The wood mast for a SCAMP is 16' long, and uses birds mouth construction, which means it is hollow and built like a long skinny barrel. I found a number of articles on the web which were quite helpful in learning about this technique. And I learned a few things from the attendees of the SCAMP Mast Camp at the NW School of Wooden Boat Building in Port Townsend.
Here, a stave is being cut to width.
I tried using a scarf jig that uses a router, which I got from the guys at RiversWest Small Craft Center (www.riverswest.org), but found it didn't do any better job than my table saw jig, and was a lot more work and time consuming.
I planed the test mast to 32 sides, and then sanded it on a spar lathe, that I made for this project. This seemed to work well.
I bought two pieces of sitka spruce at Crosscut Hardwood in Portland - they were 8/4 and just over 12' long, about 8-9" wide, pretty straight, and pretty straight grained - as far as I could tell.
I ran one of the spruce boards through a thickness planer (at the RiversWest shop - I don't have one myself), to give a smooth flat surface to start with. Then, I ripped 6 35mm (or so) pieces. These were later ripped in half to yield 12 16mmx35mm pieces, which were then trimmed to 16x30, the non-tapered stave dimension. These 12 staves were just over 12' long. So, the plan is to cut 4 of them in half to scarf to the remaining 8 to yield 18' staves.
I was somewhat alarmed at the crookedness of some of the resulting staves. When the spruce was ripped to narrower widths, internal stresses were released and boards went opposite directions. But, I could easily clamp the batch of staves together and they would lay flat. So, maybe it will be ok.
Then I reviewed the layout of the scarf joints in the mast, and decided I didn't like it after all. The joints were distributed too closely together, in my opinion. So, I ripped some from the other spruce board (which is to supply the yard and boom), and cut a few more stave-size boards. It was unfortunate that I had to do this, because it was nearly impossible to get exactly the same setup on the saw to get the same width and height as the first batch of staves. Turns out they were close enough, though.
I was pleased that the somewhat crooked staves, when clamped together into a mast, were nicely straightened by their neighbours' birdsmouth cut, resulting in a straight mast. Whew!
So, I called up my buddy John Bouwsma to help me with the glue-up and real assembly.
We spread straight epoxy on three sides of the staves (all but the outside), and then applied thickened epoxy to the birdsmouths. This last step took us about 45 minutes, so I was definitely glad for the help. We used small brushes to spread the goo - perhaps using the pastry bag fillet approach might have taken less time - not sure.
The pix shows the assembled mast after assembly - things were busy enough I forgot to take pictures before this point. I mostly used hose clamps, with a few plastic ties between. It was hard to get much clamping pressure with the ties though.
I then spent a fair amount of time cleaning up squeeze out, and John got bored with that and went home.
I started by going over the glue joints with a scraper to remove as much squeeze-out as I could, to reduce the amount of plane blade sharpening I would need to do.
Marked it for planing to 16 sides by drawing a line down the middle of each stave. We plane off the wood between this line and the edge of the birdsmouth of the adjacent stave - removing the point of the octagon.
So, I setup the mast on the lathe, and got started. After one pass down the mast, I realized that the roller blade wheels were hard enough that they were making a circumferential dent. I guess the douglas fir is hard enough, that I didn't see this with the test mast. Gads! So, rather than fiddle with different wheels, I decided to bag the lathe, and proceeded to sand by hand, as I was anxious to get a mast done, and not spend more time fiddling with build fixtures.
Took a while, and was fairly tiring. But in a different way than planing to 16 sides was tiring.
I will cut the halyard hole at the head, and apply a finish later. For now, the mast is hanging from the ceiling joists in my shop, waiting for me to build a boat to put under it.