I thought that the tapered aluminium tube was a bit marginal. Maybe it's OK, maybe it isn't, but in view of your comment, Jami, that you expected to sail in strong conditions, I came down against it. It won't be a case of short term catastrophe, with failure in the first big blow, but more a case of "what is the service life going to be?", remembering that aluminium alloy does not have a fatigue limit, a fixed level of stress below which fatigue failure does not occur (unlike steel, for example). The higher the stresses, the shorter the lifespan, and the lower the stresses the longer the lifespan, but every aluminium mast is going to fail, eventually. This isn't really a problem, we have to remember that every aircraft flies on the basis that its components have a safe lifespan, after which they need to be replaced. We just have to ensure that the service life is as long as we need it to be.

But notwithstanding the above, in view of your difficulty in finding anything else, it's looking like it has to be the tapered aluminium tube. So how to reinforce that vital area just above and below the deck? We've eliminated a matching sleeve of aluminium tube as being unavailable. I think I'd put on unidirectional glass/epoxy, with the fibres vertical. A cloth 1 metre wide will go around twice. I'd put on one piece 1 metre long, so 500mm above and below deck, followed by two more pieces, increasing in length, a 2 metre piece and then a 2.5 or 3 metre piece, so that it extends to the heel and then to the same distance above deck.

I can see your point, Jami.

I am in a similar situation, but for the all-wooden masts I paid a boatbuilder to do the difficult bits, and only did the glassing and painting myself.

Now I looked up that aluminium flagpole at 145 x 2.8mm.

Its strength (max bending moment) depends on the kind of alloy used as well.

If it is 6060-T6 at 150MPa, its yield strength should be 667kpm.
If it is 6082-T6 at 250MPa, it yield strength should be 1112kpm.

Yesterday I guessed the righting moment of the Gallion 22 to be around 681kpm
(M_r=Disp. x Beam x 0.20). This is the ultimate knock-down righting moment.

If the flagpole is made of an alloy which brings its yield strength up over 800-900kpm, I would be inclined to try it (if it isn’t too expensive). The British junkies have sailed around for decades with very slim mast profiles and (mostly) got away with it. I think it is better to use a bigger section with thinner walls. These are stiffer, and quite light. I might give the mast a 0.3m tall grp bandage (10mm thick?) at the partners (And mast step?) to reduce the risk of buckling the rather thin-walled section. Can’t hurt.

What is the diameter of that pole at mast top level?

Arne

PS: Again, I haven’t double-checked my calculations, so better look over them.

Jami

In countries like Norway, Sweden and Finland, it should be easy to find a straight spruce tree for a mast.

Now I looked up the The Cambered Panel Junk Rig, Chapter six to find the needed diameter of a hollow wooden mast. First, I found the fake sale area to give a SA/disp =14:

Fake SA =18.38sqm.

Putting this and a LAP=8.3m into the PJR formula produced a resulting mast diametre

D=19.8cm.

Even by twisting the PJR formula, the masts come out on the heavy side.

Another method:
I also have another ‘home-made’ formula based one the estimated righting moment of the boat and the bending strength of  a (hollow) wooden pole. Since wood varies in strength, I have put in a needed breaking strength 3 times the estimated righting moment of the boat.

The result was D=17.36cm, or say 18cm.

I know that Jester used a mast, which was about 18.2cm. This was much taller than this one and Jester was also heavier than the Gallion 22, so maybe a diameters of 17cm would be a better choice for the coastal waters around Finland. I surely would reckon 18cm to be plenty, even if you have the North Sea in mind.

Arne

PS: I haven’t double-checked my calculations.

4. Under the "Something Else" heading. 

Build a mast maybe?

Or turn the boat into a ketch with 2 smaller masts of a diameter you can more easily get? Similar to a Hunter Liberty 22.  

Just a thought and not a very helpful one, I'm afraid.  

The mast issue seems to stay problematic, because the availability of aluminium tubes in different sizes is quite limited, and lighting poles even more so.

The options so far for a mast with total length of about 10 meters:

1) 140/5mm al-tube, 6m plus a grp flagpole on top of this. Pros: easy to get, cheap. Cons: Heavy

2) 145/2.8mm al-flagpole (2.8 meters parallel at the bottom part, total legth 12m -> 2m will be cut off at the top). Pros: Easy (not a hybrid) and light, Cons: Not strong enough. Can something be done?

3) Grp flagpole (actually a pole for airport wind indicators, 10m or 12m for added strength (2m cut off)) with 7mm wall thickness. Pros: Easy, Cons: Heavy and possible installation problems (tapered all the way to the lower end)

4) Something else?