Rivets or Machine Screws When Splicing a Mast?

[s/v Jedi]

Originally Posted by Chotu

And thank YOU.

Another good post.

In the mean time, I’ve been reading about choice of fastener diameter. They say to use 1.5-2 times the thickness of the thinner of the two parts that are fastened. This would be your mast at 3/16” wall thickness I think you posted earlier.

For metric fasteners this brings the choice to 8mm because 6mm and 10mm fall outside that range.

For imperial fasteners this would be 5/16” but 3/8” just comes into range.

Then there’s the discussion on thread. For threading into thin aluminum it is said to use course thread. I did and it works great. But if you are threading into 1/4” sleeve, I’m not sure that this is still considered “thin”.

M8 is 1.25mm thread and 5/16” is 18 tpi which translates to 1.41mm thread, so metric is a bit finer.

I would go for metric because in my experience the A4-70 grade holds up better.

[boatpoker]

Hey Chotu, when is this happening ?
Take lots of photos

[Chotu]

Originally Posted by boatpoker

Hey Chotu, when is this happening ?
Take lots of photos

It had better be happening soon! I need to step the mast in a couple weeks at the rigger.

[kelse]

If the inside sleeve is long enough then should only need several rivets as the compression from the rigging will hold the mast in place.

[Seattle 519]

A late contrary opinion. I've been working in the aerospace industry for 40+ years, commercial and defense. Hundreds of thousands of parts in every Boeing model, Space Station Freedom and many prime military programs. Virtually NEVER had threads in aluminum structural components. All connections were bolted or riveted through. Corrosion is the primary concern no matter how much sealant is used.

SAE and metric both have course and fine pitch variations. Fastener strength is dependent on material. Standard stainless is 18-8, not great, 316 is better. Monel is stronger still and more resistant to corrosion failure.

Through bolt is best if you can reach in from inside. If you are interested I can give you a specific process for installation.

[OS2Dude]

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.

Bolts, maybe. Screws are going to intrude as much if not more than rivets.

Tap the inner sleeve and use the correct length of bolt. Not sure if an aluminum bolt would be strong enough, but I'd look into that.

[neilpride]

Through bolt ?? how? as soon as you slide the mast section there is no room.
Boeing structural rivets are a different animal compared to a regular marine rivet.
And, once the mast its joined with machine screws its for the entire service life of the mast, no plan B , corrosion its likely if the mast its painted , even with rivets, in any salty enviroment ,corrosion is a possibility.

[sailorladd]

For what it's worth, I would use rivets, based on what I have always observed....

[SofaKingFishy]

Rivets!!! Use tefgel.

[P3sailor]

Personally, I would use rivets, machine screws could loosen unless something like Loktite is used on the threaded portion.
The rivets I would use, without obtaining the manufacturers recommended repair procedures, would be Cherry Lok rivets, which can be obtained through just about any aviation repair station. These rivets can be pulled with a pop rivet gun but it is recommended to use a specific cherry rivet gun to pull these properly. I'd be willing to bet the mast manufacturer may have recommended repair procedures and specific rivet patterns to get the job done properly. There are different types of cherry rivets, but my memory fails me on the correct names and part numbers, but these rivets are used in many aviation applications and are the equivalent or better load and shear ratings than standard rivets. Get the manufacturers recommended procedures and do it right.

[Ratty1978]

If the "metal guy" is a boat rigger or an aircraft mechanic, rivets.
The absolutely correct rivets with proper installation tools should work fine.
And the location of the splice is important, as is the way the mast is stepped. The location in that picture, if a deck stepped mast, is, I imagine, almost entirely under compression load. If it were a keel stepped mast, way different loads. If the splice were up where the mast bends, quite different and variable loads.

I'd have my doubts about pop rivets with a hardware store tool.
If it were do it yourself, and me doing it, and I had an adequately thick extrusion on the inside, I might opt for drill and tap. A whole lot easier a year or two later to tighten up with a screwdriver, and also figure out why the screws are loose. But I don't have the proper, heavy duty, rivet setting tools.

Originally Posted by 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?

[Chotu]

Originally Posted by P3sailor

Personally, I would use rivets, machine screws could loosen unless something like Loktite is used on the threaded portion.
The rivets I would use, without obtaining the manufacturers recommended repair procedures, would be Cherry Lok rivets, which can be obtained through just about any aviation repair station. These rivets can be pulled with a pop rivet gun but it is recommended to use a specific cherry rivet gun to pull these properly. I'd be willing to bet the mast manufacturer may have recommended repair procedures and specific rivet patterns to get the job done properly. There are different types of cherry rivets, but my memory fails me on the correct names and part numbers, but these rivets are used in many aviation applications and are the equivalent or better load and shear ratings than standard rivets. Get the manufacturers recommended procedures and do it right.

Good plan. Can you get me the contact info for FranceSpar and who to speak with? Lol

Anyway, the mast is in process now with the machine screws following Neil Pride’s earlier post. But thank you

[col50]

Chotu, as you know, an ellipse is not a simple shape, and fabricating a perfectly fitting solid elliptical sleeve is a nearly impossible thing. That said, a common and easy way to make a sleeve is to take piece of the mast extrusion and cut it in half, lengthwise. There is relatively little difference between the inside and outside diameter of a mast extrusion and the resulting pieces will fit almost perfectly and can either be bent slightly more or simply pulled into place with the screws. I would not use rivets for this method of sleeving. BTW, the sleeves in my 61ft tall mast are about 5ft long.

[Chotu]

Originally Posted by col50

Chotu, as you know, an ellipse is not a simple shape, and fabricating a perfectly fitting solid elliptical sleeve is a nearly impossible thing. That said, a common and easy way to make a sleeve is to take piece of the mast extrusion and cut it in half, lengthwise. There is relatively little difference between the inside and outside diameter of a mast extrusion and the resulting pieces will fit almost perfectly and can either be bent slightly more or simply pulled into place with the screws. I would not use rivets for this method of sleeving. BTW, the sleeves in my 61ft tall mast are about 5ft long.

Um… an ellipse is probably the most simple mast shape there is. It’s the second most simple after a round pole.

My metal guy isn’t too scared of creating a perfect match.

So get me a piece of my mast then. 11 1/2 x 7 1/2. Perfect ellipse. Made by FranceSpar. Go! Lol


I’ll be done my boat by the time you find one.

My sleeve is also 5ft long. Good data. Thank you

[col50]

Originally Posted by Chotu

Um… an ellipse is probably the most simple mast shape there is. It’s the second most simple after a round pole.

My metal guy isn’t too scared of creating a perfect match.

So get me a piece of my mast then. 11 1/2 x 7 1/2. Perfect ellipse. Made by FranceSpar. Go! Lol


I’ll be done my boat by the time you find one.

My sleeve is also 5ft long. Good data. Thank you

Do you mean it will be 5 ft long; or is it already done? Anything is possible if you sink enough money into it. I like to follow the KISS principle. Good luck.