jasonsansfleece

Boom vang loads?

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Hi there,

 I have a question about Vang loads, perhaps you can help me out. I have a CL 16 (a Canadian built Wayfarer clone) which has a little  Cuddy cabin. This prevents me using a conventional Vang. I’m planning on installing an upside down vang, a GNAV.  I’m going to use some fittings from Selden and for the sliding connection on the boom I want to use a Harken car with recirculating balls and short piece of track.

 The cars  come with SWL‘s of 310 pounds for the micro and 500 and 850 for the 22 mm regular and high load cars. Which one to use?

 I did buy the micro but holding it in my hands I have some misgivings compounded by the fact that I’m not an engineer.

The boom is 120 inches long and the original vang attachment point is 28 inches from the gooseneck.  The main sheet attaches to the end of the boom and has a 3 to 1 purchase. The main sheet attachment point and the thing attachment point have a ratio of 4.3 :1 . Would the vang load be 4.3 times higher than the main sheet load? If you see where I’m going. Or none of the above?

Save me from analysis paralysis and choose the right car

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Ok, so you are talking about this

I think your question is about the rating on the tackle that pulls the strut in towards the gooseneck. 

If you look at the load as a torque around the gooseneck, then the vertical component of force at the Vang strut would need to be 4.3 x the downward force of the sheet tackle. 

Assuming that the vang strut attached to the mast at about the same height for a 45 degree angle as shown in diagram, then the solution of a free body diagram would give you a load on the tackle approximately 1/cos(45) * 4.3 or more like 6 times the downward force of the Main sheet tackle

if you have a sense of the amount of force to pull in your main when hardened in (say 100lbs) * 3:1 tackle that would give you a working load of about 1800 lbs on the pull in tackle 

round it off to 2000 to account for some friction. 

Disclaimer: I took mechanics back in 1975...

 

 

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I am more interested in seeing what a CL16 with a cutty looks like

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It looks like Selden isn't too concerned about friction. You might be able to get away with a car that has delrin sliders, but that would be t-track. 

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 The Selden fitting that fits on the boom certainly doesn’t look like a low friction item.  It fits nicely on their flat top boom sections but not on the section I have.

 How much mainsheet load can I create given my weight and strength? Let’s say 100 pounds then multiply that by the main sheet purchase, 300 pounds. Now multiply that by the  sheet attachment Vang attachment ratio, 4.3 to 1 and we get 1290 pounds.  So, for a theoretical full on Vang sheeted mode that would be 1290 pounds of load on the vang. Does that seem reasonable? When I look at the vang tackle and it’s attachment points that were Originally installed I doubt they ever saw or were designed for that kind of load.

 But in practice, hiked out with one hand on the main sheet I doubt I’m going to be exerting 100 pounds. Maybe 50 pounds?In which case the vang load is reduced by half.  At these loads the Harken micro car is being loaded at twice it’s SWL Half the loads again and we’re only just in the limits.

 So if this argument is correct and I would appreciate your input then the 22 mm car would be the correct choice, the high load version. 

 

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13 hours ago, Skaf said:

I am more interested in seeing what a CL16 with a cutty looks like

+1

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 The Selden fitting that fits on the boom certainly doesn’t look like a low friction item.  It fits nicely on their flat top boom sections but not on the section I have.

 How much mainsheet load can I create given my weight and strength? Let’s say 100 pounds then multiply that by the main sheet purchase, 300 pounds. Now multiply that by the  sheet attachment Vang attachment ratio, 4.3 to 1 and we get 1290 pounds.  So, for a theoretical full on Vang sheeted mode that would be 1290 pounds of load on the vang. Does that seem reasonable? When I look at the vang tackle and it’s attachment points that were Originally installed I doubt they ever saw or were designed for that kind of load.

 But in practice, hiked out with one hand on the main sheet I doubt I’m going to be exerting 100 pounds. Maybe 50 pounds?In which case the vang load is reduced by half.  At these loads the Harken micro car is being loaded at twice it’s SWL Half the loads again and we’re only just in the limits.

 So if this argument is correct and I would appreciate your input then the 22 mm car would be the correct choice, the high load version. 

Skaf,  I would upload a picture if I could. It says click to choose files Max total size 1MB

When I try to upload a picture from my phone it tells me the max upload is 1024 kB, not enough for one picture. What am I doing wrong?

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The other thing to consider, which is mentioned in the selden literature above, you will need to support the mast at the top of the gnav with inner D shrouds like the 49er or you will bend the mast considerably at a point its unsupported. I know the daysailer has a beefy mast but I would be concerned about how much bend there is in the mast from 1290 pounds 2' above the gooseneck.

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 I have considered that. I’m thinking that vang loads will be proportional to the wind velocity and depending on how it’s bends the mast, will have a desirable sail flattening effect. I can always add lower shrouds if necessary.

1290 pounds is some theoretical maximum that my non-engineer brain conjured up. It seems really high to me, it’s more than three times what the boat weighs . 

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Upload pic to imgur or postimages.org

When uploaded, right click* image and choose open image in new tab. Copy image url and paste url into body of post. The forum software does the rest.

*From phone, long press on image instead of right click

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The mast sits in the step then passes through a mast gate at deck level. A couple chocks and things are pretty secure. i can''t imagine you plan on aggresively racing this boat, and would consider the GNAV will mainly fill the role of a preventer, with some twist control. No reason to pound a bunch of pressure on it. 

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7 hours ago, jasonsansfleece said:

 The Selden fitting that fits on the boom certainly doesn’t look like a low friction item.  It fits nicely on their flat top boom sections but not on the section I have.

 How much mainsheet load can I create given my weight and strength? Let’s say 100 pounds then multiply that by the main sheet purchase, 300 pounds. Now multiply that by the  sheet attachment Vang attachment ratio, 4.3 to 1 and we get 1290 pounds.  So, for a theoretical full on Vang sheeted mode that would be 1290 pounds of load on the vang. Does that seem reasonable? When I look at the vang tackle and it’s attachment points that were Originally installed I doubt they ever saw or were designed for that kind of load.

 But in practice, hiked out with one hand on the main sheet I doubt I’m going to be exerting 100 pounds. Maybe 50 pounds?In which case the vang load is reduced by half.  At these loads the Harken micro car is being loaded at twice it’s SWL Half the loads again and we’re only just in the limits.

 So if this argument is correct and I would appreciate your input then the 22 mm car would be the correct choice, the high load version. 

Skaf,  I would upload a picture if I could. It says click to choose files Max total size 1MB

When I try to upload a picture from my phone it tells me the max upload is 1024 kB, not enough for one picture. What am I doing wrong?

Email it to yourself, save the image, And then it should post

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 I’ve tried two different image hosting sites, Flickr and post image.com. When I try to copy in the URL, the box on the “insert image from URL” page on this site turns red and nothing else happens

Bill4,  no aggressive racing until I see another boat. I certainly want  twist control and I don’t have to load the system completely but, if it’s there, it might happen

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4 minutes ago, jasonsansfleece said:

 I’ve tried two different image hosting sites, Flickr and post image.com. When I try to copy in the URL, the box on the “insert image from URL” page on this site turns red and nothing else happens

Bill4,  no aggressive racing until I see another boat. I certainly want  twist control and I don’t have to load the system completely but, if it’s there, it might happen

When you host image elsewhere, you don't use the "post image" tool.

Just put the url in the body of the post like this

www.myimage.imagehost. com

 

Forum sw will turn it into a pic

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