Howdy Robert,
I've put some pics of a beth building and one sailing on my first post in this thread so ppl can see what we are talking about
http://www.woodworkforums.ubeaut.com...226#post649226
No - you have it wrong! Probably my fault for being to verbose!
1/ It is possible to build the bottom of the boat out of 6mm ply as per the plans without any additional bottom stiffening.
2/ If using gaboon it is possible to use 9mm without increasing the weight of the boat. The bottom will weigh the same as that part of the original boat.
Thanks for correcting my memory with the plywood for Beth.
I think a good strategy is to ignore this discussion about longitudinal bottom stiffeners and build the boat without them. If there is a problem then it is pretty easy to add them later. If the bottom ply is 5-ply (5 layers) it will be much better than my original Beth anyhow!
I would suggest using the lightest ply of good quality that you can get for the rest of the structure if you can't get gaboon.
Best wishes
MIK