Nice project, Thomas! Good to read that you start tackling it! :)

Of course I understand your point about that mast is what you habe... but still: On Ilvy, the mast is 177x5mm for roughly the lower half, at 35m2 sail ares. It is quite bendy, I wouldn't feel comfortable with an even lower diameter... 

Do you know any further specs about the aluminium? Which one is it?

PS: backstays unfortunately rule out some major junk rig advantages...

It looks good.  I had a very similar, 35 sq m sailplan on 5-tonne Arion, and found it more than enough, very powerful once the wind was free, from a close reach to a run.  I could reef a panel down in 15 knots on a broad reach and not slow down, and often had two panels reefed down in 20 knots of wind.

I did have a heavier mast, 200mm dia at the partners and 110mm at the truck, with a 5mm wall thickness, spun tapered.  150mm dia seems a bit light to me, but then I am a conservative sailor. I am hoping to find something similar to Arion's mast for my latest project, Arion II, in a year or two.

Anyway, lovely project, and I look forward to hearing of your progress.

Thomas,
Now I tried your boat with a copy of the JR I use on my own boat, Ingeborg. The mast position and the original rig’s CE forces me to pull the sail quite far aft. To get a moderate halyard angle of just 15°, I needed to make the mast fairly tall, but still within the length of the pole you have.

The advantage with going for that sail is that you will find the complete 4-sheet sailplan for it with all dimensions on it. No need for scaling up or down. (https://bit.ly/2FGM0ap )

Have a look.

Arne

(Edit I see now that the mast position was to be 1.75m, not 1.70m from the bow. Those 1.75m is better, of course.)

(See Arne's sketches, section 8)