The two boats that I've had with aluminium battens have both been 26 ft and fairly stiff.  Sail area around the 350 sq ft mark.  I bent one or two battens on Fantail and compeltely destoryed the high-tech fibre and epoxy ones that I had on FanShi and nobody could accuse me of being a gung-ho sailor.  I wouldn't go less than 50mm if you are intending to go offshore. 

Breaking a wooden batten is much less of an issue than severely bending an alloy one, because the broken batten is easier both to remove and to reef out.  A bent batten high up in the rig could make the boat very difficult to sail.

Andrew,

I haven’t found an accurate way of actually calculating the dimensions of the boom, battens and yard.

I can only suggest dimensions based on experience with what I have used, myself.

·         For the boom and two upper battens, I would look for tubes of Ø35 x 2mm.

·         For the other battens, I would aim for Ø30 x 2mm.

·         I would make the yard from two tubes on top of each others, which has worked well on my two last boats, Frøken Sørensen and Ingeborg. For the main tube, I would aim for Ø50 x 3mm, and on top of that I would put another ‘batten tube’ of Ø30 x 2mm.

Good luck  -  no guarantees...

Arne

Andrew

a quick comparison between the Hurley 22 and my IF Ingeborg, makes it appear that the Hurley's righting moment will be about 80% of that of Ingeborg. Ingeborg's mast is 150mm with 5mm wall. A mast of 140mm should give 81% strength.

Frankly, this is not rocket science. Ingeborg's mast appears to be strong, without any sign of stress  when I sail her. 
If the project were mine, I would look for anything between 120 and 150mm.

Arne