The Tongass!
Step 8) Building the Bottom Panels

Previous Step   Home   Next Step

(Click pictures for full size image)

Lofting bottom panels
First task is to draw the pseudo-station lines for marking off offsets. Next, mark the offsets and put a thin nail through each, then clamp a batten to them and ...start looking, thinking, adjusting. It probably took me 3 iterations to get a smooth curve that was the best average of all the offsets. I think one mark ended up being about 1/8" high, another 1/8" low. Getting 'close' is good enough because all wood bends slightly differently and you're going to have to do some edge planing or sanding right before putting the chine flats on to make sure the curve is smooth and perfect when the panels are in the bottom molds and glued up. The curve that defines the bottom (of boat) edges were perfect, right out of the book.

Note that prior to putting together the bottom panels, that I used them as a template to pre-mark and cut the second-layer 1/4" plywood which will be cold-molded onto the hull later (note that the 2nd layer plywood already had the scarf cut at this point and had been set aside.)

Here you can see the bottom molds on the building jig and the panels laid in place. Note that the second panel is a mirror image of the first (of course). I flipped the first onto the second, drew the outline, then cut the second (Bosch jig saw.) I could've used my router with a top-bearing template bit to cut out the second panel, but if you recall, I burned up the bearing when making the shelves for the sheer deck (haven't replaced the bit yet.)

Prior to putting the panels on the molds, I used a sander to put a bevel on the edges that would be against each other when stitching, and I drilled 1/8" holes about 1/2" back from the edges for the stitches. Do this with both panels cut out and clamped to each other with perfect alignment. Spacing of the holes can be seen in the following pictures.

I took opportunity here to raise and lower one panel (the other settles against it) to get the edges to align perfectly. Note the clamps holding only the port side panel at this point.

Panels laid in the molds
Stitching, with dowels Prior to cutting out the panels, I had marked the location of the forward edge of the forward mold so that I could align the two panels perfectly. The stitching holes are another way of ensuring alignment. Once aligned with the forward mold and along the panel edges, the stitching goes in. I started at the stern, work my way forward to around Station #6 (loosely), then iterated a time or two to get the stitching right. I started with the wire that I had, but it kept breaking, so I switched to tie-wraps. Notice the sharpened dowels under the ties. Tie-wraps don't pull quite tightly enough, so I used a light hammer to drive a sharpened piece of 1/4" dowel under each tie. This not only drew the panels tight together, it also helped give the edges good alignment. The dowels were placed on the inside ties when the panel angles were small (stern to Station #6) ...

...and placed under the outside ties when the panel angles and curvature was high, as shown in the bow area here.

Because I was working by myself, I used a ratcheting tie-down strap (see below) to help pull the bow sections together. The blocks and clamps (shown) were used to temporarily hold the bow points together to I could add the last tie-wrap and get them all tightened up. This is where you realize that beveling the inner edges is required! The dowels helped a lot in aligning these edges (lots of pressure here...).

Bow stitching, with dowels
Adjusting 40\ A couple of clamps and a tie-down strap were used to set the hull width to 42" at the 40"-from-bow station line. After adjusting this point to the required width, the 59-1/2" critical dimension (not really critical though) happened to be right on the money. And as Renn said, the panels were verified to be 31-1/2" wide at this point (centerline to chine.)

To prevent crevice corrosion in buried metals, I don't like to leave any metal or fasteners in a boat that doesn't have to be there, so prior to doing the fillet and glassing (fairbody line), I did what I've done on previous boat building projects ...I used slim, low profile, 'tack welds' of thickened epoxy (wood flour + silica) in between all the stitches to epoxy-stitch the panels together. This adds a day to the schedule for curing, but when you are done you can remove all the ties rather than have to work over and around them, leaving them in. In the high-curvature areas, I applied these 'tack welds' along the inside and outside of the seam for double the holding power.

Epoxy 'tack welds'
Filleting and glassing the fairbody I'd have more pictures, but this step kept me pretty busy for awhile ...trying to get it done without the epoxy kicking off. Turned out great and Renn's directions were perfect. I used a 1/2-gallon plastic bucket and a wooden paint mixing stick to make batches of thickened (80% wood flour, 20% silica) epoxy. Renn thickens with wood flour and micro-balloons instead ...I'm a nonconformist.

To give you an idea how much epoxy is required here, here's the stats from my session:

  • First bucket made from 30 pumps from my Michael Engineering Sticky Stuff Dispensor (it's not the biggest size pump... I'm cheap) plus wood flour/silica
  • Second bucket was made from 20 pumps
  • The third bucket was made from 15 pumps, then I finished up with a little more mixed in a 6-oz Solo Cup
  • Several 12-pump batches to do the glassing
  • TOTAL: About 1-1/4 gallons of epoxy for fillet and glassing work

I stopped the fillet and glass about 14" short of the transom since I didn't know exactly where the transom would strike the bottom when the whole stack is on the frame upside down. This will let the 'V' in the transom nest into the bottom panels when it is put together. I used a 3" wide putty knife to lay a flat epoxy fillet up to where the curve of the bow starts, then a 2" wide putty knife followed by a 1" putty knife so the fillet would naturally narrow as it went up the bow.

For the glassing, I did as Renn suggested and cross-brushed a lot of epoxy back and forth along the entire fillet prior to each layer of glass. Renn uses 2 layers of 10-oz glass tape (cut from cloth), 6" wide over 4" wide. Since I couldn't find someone selling 10-oz tape, I selected what I could find: 4" wide 9-oz woven tape followed by 6" wide 12-oz biaxial tape. Including the 10-oz glassing on the inside of these panels, this will give me 31-oz of glass on this seam, versus the 30-oz that Renn called for, and I'll have biaxial sandwiched in the middle.

After letting the glass/epoxy gel up, I went back over it with a fill-coat of clear epoxy and brushed it out (I had also used a squeegee when the glass was fresh to give the fillet a nice smooth concaveness). Finally, note that I did check the squareness of the building jig prior to laying in the panels, and I did level the jig on all 4 sides prior to doing the fillet and glass work.

Previous Step   Home   Next Step

For Questions, Comments, or Additional Information
Please E-Mail At: briandixon7@comcast.net

© Copyright 2004 Brian Dixon