Erez,
Just got back from holidays.
Will give you a call in the next couple of days to discuss several possible sollutions that I have in mind.

Out of interest - how heavy is the Birch ply?
4mm Gaboon / Okume varies from 5.5 to 6kg. I have weighed 3mm between 4.5 and 5kg per sheet.
One sheet 1220mm x 2500mm is 3.05 sq metres.
Regards,
Phill

The birch ply is about 30% heavier than Okume, so a big difference!

Phill,
I am looking forward for that call, (sent you a message)

This is data from "The gouageon brothers on boat constraction" I almost forgot I had this book until Rolf mentioned it, Thank you Rolf,
This is a great book.


More resources:
http://plywood.e-boat.net/plyhelp.php
http://dixdesign.com/woodimp.htm
http://www.resourcesintl-wa.com/properties.html
http://www.westsystem.com/ewmag/18/pdf/plywood.pdf

If I use Birch over Okoume The Weight of the hulls will increase by maximum 6 kg (13.228 pound) minus the weight of the leftovers after you cut the ply.

How bad is that?
I need to find a way to reduce the extra weight some where else.

I also think that birch has more of branches than Okume. At least I have never seen so few branch spots in plywood than in my marine ply. The branches may have bad effect when toruring i.e. they might crack more easily. So it's not just weight...

--
Valtteri

When you count on weight, don't use kg, count in % and you get a good idea how bad it is

Gato,
Using the Birch ply will increase the weight of the hulls by 23.5%,
and the overall weight of the boat by 11.2%.

The boat will weight 119kg