Rolf and Gato, I have the feeling that we are approaching, for the time being, the end of this little thread and maybe not commonly done, but I would like to thank you both for the interest shown.

I would still like to add two small technical details. First the question about how to catch the severe stress loads froms the stays on my puttings mounted on a skin from 1mm (on a soft foam interior). This point gave a lot pain in the stomach in the design state.
The solution was quite obvious: a wooden underlayment built in the foam, sort of half bulkhead, to have "meat" for the screws and to spread the load. Further on the skin was enforced ofcourse at that places with extra layers to divide the stress.

Second question was how to make the rather complicated hullshape (assymetrical and not straight) mirrorlike identical to the second hull. Well I didn't succeed 100% in that; there was also a time period of several months between making the hulls. And my working space, a cold and very narrow shed with a leaking roof, didn't help much.
In sailing I can notice the difference between the hulls quite well, but I tried to compensate that with different rudderangles, which helps a bit.

Finally I would like to add an anecdote which actually happened to me a few weeks ago and clarifies a lot of my ideas of homebuilding:

I live in village on the dutch seacoast in a very old cottage about 1000 meters from the sea. I don't let my cat on the beach because of vandalism. So I drive it with a little drawer on small road through the village. I was used to do that with my mast mounted standing-up, but because of overhanging trees and lighting poles, I had to divert a lot which was annoying for my fellow roadusers (summertime, tourists).
So this year I used myself to mount and dismount the mast on the beach each time I went sailing. But because of my shoulderproblems I cannot walkup the mast in the old fashioned way. So, I put the cat on its side and walk the mast, already in its side stays, in a horizontal way up on its ball on the frontbeam.
A few weeks ago, my worst nightmare came through. Just after loosening my mast with dismounting, the cat started to fall towards me and the mast. Ofcourse careless, but in a hurry for the diner and still high from a afternoon nice sailing.
(on one hull showing off for a fully loaded beach with tourists)
The devil or god, I don't know which, punished this immediately and with a bang that let every body on the beach rise, my cat fell upside down on the mast. People started running at me. Mast was gone, dented and bent.

But the miracle was that the cat who hit the mast upside down with its forebeam, was not damaged at all. No dents, blushes, not even a scratch!

My intuition for choosing a wooden based over-solid beam construction payed off exactly that moment.

So I thank hereby "the spirit of sea" (or whatever supranatural phenomenon it is), who I spent so many time with at sea, for helping me with my design.