Have you seen these balsa boards?
They are solid classic traditional boards.
They also make light strong eco friendly performance short boards and longboards - for example a 9 foot longboard can weigh 8kgs.
Its 12'6" and solid 24kgs.
I have ridden it and Barton Lynch also.
You will be surprised what it can do it the water.
Balsa is amazing in the water.
Check out these links
Video with Barton Lynch on RA - Fox