Vang mount distance from mast

[Fly4rfun]

I am putting a vang on my DS1, not racing and am a novice with old sailing experience. i am trying to figure out how far from the mast does the vang attach on the boom. was given 28 inches as a number, but looking at some of the photos on line it appears to me that the distance is more. right now i have a 4:1 but may go bigger once i get this figured out, and would like to locate it with that in mind. also most of my sailing probably will be solo.
Thanks.

G.

[GreenLake]

It's vexing. There simply seem to be no photos of my boat that show the full boom side on. . . Except one with a reefed sail covering any view of the vang attachment.

However, I think the location of the cleat towards the boom end is something like 12-18" from the cuddy edge (and the length of a becket + shackle gets added from there). Adding the distance mast-cuddy edge should give you a ballpark distance. You might also google to see whether anyone posts a suggested angle for a vang.

Anyway, don't do a 4:1. As I understand it, those are the "downwind only" vangs, where the main purpose is to keep the boom from swinging up and the maximum sail area exposed.

If you have a 4:1 that you want to re-use, add a double cascade and you get 16:1 for the cost of only two single blocks and a bit of line.

[GreenLake]

OK. Went back and did another search which located pictures. Looks like my vang is attached pretty close to 1/4 along the length of the boom (actually closer to 2/7th the length, to be more precise, or 35" assuming a 10' boom). That's locating the position where the boom bail is attached on mine. Given that I took the numbers off a screen and not from the actual, they are probably +/- 1" at least, but also, they just represent what I have, not what theory demands . . . (I don't know any more where I looked when I had the same decision to make as you now).

[Fly4rfun]

GL

I would agree with you on the distance. Rudy at DR suggested 28 in, but i was seeing what looked like to me to be longer. i do have some extra single blocks i got off eBay for cheap and I'll have one more as I'm going to purchase a ratcheting block for the main sheeting. ok how would that look using the 4:1 vang and the two single blocks?

G

[GreenLake]

You do know how a cascade works? Anycase, here is a diagram:

A 16:1 dual cascade with integral 4:1 purchase

Cascade.gif (8.04 KiB) Viewed 25444 times

If the cascade needs to hold up to 500lbs (MWL), the outer block needs to be rated to that. The line running through it needs to be rated to 250 lbs as does the inner block. The purchase only has to hold 125lbs. (Because of friction, the purchase would need to pull with 150lbs or so to tighten the cascade when fully loaded, but that's in the noise.)

Now,I've used 500lbs as an example, but the vang is one of the most highly loaded pieces of the rigging. Assuming you can bring 50lbs of pull to bear on the free end, you'd get nearly 800lbs of pull out of your cascade (minus losses due to friction). That would argue towards using an outer block rated no less than 750lbs. That way, it won't come apart from you adjusting it...

(You might want to check some of the block manufacturers sites to see if they have suggestions for selecting blocks for a boat the size of the DS; I can't tell you what I used, because I can't access the boat at the moment, and what if I was wrong, anyway?)

[Fly4rfun]

Thank you sir, I have a general Idea on the workings of it. will do more research in it.

[jalmeida51]

My boom vang is attached 36 inches back from the mast.
The cascade uses a Ronstan 40 series block. Safe working load is 880 pounds.
My vang is made up with a Harken 29mm double block safe working load is 660 pounds.
With a Harken 29mm triple block, safe working load is 990 pounds.
Both blocks are carbo air.
John

[Fly4rfun]

John,
thank you for the info, also what ratio do you get with that setup, (not good at math).(learning disability) do you have a photo?

[GreenLake]

The power of a purchase is the number of parts. (Here "part" is the nautical term for a separate piece of a line).

If you rig a purchase so the free end leaves the moving block (in the direction of its travel) you count the free end as a part as well. That's rigging your purchase "to advantage".

Each step of a cascade multiplies by a factor of two.

No higher math required.

PS: I fixed the diagram, one of the parts in the purchase needs to be tied off to some becket, so to show that schematically, it goes to the center now, not the edge of the block.

[GreenLake]

With the triple/double combo john should be getting a 5:1 and with two cascade steps he should be getting 5x2x2 = 20:1.

Mine is a 6:1 x 2 or 12:1.

I drew you a 16:1 in case you want to salvage your existing 4:1.

In high winds, mine may be a bit marginal, but there shouldn't be a word of difference between 16:1 and 20:1. (Less than the raw numbers seem to imply because of losses due to friction)

[Fly4rfun]

I take it that the bottom two blocks in the diagram are fiddle blocks?(my existing vang)

[tomodda]

Usually double blocks. Fiddle blocks take up to much space.

[Fly4rfun]

ok, my vang has fiddle blocks, guess i could try to sell it on eBay and get a couple of double blocks, unless i am not understanding the mechanics of it, trying to figure out where the last block attaches. ( the one with the end coming out, Sorry don't mean to sound so stupid about this.

this is what my vang looks like

s-l140.jpg (1.94 KiB) Viewed 25442 times

its a viadana brand

[GreenLake]

If you have fiddle blocks, I'd try to make that work, before replacing things. You are on a budget.

What you need to figure out is, given the length of the diagonal to a mounting point at 36", how much room is left between the tips of the fiddle blocks, given that you need to fit them into the diagram where I showed the pair of double blocks. (You'll loos additional distance due to boom bail, shackles etc.)

With an added 4:1 cascade, 1/4 of the distance between the tips of the inner blocks is the total range of travel for your cascade towards the tighter end. You'll want to be able to let the boom rise a bit as well, so you when you lay out the longest position, it needs to be a bit longer than required to just reach.

My suggestion would be to rig this up with parts you have, perhaps using knots, not splices, and do a test setup. I bet it'll become clear pretty quickly whether your existing vang can be incorporated, but, more importantly, independent of how you are doing the blocks, you'll be able to verify whether your ideas of the required range of travel for that vang will work out (including what length the vang should have at its "mid point").

The maximum length will be where the outer fiddle block and the two blocks of the cascade are all three chock-a-block (that is, effectively touch each other or can't get any closer). The minimum length will be when the fiddle blocks are chock-a-block (their inner end touch).

[tomodda]

Gary:

I agree with GL - use what you have. Fiddle block isn't ideal, but will do with some careful measuring. One caveat - I find those blocks with V-shaped jam-cleats to hold the end of the rope next to useless. Can't see form your photo if that is what you have, but be aware that there will be at least 50 lbs of force on the rope when you are sailing in any sort of breeze. It's all bearing on e one short piece of the cover of the rope - so rope will soon fray - and it's a real pain to unjam it from the V when you want to adjust the vang.. it's at a bad angle, think of where you sit when you're sailing. Anyway, for what it's worth, my "ghosting around" photo from another thread has a pretty clear view of my vang, I resized it here for you:

20:1 Vang

DS1-37 (2).jpeg (154.38 KiB) Viewed 25434 times

This is a 20:1 vang, like in GL's diagram above. I hope this helps illustrate what he's written about re; distances in the previous post. At max extension, the two cascade blocks (on top) will meet - this happens when you are at a dead run, mostly. Of course, you want a bit of vang tension even at dead run, so not that likely to happen. More usual is the two bottom blocks touching when you have the vang really cranked on, beating upwind.

Please remember for your measuring, everything depends on how high your boom sits. I try to keep the gooseneck exactly at Band #2 - in other words the class-legal minimum height off the top of the cuddy. Check out the DS Association Specifications and measurements guide, fi you haven't already:

https://www.daysailer.org/resources/Documents/dsbylaw3.pdf

I have the bands laid out in sections 7 and 8 marked off on my mast and boom using electrical tape. Keeps me semi-sane as I fiddle with sail adjustments. Not that I'm racing, but at least I know I'm "in the ballpark" of what intended for the Daysailer.

Anyway, good luck and please keep asking questions!

Tom

P.S. Ebay and used boat part sites are your friends for cheap blocks - get yourself some "oldies but goodies," in other words name-brand blocks at a discount, Schaefer or Harken for instance. For example:

https://www.nandjmarine.com/store/double

Right now they're selling 2-inch Schaefers for $25, a steal. You'll need to buy some shackles, but you'll still come in under $100. Buy some good single-blocks for top part of cascade, some Dyneema line... You'll be around $150 for a 20:1 cascade. And as someone else pointed out, you don't necessarily need 20:1. This is all just food for thought.