Hi Annym,

If you are not building from a kit, then you should do a scarf joint or a butt joint.  As you point out, a puzzle joint really is a technique where you have a CNC machine.

Further, as you point out, it is best to join your board prior to the your final cut.  The reason is mostly about not ending up with a piece that is too short due to a scarf or butt joint that needs to get reworked a bit.

On the scarf joint, https://www.youtube.com/watch?v=pwmAQzUta88  at 1:50 gives you an overview of a scarf joint.  This video shows how to do a scarf https://www.youtube.com/watch?v=iFUIH1tdl2Y

For this boat, I think a butt joint could also work.  For a butt joint, you can see the following video:  https://www.youtube.com/watch?v=bxQA4v4_PqU    For taping, I use two pieces of 3 inch fibreglass tape overlapped 1 and ½ inch over the joint.  like the video (which uses one strip of glass over the joint)  make sure you set that tape up to be on the inside of the boat.  

I have built kayaks with butt joints before and had no issues.  It is important however, that the joint is eventually glassed on both sides.  So on a kayak, the glassing on the outside occurs when you glass the assembled hull, and usually there is another layer of glass on the inside of the boat as well.

i hope these videos and description helps

h

Stricyly speaking, you don't need a CNC machine to cut puzzle joints, but if you don't have one you need a lot of skill. It's high precision joinery using thin plywood. While theoretically it could be done using nothing but unpowered hand tools, a router would make it a lot faster. But then you have to make a precision router jig. You'd also have to practice and dial in all the jig, router and clamping settings, In the time to do that you could have cut the scarphs for 5 or 6 boats. So take Howard's advice and go with a different joint. Based on my WD12 build, I'd go for a scarph instead of a butt joint and try to keep any joints towards the middle of the boat. This is because of the extreme twisting at the ends of the boat.

If you really want the scratch build experience but with puzzle joints, CLC sells full plywood sheets with precut puzzle joints. You simply glue them together, then do the layout and cutting as if you had an extra long sheet of plywood. I used them to build an 18-ft schooner and they worked very well. Since I live within easy driving distance of CLC and could jut pick them up at the store, they weren't that much more expensive than just buying the wood. Your situation may vary.

Laszlo

I have made similar puzzle joints by putting one piece over another then cutting "puzzle" pattern with a scroll blade on my saber saw.  It gives a joint with the smoothness of your hand and a gap of the saw kerf. Which can be filled with epoxy thickened with wood flour providing a dark line. A layer of cloth and epoxy on both sides and it was done.    A scarf joint is easier to get a finer line. Puzzle joint has a lot of opportunities for sloppy joints. 

Otherwise you have to cut and sand one side then place that cut piece over the other and scribe the line with a fine knife. Then cut the second, proud, and sand down to the line. Sand both to fit. 

   Thank you all so much for the information! I think I will try using a scarf joint (after practicing a few times).