John,
I was looking at that site and was surprised to see those boats are built using the old fashioned ply-on-a-stick-frame construction. Can't see how the weight can be kept low with all that interior lumber. And using open cell building insulation is an invite to having your own interior water supply. That stuff will soak up water if given the chance. If it does it has to come out or you boat will rot. And the use of luan scares the daylights out of me. The few boats I have seen made from luan all had many dollars worth of glass and epoxy laminated to them because it would have been very easy to put you foot thru' the luan without them.
Everything about the PDR is retrograde and it looks like it would take as much time and dollars as building a well designed hull using a modern technique.
Here are the free plans for the D4 Dinghy. I built one and it has never given me a bit of trouble in four years sailing. The hull cost $300 and a ready made sail $200. Designed by a naval architect.
Even if you are not interested in the boat the construction tutorial will give you and idea of what modern S&G construction is all about.
http://www.bateau.com/freeplans.php

: Hi Charlie,

: The foam experiment does show the strips may be slightly heavier then the
: Luan, maybe, because I slopped the epoxy on the foam, laid the glass on,
: slop coated and laid on the strips, laid on the second layer of glass 8
: oz, and slopped it with resin. This was just for a one day quick set up of
: the experiment. Normally I squeegee the excess epoxy for weight savings.
: Now if you add a finish to the Luan plywood that would add some weight
: also. So all in all they are probably close to being equal in weight.
: Strips for the hull bottom simple aren’t practical or strong enough. If I
: can find Oakum I’ll check it out. I’m leaning towards the Dave Gray type
: of construction and add strips on the foam glassed sandwiched like in the
: experiment just to add a different look. It won’t be for weight savings as
: you pointed out and as the experiment shows.

: John