The strength is not a problem. Greenland kayaks are built from two,identical as possible, sheer planks. These are the foundation of the boat. Morris goes thru a lot of text showing how to select and produce those planks so as to get pieces that produce nice,mirror image bends. With scarfed up pieces there is bound to be some differences because the wood grain varies a bit in density or orientation from one section to another. They may work without a problem but if they don't it may be necessary to massage one or the other to make them both curve the same. With any other long pieces the number of or location of scarfs shouldn't be a problem.

: Thanks for the info. I'll check out the Home Depot stock of red cedar and see
: what they've got. Home Depot also has "premium" pine, that is
: completely clear, and comes in lengths up to 8'. I'm not sure of the
: species, but the sticker on it says the company is in New Zealand. I'm
: guessing Radiata based on some googling. It isn't cheap, but there would
: be little waste.

: Is there a reason you limit things to one scarf joint? I'd like to make an
: 18' boat, so I'd need to scarf together three boards to get the necessary
: length. My understanding is that if done properly, the joints should be
: stronger than the wood.