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boom vang attachment - threads stripped

Jenkins

Member II
Hi all,

I have a rigid vang on my boat (77 e29) and it attaches to the boom with a fitting like this.
vang.jpg
Several of the machine screws that hold the bracket to the boom have their holes stripped in the boom.

I am wondering what the best strategy is to remedy this. I am not keen on simply moving the bracket and drilling new holes as I think this would weaken the boom somewhat.

Ideas I have come up with are:

1) get larger machine screws and re-tap the existing holes
2) line existing holes with something (JB Weld?), re-tap and use existing screws

Looking for thoughts/suggestions.

Thanks,

Peter
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Plan B ?

Hard to see, but it looks like there might be two holes on each side of the curved plate.
It will work fine with only screws for holding up the boom, but very poorly for pulling down, acting as a vang.

I would take the boom off, remove the ends for access, and put a curved plate inside, with pre-tapped holes for fastenings. I would probably use 1/4 " aluminum for the internal plate - maybe 3/8.
Probably have to tape it to a stick and slide it down the inside that way... Once the screws are torqued up, pull hard and break the tape, removing the stick. Reassemble the boom hardware.
 

alcodiesel

Bill McLean
OK granted I am a large boat newbee but machine screws into aluminum? Fine threads into a soft metal? I thought this was a mistake when I began poking around my E27.

Also, when the machine screws pulled out of my boom my sail maker friend said go with large pop rivets, which I did and they've held fine during my many winter sails and with some heavy vang loads. He said go with aluminum so I don't get the Al to SS corrosion where I can't see it.

What gives with the machine screws? Please straighten me out.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
OK granted I am a large boat newbee but machine screws into aluminum? Fine threads into a soft metal? I thought this was a mistake when I began poking around my E27.

Also, when the machine screws pulled out of my boom my sail maker friend said go with large pop rivets, which I did and they've held fine during my many winter sails and with some heavy vang loads. He said go with aluminum so I don't get the Al to SS corrosion where I can't see it.
What gives with the machine screws? Please straighten me out.
Your intuition is correct. However, it does depend on the direction of the load.
This is a situation where the attachment is really not suitable for threading into the boom.
It's different when the load is all in "shear". I learned this back in the 70's when I needed to install spinnaker track on my new Ranger 20 mast. I was skeptical about drilling and tapping quarter-20 screws into the thin mast face. I recall a friend in the business telling me to go ahead and really try to strip those threads. (!) I could not with my large screwdriver. Of course the in-use load was all coming straight at the spar or at 90 degrees, at most, to the spar face.

For a vang, the heaviest load is down, and distorts the aluminum - and stretches the metal and finally pulls out. This force is rather opposite of a spinn track on a mast.

As for pop rivets, that larger "shoulder" you form on the inside when you pull that rivet does give it extra bearing surface around the hole. I later put in quite a few parts on small spars with a rivet gun. I was much younger then, and it still took all my strength to pop a large SS rivet. :rolleyes:

For the boom in question, you could use a pre-threaded SS back up plate instead of aluminum. What with SS fasteners, there will be some corrosion anyway..... we also used to "bed" fittings with some silicone sealant for a cheap way to keep moisture out of the metal interface. Works well.

Regards,
Loren
 
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tenders

Innocent Bystander
The idea of using threads to hold a solid vang onto a boom seems fundamentally flawed. Pop rivets are going to loosen too.

I, being lazy, cheap, and imprecise, would modify Loren's suggestion to use two bars of 1/4" G10 as backing plates, each about the size of a stick of gum or a bit larger, placed fore-and-aft in the boom.

This removes the complexity and cost of fabricating a bent metal plate, and also reduces the potential for galvanic corrosion. I think it would be easier to install too.

Now maybe YOU could drill and tap this stuff (metal or G10) accurately enough to work with the curve of the boom, but I could not. But if slightly oversized holes were drilled in the G10, you could avoid having to match the threads perfectly and just put nylock nuts on the inside, holding them in place with a box wrench that stops itself against the inside of the boom while you tighten the machine screw from the outside. Then shake out the box wrench and go to the next machine screw. This might involve a bit of periscoping, and perhaps a spot of butyl to hold the nut to the wrench as it goes in, but the vang isn't attached too deep inside the boom to make this very difficult.
 

Jenkins

Member II
I think the idea of the bars is a good one as I was somewhat daunted by the curved plate fabrication. But, I will go with aluminum bars drilled and tapped - the time spent shaping the bars and tapping them will be (at least for me) less than the time spent trying to get a wrench on nuts down inside the boom.

Will update when I get a chance to work on it.

Sincere thanks for the ideas!


peter
 

markvone

Sustaining Member
Use the existing vang fitting INSIDE the boom?

If you have access to inside the boom,

I would consider tapping treads in the existing vang fitting (or weld/epoxy nyloc nuts to the top/inside curve), cut a slot in the boom for the tang and use the existing fitting INSIDE the boom.
Gets you a backing plate/reinforcement and MUCH stronger when pulling down in vang mode.

Just a thought,

Mark
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Mark's idea of putting the attachment plate inside does work, but note that you would need to machine an accurate slot in the bottom of the spar sections. Matter of fact... that is how Kenyon did this on the Olson 34 boom.

In the first few seasons of sailing I had that internal flat bar break on one end, beside the welded-on "fin" that sticks down thru the slot. This was from some flexing from the up-force of our standard-equipment rod vang. After disassembling the boom ends, and etc, I took the pieces to a small welding shop where the owner welded a backup piece on the top of the patched plate. I recall that getting the nuts inside with a wrench on a stick was rather challenging. Our design uses a couple stubby round head bolts with washers inserted from the bottom. BTW, that plate was never 'shaped' to fit the slight curvature of the boom bottom.

Now I wonder if other Kenyon booms on 80's era Ericson's have the same vang attachment? In spite of the one design flaw I fixed, it was rather slick looking idea.


Loren
 
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frick

Member III
Garhauer Rigid Boom Vang

My E29 has a rigid boom vang with 4 tapped SS bolts... It has been problem free for 12 years.

Rick+
 

Teranodon

Member III
Lots of good suggestions here.

I recently got a Garhauer rigid vang. Based on their recommendation, I drilled and tapped 1/4-20 holes for SS machine screws. Only took about an hour, didn't even remove the sail. Used anti-seize compound. Looks very solid now, but ask me again in ten years.
 

tenders

Innocent Bystander
You guys must have some special mojo because my efforts to drill-and-tap stuff in place have always resulted in misaligned holes and/or cockeyed machine screws. Usually "and," not "or."

May I also take this opportunity to point out that G10 taps beautifully. Were you to tap G10 for this purpose instead of aluminum, perhaps I'd use 1/4" instead of 3/16".
 

Jenkins

Member II
sucess

Hi all,

Thanks for suggestions. I fabricated two aluminum bars (had some aluminum stock lying around) along the lines of tenders suggestion - sticks of gum. Ground/filed them to be about the radius on the boom. Drilled and tapped the holes for the screws to attach the vang.

Anticipating it would be tedious to line these up inside the boom, i drilled and tapped a hole in the forward edge of each bar and threaded a rod long enough to slide the bar into place inside the boom. Attach the bar to the rod, lined it up outside the boom, put a piece of tape on the rod and then slid it in the boom to the tape mark.

With a little fine tuning of the holes in the boom it all went together quite nicely.

Again, thanks!!!

Peter
 
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