Hi Tony,

the main advantage in using 3mm okoume is the boat will be lighter and it will be easier to bend the pieces into shape...then a boat built with 4 mm.

the main disadvantage is that it will be slightly less rugged/stiff....but on the 10 foot boat...i don't think this is a discernable difference....especially if your building it for a child.

my personal perspective is that i very much like to build boats light.  they are just easier to get on/off the car and move around.   clc used to offer 'light build' options where you could order a kit with 3mm instead of 4 mm for a number of their designs.   fwiw, they stopped that practice years ago...i assume...to keep production simple.

i will note that the wood duck specification does make a point that you can also put a heavy person into it (60 to 200 lbs paddler weight) which is quite a range and that could effect your decision too.

in my view, if you can source 3mm for your project and you are building this for your grand-daughter...i would go for it....and that's what i would do. if you are going to be putting folks in it who are at the top of the range and expect to bang it around...you might want to stick with 4mm.

h

   Thanks. This is pretty much the same line of thought I'm on. 

Tony, 

One other idea i would share is that you can also combine 3mm and 4mm construction.  a good example is the chesapeake 14, which uses 3mm for the side and deck panels and standard 4mm on the bottom panels.

this puts the stength where it is needed and not carrying extra weight/strength in areas that are less likely to get stressed in certain ways.

a standard failue mode, for example is an impact from a sharpish object...like against a rock that might happen if you hit a shallow, or get into a boat for a test fit without the bottom well supported.  so these types of impacts are just more likely to involve the bottom panels....

beefing up the deck for somebody stepping on it, fwiw, is probably not going to make a bit of difference if you went with 3mm or 4mm.  you will break either of these it if somebody decided they wanted to step on it.

most of the racing kayaks...fwiw....also use 3mm consruction.

i hope this extra information is helpful.

h