Installing a rigid vang

[Guy Johnson]

I'm going to be installing a rigid vang on our 10M Puffin. 

In the past I've always drilled and tapped when attaching to the mast. 

This time I'm considering using Rivnuts to attach the vang brackets. 

Some of the Rivnut choices are material; aluminium or stainless, thread size, countersunk or flat head. 

  

Anyone have experience using Rivnuts for mounting brackets to the mast? 

I'm interested in hearing your thoughts and experiences.

Guy

Puffin 10M #6

[Dave Cole]

Id checkout the thickness of the mast where you will be drilling. Then determine the pull out force for whatever screws and threads you would be using, then compare that to a rivnut.   I think the mast is 6061.. Not sure about the temper.  

My guess is that you would be better off simply tapping the mast.  Use anti seize etc.  

Dave

10M #26

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[David Lidrbauch]

Dave, that begs for an explanation: How would the tapped screwthreads provide a more robust cross-section than the mushroom of the compressed rivnut?

thanks,
-Ishmael (DaveL)
Terrapin 
s/v P35 #106 

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[Dan Pfeiffer]

I am sure the rivnuts will be stronger than threading into the mast.  Even aluminum rivnuts.  2x the thread engagement and probably better threads. 

Mast thickness is 0.16" or a about 5/32".

Couple of things to consider. 

First, I would use aluminum rivnuts.  SS would be stronger but when you get the galvanic corrosion (and you will) it will be between the SS screw and the rivnut not the rivnut and the mast.  And the rivnut can be drilled out and replaced. 

Second, the rivnuts sit proud of the surface as can be seen in the drawing.  I would consider cutting a countersink on the backside of the vang mounting plate so it sits over the rivnut and the plate surface makes proper contact with the mast.  If the vang hardware is SS I would do something to isolate it from the aluminum.  Either some sort of insulating sheet (made from a milk jug is good) or a slathering of TefGel. 


The gooseneck mount for the boom is very similar to a vang mount.  I made backing SS plates for my gooseneck that I fished into the mast.  Mast was down for this but It might be doable with it up if you're clever?  I fished these in with a string, put screws in to hold them in place without gooseneck, then drilled a hole through mast and plate and tapped for #10 screw to hold the backing plates in place when gooseneck screws were removed.  The #10 is countersunk in mast wall. 


Dan Pfeiffer

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[Dave Cole]

Maybe, but if the brackets were designed to be attached to a mast via tapped holes, they likely designed the bracket to have sufficient holes to allow sufficient fasteners to accommodate the required loads.  

Id go to the manufacturer and ask for recommendations.  The number of required fasteners and the method of fastening should have been part of their product design.

Dave

10M #26

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[Dan Pfeiffer]

indeed.  My rigid vang (Garhauer) is attached with (8) 1/4-20 screws in threaded holes in the mast and has lasted like that for 16 years.  And I do not baby it. 

However, the rivnuts will be stronger and a backing plate like I did with my gooseneck will be stronger yet.  And given the opportunity to make it stronger I would do it.  I intend to add the same backing plates for my vang mount.  Or maybe I'll consider rivnuts. 

But sure, tapping right into the mast would be good enough.  And if good enough is OK then, OK. 

When I tap 1/4-20 holes in the mast I under-size the drill.  Aluminum is soft and a good tap can deal with it and I think you get better threads with better engagement.  Standard drill size for tapping 1/4-20 is a #7 size drill (.201) or 13/64 - only a wee but larger (.203).  A 1/4-20 screw has a minor diameter of .188 and in thin aluminum like the mast I would use a #11 (0.191) or 12 (0.189) or even 3/16 (.1875).  The hole always ends up a little larger than the drill when hand drilling.  Use cutting oil on the tap and don't rush. 

And don't use a fine thread 1/4-28.  The fastener is maybe 20% stronger with a larger minor dia (.206) but there is a lot less thread engagement in the soft aluminum and that's the weak point. 

By the way, the mast is 6061-T6 aluminum.

Dan Pfeiffer

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[Daniel Hoffman]

Have you considered oversizing and using heli-coils? You get more thread surface area in the aluminum.

Dan (the other one) 

Fourth and Goal 31-2 

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[Dave Cole]

I didnt see your gooseneck picture initially.

Ok....how did you get the backing plates to the inside of the mast in the area of the gooseneck?

Did you do that with the mast down?

Or was voodoo magic involved.  😄

Dave

10M #26

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[Dave Cole]

Helicoils need more material thickness.  I think the hole depth needs to more than 1.5 times the bolt diameter.    So for a 1/4" screw, the mast would need to be thicker than 3/8 of an inch.  

I might be off with the 1.5 figure.

Dave

10M #26

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[Daniel Hoffman]

Ah. I didn't know that. 

I've used them in the mast and boom for stripped out threads.

Dan

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[Dan Pfeiffer]

Mast was down. 

Something like this...

Made backing plates to match holes in gooseneck plate.
Drilled out holes in mast to a bit over 1/4.  Maybe 9/32?
Took some string and fed a bite into one of the holes.
Fished up in mast with boat hook to snag loop and pull out bottom.
Pulled end of string out bottom. 
Fed through hole in backing plate and tied fat knot with enough tail to pull it back out.
Rolled mast so holes were down.
Fished the backing plate up into position.
Grabbed plate through another hole with hook
pulled it tight to inside of mast and got screws in other holes.
Pulled out string and put in rest of screws.
drilled hole for #10 tapped hole through mast and plate.
Opened part of hole in mast and drilled countersink in mast.
tapped hole in plate.  Put in #10 screw to hold plate when gooseneck mounting screws were removed. 

Repeat for other backing plate

SS plates were slathered with TefGel on face where they contact inside if mast and all fasteners were installed with TefGel.   I ground off the corners of the plate to get a better fit to the curve of the inside of the mast. 

I think this could be done with the mast up from a halyard exit slot or maybe from the wiring hole below.  Hardest part is fishing out the string to get started?

Dan Pfeiffer

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[Dave Cole]

Good to know!  

I think it would be harder with the mast up...    

But probably doable, with a lot of determination, misc bits of wire, string, probes, etc.

Dave

10M #26

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[darin doherty]

Good evening all,

I love this discussion, as it is on my list of projects.

Question for you guys, for the P 10M, how do you determining the length and angle for the solid vang?  There does not seem to be much distance between the cabin top and the bottom of the boom.

Also, how many parts in the vang tensioning set up?

Thanks,

Darin

Charis P10M #108

Titusville, Fl.

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