The size of the blanks should be listed in the plans.  Generally speaking, assuming you're talking about strictly stitch and glue, you should be able to get the hull panels and shear panels from 3 sheets of 4x8 ply scarfed together to form a 4x23 ply sheet.  If you're doing a stitch and glue deck, you should be able to get the decks from the same size sheet.

It will definitely be easier to build the blank and then loft the plans onto it for cut out.

FrankP 

Well it seems I shall have to lay out 3 4x8 sheets then lay the plans on these, do a rough cut out and then scarf together, then transfer the plans onto the blanks again for the final cut out which means I cannot stack the ply for cutting 2 sides 2 bottoms 2 bevel sides etc., which is what I was hoping to do for accuracy and efficiency. Otherwise scarfing toghether the 3 sheets of 4x8 seems rather clumsy and inefficient. Who has done this? What is the best way to go? I was hoping someone could tell me a width to make  a wide blank from which I could get the 2 sides, 2 bottoms and 2 bevel sides. No the plans do not give this, they seem to indicate the first method.

Well it seems I shall have to lay out 3 4x8 sheets then lay the plans on these, do a rough cut out and then scarf together, then transfer the plans onto the blanks again for the final cut out which means I cannot stack the ply for cutting 2 sides 2 bottoms 2 bevel sides etc., which is what I was hoping to do for accuracy and efficiency. Otherwise scarfing together the 3 sheets of 4x8 seems rather clumsy and inefficient. Who has done this? What is the best way to go? I was hoping someone could tell me a width to make  a wide blank from which I could get the 2 sides, 2 bottoms and 2 bevel sides. No the plans do not give this, they seem to indicate the first method.

I think you have the right idea.  I also think the vast majority of the Shearwater builders are building form kits and taking advantage of the puzzle joints.

 Jon T

revensdale, I'd glue up the panels, then cut them in strips wide enough to fit each piece, say 1 foot.  That will give you 4 panels that are sure to fit your individual boat panels that you can then stack as you indicate.  I just think the scarf and glue up will be easier to "line up" and get even across the larger boards.  If you have the plans, you can measure the widest panel and know how wide to "precut" the panels if you'd rather cut them before glue up. 

I thought you meant do final cuts before glue-up, which is just asking for mistakes.

FrankP