Sidestay back plate pulling through hull

[PassingWind]

Once they've had a few years to weather, aluminum rivets are dull, while SS ones remain shiny.

(note, if you use rivets that are hollow, you might want to seal them so your mast doesn't fill with water on a capsize).

Fastenel sells the rivets much cheaper than west marine. You can also buy a rivet casings that go in before the rivet . The rivet then gets inserted into this casing. This is the proper way to seal the mast with pop rivets.
http://www.murrays.com/mm5/merchant.mvc ... gory_Code=


Harbor freight sells a heavy duty rivet gun that works way better than the cheape single hand guns. They sell it for 20 bucks.

http://www.harborfreight.com/heavy-duty ... 66422.html

[PassingWind]

For attaching the tangs to the mast, rivets are way stronger. There’s not enough wall thickness in the mast to hold threads. Pop rivets are easy to drill out because the center hole guides the drill bit. Of course, the aluminum ones are far easier to drill out than the stainless ones. One does need a pretty heavy duty riveter for the 3/16 stainless rivets, though. A lot of the aluminum rivets on my boat are still holding after 35+ years. I did have a boom bail for the main sheet break off last summer with no sign of problems before hand. The aluminum rivets were all sheared. Dwyer Mast uses stainless steel rivets and when I inquired about anticorrosion they said, “sure, you can do that but we don’t”. I use LanoCote.

So... just to get the question out of the way, would it be an incredibly bad or foolish (could be both I guess) idea to use three long stainless steel screws and locking nuts passed through the mast to attach both sidestay tangs (on the same screws)?

Thanks - Scott

I wouldnt do this. If applied to tight you can deform the mast and i think it wouldnt be good without some sort of internal collar to keep some outward pressure on the inside of the mast

[Breakin Wind]

I wouldn't do this. If applied to tight you can deform the mast and i think it wouldn't be good without some sort of internal collar to keep some outward pressure on the inside of the mast

Yes, I thought about that too as part of the deliberation process. My end reasoning was that most, but admittedly not all of the pressure is on the shear. Since the tangs bend out, there is going to be some outward and down pressure on the first attachment point, and I suppose a little "in" pressure on the upper attachment point. So with that thinking, and if I am assuming equal tension on both sides, the nuts and bolts would not need to be torqued down hard, really not hard at all. Using nylon centered locking nuts, I would think you'd just snug them up well, and that would be that. I really don't know enough to understand the pressure point dynamics of two opposite surface mountings versus a bolt through setup. The answer probably is that maybe each has it's plus and minus, but at the end of the production day, the rivets are faster and cheaper (if you have the proper equipment) and work equally well, so that's why they are used on the original boat.

[GreenLake]

My end reasoning was that most, but admittedly not all of the pressure is on the shear.

That's technically correct, but.

The whole point of the shrouds is to transmit lateral loads, the downward loads are a necessary by-product. So, while the shear loads are high, the other loads are not small (and they vary in direction as you tack or bounce in waves).

Since the tangs bend out, there is going to be some outward and down pressure on the first attachment point, and I suppose a little "in" pressure on the upper attachment point.

Again, that's technically correct, but.

Here, the "but" comes from the fact that the tangs aren't very stiff when it comes to bending (at least not stiff relative to the strong tension on the shrouds). Therefore, that leveraging action that you envisage will mostly result in the tang bending a bit, rather than transmitting a lot of pressure at the location of the upper rivet.

So with that thinking, and if I am assuming equal tension on both sides, the nuts and bolts would not need to be torqued down hard, really not hard at all. Using nylon centered locking nuts, I would think you'd just snug them up well, and that would be that. I really don't know enough to understand the pressure point dynamics of two opposite surface mountings versus a bolt through setup.

If you bolt two surfaces together, you get friction between them as well, which adds to the holding power. So, in the rivet case, there may in fact be less shear stress on the rivets than on your bolt. With a bolt, you end up with a pull where the opposite nut is being pulled against the mast, slightly compressing it, and allowing the bolt to slightly shift to the loaded side. That would make the loaded tang separate slightly from the mast surface. I would be worried about any possibility of "play" here and of the side effects of (even very slight) movement on load change.

You could compensate by tightening the nuts more, but then you'd have permanent compressive loading of the mast profile.

So, why not go with "tried & true" ?

Now, the bails for boom vangs are routinely fastened with through bolts. But those work more like an "axle" would, with even shear loads on both ends.

[Breakin Wind]

Whew! it makes my brain hurt to try to think of all that...

Fortunately, (I think) the tangs and rivets look pretty good. I want to check when I get back to the boat if they are aluminum or stainless. I don't recall anyone giving a definite answer as to what was factory standard so I'll check to see what I have.
If the latter (SS) I'll probably just leave them alone. If they're aluminum, it means they'll be easier to get out, and I'll probably cough up the $20 for a harbor freight rivet gun (thanks for the link) and replace them as long as I'm doing the rest of the standing rigging anyway.

My only problem with harbor freight is, every time I go there I end up buying 2-3 more items than I'd intended.

Thanks for the lesson... I learn more every time I come here.

[PassingWind]

Ss rivets are easy to drill out. They will just dull out your bits if they are cheap.

[GreenLake]

the drill bits, not the rivets.