Aluminum mast from thin wall vaccum tubing

[valery gaulin]

I need a 36ft aluminum round mast for a sailboat.

The max RM 1.5 T*m

Standard aluminum tubing found the wall is too thick at 0.125" and therefore too heavy for the sailboat I am building

I finally discovered while searching that aluminum vaccum or compressed air tubing is available in thin wall 0.083".

Prevost Aluminum Blue Pipe For Compressed Air - PPS BTU https://airpipingdirect.com/products/prevost-aluminum-blue-pipe-for-compressed-air?variant=41160130592873

Anyone is against my solutions of buying two 6" x 0.083" x 18 ft aluminum tube from the above website and joining the two together with an internal sleeve to make a 36 foot lenght mast?

It seams a reasonable cost vs weight solutions.

I checked for buckling and it seams to pass according to my calculations

 

[seasquirt]

You'll need a sleeve of 8 feet or much longer, which has an outside diam extremely close to the inside diam of your mast sections. That may be hard to find. And what are the I.D. tolerances of your mast sections; one may be too tight and the other loose, even if you specify to be sourced from the same batch. You could be lucky, or disappointed. What about a tapered mast section ? It would be lighter at the top.

 

[valery gaulin]

You'll need a sleeve of 8 feet or much longer, which has an outside diam extremely close to the inside diam of your mast sections. That may be hard to find. And what are the I.D. tolerances of your mast sections; one may be too tight and the other loose, even if you specify to be sourced from the same batch. You could be lucky, or disappointed. What about a tapered mast section ? It would be lighter at the top.

Why 8 feet sleeve? I was thinking of 2 feet lenght using the same tube for the sleeve but cut lenght wise to allow to slip inside.

 

[Barry]

Check out Sail Exchange. Theyspecialize in used masts and often come complete with stays, etc.
$2,000 or less.
Then Craigs, Facebook market etc.

 

[seasquirt]

You need the inner section long to spread the load of wanting to fold or stretch at the join, and also at the insert's ends, which will load shear pressure on the inside of your sections. With a 2 foot insert the mast will bend, kink, and fold where the insert stops. Or the butted mast sections will get elongated openings and even split from the join upward and downward, stretched by the short insert wanting to bend. Unless you re-roll and re weld your modified insert after reducing its diameter to a perfect fit, it will be egg shaped, giving much less support in 2 directions, and your insert may just curl inside itself like a scroll and allow the mast to fold at the join very easily. Look at it like you have two 18 foot long levers, levering at 18 feet up where the weakest point is, at the join, stressing rivets, bolts and holes, and or welds securing the insert. If the mast requires diamonds, the stresses are even more complex. I'm a metal worker and I wouldn't do it with a 20 foot mast. Then what if they are kinked already on delivery ? Delivery operators aren't always the most gentle of service providers. Like Barry said, probably easier and cheaper in the long run to source a second hand mast to adapt to your needs. Even a scruffy one can be polished up good enough as is, and then painted if you want a 'new' look.

 

[valery gaulin]

You need the inner section long to spread the load of wanting to fold or stretch at the join, and also at the insert's ends, which will load shear pressure on the inside of your sections. With a 2 foot insert the mast will bend, kink, and fold where the insert stops. Or the butted mast sections will get elongated openings and even split from the join upward and downward, stretched by the short insert wanting to bend. Unless you re-roll and re weld your modified insert after reducing its diameter to a perfect fit, it will be egg shaped, giving much less support in 2 directions, and your insert may just curl inside itself like a scroll and allow the mast to fold at the join very easily. Look at it like you have two 18 foot long levers, levering at 18 feet up where the weakest point is, at the join, stressing rivets, bolts and holes, and or welds securing the insert. If the mast requires diamonds, the stresses are even more complex. I'm a metal worker and I wouldn't do it with a 20 foot mast. Then what if they are kinked already on delivery ? Delivery operators aren't always the most gentle of service providers. Like Barry said, probably easier and cheaper in the long run to source a second hand mast to adapt to your needs. Even a scruffy one can be polished up good enough as is, and then painted if you want a 'new' look.

Thanks for your concern but after a little bit of research I have found that most mast manufacturer splice their mast when over 40 foot lenght as shipping is too expensive, also most mast when repaired are also splice.

The way it is done from my research is by taking the same mast section to make an insert by cutting the mast track. This allow for the inner sleeve to slide inside both mast section. After they only rivet or screw at many place both section with the inner insert.

The rules of thumbs that I ave found is that it should insert minimally twice the lenght of the widdest section, therefore a 6" section should insert 12" on each side. Therefore an insert of around 24" should be good enought.

Also welding is not recommended on most 6061-T6 or any tempered aluminum as it weakens the aluminum

I probably will splice both tube section using methacrylate adhesive ( MMA) and a few screws.

 

[Barry]

Thanks for your concern but after a little bit of research I have found that most mast manufacturer splice their mast when over 40 foot lenght as shipping is too expensive, also most mast when repaired are also splice.

The way it is done from my research is by taking the same mast section to make an insert by cutting the mast track. This allow for the inner sleeve to slide inside both mast section. After they only rivet or screw at many place both section with the inner insert.

The rules of thumbs that I ave found is that it should insert minimally twice the lenght of the widdest section, therefore a 6" section should insert 12" on each side. Therefore an insert of around 24" should be good enought.

Also welding is not recommended on most 6061-T6 or any tempered aluminum as it weakens the aluminum

I probably will splice both tube section using methacrylate adhesive ( MMA) and a few screws.

And is the mast thickness .063 as you are planning?

How will you attach the thin base, stays and pulley?

 

[valery gaulin]

And is the mast thickness .063 as you are planning?

How will you attach the thin base, stays and pulley?

The wall thickness is 0.083" = 2.1 mm. This wall thickness is no thinner than a regular mast!

 

[CT249]

The section of the mast on the very popular J/35, to use one example, is far more than 2.1mm. It varies from 3.5mm to 7.5mm. Looking at the rough section drawing, the stays and spreaders attach to a 5mm thick (approx) section.

The Kenyon section used on J/24s and Etchells is a uniform 2.25mm wall thickness.

I think the Laser lower mast section is 3mm thick.

 

[CarlosK2]

Yes

The price of things for sailboats went from expensive to very expensive to extremely expensive and when it seemed impossible it went straight to a joke

Lately when I see the prices I just burst out laughing

What can we do

I don't know

 

[valery gaulin]

The section of the mast on the very popular J/35, to use one example, is far more than 2.1mm. It varies from 3.5mm to 7.5mm. Looking at the rough section drawing, the stays and spreaders attach to a 5mm thick (approx) section.

The Kenyon section used on J/24s and Etchells is a uniform 2.25mm wall thickness.

I think the Laser lower mast section is 3mm thick.

Thanks for sharing your info.

See also the Zspar website company as an example, 01/02 Series Masts | Zspars https://zsparsuk.com/01-02-series-masts

For example section Z351 160mmx105mm as a wall thickness of 2.2 mm

My understanding is that for racing sailboat they tend to go with a thinner profile with a larger wall thickness for aerodynamics purpose above weight a loft and they increase the number of spreader.

For cruising purposes they try to go with a larger mast profile with skinnier wall and fewer spreader. Prefering less weight aloft than aerodynamic purposes.

Anyway the important part is to have the right I (section moment of inertia) to do the job.

 

[valery gaulin]

Yes

The price of things for sailboats went from expensive to very expensive to extremely expensive and when it seemed impossible it went straight to a joke

Lately when I see the prices I just burst out laughing

What can we do

I don't know

Yes, it is getting crazy expensive! This is the reason why I ma investigating using most standad aluminum tubing and using traditionnal rigging theory and pratice with modern material.

I have seen a couple DIY sailboat on youtube that utilise this principle and philosophy and they don't loose that efficiency over all! Of curse they are not racers but they do *** good as all the plastic fantastic cruing sailboat from standard manufacturer.

Also when it is time to repair it is very easy, since it is just rope, like dynema, SS wire rope woth traditional splicing.

Anyway just investigating for now!

 

[wet feet]

If you really need to go cheap, try contacting a few marinas to see if they have any broken masts around the general section size that you need.It might mean visiting a few different places with a rule and a camera in the hope of finding enough parts, but you could also acquire the joining sleeves and other mast hardware. Transport might be a challenge and there will only be one person to blame if it all goes wrong a long way from home. It will still be better than a mast with a wall thickness of 0.063".

 

[Barry]

If you really need to go cheap, try contacting a few marinas to see if they have any broken masts around the general section size that you need.It might mean visiting a few different places with a rule and a camera in the hope of finding enough parts, but you could also acquire the joining sleeves and other mast hardware. Transport might be a challenge and there will only be one person to blame if it all goes wrong a long way from home. It will still be better than a mast with a wall thickness of 0.063".

I had misread the original post, the wall thickness is .083. I had referred to this thickness as .063.

 

[valery gaulin]

If you really need to go cheap, try contacting a few marinas to see if they have any broken masts around the general section size that you need.It might mean visiting a few different places with a rule and a camera in the hope of finding enough parts, but you could also acquire the joining sleeves and other mast hardware. Transport might be a challenge and there will only be one person to blame if it all goes wrong a long way from home. It will still be better than a mast with a wall thickness of 0.063".

Not 0.063, but 0.083" = 2.1 mm!!!