I don't know anything about a Petrel, having built a Skerry but I do know about frustration.  If it werent for this forum many of us would probably wanted to end it all but there is always help for any questions you have.  Here is a Youtube video explaning the difference between a scarf and a butt joint.  http://m.youtube.com/watch?v=vTKZcD448jQ  

You will most likely have too many pieces. Stagger the joints so that you have a strong beam longer than you need and cut it to length.

Dan

I have a Petrel on order.  I have been reading the book, this site and Nick Schade's web site.  He has  a several videos on building the Petrel, and if you go to his blog and there are more videos.  There is one that pertains to setting up the strong back.  It is my understanding that the strong back is long, and you cut it to length.  Before the strong back is assembled, the ends are cut to accomodate the stems.  If you add up the lengths of pieces you have, they would equal 20', using the sizes to have a good staggering of the butt joints.  The top and bottom  butts  of strong back would be offset 2' from the joints in the sides.  I could be wrong.

I’m sure that by this point the strongback ‘puzzle’ has been solved, but if not, take a look at the catalog page for the ‘strongback for strip building’.  There is a picture showing the side/top assembly.

I believe that the strongback is 20’ long then you cut it down to the size.  It is assembled so that no two joints at the same place, with each joint at least 2’ apart.  If you have the room, I would assemble the strongback to the full 20’ and then cut it down.

                One side is made up of 8’ + 8’ + 4’ pieces.  The second side is 4’ + 8’ + 8’.  The top (or bottom) is 2’ + 8’ + 8’ +2’, and the opposite is 6’ + 8’ +6’.

                I hope this helps!  Enjoy your build.  Mike

I've just received my Petrel kit and arrived at the same canundrum.

I follow all of the logic of the above posts and they are correct in their layout descriptions; matches the box beam layout diagram for staggered joints in the kit.

BUT, one could use the same stagger pattern AND omit an 8' board (or equivelant) from each face and still end up with the 12' beam needed. That's a savings of 32 board-feet!

Signed, Confused

But moving forward!

Guys I will try and help you. I have built a Guillemot L from the CLC plans/kit. I don't know if your plans are different.

First, a butt joint is just placing the cut panels end to end to assembly the strongback. Of course you do this per your discussions noted above.

In my plans I had an overall diagram of the spacing of the stations along the length of the kayak.  The diagram also included the shape of the end stations, that face/align with the centerline of the kayak.

From this diagram you can calculate the length of the strongback. Usually you have 12 inch spacing from station to station. For example the spacinng from the right side of one station to the right side of the next station is 12 inches.  The distance in "between" the station would be the 12 inches minus the thickness of the station material.

First a definition:  I define an end station is the station at the end of the bow and stern that runs the centerline of the kayak.  Attached the end stations are the across stations (stations at a right angle to the centerline) and the strongback.

However, start counting the number of across stations per this diagram where the end stations attach to the strongback at the bow to the start of the end station at the stern. This will be the length of the strongback. 

I have had the best luck in building the strongback by using wood glue and nails or screws.  I don't set the strongback up on horses and clamp it.  Built it on a concrete floor.

I built my last strongback on a level concrete floor with Titebond III glue and brad nails attaching the sections per the discussions above.  Next, once built I kept the strongback on the "clean floor" and put weights (whatever you have) along the length of the strongback to keep it has straight as possible until the glue sets up.   This should get your strongback with an alignment within 1/8 inch.  

(PS: My first strongback I built on the horses and clamp it with C-clamp and it was off by 3/8 inches.  I guess just the weight of the clamps and setting on the horses curved the strongback.)

I hope this helps. 

K.Greer