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Snotter attachment on aluminum mast?


MisterMoon

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One area that really concerns me as I prep my CS17 for next year's EC is the snotter attachment. My boat has tracked sails and aluminum tube masts. The snotters are both little becket blocks with SS hooks that hook into a SS strap eye that is simply screwed into the mast tubes with SS flathead sheet metal screws.

Those screws scare the heck out of me that they'll pull out in the middle of a moonless night and I'll be having to figure out how to sail without a boom. I'd like to make the attachment of the SS strap eye more robust than just relying on the screw threads in tension with the thin aluminum tube walls. But for the life of me, I can't figure out a better way to use nuts and bolts to hold it on. Any ideas?

Once I figure out a way to do this better, I'm going to go ahead and bolt on spares 1" above and 1" below the current strap-eye just to be safe.

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I also didn't trust a simple saddle (eye strap) so I found a largish pad eye with 4 screw holes and about 50 mm square. I bent the base plate to match the curve of the mast and screwed into the mast. As my lower section is 3mm thick and the curve of the baseplate shifted some of the force into shear and there were 4 screws I felt this was adequate. Here's a photo where you can see half of the baseplate on the front of the mast- the curve is visible.

post-425-0-63002600-1315971685_thumb.jpg

Of course if you want a really unbreakable option you could go for something like this.

https://www.whitwort...tAbsolutePage=1

Cheers

Peter HK

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I used pop rivets on mine. is it better? I don't know, i used rivets for attaching hardware to the mast in my spindrift. going on 5 years now and no failure yet...

Rivets have their own problems. Aluminium rivets are relatively weak, stainless or monel rivets have electrolysis problems which limit their lifespan, rivnuts are very good but expensive. In general though these fasteners (and screws) are best when subjected to shear forces rather than tension. Having something that wraps around the mast with a few attachments in different planes is ideal.

Will a couple of rivets in tension hold adequately? Depends on how hard you push it and how much corrosion. If it fails, it will be at the worst time...when being really stressed. Also as size goes up so does stress on each element of the boat, often exponentially. What works on a spindrift may not work on a larger boat.

Cheers

Peter HK

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I would not depend on sheet metal screws or rivets.

I drill and tap the holes with the largest screws that can fit in the eyestrap (saddle). I use 1/8 inch thickness tube in this area. I also will apply tefgell in the threads to stop galvanic cells from occurring in the stainless screw to aluminum mast connection and also use lock washers between the head of the screw and the eyestrap base to prevent them from backing out.

If you can devise a method to get nylocks on the backs of the screws inside the mast, that would be better still, but gaining access there and tightening the screws se3em incredibly awkward to me...

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I have never rigged a sprit boom mast. Maybe this is why I have this thought. Why not lash the block on? It might require some kind of textured or such finish on the mast first to keep it from slipping.

That would be the simplest solution except that I have sail track. Lashing would interfere with raising and lowering the sail and would be a pain to rig once the sail was set up.

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First thought is to ask if anyone has ever had screws pull out as designed. If not, it may well be tough enough as designed.

But since you asked, some modifications to suggest. First, take Ray's method and go one step further. Lay the mast flat and inject a thick, non-sagging mix of epoxy through the tapped hole ( rotate mast so the holes are on the bottom), then thread a waxed screw into the mini volcano of epoxy inside the mast. Once that sets up, back the screws out. You would then have a threaded backing plate inside the mast. It won't pull out of that.

Second idea is to use TWO vertical oriented eye straps, one on either side of the mast, each about 45 degrees off the mast track. Use Ray's method to install them. Connect those with a thick piece of line and let your snotter turning block run on that. The pull would then be a shear force shared by two straps vs. one in tension. A secondary benefit might be that the snotter block retains the same tension as you let the sail swing forward.

For a clean and elegant solution, I like the looks of the spinaker pole mast pad ring. It costs more, but you would gladly pay the extra on a dark, moonless night bobbing around looking for a way to get your snotter back up. You are building for an extreme adventure. You may need to take a few extra steps like this to make sure it all survives the trip.

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The sky is not falling. Almost everyone will use some kind of fastener inserted in the mast to secure fittings. Almost all of these will have a similar galvanic electrolysis potential. In almost all cases the fastener will be stainless. How often to these fail? I don't know since I have never had one fail in over 45 years in small boats. In sheer, I have used stainless sheetmetal screws often but not in tension where the thin mast wall provides little anchoring support. My fastener of choice in thin walled masts is stainless pop rivets and often in more substantial masts also. I do often use drilled and tapped machine screws in thicker masts. Even around salt(y) water, there have been no failures. Some corrosion protection is advised though. Paint is much better than nothing, especially on non anodized aluminum, which most of us are reduced to using these days.

I would never use aluminum pop rivets in any loaded location. They are not very strong.

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To date I have not heard of drilled and tapped machine screws coming out.

It happened to Doug Cameron and me on a dark night in the gulf after an uncontrolled (unanticipated) jibe. I think that he had drilled and tapped machine screws, but I my old memory sometimes fails me. Maybe it was sheet metal screws.

Doug tied a loop in a line and lashed it around the mast to get us to Key Largo and finish an Everglades Challenge. Doug is a regular here and he can describe his long-term repair.

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MisterMoon and all

My two cents worth...

I used SS machine screws with SS washers and nylocs for my snotter attachments.

Taped a spanner to a lonnnngggg stick...... tape the nyloc in the spanner, add a bit of sticky-goo of choice to hold the washer in place, slide the stick up the inside of mast to line the nut up with the hole, and drive the screw from outside...

Wasn't really difficult and I know they won't pull out....

Cheers

Dave

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I've repaired and setup many aluminum masts over the years and haven't seen many fastener failures, though the ones I have seen have been tapped (not counting catastrophic failures from broken elements or impacts). I too use stainless rivets, so do the major spar manufactures, who also use sheet metal screws on some attachments.

A through bolt would need a compression tube or you could easily deform the mast tightening up the arrangement, which would dramatically weaken the spar.

I would double the corrosion protection advice.

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