Pat and Ian:
Thank you both for your input reassuring that everyone that has installed the Atlantic arch seems to be happy with it. Also from what I hear, everyone has added some lateral support of the arch, whether or not you are carrying the dink.
I don't plan to carry the dink on the arch during passages but believe that even without it, the greater its stiffness the better it will be in the case on faces very bad weather along the way.
Perhaps when we meet along the way we can test if, and by how much, the lateral stiffness is increased by the prestressing the arch pulling the legs apart compared with that bringing them closer.
Thanks for everyone's comments
SV IPANEMA SM178