Gary Pick said: "Wondering if I should either rename the topic or move the discussion to say Batten Specs?"

Gary King wrote:

Gary Pick wrote:I'm giving up on trying to get T6 in this country and will go for T5 45mm. I am assuming a wall thickness of around 2.5mm would be sufficient?

Gary, all you need to do is find a steel retailer who sells OneSteel products. Looks like Metaland in Lismore or Gold Coast is one. Their catalogue has all the OneSteel aluminium tubes listed, including that 38x3mm T6. They can order anything for you.

  

I'll call the Lismore office tomorrow but I'm not holding my breathe on the T6.

I'd be happier if it were T6 but it should be fine. You could possibly consider going for the 3mm wall for the top two sheeted battens.

I've just bent one sail onto battens, have done nothing on the other sail, and haven't sailed yet, and I've found it disturbingly easy to bend my battens by accident.

I too got T5 battens because I was unable to find T6 when I was constructing my rig. So far I'm planning to hoist them, hope for the best, and adjust as needed.

However as far as the "required" diameter, I would like to point out two things:

1. The resistance to bending under load has NOTHING to do with the heat treating. More heat treating will give it more strength before it takes a permanent bend.

2. Stiffness goes up linearly with wall thickness, but goes up with the cube of diameter. Weight goes up at about the same rate with either. So if you want to double stiffness, you need to increase the diameter by 25% or the wall thickness by 100%. The latter adds weight MUCH faster.

As for wall thickness, 2.5mm sounds sufficient: My research points me at a range of 1.5mm on the thin side to 3mm on the thick side. If you are afraid it isn't stiff enough, just go bigger instead of thicker.

Gary Pick wrote:

Gary King wrote:Ullrich here supplies a fraction of the tube shown on their NZ website, they appear to be for the scaffolding business only. The main supplier in Aus is Onesteel.

All their smaller dia tube is T5, and larger stuff is T6. (The yield strength of T5 is about half that of T6.) Don't see any T8 in the link.

Gary your link is to the commercial stuff, if you look at the structural you'll see smaller T6. They have 38.09 x 2.03 T6. I'm wondering if that would be strong enough?

That 38.09x2.03 T6 has slightly thicker wall too, probably stiffer and stronger than the 40x1.6 I was looking at (which is only $28 per 6.5m length).