From a wastage/labor perspective, 9’ strips for a 17’ boat sounds like a good idea, but in reality, not so.  If you joined two 9’ strips to make full length strips, this would place all the joints concentrated in the center of the boat.  This is not good from either a strength or cosmetic perspective.  On a strip build like so many other wooden projects, you want the joints distributed so that they are not all bunched together.

If you can buy (or cut your own) full length strips, then that would be best cosmetically.  If you already have shorter strips, do not waste your time scarfing them together.  Scarfing will not make the joints any less visible, but it will make the strips much harder to handle while you are scarfing them to fit.  I promise that you will find a 6-8’ strip much easier to deal with than one 17’ long. 

I am on my 6th strip build and I butt join the shorter strips on the boat as I go as recommended in Nick’s book.  You can really minimize the appearance of the butt joints if you match the wood color/grain of the strips forming the joint.  I do my butt joints on the 45 degree and use a clamp with a short strip behind to hold everything flush while the glue dries.  I also avoid doing a joint in an area where the strip has a lot of bend and/or twist.

Top picture shows a butt joint that I glued up today.  Second picture shows six joints on my Mystery.  There is a joint just to the left of each piece of tape.

Hope that this helps.     

Shipping fees for stuff over 8' long gets pretty steep really fast. May be why CLC works with 8' material.

I scarfed half my joints (sides) and butt-joined the other half on my build.

Scarf: I cut the scarfs on the bench, but glued them up on the boat as I applied the strips. That was way easier than dealing with a full-length strip. A simple 1-inch spring clamp held the scarf together while the glue set. However: Unless your scarf cuts are absolutely perfect, they will not be nice, neat straight lines after you scrape and sand the layup. Think contour lines.

Butt-joint: Easy peasy. Nick points out the real strength of the layup comes from the fiberglass sandwich separated by the cedar core. That doesn't change with a butt joint sprinkled in here and there. Whether you do your butt joints at 90º, 45º or some other angle is a mater of taste, not strength. I think the 45º looks nice - wish I'd thought of it.

i am a big fan of butt joints.  very easy and as mark said, above, the real strength is the sandwich.

mark's other points about ensuring you don't line up all the joints is important as well as his tips about twist and potential color match if you are concerned about trying to get a particular effect (e.g., one long board look vs a wooden floor look....both can look nice).

i do, however, typically use scarf joints and make several  'boat-length-pieces" for reference strips on each side of a build.  on a kayak this will often be the shear line and a waterline piece.   this way i  can ensure the basic line up is right....and safely handle the rest with butt-joints.

h