Too much vang

[tmittner]

Hi, I would like to jump into this thread as I am building a vang for my DSII restoration project. My current set up is hinged mast and mid-boom sheeting with 4:1 manual ratchet fiddle blocks. I want to keep my stern clear of lines for the grandchildren to easily use my stern mounted swim ladder. I have Dwyer mast, boom and sliding gooseneck (although the gooseneck is kind of mangled and I will be replacing parts). I want to keep the sliding gooseneck so the boom can be used for tent/awning. I do not have or want a mid-boom traveler, again for recreational convenience.

Studying various threads on the forum I am amazed at the amount of information available to a newby like me! A powerful vang seems to be a good solution to control mainsail leech on all points of sail without a traveler, along with outhaul, boom downhaul, cunningham, jib halyard tensioning, and barber haulers sail shaping and positioning controls.

I am planning on tuning my rigging as per North Sails guide. Approximately 25' initial distance from masthead to transom, and then increasing this distance to 25' 1" or 2" by tensioning the forestay putting approximately 150# on each shroud, (approximately 100# on forestay?). I am putting all of this info into the question because each variable seems to impact other variables in not always foreseen ways.

My question is, given this scenario, does anyone have a feel for how much vang purchase my Dwyer gooseneck will take with a reasonable cushion for error? Reading between the lines, it seems that a 20:1 vang will mangle the gooseneck, where as a 4:1 vang will not take the place of a traveler in controlling the leech? Am I off base here? Any insights will be greatly appreciated!!!

[K.C. Walker]

I think that the way you are intending to set up your rig will work very well. Also, I think that 20:1 boom vang will work just fine with the sliding gooseneck, as that's what I have been using for the last six years and I don't notice any problems with it getting mangled. Do set the plug in the mast track (that holds the downhaul cleat) so that the gooseneck rests on it at the proper height. This provides the hinge point so that the vang will control the leech instead of acting as a luff downhaul. At 20:1 the vang is indeed powerful but you don't have to use all of its power. The tension on my end is still light when I have it pulled on enough to give me all the mast bend I want. It does provide nice precision and ease-of-use at that ratio.


One downside to using the sliding gooseneck is that it's a little floppy side to side. Under certain vang tensions you might get a very disconcerting pop that sort of sounds like the whole rig is going to come down. What happens is because the boom is being driven forward and if you don't release the vang while tacking, the gooseneck is held flopped to one side. After you tack and power up it can push the the gooseneck to the other side. With a lot of tension on it, it flops and bangs to the other side. I haven't noticed it mangling anything yet and it doesn't happen all that often for me. Just a heads up on that one…

[tmittner]

KC, Six years without problems is good enough for me! I stand corrected on my assumption that 20:1 was too hard on the gooseneck. I understand the popping issue and how to deal with it, ease the vang as you come about. I believe Tim Webb has had the same experience. One question, is your gooseneck the roller furling kind? Some have talked about beefing up the square middle piece in the universal joint, but that is the one piece that isn't mangled on mine. I did notice that the PO put that piece in backward compared to Dwyer diagrams. Maybe that caused his problems. Now to put together the vang as inexpensively as I can. I noticed you used Racelite blocks, first cascade will probably take the highest load, what size did you use there?

[tmittner]

My mistake KC, you were referring to barber haulers when you said you used Racelite blocks earlier in the thread. I need to research sizing of various lines and blocks for 20:1 vang.

[K.C. Walker]

I used a couple of small Ronstan triple blocks, I think 20 mm. I used 1/8 inch amsteel line with those spliced to a quarter inch line to go back to the swivel cleat next to the main sheet swivel block. I tied off to one of the triple blocks making it 5:1 then I used a double cascade with 40 mm blocks, both old Ronstan blocks that I had. When you get up to 20:1 you need it as slippery a setup as possible so that it releases easily, so good blocks are important. With few exceptions I bought blocks off eBay at very good prices. It does take time, though.

[TIM WEBB]

TRW's vang was given to me by a friend who has a Precision 18. No idea what the purchase is (math has never been my strong point!), but I added a cascade:



Ronstan hardware, and the thing works great. KC is right about the "gooseneck pop", and I get that if I tack with vang on. Doesn't deform the gooseneck slide so much as the "U-joint" that connects said slide to the boom, so I made a solid SS block for that part, and it's worked like a charm since!

I think the "serious racers" who use "serious vangs" are using fixed goosenecks.

Love the name White Fox! What's the origin?

[Salty Dog]

looks like it is 8:1 from what I can tell Tim
I'm going to put a better one than what I have on my DSII see if I can figure out how to play it.
SD

[GreenLake]

No idea what the purchase is (math has never been my strong point!), but I added a cascade:

Each layer of cascade multiplies the purchase with a 2:1.

For the rest, in your picture, you can clearly see the 4 parts. Anytime you pull, all 4 parts get shorter by the reduced distance between the block. That means, you are pulling out line at 4 times the rate the blocks move, so you have a 4:1.

With one cascade you have an 8:1.

With the same blocks you can rig a 5:1 (or 10:1 with the cascade). You'd just have to turn the entire vang around, and, instead of pulling sideways, pull down (that is, away from the end of the purchase that moves). By pulling away from the moving end you'd effectively have 5 parts that get shorter (as the boom moves down, the distance between the top block and your pulling hand also gets shorter). That configuration is known as "rigged to advantage", and turns that 4:1 into a 5:1 purchase.

So, the "math" is really not very deep. Just count the number of parts in your purchase and you get "parts":1 as the ratio. If you've rigged things "to advantage" you add 1 to the "parts", because now you count the free end of the line as one of the parts.

For each cascade, multiply by two, that is, for a triple cascade you get a factor 8.

That's the theory. In practice, you loose a bit to friction. If each block looses 10%, after two blocks, you have only 81% left, after four, it's around 65%. Good blocks matter. Cascades help, because they add such a high ratio per number of additional blocks. Their downside is that they reduce the range of possible adjustment. That's one of the reason that you find them paired with a purchase, as in your setup.

If the losses in your blocks were only 5%, with five blocks you'd be at 77% remaining. If you had done an 8:1 purchase, you'd be at 66%. (Now, that math is one I use the calculator for, 95% to the 8th power is not something I do in my head )

[K.C. Walker]

I copied Mike Gillum's setup which this is a picture of. I used 1/8 Amsteel for less friction where you see the red line.

And, yes I've got the "roller furling" boom attachment.

[TIM WEBB]

Now THAT'S a serious vang! Wonder what that other red line is used for? The one that's hanging down loosely.

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.

And all that math still makes my brain itch! ;-P

[tmittner]

KC great information to know. I live in Michigan so I have a bit of time to surf eBay for good blocks. At least initially, I plan to place a cam cleat with a wide angle quick release fairlead centered on the aft top edge of my cuddy, ala Phill Root style. I admit I am phobic about drilling any more holes than necessary and can use the holes already there for the CB down haul eye strap. Since I have a two part hatch cover I can easily work around the line. Mike Gillum's posts have convinced me the vang line will "always" be in my lap for emergency release.

Tim +1 on 8:1. Actually, you helped inspire the name for my DSII. My boat was formally" Big Truck" which didn't do it for me. Reading the forum, I saw your posts and thought The Red Witch was a great name for a red hulled boat. I also, loved the fact that our hulls were designed by Uffa Fox. Since my hull is white, I came up with "White Fox," which also plays into my love of nature. Thanks for asking.

So far, I've been sailing my boat "vicariously" through the members on the forum. Can't wait to get her into the water this spring. Thanks to all!

[K.C. Walker]

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.

[Alan]

Harken has some systems here:

http://www.harken.com/content.aspx?id=3897

Unsurprisingly, they recommend Harken blocks, but you can get an idea of sizes and kinds from the drawings.

I'm using this, which I'm pretty sure is supposed to be a 6:1 mainsheet, but it came with the boat, so what the heck:

Boom vang, maybe...jpg (230.84 KiB) Viewed 27025 times

I didn't really get a chance to put it to the test last July at Lake Tahoe, but it seemed to work well enough.

[tmittner]

Alan, I can't tell from the picture how big the blocks actually are. If I do a double cascade and 5:1 tackle, I think the first cascade block will have to take the highest load, the second cascade block half of that, and the tackle half of the second cascade block load. I think I can easily use Harken micro blocks or equivalent for the 5:1 block and tackle. Perhaps, because I always overbuild, a 57mm for the first, and a 40mm for the second block. Roughly equivalent Ronstan blocks would work great too. GreenLake might weigh in on my plan. He is very good at this stuff.

[TIM WEBB]

Tim +1 on 8:1. Actually, you helped inspire the name for my DSII. My boat was formally" Big Truck" which didn't do it for me. Reading the forum, I saw your posts and thought The Red Witch was a great name for a red hulled boat. I also, loved the fact that our hulls were designed by Uffa Fox. Since my hull is white, I came up with "White Fox," which also plays into my love of nature. Thanks for asking.

Ah, now I see the connection!