Broken aluminium mast

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Bill
Posts: 18
Joined: Wed Aug 05, 2020 6:57 pm

Broken aluminium mast

Post by Bill »

Hi I'm Bill I sail in the UK
My mast which is a 15 m aluminium on a 1989 freedom 33 sloop has snapped at the base around the cabin top splitting neatly on the outside but pulling out the plate sleaves on the inside
Any suggestions as to how to repair, replacement is not an option ,mainly what happens if the repair is too strong and can the base be shortened by a few inches ,to move the stress point

Have pictures but not sure how to attach

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arrancomrades
Posts: 54
Joined: Mon Aug 22, 2016 7:11 am

Re: Broken aluminium mast

Post by arrancomrades »

Bill, Oops and sorry.

There's a very good article on the Junk Rig Association pages about new masts being made from Dutch spun alloy tubes (same as lamp standards/lighting columns) with a wooden insert to about 33% height - I think carefully crafted by trial and error in an X shape and rammed up the bottom part of the tapered tube to beyond the stress points. I've met the owner and seen them from the outside. The remains of your tapered tube may be of a constant section that could either be sleeved or sheathed in a short standard alloy section much as the CK masts are made. I have a drawing.

Given a few days I can dig out the details if you want.
Mike Johnston

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newt2u
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Joined: Wed Sep 11, 2019 11:24 am
Location: UK

Re: Broken aluminium mast

Post by newt2u »

The problem with sleeving is that you create new stress points at the ends of the sleeve. Any strain is resisted by the double wall of the sleeve and concentrated where the sleeve ends. This is not unlike the stress point where your mast originally parted, i.e where it exits the deck. However, that is just one fixed point and the stress is relieved both above and below that point. In different applications (grp fuselages) I have seen tapered sleeves used.
Rockin - F21 twin drop keels - located Whitehaven, Cumbria, UK

Bill
Posts: 18
Joined: Wed Aug 05, 2020 6:57 pm

Re: Broken aluminium mast

Post by Bill »

Thank you any information would be greatly appreciated
I accept there will always be a stress point but my concern is can I make it too rigid with the sleeve
I intend to replace the bottom end ,cut away at least 18 in past the break in the upper section and joint with an inner sleeve of rolled aluminium I intend to bond it with epoxy and then rivet using monal metal rivets
The sleeve will extend About 24 in into the top section which is slightly longer than the 18 in that seems to be how stayed masts are repaired
Again any information on the original construction of my proctor mast would be really helpful
Thanks

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arrancomrades
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Re: Broken aluminium mast

Post by arrancomrades »

Bill, this is all I have and it's a scan of a copy of a print etc.

Also an interesting, but irrelevant email about the early F40 masts.

Mike.
Attachments
F40alloymast_email.pdf
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F35CKbackmast.pdf
(1.32 MiB) Downloaded 119 times
Mike Johnston

Mark K.
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Joined: Sun Jul 31, 2016 4:32 pm

Re: Broken aluminium mast

Post by Mark K. »

I once read an article in a sailing magazine where the author encountered a thrifty sailor who needed a new mast and made one out of a discarded aluminum lamp pole. The kind they use to mount those really tall sodium lights for highways. They are made of aluminum and tapered. Just a thought. Albeit a kind of crazy thought.

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arrancomrades
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Re: Broken aluminium mast

Post by arrancomrades »

Re lamp poles, these were very hard to come by until about 20 years ago when they started sprouting, particularly in coastal areas where corrosion resistance was important. I measured the local ones and they matched my masts. So just need a digger and a dark night(?) but I have spoken to some roads engineers in Scottish councils and they are readily available. So not so crazy. The Junk Rig folks are well into this.

My understanding is that carbon is much lighter and bends more, making the possibilities for matching sail to mast much greater. Most of the early experts,(Hoyt, Oakley etc) were Olympic Finn Class sailors who knew their stuff and could turn the handle of a sewing machine. There have been disappointing failures of both types and neither take kindly to being drilled for whatever purpose.

For Bill's problem, I would head down the wood-inset route which can be a DIY project. Insurance might be the biggest issue. Short of paying for a full structural analysis, the alloy-welding mast-makers are probably just as much in the dark as there's no body of experience as exists for the archaic Bermudan rig with all its wires and compression/tension wracking the hull. And Bermudan masts fall down quite often too.
Mike Johnston

Bill
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Joined: Wed Aug 05, 2020 6:57 pm

Re: Broken aluminium mast

Post by Bill »

Thanks Mike and everyone else
The drawing was really helpful As was the other article
Looked at lampposts but the base diameter was too small and the taper was the wrong profile
Think I'm going to try to separate the top section which has the taper and renew the complete bottom section
Will photograph my progress and post it on completion or Wii show how well freedoms motor!!

Also the junk rig forums a good site

Thanks
Bill

Bill
Posts: 18
Joined: Wed Aug 05, 2020 6:57 pm

Re: Broken aluminium mast

Post by Bill »

Mast fully repaired forgot to take photos but it took a lot longer than I thought
This was not helped by catching COVID and waiting for the insurance to tell me it was wear and tear so no claim
Which brings up the issue of a 35 yr old boat ,what isn't wear and tear ?
Rebuilt the mast with 6082 t6 aluminium tubes used 4 x 6 mm concentric tubes which are readily available stripped the mast back to the original joint about 4.2 m rather then repairing the 2 m break . made up of 4 sections with 1.6 m extended from the two inner tubes as a slice into the old top section had to make it this thickto ensure splice was thick enough
Used a generic two pack slow cure epoxy , got 4 lts for cost of 1 lt west ,filled with cabosil on the splice plus 6 mm stainless countersunk screws (couldn't find long enough Monel rivets for 24 mm) following the original diamond pattern .also set the mast with generic two pack urethane about 25% cost of Spartite
First sail out winds gusted to 35 kts and lots of pounding all ok
Again thanks to everyone for their help
Bill

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