Rivets or Machine Screws When Splicing a Mast?

[Chotu]

The mast splice is taking place next week.

The metal guy needs to know if it’s rivets or machine screws for this.

I see the jury can be very much out on this topic. Any opinions?


Basically there will be two mast sections butt joined together.

Inside, there is another smaller section that is there to keep the outer sections lined up with each other in all sorts of dynamic situations.

The rivets or screws securely fasten the inner section and outer sections to each other.

Like this pic.



So would you use rivets or machine screws? Why?

[Searles]

Have seen and used both on masts of over 80 ft ,rivets were monel counted sunk 1/4 or 6 mills , same with c/s socket head s/s metal threads ,best consult a mast maker fo pattern for best stress .⛵️⚓️

[jt11791]

The Selden mast on my boat is held together with rivets.

[HeywoodJ]

IIRC this is a longer extension? Will any internal halyards run down the inside past the highest fastener? If yes, rivets leave lots of nice chafe points inside the mast. Machine screws, of the right length, much less so.

[Chotu]

Originally Posted by HeywoodJ

IIRC this is a longer extension? Will any internal halyards run down the inside past the highest fastener? If yes, rivets leave lots of nice chafe points inside the mast. Machine screws, of the right length, much less so.

Yes. There may be internal chafe from the fasteners.

That’s pretty much the only concern between the two, right? They are basically interchangeable then?

Either way, I don’t want to have too much stuff sticking into the inside of the mast where halyards can chafe and wires can lose insulating covers

[Wolfe10]

How far from open end of mast to splice?


If not too far, and you can reach in, through bolt and finish inside with acorn nuts and lock washers.

[Chotu]

Originally Posted by Wolfe10

How far from open end of mast to splice?


If not too far, and you can reach in, through bolt and finish inside with acorn nuts and lock washers.

Much too far. It’s only accessible from the outside of the mast.

A good thought though.

[boatpoker]

Either works as long as they are Monel and Tefgel'd

[Benz]

Definitely machine screws with loctite. I've seen enough rivets, even factory ones, fail. Never seen a machine screw fail like a rivet.

[Chotu]

Originally Posted by Benz

Definitely machine screws with loctite. I've seen enough rivets, even factory ones, fail. Never seen a machine screw fail like a rivet.

That settles it. Machine screws it is. Made out of stainless? Monel?

Loctite instead of tefgel?

Short stubby screws so they don’t intrude too far into the area the lines and wiring runs through?

Anyone know what diameter the screws should be? 1/4”? 3/8”? Mast is 3/16” thick plus there is the flange thing inside to keep the alignment of the butt joint.

Just tap the threads into the aluminum and screw them in?

I want to make sure I understand this fully so that I can be sure the fabricator is doing things the way that it is expected.


And finally, what should the heads look like? Having them flush would look good. But there is also only 3/16 of an inch of thickness to play with.

What style from this chart is the correct one?

[Rumrace]

Rivets pull metal together screw tear at the aluminum assuring corrosion and the mast looses. The rims on my summer car have 40 rivets to hold 3 pieces of the rim together. The front ones wore out so I had all 4 rims reworked. We’re they threaded or screwed they’d be junk.

[wyb2]

People always seems to jump to exotic solutions, maybe they know more than I do. Seems the advantage to rivets is everything can be aluminum, no dissimilar metals. A quick search on McMaster turns up only 1 size of nickel 400 (Monel) rivet, and it has a steel mandrel which means it will leave a steel ball inside that leaves rust stains for years to come. Nickel 400 cap screws are available at a whopping $15 per screw.

If going with machine screws, a larger number of smaller screws will be better than fewer large screws. I would think 1/4” max. Incidentally 1/4” seems to be the largest size blind rivet that is commonly available.

Does the inner piece fit tightly inside the mast? If you need to draw the inner piece tight against the inside of the mast, than you can only thread the inner piece, with clearance holes in the mast section.

[SVTatia]

If you decide on screws, the thread type is important, I read somewhere (I wish I could remember the source) that coarse thread is recomended rather than fine. Apparently coarse has a deeper "grab" on the thin al. wall. I was researching this for attaching my al. mast steps.

Edit: source for the coarse vs fine threads.
https://resources.tannerbolt.com/art...type-do-i-need

[Breaking Waves]

Originally Posted by Chotu

rivets or machine screws

OK - basic point first - there are two fundamental types of rivets - 'pop' rivets and solid rivets.

Solid rivets are the technical best choice for basically all factors (strength & vibration resistance). But they require special tools and access to both sides.

So your guy would probably provide pop rivets.

Threaded fasteners (eg machine screws) will provide greater strength than pop rivets (size for size, same material to same material), because the pop rivet shaft is hollow. With Loctite on the fastener, vibration resistance should not be an issue for either.

Pop rivets are faster to install when you have a lot of them, as you have to thread the holes for machine screws. (and yes, course threads for thin aluminum). For fasteners into aluminum usually, you want hex heads or torx - this both allows you to more careful torque and helps if/when you need to get them out later and they is some corrosion - less likely to strip the head.

Either will work (properly done), but generally, machine screws are viewed as stronger/more durable.

[neilpride]

Originally Posted by Chotu

That settles it. Machine screws it is. Made out of stainless? Monel?

Loctite instead of tefgel?

Short stubby screws so they don’t intrude too far into the area the lines and wiring runs through?

Anyone know what diameter the screws should be? 1/4”? 3/8”? Mast is 3/16” thick plus there is the flange thing inside to keep the alignment of the butt joint.

Just tap the threads into the aluminum and screw them in?

I want to make sure I understand this fully so that I can be sure the fabricator is doing things the way that it is expected.


And finally, what should the heads look like? Having them flush would look good. But there is also only 3/16 of an inch of thickness to play with.

What style from this chart is the correct one?

Both ways are ok, monel its the answer if its riveted, air hydraulic gun, you need one, machine screws the best option, FLAT 82º, allen head, dont even try to use flat or phillips heads, Loctite , just a bit.

https://www.cruisersforum.com/forums...-a-138817.html