Hi Wouter,

did the measument as suggested, 100mm. was the result. I never expected Altered to be stiff and as I said she doesn't feel stiff in the water. I have seen Hobie 16s that looked very flexible, wonder what they measure.
I would put it down to a number of factors.
Narrow decks = longer unsupported beams, allowing beam to flex.
Rear beam is fixed with a bolt at the outer end but has saddle riveted to beam bolted each end on inner edge.
Rear beam deck cut out is only about 1/3 depth of beam diameter.
A class beam mounts are built light.

All of the above I could expect when I went into this experiment and am happy to accept. The boat is a compromise and could never be as stiff as a purpose built F16 which would have the strength and stiffness where it matters.

Interesting thought though, when doing this measurement unless you picked up Altered from the bow, say 6" back it would prefer to lift the complete hull on one side before the other bow. Since the repair, the boat almost balances at the main beam, which is almost half way along hull.
Does this mean balance of hull weight effects this meausurement, ie. heavy bows puts more pressure on lifting just one bow. So is it a directly compareable measurement between boats of different centres of balance and beam positioning.

Still wonder if carbon beams would be stiffer. Not about to run out and buy some though. People forget this is still a low cost project despite the way it looks.

Regards Gary.