question for you mechanical engineers

[delmarrey]

Just grease the hell out of whatever pin you use on a regular basis with wheel bearing grease. So long as it doesn't drip on a hot day. Corrosion will not be a factor.

FYI -Wheel bearing grease is water resistant.

[Cavalier MK2]

My suggestion is to throw it away and use a set up I learned from a Tom Speers post since you have a cat. Your regular mainsheet goes to the centerline with whatever you need for a purchase 4-6 is typical. Then you run a continuous line to blocks set a ways forward on your hull sides with the ends secured to the boom end on each side. The body of the line is in the cockpit with a cleat for adjustment. Let your boom out a little farther than normal for the course, cleat the vang/preventer line and use the mainsheet to cinch it down. This set up can flatten the main better with less twist than a conventional set up and gives the security of a off wind preventer at the same time because of the location of the vang/preventer blocks on the hull sides. Push the boom out when locating to put them in the correct position for the arc of travel. A turn block might be needed on the sides back towards the cockpit to help keep the control end of the continuous line out of the way. There is a little extra spagetti but it can be left off or centered for short tacking and the automatic safety of the prevent is a great feature. I'm getting more power out of my main now in a wider range of wind strengths. The cost is very affordable because you just need 2-4 single blocks and a cleat plus enough line.

[foufou]

Aluminum emt is pretty soft stuff. Doubt it is 6061. And certainly not T6. That is not temperature hardened. You might find appropriate material ag a metal recycle yard

[jimbunyard]

1" aluminum EMT is typically 6005 alloy and is perfectly adequate (appropriate) in this application.

[TheThunderbird]

You dont find pins large enough imo.

I would wield the two pieces for good.


If you want, you can use a pair bolts (3/8") possibly with no threads in the engaged section.
Even better, I would get solid 316 (or bronze!) rods that you can fix both sides with a little clevis pin (this is what they are meant for!!!!! Only this!)

Using a pair of bolts/rod, you double the working sections, and if turned 90° from each other you better spread tensions.



PS a machine shop is a necessity imo

[Schrewsburyduo]

Boomkicker or something similar maybe? Not sure boomkicker has one for your size boom. Else garhauer. You will be so happy to be able to adjust to conditions. Worth doing it right.

[JOHNMARDALL]

While you sort this out, why not rig a rope topping lift as a temporary measure? You may find it better than the rigid boom prop, and add a conventional rope and blocks vang for control of sail shape at small cost. As an added benefit, when going downwind, you can unhitch the vang and use it as a preventer.
Just saying
John Mardall
Vetus Maxwell Group

[Captain Bill]

Well I finally talked to a reputable machine shop today and the quote to make a new fork and to drill out and rethread the tube was $900. Ouch! That puts a repair in he same ball park as a new rigid vang. He said it was an all day job. I'm not a machinist but I have seen people turn out stuff much more complicated in a couple of hours. I suspect he did not really want to do the job so he gave me an outrageous bid. He kept saying I should get an off the shelf part.

I got a PM requesting photos so I'll see if I cab attach a few here.

[Captain Bill]

Ok only 2 out of 3 worked so here is another attempt at the 3rd.

[delmarrey]

Originally Posted by Captain Bill

Well I finally talked to a reputable machine shop today and the quote to make a new fork and to drill out and rethread the tube was $900. Ouch! That puts a repair in he same ball park as a new rigid vang. He said it was an all day job. I'm not a machinist but I have seen people turn out stuff much more complicated in a couple of hours. I suspect he did not really want to do the job so he gave me an outrageous bid. He kept saying I should get an off the shelf part.

I got a PM requesting photos so I'll see if I cab attach a few here.

As a retired Machinist I can tell you to get several quotes. Every machine shop has different capabilities. The tools to do that kind of job are not common items in a lot of shops. And some shops specialize in those types of parts. I've worked in both +. With the right tooling that could be made in 2-3 hours, w/o one has to do it the hard way. As well, is the material & tooling in their stock, or do they have to order it? Which takes time and more $$$$.

[Captsteve53]

For input regarding these computations, unlike tensile and yield strengths, there are no published shear strength values or requirements for ASTM specifications. The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8) states that shear strength is approximately 60% of the minimum tensile strength.

[GordMay]

Originally Posted by jimbunyard

1" aluminum EMT is typically 6005 alloy and is perfectly adequate (appropriate) in this application.

For instance:
American Conduit rigid aluminum electrical metallic tubing (EMT) uses a 6005 alloy, 98.5% pure aluminum.
➥ Specifications of Aluminum EMT Electrical Metallic Tubing | American Conduit by Sapa Extrusions

[jimbunyard]

Originally Posted by jimbunyard

1" aluminum EMT is typically 6005 alloy and is perfectly adequate (appropriate) in this application.

Originally Posted by GordMay

For instance:
American Conduit rigid aluminum electrical metallic tubing (EMT) uses a 6005 alloy, 98.5% pure aluminum.
➥ Specifications of Aluminum EMT Electrical Metallic Tubing | American Conduit by Sapa Extrusions

And for anyone susceptible to TLDR, 'this application' is;

"...in the interest of your original goal (you can always buy what ever vang you find appropriate), I would get a piece of 1" aluminum EMT, cut it to the correct length to fit into the body of the vang to hold the fork at the correct extension and absorb compression, buy two 1/2" x 5 1/2" or so ss bolts, drill two holes through the vang body and fork shaft (there are, after all, two 1/2" pins holding the vang in place...), fasten the bolts with nylocs, cut off the extra bolt length, and go sailing for a total cost of about 10 dollars. But that's just me..."

and not to build a new vang out of 1" aluminum EMT...

[Cavalier MK2]

I use a topping lift with the vang/preventer I described. You get the same control as you do with a full width curved traveler at small cost. It isn't set and forget but when you get more power you don't want to forget.

As a former machinist the biggest price variable I noticed is what the owner thinks he can get out of you so for sure check around. If you can't talk to the actual workers the time might be stretchinggggg out.

The other reminder is that off the shelf solutions for cruising boats are much easier to repair/replace in out of the way places.

[Eigenvector]

Cross drilling and installing two 304,316 or even an aluminum bolt or pin would be fine. Requires a minimum yield strength of 30 ksi.

Here's the calculations:

The attachment at either end is assumed to be a 1/2 pin of SS304 with a nominal yield strength of 31,200 psi. In general the shear strength is half the tensile properties. This gives us a Shear Yield = 15,600 psi.

The allowable load in double shear would be:

0.196 in^2 * 2 * 15,600 psi = 6,123 lbs

For a cross drilled hole the shear stress of be identical to the attachment pin. However, we are now bearing on the tube. So this must be checked.

Tube ID = 1.5 OD = 3.0

The hole bearing area (for tear out) is 1/2 * 3/4 = 0.375 in^2 each side.
Total bearing area would be 0.75 in^2.

Bearing stress at 6123 lbs would be 6123/.75 = 8164 psi.

8164 psi > 8,000 yield stress of AL6061-T0. One pin will not work.

Two will work.

This assumes that the Vang is dead soft aluminum with a Tensile Yield strength of 8 ksi.