Vang questions

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Vang questions

Postby RobH912 » Mon Oct 14, 2019 10:57 am

GL - yes I am not sure that the Vang set up is optimal.

There was some new hardware added to the boat recently in the process of selling the boat.

Looks like Harken 40C blocks, cleated block attaches to the mast, but has a small line, and not very much mechanical advantage.

I will do something different in the spring.

Suggestions or pictures from others on their Vangs?
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Rob


DS1 #2444
Cape Cod
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Re: Internal Halyards

Postby GreenLake » Mon Oct 14, 2019 5:59 pm

The cleat on the van needs to ope then other way, if you want to be able to release it.

I have mine strung so the cleat is in the other end (I could have also set it up so the cleat is in the middle, but as rigged, I can almost reach it from the helm position). Some people do without the cleat and lead the free end to some cleat on the CB. That's also an option. My setup isn't ideal for being operated with crew on the rail, but it works for our (often moderate) conditions. In stronger winds we simply set a tight vang and don't play it constantly.

Our vang has a cascade + 6:1 for 12:1 total purchase. Can't quickly tell where yours is at, but if it's less than that, you might want to add a 2:1 or 4:1 cascade.

So that's something you should consider

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Vang setup

Postby RobH912 » Mon Oct 14, 2019 11:24 pm

GL - Yes I can see that the cleat would be more accessible at the boom end rather than at the mast.

I’ll need to look at it in the morning, but isn’t it simply just undoing shackles and switching it around?

It is 4:1 and have not see a cascade pulley set up before. I like that idea.

WDYT of the current size of the blocks 40, and the line which I think is 1/4 “ ? Setup seems / looks small to me.

Maybe a 55 mm set of blocks with 5/16 line... and try to increase purchase.
Rob


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Cape Cod
Eastham, MA
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Re: Vang questions

Postby GreenLake » Tue Oct 15, 2019 4:55 pm

I don't think mine are even 30mm.

the thing with a cascade is that the last block carries the full load (everything else is at half load).

If you have a multipart purchase, the load on each part of the line should be the same fraction of the total load. (However, because of friction, it's not 100% so).

With modern rope you can get to rather small diameters, the blue line I have on my vang isn't even 3/16" and it's plenty.

The purchase needs to be set up so that the attachment points to the blocks can handle 1/2 of the load of the vang (or 1/4 if you go for a dual cascade). For a 2:1 that's still significant but only half of what you would get if you used the purchase directly. Now, each sheave, only takes about the pull that you apply maximally at the free end - double that, if you want for dynamic loads on the vang when cleated.

In my case, it still comes to 1/12 of load on the vang (actually 1/6, because of the 180 degree turn around the sheave). Still, if each sheave can handle 150 lbs, the vang could pull at 900lbs. You simply don't need excessive diameters.
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Re: Vang questions

Postby RobH912 » Fri Oct 18, 2019 1:00 pm

GL & John - just wanted to wrap this thread up.

Took #2444 to a local boat yard (next town over from me), they service small sail boats, it is the "go to place" for repairs by folks at my sailing club, and they also still that make new Cat sail boats. Met with one of their riggers, he was familiar with DS, said he has worked on them, and we talked about adding a spinnaker set up. He looked at the mast, "restoration" work that had been done, and he thought it all looked fine.

He thought the best place was to add a third exit sheave was at the bottom of the mast, near the existing main & jib exit, then back up to the deck.
GreenLake wrote:There seems space for a third exit sheave - there's that flat spot that extends above the other two. Perhaps all it takes is to cut a slot and add one.


He will also get back to me with his thoughts on adding a third cam cleat on deck top for the spinnaker, or look for a another solution, e.g., 3 line clutch to mange all three halyards... was leaning toward 3 line clutch as it would be simpler.

He liked the idea of lashing 40mm blocks to the existing aft horn cleats and liked the picture I had posted of a friends DS front block set up, basically a cheek block, cam cleat and the fairlead with the rubber piece so the guy line can slip into the fairlead. We talked about having a small ratchet block forward (Ronstan Orbit 40) but he thought that was not necessary "simple solutions are good on DS". He was not concerned about accidental cleating on the cam cleat.

He is going to get back to me before he worked on the boat this winter to talk about downhaul and topping lift set up, spinnaker halyard, shackles, other hardware needed.

GL - he too thought that the size of the 4:1 Vang / line was fine and I'll figure out a cascade system myself to add in the spring when I get the boat back.

Left #2444 at their yard to be stored, they got it covered before the Nor'easter hit here the next day. The other DS in my driveway got shrink wrapped also before the storm. We are not on Cape Cod for the winter, so it was great getting boats put away for the winter and knowing that I'll be sailing in the spring.

Thank you all for good thoughts on spinnaker rigging. Very helpful, I learned a lot.
Rob


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Revisiting Vang Set Up

Postby RobH912 » Sat Dec 21, 2019 6:05 pm

GL - My original reply to your question on a picture of my vang, and a couple of subsequent posts on Vangs, were originally under this "Internal Halyards" thread. Not sure if you want to move the Vang portion of this thread somewhere else...

It is winter, spending time on the internet trying to learn more about sailing, hardware, etc. and I wanted to revisit a couple of things in your comments / ask some questions.

Focusing on your post, in particular the color highlighted text / 900 lb reference.

GreenLake wrote:I don't think mine are even 30mm.

the thing with a cascade is that the last block carries the full load (everything else is at half load).

If you have a multipart purchase, the load on each part of the line should be the same fraction of the total load. (However, because of friction, it's not 100% so).

With modern rope you can get to rather small diameters, the blue line I have on my vang isn't even 3/16" and it's plenty.

The purchase needs to be set up so that the attachment points to the blocks can handle 1/2 of the load of the vang (or 1/4 if you go for a dual cascade). For a 2:1 that's still significant but only half of what you would get if you used the purchase directly. Now, each sheave, only takes about the pull that you apply maximally at the free end - double that, if you want for dynamic loads on the vang when cleated.

In my case, it still comes to 1/12 of load on the vang (actually 1/6, because of the 180 degree turn around the sheave). Still, if each sheave can handle 150 lbs, the vang could pull at 900lbs. You simply don't need excessive diameters.


Your posts on vangs always mention having a 12:1 purchase (6:1 + cascade), my current set up is a 4:1 purchase vang set up using a pair of Harken 40C fiddle blocks. Looking at the Harken site, these blocks have a maximum working load of 485 lbs.

Don't really understand the physics so these may not be the "right" questions....

Is the 150 lb per sheave / 900 lbs capability just an assumption made / an example of the lifting power that the 12:1 set up could provide?

Is that much capability needed for a DS, should that be a goal for setting up a new vang?

As an example looking at Harken triple blocks https://www.harken.com/productdetail.as ... &taxid=417, which have a maximum working load of 1455 lbs. If I had a pair of these I could get to 6:1. Do I need this much working load?

Thanks in advance for your reply ! :D
Rob


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Re: Revisiting Vang Set Up

Postby GreenLake » Sat Dec 21, 2019 6:37 pm

RobH912 wrote:GL - My original reply to your question on a picture of my vang, and a couple of subsequent posts on Vangs, were originally under this "Internal Halyards" thread. Not sure if you want to move the Vang portion of this thread somewhere else...


Done.
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Re: Revisiting Vang Set Up

Postby GreenLake » Sat Dec 21, 2019 7:08 pm

RobH912 wrote:
GreenLake wrote:...
In my case, it still comes to 1/12 of load on the vang (actually 1/6, because of the 180 degree turn around the sheave). Still, if each sheave can handle 150 lbs, the vang could pull at 900lbs. You simply don't need excessive diameters.


Your posts on vangs always mention having a 12:1 purchase (6:1 + cascade), my current set up is a 4:1 purchase vang set up using a pair of Harken 40C fiddle blocks. Looking at the Harken site, these blocks have a maximum working load of 485 lbs.


That means that the maximum rated pull on the vang line is a theoretical 121lbs (here I'm assuming 4:1, but otherwise the calculation would - in principle - be the same for 6:1). With that the total pull would be 484lbs. Now, if you put that in a 2:1 cascade, you'd get 968 lbs total rated pull and the block for the cascade better be rated at 1000lbs or else it's the weak point.

Because of friction, you actually need to pull harder. Let's say 5%. Instead of 968, you get .95 that or 920, due to loss in the cascade. However you need to pull 1.05x1.05x1.05x1.05x121 or ~147lbs to get the rated pull from your fiddle blocks.

RobH912 wrote:Don't really understand the physics so these may not be the "right" questions....

Is the 150 lb per sheave / 900 lbs capability just an assumption made / an example of the lifting power that the 12:1 set up could provide?

Is that much capability needed for a DS, should that be a goal for setting up a new vang?

As an example looking at Harken triple blocks https://www.harken.com/productdetail.as ... &taxid=417, which have a maximum working load of 1455 lbs. If I had a pair of these I could get to 6:1. Do I need this much working load?


The numbers I use(d) are always for illustration, except where I plugged in the real max working load of your fiddle.

How much do you need?

You can actually estimate that. You'll need the maximum righting moment that you can achieve. Beyond that, you capsize, so that defines the max sail force (righting moment divided by the lever arm, given by location to center of effort). Now assume that force pulls at the boom and the vang needs to hold that. For a vang at 30° the total force is 4x the force pulling up.

At 14 knots there's about 1lb/sqft of force generated by the sails, or 100lbs by the main. we know you can easily hold her upright, so your vang will need to hold 100lbs. Comes to 900lbs easily, given the way the vang kind of attaches mid boom and at an angle.

There may be a worst case scenario here in assuming the vang needs to hold the entire sail force, so perhaps 500 would be enough, but this is the kind of reasoning behind sizing parts like that.
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Re: Vang questions

Postby GreenLake » Sat Dec 21, 2019 7:47 pm

Here's another way to do it:

  1. Use the Harken mainsheet calculator
  2. Enter the dimension for the vang attachment point, instead of the one for the mainsheet
  3. Account for geometry: sideways angle pull, instead of down

You get 4x504=2000 lbs for 14 knots or > 4,000 for 20 knots

However, without at least some tension on the mainsheet, your main will be depowered (except dead downwind). If main takes half the load, we are back at 1,000. By 20 knots I think your main would be depowered some to keep the boat upright...

I'm using Ronstan RF20332 triples for my 6:1, they have 880 max load; I should be using a 50mm block for the cascade to get the at least 1100 working load, but instead I am using a 30mm (660). That should make that block the weak point, but so far the weak point seems to be the strap on the boom, that one has deformed a bit...
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Re: Vang questions

Postby jalmeida51 » Sat Dec 21, 2019 11:48 pm

My vang is 5 to 1 with a 2 to 1 cascade makes it 10 to 1. I use Harken 29 carbo blocks with 1/4 stay set line. I attach it to the boom with a vang plate. I don't worry about the blocks or line failing. If it is going to fail, I believe it will fail at the boom. The diameter of the boom is small in my way of thinking. But I believe it is the same diameter of the boom used on the Rhodes 19. I know there has been boom failures on the Rhodes for coming too hard on the vang. One solution was to slide a reinforcement sleeve down the inside of the boom. At 10 to 1 I have more than enough purchase. Of course I don't race. I had 4 to 1 on the Rhodes19 I used to own and that was useless. But being old could be part of the problem? Happy Holidays, John
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Re: Vang questions

Postby GreenLake » Sun Dec 22, 2019 5:36 am

If your cascade is using a 29mm block, that would limit you to 350lbs WL. While the calculated values appear high (a sentiment echoed in other discussions I've read) that value seems low. The WL for multiple sheaves 29mm blocks is much higher, so that issue only affects the single block for the cascade.

Now, I get where you are coming from with max load on your boom. Undersized booms are at risk if they hit the water with vang tight.
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Re: Vang questions

Postby jalmeida51 » Sun Dec 22, 2019 11:04 am

On my cascade the single block is a Ronstan55 with 5/16 stay set line.

John
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Re: Vang questions

Postby GreenLake » Sun Dec 22, 2019 7:56 pm

That would be a bit beefier, 1100lbs.
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Re: Vang questions

Postby RobH912 » Mon Dec 23, 2019 3:29 pm

GL & John - thank you for posting a lot of great info to my Vang questions.

I need to re-read & think through the information, and I know I'll have some follow up questions.

It is a busy time of year... Happy Holidays and a Merry Christmas.

Thanks!
Rob


DS1 #2444
Cape Cod
Eastham, MA
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Re: Vang questions

Postby GreenLake » Mon Dec 23, 2019 6:39 pm

Always welcome.
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