Chapter 5, Inside, outside, flip side...

Making the longerons, forming the sides.

Not much to it, at least here. Ripped up some 3/4 MDF to 6" width on the table saw for the FJ jigs, used the cross-cut sled to saw to length per plans. Take one rectangle, lay it on a straight "off cut" (scrap) about 55" long at least 5" wide. Mark out 1.5" on one end of the top piece, and 6" (or 5" depending) on the other. Now rotate the top piece so the marks line up with the edge of the lower piece, tack it to the lower piece with two 1" brads from the brad nailer. Run this whole assembly through the saw again to get the sloped angle cut.

Giant compass?Cutting the curve on FJA was just about as easy. Mark the 2" spacing, pencil in perpendicular lines with your square. Mark the cut point on each line by setting your dial caliper to the measurement in the drawing. Most calipers will do inside, outside, depth, and STEP measurements. Use the step measurement process to make your marks. Now this is trick... Take a long length of 1/4" plywood and use it as a bow to mark the curve. I used a piece of 6mm Baltic Birch, 60" long and 1.5" wide. Radius the corners on the ends so the sharp edge doesn't cut the tape in the next step. Set the board on the FJA stock, bend to a curve intersecting as many of the points as you can, run a 70" piece of fiber strapping tape to hold the curve. FWIW, my chord height was about 2". Other stuff will work too, make sure any grain is straight and uniform. A piece of metal strapping, ...

Now over to the band saw to cut just shy of the line. Setup the sleeve sander (3") on the drill press, finish sand to the line. Knock off the minor bumps and imperfections with a small flat sanding block (it'll follow the radius close enough). Trace this curve on the other three boards, bandsaw to .125" shy of the line. Finish with the .5" bottom bearing straight router bit (laminate trimmer bit) in the router. Tack the master on one board, rout, repeat for the other two.

Cleaned and re-varnished (waterborne) the work table again, struck a straight line with the chalk line on the work table, taped up the FJx jigs with packing tape and nailed them to the work table with 1" brads from the nail gun. Don't forget the .5" total gap at each end.

I ripped a handful of 1" strips from 6mm Baltic Birch (the firewall material) for the longerons. Eleven strips 60" long as I recall. I'm using birch plywood for several reasons. It's dimensionally stable, I have a ton of it, the plans Sitka Spruce gets slotted several places so I have to assume the longerons are not exactly structural, the ACS catalog mentions "cap strip" may be cut from 'generic' spruce stock as it's non structural, I saved on shipping, and I've read where some builders rip up a 2x4 from the Big-Box-Store for longeron material. Disadvantages are it's heavier, it doesn't come in 105" lengths, the finished three strip width is .70 inches. Note the staggered joints (a scarf joint would be ideal), and if you've got good eyes, the slight gap where the longerons meet the junction of FJB and FJC. Also note the shims ripped to 1" from shim-shingles (roof shingles) under the clamps where the curves are extreme to keep the clamps from slipping. I used 12 clamps FWIW.

Welded two 3/8" H-45 foam sheets together with 5-minute weld-o-matic in the dual squeeze bottle.When I ordered the sheets from Wicks, I had them cut it down to 24" wide to fit in the box to save ($$$) on shipping. This worked out better than I thought, the sides are 21" tall, saved me a little trimming.

I ripped the 1/8" Masonite to 20.75", then added 6" to the end to make it 102" OAL. I cut the side foam to the dimensions in the plans, a strip of 6mm Baltic Birch worked well to get a smooth curve between the points. Welded the FJx jigs to the table with Mondo-Bondo (probably should have used more), then glued the foam to the Masonite with 5-minute weld-o-matic in the ever popular dual squeeze bottle. I used drops of 5-minute, maybe the size of a paper match head, placing the drops near the edge where the foam will get sanded away during contour in a later chapter. The foam lays down pretty well on it's own, a few spots of glues helps.

Personal comment: I think that being anal retentive in getting the foam to the exact dimensions (top to bottom direction) is a waste. As I read the plans, the important dimension is the location of the lower triangular longeron, which can be gauged when it is floxed to the sides. You do need to be to dimension, but a few mm longer won't sink the boat IMHO.

I ripped the Last-a-foam spacers to width, the ripped the bevel on the table saw. The solid aft spacer gave me some fits (the dimensions in the plans book seem lacking), but it does work out. Make the top and bottom spacers first (including the bevels), then the bevels of this aft spacer will become apparent. In the "hope it helps" department, after ripping the spacers to width I found the following angles to use on the saw if you pass the spacers through the blade standing up. Section A-A 36°. Section B-B 26.5° Section C-C 34°. Section E-E 17.75°

I routed the stick depression, and the depression in the back of the boat for the fuel sight gauge. I'm using the Vance Atkinson gauge, a real sweet unit BTW. While routing the stick depression, Britney Spears called and asked for a date on the speaker phone. I slipped with the router and gouged down to the masonite. A sliver of foam, about 3/16" thick, placed over the boo-boo. Use the Xacto knife to cut through both the patch and side foam. Lift out the mistake, press the patch in. No micro on the edges, I figure It'll get a little that flows down when I glass up the inside. Sand to the surrounding level, even Stevie Wonder can't see the repair. I told Britney I was busy.

Micro'd the spacers to the sides. Buttered up the spacer, put it in position to 'mark' where I needed to squeegee the side foam. Removed the spacer, then squeegeed the side foam as appropriate to fill the marked space. Doing the same on the mating surface of the spacer, I added a little more micro to ensure I had an ever so slight squeeze out all around. Pin with finish nails, and weight the ends with the ever popular oil cans. 10W-30 seems to work about right.

You may notice the spacer foam extends slightly 'long' of the side foam. Compound curve and all, some builders have come up short in the foam department when they add the lower longerons. I don't care (mostly) about the excess overhang, I'll be measuring the exact side contour when I place the triangular longeron, as the bottom of the tub locates against these. I can sand any foam overhang after the lower longeron cures. If this comes to bite me in the posterior, I'll delete this paragraph. Shhhh....

Glued one of the triangular longerons on, as one longeron used up all my hand screw clamps. No nails. I put a bow to stern strip of masking tape near the upper longeron, marked the dimensions to locate the lower longeron every 10", then checked and adjusted this length as I located and clamped the lower longeron on. Just like you're supposed to measure/cut the foam and Masonite. Worked well. Note: It looks like I'll be able to make a 'skid' for the router to ride on, then use a flush trim bit guided on the lower longeron, to trim the side foam and spacer foam perfectly flush. See my comments above, and on 2-01-08 above. Stay tuned.

Floxed in the other lower longeron this AM.
Trimmed up the glass on the electrical channel cutout in the aft foam, laid in one BID ply. Made the plugs for the other half, and used the lo-vac process to lay the one ply of BID. It works to keep the flange flat, but took a lot of time to setup. A lot. If you make the plug with a square end at the taper, make sure you leave a flag of glass long enough to reach to the LWX reinforcement, else you'll have a bit of unglassed foam inside the electrical channel when you add the filler foam between the LWx stringers.

I cut 102" of UNI from the roll, folded it in half lengthwise, then in half again. Made sure the fibers were straight and the folds 'neat', brushed a heavy coat of epoxy on the upper longerons, then carefully placed this four ply sandwich on top. Drizzled on more epoxy, brushed, used my fingers, poked the corners with a stick. Cut along the gap between the two sides, as well as trimming with the scissors to a 1.5" lap at the lower edge once totally wetted out and squeegee' d. Worked out pretty slick! Don't forget to radius the inside (only) edges of the longerons beforehand. The top edge of the longeron remains square.

Fitted the foam between LWX, LWY, and the lower longeron. The fit isn't perfect around the electrical channel. Micro'd the insert onto the side foam, then added more balloons to make a stiff mix and used that to fill the big gaps.

Made a jig to trim the bow end square using the Binford high torque five speed soft start router, and a super magnum diamond honed micro-grain Unobtanium Carbide extra long router bit. The picture should give you an idea how it went together. About a 10 degree bevel on the legs. You can see a drywall square laying on the longerons in the background, used to get the jig square before clamping. Flip the square over and measure again. Often they're not exactly 90 degrees after being used (dropped, stepped on, ...). Split the difference if so.

I'll do something similar at the exhaust end, once the 6 ply BID over the foam is added and has cured.

I took some time to trim the bulkheads to fit the sides too. F-22 fits perfect, and the seat back needed the corners trimmed (this was planned) But like some have found, my IP is a bit short on the bottom, maybe 3/16" at the outside corner. I think the center should be OK, I didn't make it flat, rather followed the slight bulge in the center per my full size "M" drawing. Looks like two loooong tapered wedges of foam are in order. I'll know more in the next chapter when I jig all these parts together and add the bottom.

Aft lay up was cured, whacked out another template on the table saw so I could use the Binford router to cut the sides to length and rough out the spar opening. Final length came in at 101.81" (101.75 called for), and the spar cutout is 1/8" short on three sides. I can sand to final length (bow or stern, I haven't decided yet), the exercise will to the old biceps good. Popped the sides off the Masonite, my matchstick sized drops of epoxy were just the right size. A few divots, maybe 3/8" diameter max, on the sides that should eventually be sanded out in a countour stage. I also needed to 'adjust' the temp firewall 1/16" on a couple of edges, and will need to square up the foam/glass/wood intersections at the aft end to be square and flat before I jig up for chapter six.

I sanded (router skid per above wasn't used) the foam and glass at the lower longern to be square with the face of longeron, though question the effort. This longeron has a compound curve (curving in) near the aft end, but the bottom foam assembly in the next chapter is fitted in at 90°.

I do think cutting the spacer foam long at the bottom (per above) was an advantage.

Only defects I noticed were a slight void where I glued the foam spacers in (near the top of the seatback), a larger than preferred flox joint in a few places along the top longeron glue line, and a few ripples in the inside glass work. Nothing a heavy coat of Zolatone won't fix...


  • Don't skimp on the bondo blobs holding the FJ jigs to the table. Adding a few right angle brackets might be good.
  • Cut the masonite slightly shorter on the bottom. Makes for easier sanding of the foam spacers and lower longeron.
  • Glue the side foam (3/8") to the Masonite with very small dots of 5-minute. Place the dots every 6-8", and no more than 2" from the top and bottom edges.
  • Overhang the bottom foam spacers 1/8" - 1/4" on the bottom, 1/4-3/8" on the front and aft ends.
  • Lay the lower spacer foam in place, then mark and rough cut the aft spacer foam to match.
  • Cut your fiberglass per plan (enough length to span both sides) but cut it in half at the top longerons before you start the layup.
  • Measure and attach the triangular lower longeron as you go.