Stoo, thanks. I'm not a professor but I now some things about structures. so before sawing I will sure check where and how. I will search for the discussions about reverse thread inserts.
Zodiac was quite helpfully but plans of this type of boat is Out of the question. and it seems that the boat owners of this type aren't that active on the www.
I didn't spoke to 1 yet but sure searching for them.
I just remember that zodiac offers a kit for installing treads including drill and instruction. I did see them on the zodiac site with part number