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The low friction rings come into their on the high load parts of the system where you are not requiring much travel out of them, when everything loads up you have confidence that they are not going to explode, and they are a fraction of the cost of similar rating high load blocks.

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