I'm indeed looking at 6.00 mtr mast length.

The reasoning I had was as follows.

I want 7.00 sq. mtr sailarea as that is a good amount and the same as the Laser dinghy

I want at least a mainsail aspect ratio of 4

Therefor my mainsail luff length needs to be 5.3 mtr

I need 0.7 mtr clearence between mast foot and underside boom for my unstayed mast support structure. My design also uses a reinforced boom with a ram-vang and 0.70 mtr clearence is nice for the crew (banging heads etc). This rig can in principe rotate 360 degrees around the mast while keeping a good flying shape.

And so I arrive at 6.00 mtr total mast length. Stress analyses pretty much make this a maximum as well. My mast is basically tapered from 50 mm at the bottom to 30 mm at the top so I'm adding much heeling moment by going to 6.00 mtr.

Additionally this is a nice round number that will look nice in any class rules.

Wouter