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Discussion Starter · #1 ·
I'm replacing a bracket on my Merit 25's mast. It uses Kenyon's 3350 mast section - rigrite.com/spars/kenyon_spars/3350-MORC.html - and they state it "attaches to the mast with (8) 3/16" (#10) fasteners."

Question is: what depth? Anybody have experience with this?

Thanks!
 

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I'm replacing a bracket on my Merit 25's mast. It uses Kenyon's 3350 mast section - rigrite.com/spars/kenyon_spars/3350-MORC.html - and they state it "attaches to the mast with (8) 3/16" (#10) fasteners."

Question is: what depth? Anybody have experience with this?

Thanks!
Likely no more than an 1/8 of an inch or so. But if they are saying to use #10 fasteners, they probably mean 10-24 or 10-32 machine screws.
 

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What is holding on the old one ?

A 3350 has a .90 wall + what ever your putting on

If its rivets i used the 3/16 X .250 grip range when i did my .90 wall mast and boom and it worked out fine

The problem is your going to need a BIG rivet tool to set 3/16
 

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What is holding on the old one ?

A 3350 has a .90 wall + what ever your putting on

If its rivets i used the 3/16 X .250 grip range when i did my .90 wall mast and boom and it worked out fine

The problem is your going to need a BIG rivet tool to set 3/16
Big Daddy.

 

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The big daddy set me back 100 bucks and you will be better off buying the rivets lose as a box of 100 is 50 bucks
 

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Polson, Not sure what bracket you're replacing but after looking at the link you provided, looks like maybe a spreader bracket. (8 holes) I would think that the type of loads the bracket will experience would determine which fastener to use, ie compression - rivets would do...heavy sheer or shock loads, I'd favor taping the holes for SS machine screws. With a wall thickness of .090, I'd go with no less than 10-24 and would probably favor a 10-32. And of course use some type of sealer/lube to isolate the treads from the mast. On a mast I completely overhauled, I use some aircraft goop to isolate the fasteners, others can tell you better what is suitable.

I opted to use all machine screws (some I had to step up to the next size due to corrosion) because the halyards were internal along with the mast anchor light wiring (no conduit). 'Pop' rivets normally require a 'tail' of one and a half times their diameter in length on the inside of the mast to be structurally viable and if one doesn't punch out the steel shaft out of the center after the rivet's pulled, it leaves sharp edges to chafe your halyards and wiring. I used a hole grip guage (available in most places that sell pop rivets) to determine the total length of machine screw I'd need to keep the fastener intrusion to a minimum. If there's nothing in your mast...go with the rivets if the loads are not too heavy...much easier installation.
 

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The 3/16 rivet is pretty normal to use and massively stronger than a 10-24 screw

Nothing on my mast under any load used screws BUT there are 60 rivets between the mast and boom which have never cause a problem with the 5 internal lines or 2 wires
 

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The 3/16 rivet is pretty normal to use and massively stronger than a 10-24 screw

Nothing on my mast under any load used screws BUT there are 60 rivets between the mast and boom which have never cause a problem with the 5 internal lines or 2 wires
Yeah, the pop rivets would propably be OK as far as chafe, see 'em all the time, but I still wonder... I used the short SS screws to eliminate any possibility of chafing (new halyards and wiring), just too much work to take the chance...anal I suppose.:eek:

Admittedly, I'm no engineer but some of my training makes me wonder how a hollow aluminum or stainless rivet could be stronger than a solid stainless machine screw. Both rivets are thin walled and I would think neither would have the same sheer or tensile strength as a solid stainless machine screw due to their lack of cross sectional area. ??:confused:
 

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In most applications the they are in tension, not shear. with a rivet you have an unbroken cylender doing the clamping, with a screw you have a very small portion of the screw doing it, and in a mast it's holding in a much softer material, so your calculations should be done using the aluminum's qualifications

Most things are 'clamped' in position by the screws or rivets, so it's mostly the friction induced by that clamping that actually does the holding.

Ken.
 

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Discussion Starter · #10 ·
Thanks for the ideas -- it is the spreader bracket and it is currently installed with 8 rivets. I was planning to drill them out and install the new, non-cracked bracket (haven't figured out how to get the remaining shrapnel out of the mast yet). A .25 seems like not enough rivet to do the job, but it may be.
 

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Better to err on the side of a bit long than too short... btw, make sure you get the mandrel to snap off completely... it can cause corrosion problems otherwise. Also, make sure to coat the pop rivets with tefgel or lanocote to help stave off galvanic corrosion problems.
 
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