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      A Few Simple Rules   05/22/2017

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fatcat1111

Adding an eye to a mast for a boom vang

39 posts in this topic

My good old boat doesn't have a boom vang, so I'm adding one (not a rigid one (I already have a topping lift, and the fiddle blocks and line have cut in to my beer budget enough already), just an 8:1 cascaded fiddle). There's a bail on the boom for one side to attach to, but nothing on the mast. What is the best way to attach one?

 

She's 37' LOA. The stick is aluminum; rounded-rectangle in cross-section; 43' from the deck to the masthead (S.A. for the main is 288 sq. ft.); I'm not sure about the wall thickness exactly but it's a pretty heavy section (I can find out the exact thickness if necessary); internal wiring grooves are to either side of the slide track; no slide track below the gooseneck. My sailing is mostly coastal cruising with the occasional offshore passage.

 

I think that my options are:

  1. Attach a bracket or a tang to the aft face, probably by drilling and tapping for machine screws. Will this be strong enough? What type of metal for the tang and the screws?
     
  2. Drill a hole through the sides of the mast, run a long threaded rod through it, and use that to attach a large bail. This would be stronger and more reliable, but I'm concerned with finding a bail of the right width (though I could probably pad it with washers if it were slightly too wide). What diameter threaded rod should I use?

Other options?

 

Any advice on this project would be appreciated.

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Hi Fatcat,

 

Whenever I see a hardware connection dilemma these days I think soft-attach. Partly because it can be stronger, but mostly because it's cheaper and I watch my beer budget too ;-)

 

In this case, to do it strong and cheap I think you need a combination of hard-attach and soft-attach. Think about drilling & tapping Harken 688 Diamond Pad Eyes on each side of the mast. Then think about using a using those pad eyes to make a lashing around the mast. This would put the pad eyes in shear load rather than tension load which means less chance of a blow-out, and it would allow the vang tackle to articulate properly.

 

Food for thought...Dream on....

 

Cheers,

Rob

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Keel or deck stepped? Mast steps offer options like drilling through or even using big-ass eye nuts (flip the bolts that attach step to the deck so the head is below deck if needed).

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My good old boat doesn't have a boom vang, so I'm adding one (not a rigid one (I already have a topping lift, and the fiddle blocks and line have cut in to my beer budget enough already), just an 8:1 cascaded fiddle). There's a bail on the boom for one side to attach to, but nothing on the mast. What is the best way to attach one?

 

She's 37' LOA. The stick is aluminum; rounded-rectangle in cross-section; 43' from the deck to the masthead (S.A. for the main is 288 sq. ft.); I'm not sure about the wall thickness exactly but it's a pretty heavy section (I can find out the exact thickness if necessary); internal wiring grooves are to either side of the slide track; no slide track below the gooseneck. My sailing is mostly coastal cruising with the occasional offshore passage.

 

I think that my options are:

  1. Attach a bracket or a tang to the aft face, probably by drilling and tapping for machine screws. Will this be strong enough? What type of metal for the tang and the screws?
     
  2. Drill a hole through the sides of the mast, run a long threaded rod through it, and use that to attach a large bail. This would be stronger and more reliable, but I'm concerned with finding a bail of the right width (though I could probably pad it with washers if it were slightly too wide). What diameter threaded rod should I use?

Other options?

 

Any advice on this project would be appreciated.

 

Drilling and tapping eye straps to the back side of the mast is not going to be strong enough for the pulling loads of the vang.

 

I am not a big fan of drilling the mast for obviuous reasons, however if the boat is deck stepped you may be able to drill for the trhrough bolted bail because on a deck stepped mast you have compression at the deck level instead of the bending stress that a keel stepped mast will have at the partners. Also on a keel stepped mast you may have some hardware you can attach shackle to or probably just getting a mast plate will help. If that is not the case and you don't want or can't get a mast plate, then go to plan B: install hardware thru-bolted (and watertight) on the deck. Can you drill through the deck next the backside of the mast without damaging a liner ?

 

If you can install and eye strap or pad eye, right there, then problem solved. Then you just make the call of what to install: the fiddle block directly to the pad eye, the Triangular plate (inset) a soft shackle, etc.

 

This piece will be of help for the cascade:

BKV1521-2T.jpg

Feel free to drop me a note if you have any questions.

 

Rod

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Do NOT drill holes in the aft edge of the mast and attach an eyestrap. The PO of my boat did that. It split the mast.

 

I'm thinking about some kind of strap on the front of the mast to hold some line looped around the mast down. Most of the force would then be spread by the line over the entire back half of the mast. The strap would only be holding the line downward and be in sheer loaded.

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Hi,

I assume you already have turning blocks at the foot of your mast. If that is the case you can just use a dyneema strop to create an attachment point for your vang.

 

The way it works on my boat is that the two turning blocks right aft of the mast have beckets. I then have a dyneema strop with eyes spliced into both ends. Now push the strop through the first becket, wrap it twice around the mast and come back through the other becket.

Now you can attach a new block to the two dyneema eyes and you have an attachment point for your vang.

 

No need to drill into your mast and it also saves weight.

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Is it feasible to fashion a 2-piece metal strap that would clamp around the mast, and for that strap to have a protrusion on the aft side of the mast to which the vang would attach? I'm envisioning something akin to the clamp that goes around a fork tube to mount a motorcycle windshield.

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Scaprat, do you have a picture of this?

 

I don't but I found one on the net that shows it

img_1301.jpg?w=640&h=477

 

You can see a black dyneema strop running through the beckets around the mast.

 

On this picture you can see that a big block is attached to the dyneema for the vang:

img_1310.jpg?w=640&h=480

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In this case, to do it strong and cheap I think you need a combination of hard-attach and soft-attach. Think about drilling & tapping Harken 688 Diamond Pad Eyes on each side of the mast. Then think about using a using those pad eyes to make a lashing around the mast. This would put the pad eyes in shear load rather than tension load which means less chance of a blow-out, and it would allow the vang tackle to articulate properly.

 

Thanks Rob, this is an interesting idea that I hadn't considered. What sort of line would I lash with? Amsteel? Also, how tight? And how should I terminate the ends? Finally, xyzzy came up with a similar idea, but with a single eye on the forward face of the mast. How do you think that compares to an eye on either side?

 

Keel or deck stepped? Mast steps offer options like drilling through or even using big-ass eye nuts (flip the bolts that attach step to the deck so the head is below deck if needed).

 

I should have mentioned this: it's keel stepped.

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Drilling and tapping eye straps to the back side of the mast is not going to be strong enough for the pulling loads of the vang.

 

I am not a big fan of drilling the mast for obviuous reasons, however if the boat is deck stepped you may be able to drill for the trhrough bolted bail because on a deck stepped mast you have compression at the deck level instead of the bending stress that a keel stepped mast will have at the partners. Also on a keel stepped mast you may have some hardware you can attach shackle to or probably just getting a mast plate will help. If that is not the case and you don't want or can't get a mast plate, then go to plan B: install hardware thru-bolted (and watertight) on the deck. Can you drill through the deck next the backside of the mast without damaging a liner ?

 

If you can install and eye strap or pad eye, right there, then problem solved. Then you just make the call of what to install: the fiddle block directly to the pad eye, the Triangular plate (inset) a soft shackle, etc.

 

Shoot, I was afraid that it would be too weak to tap it. Thanks for confirming my hunch.

 

The mast is keel stepped. I wish I had a mast plate - that would solve my problem (not to mention preventing the occasional tangling of the halyards). A through bolted eye might be just the thing though. There is already a baking plate (maybe 1/4") on the interior of the deck with a couple of struts to the mast. Would it be a problem that the vang attachment point is no longer exactly in line with the gooseneck?

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Do NOT drill holes in the aft edge of the mast and attach an eyestrap. The PO of my boat did that. It split the mast.

 

Holy crap that sucks.

 

I'm thinking about some kind of strap on the front of the mast to hold some line looped around the mast down. Most of the force would then be spread by the line over the entire back half of the mast. The strap would only be holding the line downward and be in sheer loaded.

 

I like this idea. P2 had a similar idea, but with the eyes on the side. How tight do you think the strap should be?

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What is there to be said for soft attachment vs hard attachment?

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There's not a damn thing wrong with drilling and tapping the proper fitting into an aluminum mast for a vang. Check out the specs on these vangs and the associated fittings you'll see they are spec'd for boats much larger than 37 ft. NO, do not drill and tap into the track area but into the meat of the spar on either side. Make SURE you are using the properly sized drill for the tap.

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Drilling and tapping eye straps to the back side of the mast is not going to be strong enough for the pulling loads of the vang.

 

I am not a big fan of drilling the mast for obviuous reasons, however if the boat is deck stepped you may be able to drill for the trhrough bolted bail because on a deck stepped mast you have compression at the deck level instead of the bending stress that a keel stepped mast will have at the partners. Also on a keel stepped mast you may have some hardware you can attach shackle to or probably just getting a mast plate will help. If that is not the case and you don't want or can't get a mast plate, then go to plan B: install hardware thru-bolted (and watertight) on the deck. Can you drill through the deck next the backside of the mast without damaging a liner ?

 

If you can install and eye strap or pad eye, right there, then problem solved. Then you just make the call of what to install: the fiddle block directly to the pad eye, the Triangular plate (inset) a soft shackle, etc.

 

Shoot, I was afraid that it would be too weak to tap it. Thanks for confirming my hunch.

 

The mast is keel stepped. I wish I had a mast plate - that would solve my problem (not to mention preventing the occasional tangling of the halyards). A through bolted eye might be just the thing though. There is already a baking plate (maybe 1/4") on the interior of the deck with a couple of struts to the mast. Would it be a problem that the vang attachment point is no longer exactly in line with the gooseneck?

Not a problem so much as remember that the distances to the attachment points change as as the boom arcs through it's gooseneck radius.

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Thanks for the advice all. I've decided to go with a soft attachment through single eye on the forward face of the mast, rather than an eye on each side (as the side-attached eyes would be partially in tension once the boom was out, given that the lower block of the vang will be able to slide along the line). For cordage I'm going with 3/8" Amsteel Blue - spendy, I know, but I need only a yard - with eye splices in each end (this will be my first time splicing Amsteel). Small shackle between the eyes and the purchase plate that Rod suggested, and I'll have a working system.

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Did you know that inmates are able to saw through steel bars in prison with the nylon strings in the waistband of boxer underwear? Keep an eye on it and make sure your attachment does not saw through your spar. Not saying don't do it, just keep an eye. UHMW is slippery so prolly not a worry.

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Thanks for the advice all. I've decided to go with a soft attachment through single eye on the forward face of the mast, rather than an eye on each side (as the side-attached eyes would be partially in tension once the boom was out, given that the lower block of the vang will be able to slide along the line). For cordage I'm going with 3/8" Amsteel Blue - spendy, I know, but I need only a yard - with eye splices in each end (this will be my first time splicing Amsteel). Small shackle between the eyes and the purchase plate that Rod suggested, and I'll have a working system.

3/8" Dyneema needs 72 or so diameters of bury to get full strength from the splice, so 27" at each end. You can't properly splice even one end with a yard of line. It seems you're better off with an endless loop of smaller stuff.

 

Is the plan to splice the ends to the eye on the front of the mast (the vang block/shackle then rides back and forth on it like a bridle), or to have the splices aft with the middle of the strop simply passing through the eye (the strop rotates around the mast)?

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Did you know that inmates are able to saw through steel bars in prison with the nylon strings in the waistband of boxer underwear? Keep an eye on it and make sure your attachment does not saw through your spar. Not saying don't do it, just keep an eye. UHMW is slippery so prolly not a worry.

 

I hadn't considered this. I always think of chafe going the other way, with the hard things (like aluminum hardware) tearing up the soft things (like lines). Something to watch for though.

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Thanks for the advice all. I've decided to go with a soft attachment through single eye on the forward face of the mast, rather than an eye on each side (as the side-attached eyes would be partially in tension once the boom was out, given that the lower block of the vang will be able to slide along the line). For cordage I'm going with 3/8" Amsteel Blue - spendy, I know, but I need only a yard - with eye splices in each end (this will be my first time splicing Amsteel). Small shackle between the eyes and the purchase plate that Rod suggested, and I'll have a working system.

3/8" Dyneema needs 72 or so diameters of bury to get full strength from the splice, so 27" at each end. You can't properly splice even one end with a yard of line. It seems you're better off with an endless loop of smaller stuff.

 

Is the plan to splice the ends to the eye on the front of the mast (the vang block/shackle then rides back and forth on it like a bridle), or to have the splices aft with the middle of the strop simply passing through the eye (the strop rotates around the mast)?

 

Obviously I didn't do my homework w/r/t splicing this (I'm assuming that since Amsteel is slicker than Dyneema the splice length will need to be even longer than you indicated) (Btw, is there a table somewhere with that data by material? I checked Rigger's Apprentice and didn't see anything, which is unfortunate since this is valuable information). Thanks so much for saying something. So, it sounds like I should get the line in place through the eye and then long splice the ends together? Can I even do a long splice in that length of line? Or did you mean some other means of producing a loop? As to smaller stuff, what do you think about using 5/16" line?

 

The plan was to have the splices aft, with the middle of the strop passing through the eyes.

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Amsteel is just a rope manufacturer's name for a line made from Dyneema or Spectra. 72ø's is as much bury as I've heard anybody recommend for a high mod line (I think in his books Brion uses "high mod" for any high tech line, whether dyneema or vectran based).

 

How I see it working:

post-4941-0-32167900-1355347502_thumb.jpg

A loop like this, with each tail buried into the opposite side of the loop, in 1/4" Amsteel is only a little weaker than 3/8" Amsteel, probably cheaper, and the strop has enough length to achieve the buries. I don't know what you planned for the mounting of the vang blocks, but I wouldn't use just a shackle riding on the bare Amsteel. I sketched a ferrule, to be lashed to whatever your lower part might be, such as the splitting plate that Vela showed above.

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wouldnt a nylon strap be better? A little more give when the system loads up out of a gybe, and a thicker surface to wear against the mast? id envision having a sailmaker sew rings into the ends to attach the primary part of the vang cascade.

 

Also, pieceofstring is right about Amstel, its just a product/brand name for Spectra. Same as Vectrus and Vectran.

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wouldnt a nylon strap be better? A little more give when the system loads up out of a gybe, and a thicker surface to wear against the mast? id envision having a sailmaker sew rings into the ends to attach the primary part of the vang cascade.

 

Also, pieceofstring is right about Amstel, its just a product/brand name for Spectra. Same as Vectrus and Vectran.

 

And Spectra is just one of the brand names for UHMWPE, Dyneema is the other common one you will see.

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How I see it working:

post-4941-0-32167900-1355347502_thumb.jpg

A loop like this, with each tail buried into the opposite side of the loop, in 1/4" Amsteel is only a little weaker than 3/8" Amsteel, probably cheaper, and the strop has enough length to achieve the buries. I don't know what you planned for the mounting of the vang blocks, but I wouldn't use just a shackle riding on the bare Amsteel. I sketched a ferrule, to be lashed to whatever your lower part might be, such as the splitting plate that Vela showed above.

 

Been there, done that. Had it set up that way for 12 years on my old boat. Worked fine with no issues. One difference from the above description was that I spiced a loop into each end of the line. Loop the line around the mast and feed one end through the loop on the other end.This tightens the loop around the mast. Attach vang to the empty loop.

post-37611-0-91125700-1355431554_thumb.jpg[

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wouldnt a nylon strap be better? A little more give when the system loads up out of a gybe, and a thicker surface to wear against the mast? id envision having a sailmaker sew rings into the ends to attach the primary part of the vang cascade.

 

Also, pieceofstring is right about Amstel, its just a product/brand name for Spectra. Same as Vectrus and Vectran.

 

I like the idea of using nylon to take the shock loads, but it has poor abrasion resistance right?

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You could use one (or more) of these: http://www.colligoma...ms/i-Loupes.htm

 

Thanks Casc, this looks like a good product. However, it appears that the largest they make is 225 mm (< 9"), which will be too small.

 

However, this design puts me in mind of a rock climber's runner. Those can be had in just about any length, and in a variety of materials, plus they're relatively inexpensive. I think this is the way to go.

 

Now I just need to decide between nylon and Dyneema. Nylon has much better shock loading characteristics, which is important given the application. However Dyneema stands up better to UV and chafe, and has a higher static strength. Maybe I should get a blended one.

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You could use one (or more) of these: http://www.colligoma...ms/i-Loupes.htm

 

Thanks Casc, this looks like a good product. However, it appears that the largest they make is 225 mm (< 9"), which will be too small.

 

However, this design puts me in mind of a rock climber's runner. Those can be had in just about any length, and in a variety of materials, plus they're relatively inexpensive. I think this is the way to go.

 

Now I just need to decide between nylon and Dyneema. Nylon has much better shock loading characteristics, which is important given the application. However Dyneema stands up better to UV and chafe, and has a higher static strength. Maybe I should get a blended one.

 

You could use more than one, interlaced and wrapped around the mast. Or ask if they make custom lengths. Was just a thought.

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If your mast has a track in the extrusion you can simply cut a notch near the boom in that track to receive a d-ring on a plate. The notch is like the one above the boom that allows the mainsail slides to be fed in as you raise the main. Slide it into position and the track will hold the vang's load just fine. Hold it in place with a pair of machine screws tapped so it will not slide up or down. All the working load is on the track. Clean, no chafing and strong. Simple and low tech.

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If your mast has a track in the extrusion you can simply cut a notch near the boom in that track to receive a d-ring on a plate. The notch is like the one above the boom that allows the mainsail slides to be fed in as you raise the main. Slide it into position and the track will hold the vang's load just fine. Hold it in place with a pair of machine screws tapped so it will not slide up or down. All the working load is on the track. Clean, no chafing and strong. Simple and low tech.

 

Alas, no track below the goosneck (well, there is a couple-few inches of track, but it doesn't run anywhere close to the deck).

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Now I just need to decide between nylon and Dyneema. Nylon has much better shock loading characteristics, which is important given the application. However Dyneema stands up better to UV and chafe, and has a higher static strength. Maybe I should get a blended one.

 

I'd go with dyneema. Good UV resistance and easy to splice yourself.

And for shock loads I'd rather put a 1 or 1.5mm dyneema loop (depending on the loads you expect) somewhere in the system to act as a fuse that will break before your boom does.

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I'd go with dyneema. Good UV resistance and easy to splice yourself.

And for shock loads I'd rather put a 1 or 1.5mm dyneema loop (depending on the loads you expect) somewhere in the system to act as a fuse that will break before your boom does.

 

Ah, like a daisy chain. Good thinking. Thanks for the tip!

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You could use one (or more) of these: http://www.colligoma...ms/i-Loupes.htm

 

Thanks Casc, this looks like a good product. However, it appears that the largest they make is 225 mm (< 9"), which will be too small.

 

However, this design puts me in mind of a rock climber's runner. Those can be had in just about any length, and in a variety of materials, plus they're relatively inexpensive. I think this is the way to go.

 

Now I just need to decide between nylon and Dyneema. Nylon has much better shock loading characteristics, which is important given the application. However Dyneema stands up better to UV and chafe, and has a higher static strength. Maybe I should get a blended one.

I have a climbing runner from REI as the soft bail on my boom

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the stainless vang fitting on my J30 mast broke during a gybe once. I replaced it with a length of dockline wrapped around the base of hte mast about 6 times. That lasted for the next 5 years I raced the boat... I kept wanting to get the original fitting repaired but just never got around to it.

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The Dyneema or Strap approach sound okay to me. I would be very concerned about the side loading of the strap when the boom is way out, running deep. Can you come up with a way to secure the cordage or strapping such that the load point always remains at the aft center of the mast? How about 2 short Slings affixed at the face of the mast and passing thru an eye strap aft ctr.

See attempted sketch...

post-1132-0-11581300-1357174254_thumb.jpg

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