Non-stainless bolts in rig

[markxengineerin]

The original bolts holding shroud tangs to mast were 5/8-16, stainless steel

Due to my mistake, the new "cheeky tangs" will only fit a 1/2" bolt through the middle.


Clamping load for original 5/8-16 is 17,800 pounds when fully torqued (186 foot pounds)

Clamping load for 1/2-16 stainless is 5,850 pounds when fully torqued (49 foot pounds)

Clearly a 1/2" stainless bolt will not work, but, a non-stainless steel bolt might be ok.
A high strength steel (black oxide coated) 1/2" bolt will make 15,000 pounds of clamping load when fully torqued (100 foot pounds)

So, how bad is it to use a non-stainless bolt in the rig? I would coat it thoroughly with TefGel. It is fully enclosed in an aluminum compression tube through the mast, so only the 2 ends will be seeing the light of day and water.

Will it survive 10 years if I re-coat the "ends" every year?

The alternative is to drill out the cheeky tang, but that produces a .130" thin wall which I am even less comfortable with, although I haven't looked at that in detail yet.

[Muaddib1116]

Why not get the right cheeky tangs?

[markxengineerin]

I made these ones, took a long time, got them anodized as a favor, basically don't want to do it again if there's a safe alternative.

[tkeithlu]

First, note that the bolt is side loaded, not in compression or tension. The nut is largely keeping the cheeky tangs from sliding off the end.

Since it is only 1/16" of plastic removed, consider boring out the checky tangs to 5/8".

A lesser bolt I don't think a good idea, both because you need its strength in shear and because you don't need even a possible failure up your mast. You're talking about a successive failure demasting under the conditions a demasting will occur, which are likely not convenient.

[markxengineerin]

It is not a good practice to load a bolt in shear, especially with such a long overhang, so I would prefer to have enough compression to make sure the bolt is in pure tension, no bending. It is a moot point anyway, as the existing design with a 1/2" hole can't take a 15,000 pound compression force (bolt torque) without yielding. Back to the drawing board.

[Muaddib1116]

If you bore it out to have 0.130" wall thickness are you concerned about crushing the tang at the thin part? Or are you concerned about the load of the dyneema tearing the aluminum apart? Most of the load will be transferred directly into the bolt through the thin wall.

[KP44]

Originally Posted by markxengineerin

So, how bad is it to use a non-stainless bolt in the rig? I would coat it thoroughly with TefGel.

I am a fan of TefGel and use it often.
I am not a fan of non-stainless. Every place where the previous owner used non-stainless has been a problem. I use only stainless on my boat.

[Benz]

I'd be uncomfortable with the legerage exerted by that outboard tang. I see why you want the full compression load and bigger bolt.
I'd say drill out the tang, and coat the surface where it touches the SS bolt with tef-gel. This will be better than trying to get a steel bolt not to rust. As long as there's something filling the hole in the tang, (the 5/8" bolt in this case), the aluminum will not crush.
As per your drawing, the thin spot is only in one small area, with the rest of the piece still picking up most of the load. You'd have to apply a bending force right in that spot, I reckon, which would be hard to do.

[waterman46]

You did a lot of nice work on the design. Have not seen these before. Do the cheeky tangs have any advantage over a standard stainless tang with a teflon washer (for corrosion) bolted up tight against the mast?

[pjShap]

Maybe you can use a higher strength stainless steel, like Duplex or 17-4PH, or titanium Grade 5? This company seems to specialize: https://www.extreme-bolt.com/

[NPCampbell]

Originally Posted by markxengineerin

A high strength steel (black oxide coated) 1/2" bolt will make 15,000 pounds of clamping load when fully torqued (100 foot pounds)

I used black oxide coated hardware to mount some black gear on my fishing boat. The washers rusted in a freshwater only environment within a year.

[NPCampbell]

Originally Posted by pjShap

Maybe you can use a higher strength stainless steel, like Duplex or 17-4PH, or titanium Grade 5? This company seems to specialize: https://www.extreme-bolt.com/

2205 duplex seems like the most widely available of those. I think it has higher UTS than most HS steel and better corrosion resistance than 17-4PH.

[Cwens]

Clamping load for original 5/8-16 is 17,800 pounds when fully torqued (186 foot pounds)

Clamping load for 1/2-16 stainless is 5,850 pounds when fully torqued (49 foot pounds)

I'm not a mechanical engineer. Cross section of a 5/8" bolt is about one and a half times the cross section of a 1/2" bolt. Why such a big difference in clamping force?