Tapered aluminum light/flag pole

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SPC
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Joined: Thu Apr 01, 2021 4:45 am

Tapered aluminum light/flag pole

Post by SPC »

How thick are the aluminum masts? I'm pondering what could be done to replace a carbon mast in case it were to break, and found that tapered aluminum masts can be found fairly affordably (compared to a new carbon mast). They have similar taper (10" - 4"), but I'm not sure about the thickness.

https://www.libertyflagpoles.com/produc ... escription

https://www.ebay.com/itm/One-30Foot-Lon ... SwbEFd0WQU

https://www.valmontstructures.com/produ ... pole-35-50

That last one has a spec-sheet; 1/4" thick walls on a 50' pole. It also says max weight 300lbs in a hurricane, for a weight at the top. I know the sails have to push the heavy boat, but how much load do they actually sustain?
Last edited by SPC on Sun Apr 04, 2021 5:48 pm, edited 1 time in total.

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mike cunningham
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Location: Jacqueline, F30 #3, Discovery Bay, California

Re: Tapered aluminum light/flag pole

Post by mike cunningham »

It is an interesting question. An engineer could probably tell you with some precision but the loading on the mast, say with full main and blade jib up in 20 Kts of wind in a seaway, must be pretty significant. Of course the load is distributed the length of the mast.

It would be fascinating to understand what the load margins are for one of our carbon masts in good condition.

With regard to mast replacement. That is also an interesting question. My sense is there is a great deal more knowledge re carbon fiber structures today than there was twenty five years ago. I see some pretty small diameter sections on the Wyliecat 30 for example. I have often wondered if my mast was broken or badly damaged whether it might be possible to retrofit a more modern lighter version? However, goodness knows what the cost would be.
Mike Cunningham
Freedom 30 (Mull) Hull #3
Build date...June, 1986 . Freedom Yachts USA, sloop, shoal keel
Gun Mount and pole retrofitted (purchased from a Hoyt Freedom 32)
Yanmar 2gm20F , 1600 hrs fixed two blade prop
e-rud and ocean racing equipment

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newt2u
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Location: UK

Re: Tapered aluminum light/flag pole

Post by newt2u »

Hi I notice only one of the ads mentioned aluminium grade and then only generally, i.e. 6000. Structual aluminium, the most common being 6082, has the greatest strength, however I am not sure how these poles are manufactured and the compatibility of the stronger alloys in the orocess.

I do know that there are some F21s in the UK with aluminium masts, it would be interesting to see the spec of those. Wilf Bishop who posted a lot of useful stuff here had one, indeed there are some pictures in a doc he posted of his. “Hoisting a mast on a freedom 21 Daydream”. Mine is CF.
Rockin - F21 twin drop keels - located Milford Haven
Wintered in Shropshire where I am when I’m not sailing

bad
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Re: Tapered aluminum light/flag pole

Post by bad »

The original F40 CC had Al masts - Two sections, the lower a fixed 10" diameter 1/4 wall. At about 15 ft a tapered section was pushed in and fastened w screws. I've not determine the wall thickness. The masts don't have a history of failure unless meeting bridges and such. They are rather flexible.

The junk rig guys use flag poles for masts. A naval architect can run the numbers. For the F40 there was an emphasis to reef both sails equally as the wind increased to avoid overloading the masts.

Carbon is lighter and stiffer, both rather desirable.

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Castaway
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Re: Tapered aluminum light/flag pole

Post by Castaway »

"Castaway" originally had two aluminium masts; two part tapered spars made by Proctor Spars in the UK, joined by an internal sleeve about 1/3rd of their length from the base. The main mast broke at the join; the PO felt this was due to sails cut with a curved luff, which kept the mast tensioned with a curve in anything other than light airs, and thus unable to bend freely in response to gusts. This is perhaps the only case of a Freedom mast breaking without the application of blunt trauma.
It was replaced with a T-P carbon fibre mast. Although the same length, the CF mast is about two thirds the weight, despite being about 2cm greater in diameter, and about the same wall thickness.
The owner of "Seorsa", Andy Freshwater, had arranged for a new CF mizzen mast to be made for his F35, which was even more lightly built, though I don't know how well this has performed. He has written about it on this site, and you might find it with a simple search.
A new mast in carbon fibre would not be cheap; I have wondered whether the only affordable option would be to find another, old, boat and buy that to get a spare. (If you do, let me know, since I could do with another CF mast for my boat!).
Last edited by Castaway on Wed Apr 07, 2021 7:13 am, edited 1 time in total.
Gerald Freshwater,
s/y 'Castaway', (UK F35 cat ketch, centreboard, 1987)
Lerwick Boating Club
Shetland Isles, Scotland

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arrancomrades
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Re: Tapered aluminum light/flag pole

Post by arrancomrades »

Hello all,

Yes, this is a fascinating question and one not to think too deeply about when you're trying to get to sleep at night. I have joined the UK Junk Rig Association which must be the most affordable club I've ever been in - a few pounds a year for a quarterly online magazine full of stuff. They have a wealth of written info on free-standing masts but for me the most interesting is of a 10m boat that I saw at Lochinver a few years ago, complete with its owner. The boat was a typical 1970's medium displacement GRP monohull with reinforced coachroof in the way of the mast.

He bought a standard lighting column (lamp post) tapered alloy tube, made in the Netherlands by some sort of spinning process and clearly of the same pedigree that the later UK 33/35 CKs were rigged with, however these have a complex liner and sleeve construction as mentioned by Gerald and are very heavy - mine 120kg each. I have heard it said that the final assembly was done by applying araldite to the tubes then ramming them together with a fork lift truck.

These tubes are now widely used for street lighting, partly due to their corrosion resistance and while I don't know the price, I think it is within reach. Weight isn't really a consideration for lamp posts, but cost is. You need to get a tube before it's cut near the ground for wiring etc. He then made a stout wooden liner in the form of a cross and by trial and error shaved it down to make a close fit inside the tube. He has sailed far and wide, including to Iceland.

Good sailing, I hope, Mike.
Mike Johnston

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