This week, I scarphed together two lengths of soft maple. Why maple? Because I can get it in approximately 8-foot lengths of 1/2" thickness by 8-9" width at an okay price. It is a hard wood destined for a canoe-styled hull. I used an 8/1 scarph ratio which is more than required. The scarph was made initially with a hand power plane for gross reduction, then followed with a belt sander and medium grit. The resulting surfaces were flat and mated well. Epoxy adhesive was followed by clamps. I have three hand belt sanders. Why didn't we have them in junior high shop class! Planes can produce 'chips'; belt sanders never do.
With epoxy and paint, also kept indoors, weather will not be a factor for the maple in this hull. Once scarphed together, I ran the combined board through a thickness planer to bring the thickness down to a uniform 7/16" (0.435"). Why that thickness? Because I wanted a balance of weight, strength, and flexibility for the slight rocker planned. These were rough boards when received, thickness was not uniform, and they initially were not entirely straight. I corrected the side curve with a hand plane and frequent checking with a straight edge. The product now is straight, uniform, and has the flexibility desired while retaining sufficient strength. This will be the plank keel creating a foundation, tying all the frames together.
Today, I bought lumber for the frames: knotty alder. Why knotty alder? It is a beautiful hardwood, but relatively light, and at a reasonable price. Of course, I hand selected the best boards and bought excess (perhaps enough for a next hull). The drawback is the knots present but, for the frames, I will be bonding together rather short lengths of wood. I think I can work around the knots.
New lumber. The keel is maple, overall length 136". Current width is 8". The other boards are 1/2-inch-thick knotty alder. As you can see, the knots are not too distracting. I can buy 1/2"x5 1/2" boards, which I can't produce on my home saws. The frames will be 1/2-inch thick, and most will be 1 1/2" wide, but with 5 1/2" overall board widths, I will not be limited if I want a wider piece for a frame.
There will be twelve frames, symmetrically spaced fore and aft. These are full-size rosin paper patterns. At the turn of the bilge, I will need to use narrower strip planks to follow the increased curve.
I chose a 13-foot length with frames spaced 11 inches on center. The length could easily be increased with 12 or 13-inch spacing. Knotty alder wood was used, but I was able to avoid almost all of the knots. Fifty-six total wood pieces were machined and bonded to make these frames. I will need to notch these frames for the sheer and a chine.
My next task will be to create the stems; they will add about 20 inches to the length you see. I will start with Douglas Fir 2x4" material to construct them. The measured sheer piece when bonded will fix the frames at proper spacing.
The hull stems are now in place, ready to be bonded. Next the sheer will be better defined with a scarfed longitudinal. I need to strengthen that area before I can turn the hull over for planking. The half angle at the stems/ends is 18.12 degrees. There will be small decks at the ends for which I need to add some support.
Many details were involved getting to this point. That curved sheer strip is 157.7 inches long by calculation. However, I didn't trust my calculations, so I made it a couple inches longer just in case I was wrong. Then when fitting it, I wasted time recutting to the proper length. The intersection point with each frame was also precalculated. Everything is held together with spring clamps currently. A next step will be to mix epoxy and bond it all together. At the ends where the sheer and stem and a short deck beam come together, the calculated intersections were perfect. The task was to cut the actual wooden pieces to fit exactly with all the intersecting angles. Hull length is currently 154 inches, but that is to the inside of the sheathing, when done it should be about 2 inches longer.
The curved laminated section of wood placed from deck beam to sheer illustrates where the edge of the small fore and aft decks will be when complete. I plan to use a herringbone design of planks for decking.
I have doubled the sheer stringer and added another wood strip to define the major chine. Next step will be to fair the hull in preparation for planking. The lower portion of the stems currently have a rectangular cross-section and will undergo major reduction to a "V" cross section (like it appears at the sheer level). Using a short straight section of planking, laid in the direction of the design mathematical projection, as a guide, I have found that an angle grinder with a coarse flap disc is best for achieving the needed reduction.
The plank keel will also need to be routed to create a landing for the first plank, the garboard. This will all wait until after the upcoming holidays.
No comments:
Post a Comment