Its not quite decision day yet but its fast approaching as to what I system I choose.

I like the "I" beam the most but the time taken to manafacture the components alone is well out there, even with my $40 band saw (god I love facebook buy/sell sites ) it will be a slow process.

the 2nd option I listed is quicker and far lass complicated, single 3inch wide strip cut to the width of the hull and with one side cut to the deck curve and 4 slots to take the stringers, by gluing them onto the side of the foam subframes they would have enough surface area inwhich to spread the load out evenly through the foam....
A 2nd strip could if warranted be placed on the top of the foam to for a "T" .... not as strong as te I beam but certainly a lot quicker.

I hadn't thought of your idea of lowering the "I" beams down the 16mm and then setting the stringers onto them ...
certainly a very strong system


mmmmmmm more food for thought